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Thread: Too much for 200A

03262008, 11:38 PM #1
Too much for 200A
Without doing a fullblown load calculation what's your first reaction to the following:
Service is 200A
3800 sq ft, 1966 built house
2 electric water heaters, 1 @ 50, 1 @ 65 gal
2 ovens, 1 cooktop with griddle  all electric
Electric dryer
A larger than typical amount of lights and plugs, including extensive outdoor lighting, lighting and power for a pool (not heater  it's solar and gas), water features, etc.
This is a custom built place and the original owner had quite a thirst for gadgets.
I'm pretty sure it's too much. I'm recommending a load calculation (in addition to a host of other things). I'm just wondering what you guys think.

03272008, 03:37 AM #2
Re: Too much for 200A
Matt, I'd say as long as they aren't cooking a Thanksgiving meal, doing the laundry, have their guests all showering, all at night, they should be OK .
I have no idea. Like you, I'd leave it up to an electrician to figure out.

03272008, 06:03 AM #3
Re: Too much for 200A
Matt,
200 amps appears to be adequate for the house. They are definitely using all of their 200 amp service.

03272008, 07:18 AM #4
Re: Too much for 200A
I probably would not have written it up. Judgement call.

03272008, 07:35 AM #5
Re: Too much for 200A

03272008, 07:52 AM #6
Re: Too much for 200A
New house or existing? If it's older and not blowing the 200 amp main, it's not too much.
Jim Robinson
New Mexico, USA

03272008, 07:57 AM #7
Re: Too much for 200A
Jim  I try to keep in mind that my client(s) may have different needs than the sellers. I'm not saying the 200 amp service is too small, just that no history of the main blowing (and how would you find that out?), in itself, might not tell you that much about performance going forward.

03272008, 10:11 AM #8
Re: Too much for 200A
There are several other panels but they're all being supplied through the service so I didn't mention it. Does that change the overall setup or impact the load calculation?
There are 2 @ 50amps and 1 @ 70amps. I figured since it's all going through the service there is no difference.

03272008, 11:13 AM #9
Re: Too much for 200A
Matt, as long as the service wires and breaker sizes to the subpanels are correct, that is fine.

03272008, 02:23 PM #10
Re: Too much for 200A
scott,
what does 220 and seperate panels have to do with anything? the 200 amp service is it.you can have 100 other panels on that 1 service and all you are gonna get is 200 amps? it may be adequate but op didn't specify heating loads and motor loads etc. iwould ask for load calcs on a new residence of that size

03272008, 03:46 PM #11
Re: Too much for 200A

03272008, 06:06 PM #12
Re: Too much for 200A
While that does seem like a lot, remember that though we list the service as 200 amps, you can concievably pull up to 199 amps through each leg prior to tripping the main. Each 220 volt breaker is getting the power from both legs, not just one. 199 + 199 = 398 amps, hit 399 or exceed 200 from either leg and the main trips.
Think of the main overload disconnect as a 220v circuit breaker. With 10 gauge conductors (30 amps) the appliance can concievably pull 29 amps through each leg prior to the breaker tripping, but if either leg exceeds the 30 amp rating, the breaker goes.

03282008, 02:39 AM #13
Re: Too much for 200A
To answer the question, without 'doing a load calculation,' is a lot like making a weather report without looking through the window. That's the only definitive way to answer the question.
In more immediate terms, you can try to pick a 'peak' time, and actually measure the amps flowing through the service drop.
Absent either approach, an 'answer' is little more than trying to count cards at the blackjack table.

03282008, 04:50 AM #14
Re: Too much for 200A
Hi,
I've seen 125 amp panels in big old high end houses around here built in the 60's that have handled the same sort of loads just fine.
ONE TEAM  ONE FIGHT!!!
Mike

03282008, 07:17 AM #15
Re: Too much for 200A
Not quite a good way to describe it.
There are two 'legs' to the 240 volt circuit, however, the same current is flowing through each one (with the exception of the off balance current which if flowing through the neutral, this is the current difference between the two hot legs).
That means (assuming a balanced load) that if there is 200 amps flowing through one leg, there will be 200 amps flowing through the other leg  the current is NOT additive.
Now (assuming an unbalanced load) there is 200 amps flowing through one leg, but only 100 amps flowing through the other leg, the other 100 amps is now flowing through the neutral  STILL not additive.
A 200 amp breaker will carry 200 amps ... period, not 200 + 200.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03282008, 05:13 PM #16

03282008, 05:34 PM #17
Re: Too much for 200A
I realize the shortcomings of my question... I was really just trying to run it by the board to see if I would be negligent in not calling it out. It sounds like I wouldn't and ended up leaving it off the report.
I think I just get used to seeing new houses 'overwired', particularly in comparrison to the 1960's. A new house of this size with this equipment would likely have 2 panels, whether needed or not.

03282008, 05:47 PM #18
Re: Too much for 200A
I read your description and if nothing has been added to home since it was built No problem but that is highly unlikely. Circuitry is your problem almost any new appliance will require dedicated grounded service so you will need more breakers, More breakers more load. This house today as you described would probably need at least a 250 ampere panel or with circuitry 2 200 side side rthe second panel fused at 125 amp.

03282008, 07:09 PM #19
Re: Too much for 200A
Jon,
First ... *it is the same current* ... going through each of the two hot conductors.
I'll try to show it below:
___________________ Phase A >
& 
& 120 volts
& 
&  Neutral >
& 
& 120 volts
& 
___________________ Phase B >
Say Phase A leg carries 80 amps > to the panel
and Phase B leg carries 100 amps > to the panel
The 80 amps circles through the transformer from A to B, the 20 amps difference circles through the transformer from Neutral to B
You do not have 180 amps, you have 100 amps  it is just split up as described above.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03282008, 08:14 PM #20
Re: Too much for 200A
Just like in preschool , it is much easier to grasp with pictures.
Thanks Jerry

03282008, 10:17 PM #21
Re: Too much for 200A
Actually you do have the equivalent of 400A available to drive 120v loads. As far as power goes, 200A of 240v is equal to 400A of 120v.

03292008, 10:02 AM #22
Re: Too much for 200A
"Actually you do have the equivalent of 400A available "
Actually, you do NOT.
Just try to push 400 amps through a 200 amp breaker (well, okay, maybe *IF* that is an FPE main ).
Nope. No way Jose.
Tim,
You are mixing "amps" and "watts".
240 volts at 200 amps = 48,000 watts
120 volts at 400 amps = 48,000 watts (but try to force that 400 amps through that same 200 amp breaker  ain't gonna work, not even considering that the conductors are going to overheat and probably melt down too)
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03302008, 03:43 PM #23
Re: Too much for 200A
That's why I said "equivalent". You could put 200A of 120v loads on one phase and 200A of 120v loads on the other phase and the breaker is fine. Thus, you are driving 400A of 120v loads.

03302008, 03:49 PM #24
Re: Too much for 200A
"you are driving 400A of 120v loads"
That's what I keep trying to explain ... you will not get 400 amps through a 200 amp breaker as long as the breaker is working correctly.
Which is why I also said " You are mixing "amps" and "watts". "
You should be using the term "watts", not "amps".
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03302008, 05:29 PM #25
Re: Too much for 200A
I'm not confused about watts and amps. I'm using the fact that 200A at 240V is equal to 400A at 120V. Like you said in your post:
240 volts at 200 amps = 48,000 watts
120 volts at 400 amps = 48,000 watts
I can put four 100A single pole (120V) breakers in that 200A panel and run four 100A motors at 120V. That is 400A (at 120V). The main breaker will only have 200A going through it (at 240V) and it will be fine. If you put a meter on each motor, you would measure 100A, times 4 = 400A.

03302008, 05:39 PM #26
Re: Too much for 200A
"I can put four 100A single pole (120V) breakers in that 200A panel and run four 100A motors at 120V. That is 400A (at 120V). "
Nope, ain't gonna work.
You ARE mixing the terms "amps" and "watts" ... either that or you have a complete lack of understanding of electricity and wiring  I don't know which for sure, but I'm beginning to think it is the latter.
If you put "four 100A single pole (120V) breakers in that 200A panel " you will only be able to run *TWO* (2) 100 amp 240 volt motors (using those 4 breakers as double pole breakers), *OR* you will only be able to run *TWO* (2) 100 amp 120 volt motors (using those breakers as single pole breakers)  either case  that is only *TWO* (2) 100 amp motors.
Try to run 4 100 amp motors and they will either smoke and burn up, trip those "four 100A single pole (120V) breakers", or trip the 200 amp main.
You ARE NOT going to be able to run 400 amps through a 200 amp main if the main is working properly.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03302008, 06:34 PM #27
Re: Too much for 200A
Sorry Jerry, Gotta call you on this one. The 200 amp 240 volt service will indeed run 4 100 amp 120 volt loads. 400 amps at 120 volts equals 200 amps at 240 volts (assuming the loads are evenly distributed). Motor loads are by nature inductive and not a good example to cite. If we were to use a resistive load such as incandescent lighting or single phase electric heaters. You can indeed load this panel with 20 single pole breakers evenly distributed feeding 20 cicuits at 120 volts. Of course some of the items mentioned in the original post are not 120 volt loads. We are not given enough information to do a proper load calculation. If the heating system is NOT electric my seat of the pants opinion is that 200 amps at 240 volts is sufficient. The fact that the main has never tripped is not really important. If the loads ever exceed 80% of that service it is not big enough and yet never trip the main even if that 40 year old breaker is still functioning correctly.

03302008, 08:16 PM #28
Re: Too much for 200A
"400 amps at 120 volts equals 200 amps at 240 volts "
Yeah (wattage wise), *WHEN RUN AT 240 VOLTS*, but when those 4 100 amp motors ARE RUN AT 120 volts (which is what Tim keeps saying)  *that's 400 amps*.
Like I keep saying ... ain't NO WAY you are going to pull 400 amps through a 200 amp main, or 200 amp rated equipment for that matter, not without damaging something in it.
Tim keeps saying he can  not going to do it.
Maybe Tim is not the only one who knows less about electrical wiring and electricity than they think?
Read what Tim keeps writing  he keeps saying 100 + 100 + 100 + 100 = 400 and he can run that through a 200 amp main  NOT GOING TO HAPPEN.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03302008, 08:17 PM #29
Re: Too much for 200A
Peter, I agree that motors was not a good example. I was trying to make it simple and not get into 80% load, power factor and inductive loads and such.

03302008, 08:22 PM #30
Re: Too much for 200A
Makes no difference ... motors ... big honking resistors ... you are NOT going to pull 400 amps through a 200 amp service  not without burning something up, and not without tripping the 200 amp (provided, I keep saying, that it is a good functioning main, one which will actually trip at or close to 200 amps).
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03302008, 08:34 PM #31
Re: Too much for 200A
Jerry,
I think the difference is where you measure the amps. I said in my post it is only 200 amps (at 240v) going through the main breaker, but it is 100amps (at 120v) measured at each of the 4 single pole loads. If you add that up for 4 loads, that is indeed 400amps (at 120v).
I'll refer back to your diagram:
___________________ Phase A >
& 
& 120 volts
& 
&  Neutral >
& 
& 120 volts
& 
___________________ Phase B >
Let's say it's just one giant motor pulling 200amps at 120v on each phase.
120v motor on Phase A pulling 200 amps, and back to Neutral.
120v motor on Phase B pulling 200 amps, and back to Neutral.
Neutral current cancels out, 400 amps of 120v motors being run. Nothing smoking, nothing tripping, only 200 amps through main breaker.
The key is, you can not run ONE 400amp (120v) motor. The current has to balance out, but you can run TWO 200amp (120v) motors for essentially 400amps of available 120v current.

03302008, 09:19 PM #32
Re: Too much for 200A
Good discussion, you are both right, Jerry is just saying that 400 amps can not flow through the main breaker and Tim is saying you can get four 120V 100A loads to work if they are wired correctly while staying within the total wattage.
The link shows the advantages of having a neutral in order to drive 120V loads seperately.
The figure that applies to this discussion is a little over half way down the web page.
Singlephase power systems : POLYPHASE AC CIRCUITS

03302008, 10:30 PM #33
Re: Too much for 200A
Yes, that's exactly what I was saying. That's a great link, Thanks Bruce.
That's why in my first post I said "equivalent" of 400A of 120v power. I never said I was putting more than 200A through the main breaker at 240v.

03302008, 10:53 PM #34
Re: Too much for 200A
Y'know, I don't think it is a good discussion. Not with comments like "You ARE mixing the terms "amps" and "watts" ... either that or you have a complete lack of understanding of electricity and wiring  I don't know which for sure, but I'm beginning to think it is the latter." and "Maybe Tim is not the only one who knows less about electrical wiring and electricity than they think?".
I can't see anything wrong with what Tim posted.
The main in a 200amp 240volt panel is actually 2 separate 200amp breakers tied together, just like any twopole breaker (ignoring quad mains). I don't have a diagram but, for simplicity, we'll assume that all breakers are single pole serving only 120volt circuits. If you only turn on the breakers attached to one leg you can pull 200 amps (at 120v) through one half of that main breaker. Turning on breakers on the other leg and drawing current up to an additional 200 amps (at 120v) will not trip the main breaker. It's no different from being able to use a 20amp double pole breaker to power two 20amp 120v circuits or a single 20amp 240v circuit.
All Tim was saying, correctly, was that you have 200amps at 240v available OR a total of 400amps at 120v available. Both would produce the same wattage (48kW) and spin the meter at the same rate as that senses the cumalative current on both legs.
Last edited by Richard Moore; 03302008 at 11:03 PM.

03312008, 06:18 AM #35
Re: Too much for 200A
Boy ... do I feel foolish, silly, and stoopid.
Bruce,
That is *EXACTLY* what I was saying ...
(I read it as Tim was adding up the 100 amp motors, as would be the case when they were all on the same phase.)
However, that was *NOT EXACTLY* what Tim was saying.
(I went back and reread it and Tim was saying, trying to tell me, that he was talking about using both phases equally.)
and Tim is saying you can get four 120V 100A loads to work if they are wired correctly while staying within the total wattage.
Bruce, thanks for splashing that bucket of ice cold water in my face and waking me up ...
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 06:26 AM #36
Re: Too much for 200A
Richard,
"All Tim was saying, correctly, was that you have 200amps at 240v available OR a total of 400amps at 120v available."
Don't start there again, that's what started all of this and that is the "wrong part".
You DO NOT have "a total of 400amps at 120v available".
All you have available is 200 AMPS regardless of the voltage.
Going beyond that in the discussion is where I went wrong, on that part, stated the way you just stated it, I was correct.
Let's not go where I was correct again as it may lead to a turn of the discussion which I will miss again and be wrong again.
No matter how you look it it, regardless how high or low the voltage is,  you only have 200 amps available  we all agree on that, right?
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 07:39 AM #37
Re: Too much for 200A
When you have 120V loads only, the 240V 200 amp main breaker is now performing as two 120V 200 amp breakers.
Now each side of the main breaker has 200 amps going through it, so it is 400 amps total. There are no free amps or watts available, if you have four 100 amp 120V loads you can bet the power company is sending you 400 amps using two 120V legs. The difference is that it is only 120V loads. The rating of the breaker as 200A is just a naming standard, it really is a 48kw breaker.
The breaker only sees wattage and converts it to heat in order to activate the trip mechanism. Since the wattage is the same as 200a/240V the breaker does not trip with 400 amps/120V.
A 200 amp breaker can trip with very low current passing if a bad connection is present nearby to transmit enough heat into the breaker.
Added with edit: These large breakers use a magnetic current sensor and not heat to sense current.
Should have put "equivalent load amps" to the reference to 400 amps but I should have used wattage and described it differently.
Last edited by Bruce King; 04062008 at 12:18 PM. Reason: added 2 lines at bottom

03312008, 08:04 AM #38
Re: Too much for 200A
Correct.
Now each side of the main breaker has 200 amps going through it, so it is 400 amps total.
There are no free amps or watts available, if you have four 100 amp 120V loads you can bet the power company is sending you 400 amps using two 120V legs.
The power company is only going to be able to squeeze 200 amps through that 200 amp breaker.
The difference is that it is only 120V loads.
The rating of the breaker as 200A is just a naming standard, it really is a 48kw breaker.
The breaker only sees wattage and converts it to heat in order to activate the trip mechanism. Since the wattage is the same as 200a/240V the breaker does not trip with 400 amps/120V.
The breaker does not care whether it is being used on a 120 volt circuit or a 240 volt circuit, it is only 'monitoring' the current flowing through it.
A properly functioning 200 amp breaker is going to trip at 200 amps (or close to it). You will not get 400 amps through a functioning 200 amp breaker  that is what I was saying above in my other posts and that is still correct.
Watts? It does not have any idea what a watt is nor does it care.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 12:42 PM #39
Re: Too much for 200A
"No matter how you look it it, regardless how high or low the voltage is,  you only have 200 amps available  we all agree on that, right?"
Jerry,
If I was simply describing the 240 volt service, then yes, but it's not "regardless" and in the context of Tim's posts it seemed very obvious, at least to me, that he was describing the total 120 volt amperage available if you added the available 200 amps on each leg. I really don't get how you can agree, finally, that it is possible to run a total of 400 amps of 120volt load by using both legs and then say that that would not be available.
So no, I don't think "we all" agree, but at this point it really is just semantics and, as I think most understand the basic principles, it's not worth a continuing argument. The only reason I got involved in this in the first place was because I found the "personal" attacks on Mr. Voss's knowledge and/or intelligence unwarranted and distasteful. Sadly, I see you have your wet noodle out again, but still haven't apologized to him for those remarks.

03312008, 03:18 PM #40
Re: Too much for 200A
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 03:26 PM #41
Re: Too much for 200A
Jerry, How many maximum watts do you think you can get from the service with only 120V balanced loads on both legs?
How many RV'ers out there have 50 amp 240V/120V on their rig?
Same thing applies, you can get 100 amps of 120V balanced distribution.
The only RV equipment that uses 240V is old dryers or ones that have residential equipment installed. The manuf's use 120V RV equipment such as 120V dryers.
Added with edit: should read "equivalant of 100 load amps"
Last edited by Bruce King; 04062008 at 12:12 PM. Reason: added last line

03312008, 04:10 PM #42
Re: Too much for 200A
Bruce,
That is exactly what I pointed out above  the misuse of the terminology.
We are talking amps and now you say "watts".
How many RV'ers out there have 50 amp 240V/120V on their rig?
Same thing applies, you can get 100 amps of 120V balanced distribution.
Make up your mind and use those terms in the correct way.
The only RV equipment that uses 240V is old dryers or ones that have residential equipment installed. The manuf's use 120V RV equipment such as 120V dryers.
RV power is connected such that there is no 240 volts available  all loads, and wiring, are 120 volts only.
Think of it as a multiwire circuit.
See my drawing to help explain where there is not 400 amps.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 06:34 PM #43
Re: Too much for 200A
Jerry, I'm starting to worry about you : )
Watts can be used in place of amps with simple math and is actually preferred in the industrial world so that no one gets confused on which voltage is being talked about, as is the case here.
Added with edit: since we KNOW what voltages we are discussing here!
Your picture is nice, just add the loads present on each leg and you have your "400 amps", (410 amps as shown on the picture)
50 amp RV's are fed with the exact same hookup as a 4wire 240V range.
The RV does not distribute the 240V but it has it available in the control box if you wanted to add a 240V outlet. The RV uses the 240V 50a circuit as two 50 amp 120V busses that distribute to various loads in the RV. 240V is present inside the RV in the control box, stick a meter across the two 50 amp busses and wham it will read 240V, but you know that, you just want to argue.
Heres a few links on the easy 50 amp 240V RV connection for anyone who might not know. The one that electricians screw up is the big 30A 120V RV outlet, they wire 240V to those all the time and smoke RV's.
http://www.myrv.us/Imgs/PDF/50amp%20Service.pdf
Well, what is 50 amp service?
I know you had a 50 amp RV and fully understand that it connects to 240V shore power so what is your problem? I see you changed the subject to only the inside distribution where I posted about the feed AND the interior distribution.
Post us some code and quit picking fights on here about theory, hahahaha.
Last edited by Bruce King; 04062008 at 12:14 PM. Reason: added line as shown

03312008, 08:32 PM #44
Re: Too much for 200A
No, power ("watts") equals amps (current) times resistance (load), "watts" and "amps" are two different animals. "Watts" is the 'power used', "amps" is the current flow through the load using that 'power'.
with simple math and is actually preferred in the industrial world so that no one gets confused on which voltage is being talked about, as is the case here.
Starting talking "watts" and it has no relationship to voltage other than based on the fact that voltage equals power ("watts") divided by amps (current).
Your picture is nice, just add the loads present on each leg and you have your "400 amps", (410 amps as shown on the picture)
There is only "200 amps" there. See drawing attached.
The RV does not distribute the 240V but it has it available in the control box if you wanted to add a 240V outlet. The RV uses the 240V 50a circuit as two 50 amp 120V busses that distribute to various loads in the RV. 240V is present inside the RV in the control box, stick a meter across the two 50 amp busses and wham it will read 240V, but you know that, you just want to argue.
What is a multiwire circuit?
Right, you just described it.
What I stated was "RV power is connected such that there is no 240 volts available  all loads, and wiring, are 120 volts only."
RVs ARE connected "such that there is no 240 volts available" and "all loads, and wiring, are 120 volts only".
RVs ARE connected that way. The exception (every rule has an exception  that's what 'they' say, it is almost always true) would be 'some' ultra high end RVs ... 'some' ultra high end RVs are wired to used the 240 volts of the supply.
RVs are supplied by three basic wiring configurations:
 20 amp / 120 volt
 30 amp / 120 volt
 50 amp / 120 volt multiwire (giving two 50 amp 120 volt circuits)
  (with those rare exceptions using the 50 amp / 120 volt multiwire as the supply for a 50 amp / 240 volt service connection)
Those exceptions are possible because EVERY multiwire circuit has 120 volt circuits with 240 volts between them  the 240 volts is just not used, in multiwire circuits, using the 240 is not allowed.
Heres a few links on the easy 50 amp 240V RV connection for anyone who might not know. The one that electricians screw up is the big 30A 120V RV outlet, they wire 240V to those all the time and smoke RV's.
Bob (or maybe it was Mary) is 'mostly right' in their comments.
This is where they are wrong:
"I have heard that there is an RV park some place in Arizona that the park owner has tied 1 leg of power using a 4/0 wire for the hot to both busses in a RV receptacle panel. He has then put in a double pole 50 amp breaker. By doing this he is really delivering 50 amps at 120 volts to the customer."
If the circuit were wired that way, it would be like using parallel conductors, in which case you could still pull 50 amps through EACH leg because EACH leg as a 50 amp breaker.
Post us some code and quit picking fights on here about theory, hahahaha.
  (A) General. Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.
  (C) LinetoNeutral Loads. Multiwire branch circuits shall supply only linetoneutral loads.
   Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
   Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branchcircuit overcurrent device.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

03312008, 09:17 PM #45
Re: Too much for 200A
Jerry, you should be kicked off this board for taking part of my sentence about amps and watts and posting it as a quote to make it look wrong. This is pure BS and you know it.
You provide absolutely no help on this board that can not be easily supplied by many other inspectors. You actually hinder the message board with this type of crap because many inspectors visit this site and do not participate because of you.
You really screwed up this time ole boy. hahahaha : )
No hard feelings, I worked with several guy's just like you for 20 years, I have to admit I liked to jerk their chains too. : )

03312008, 09:31 PM #46
Re: Too much for 200A
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 06:48 AM #47
Re: Too much for 200A
Jerry, when you know other variables, as we both do here (voltage), current and wattage *CAN* be easily interchanged wih math, watts = volts x amps.
Four loads connected as balanced 120V with 100 amps each can be seen at the main, 200A 48,000 watt breaker as any of these:
one 48000 watt feed
one 48kw feed
one 48000va feed
one 48kva feed
one 240V feed at 200 amps
two 120V feeds at 200 amps each, two x 200= 400 amps total derived from the main. 400 x 120 = 48,000va or 48,000 watts
Stop the BS Jerry, now you have the math.
But, here we go again, YOU already knew all of this!
Your goal is to get the last post, so go ahead and post some more BS! hahahahahaha!
added with edit: should have used "equivalent" to 400 load amps to prevent misunderstanding.
Last edited by Bruce King; 04062008 at 12:15 PM. Reason: added last line

04012008, 07:08 AM #48
Re: Too much for 200A
No, you still cannot interchange watts and amps or volts.
Not unless you are going to say something like 48,000 watts (240 volts times 200 amps) and interchange it with 200 amps (48,000 watts / 240 volts)  simply doing what you did does nothing and tells nothing. Now, if you want to start writing all that out when you start trying to interchange the two DIFFERENT terms, by all means, do so, but you didn't, so don't try to crap (BS) your way out of what you said.
Four loads connected as balanced 120V with 100 amps each can be seen at the main, 200A 48,000 watt breaker as any of these:
one 48000 watt feed
one 48kw feed
one 48000va feed
one 48kva feed
one 240V feed at 200 amps
two 120V feeds at 200 amps each, two x 200= 400 amps total derived from the main. 400 x 120 = 48,000va or 48,000 watts
You could say it this way:
two 120 volt 100 amp loads connected together with the center point grounded across 240 volt making one 240 volt 100 amp load, which equals 24,000 VA (watts sotospeak), there are two of these circuits for 48,000 VA total.
No where in there is there 400 amps.
You keep coming up with some fictitious 400 amps which just are not there.
Stop the BS Jerry, now you have the math.
But, here we go again, YOU already knew all of this!
Your goal is to get the last post, so go ahead and post some more BS! hahahahahaha!
Whether I post last trying to explain it to you, or whether you post last saying 'I finally got it.' makes no difference to me. Or even if someone else posts last trying to explain it to you. I'm trying to help you understand what you apparently do not understand  not that I know everything about this, as was evidenced further up the thread but maybe you cannot bring yourself to say that?
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 08:17 AM #49
Re: Too much for 200A
Jerry lets look at it this way 2002 NEC table 310.16 allows 4/0 aluminum XHHW (typical dwelling unit service wire) 180 amps ( 310.15 b allows it to be used for 200 amp service or feeder) so each phase has a allowable ampacity of 200 amps.This being said in theory phase A could have 200 amps of 120 volt loads only and a 4/0 service would not be overloaded also phase B could have 200 amps of 120 volt loads only and a 4/0 service would not be overloaded. That being said you would have 400 amps of 120 volt loads only allowable, phase A at 200 amps and phase B at 200 amps and if they were exactly balanced 0 load on the grounded conductor.

04012008, 09:01 AM #50
Re: Too much for 200A
Paul,
"That being said you would have 400 amps of 120 volt loads only allowable, phase A at 200 amps and phase B at 200 amps and if they were exactly balanced 0 load on the grounded conductor."
That's the part that you and Bruce are not getting ...
The current going in through the Phase A conductor is the same as that in the Phase B conductor, not additive, not two 200 amp current, *the same 200 amp current* ... not "400 amps".
Okay, let's try this.
Take a swimming pool filled with water, install a submersible pump which can pump 200 gallons per minute. This is the 'power source'.
Take a hose suitable in size to allow that 200 gallons per minute to flow through it and connect one end to the pump and the other end to a tee to a load which uses 100 gallons per minute to rotate a motor, then, from that tee, run another hose to another load which also uses 100 gallon per minute to rotate a motor. Got it so far?
Okay, now, connect the first 100 gpm motor to another 100 gpm motor, then connect the second 100 gallon per minute motor to another 100 gpm motor. Still following me?
Finally, connect another hose from the farthest 100 gpm motor, add a tee, connect in the nearest 100 gpm motor to the tee, and then connect the tee to a hose draining back into the swimming pool.
Got it?
This is what we have:
Hose out carrying 200 gpm, teeing off 100 gpm with 100 gpm continuing on.
The first teeing off of 100 gpm goes through two 100 gpm motors back to the return line.
The other 100 gpm goes through the other two 100 gpm motors back to the return line.
How many gpm are going through the supply and return line?
400 gpm?
Or is it just 200 gpm?
It is just 200 gpm.
Same set up with electricity and current flow. You have 100 amps, the same 100 amps, going through two 100 amps loads, with two such paths of 100 amps each, for a total of 200 amps.
NOT "400 amps".
Got it?
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 10:54 AM #51
Re: Too much for 200A
Jerry,
I forgot one thing, at the beginning of this discussion someone mentioned "equivalent to 400 amps".
I should have included that word "equivalent" in my posts but thought we were all discussing practical things and not the actual waveform behavior of the service.
Technically there are 200 amps flowing within the 240V source but we were trying to use the system as an example to show that you can use it as only a 120V system and get FOUR 100 amp loads to operate without tripping the 200 amp breaker.
I hope you do agree that the power cost to run four hundred amps of 120V loads is the same as 200 amps 240V because it really is.
Anyone that did not learn something from this thread is not being honest with themselves. I know I have learned how to also view the weird setup we were discussing as a 240V system even though we were using only 120V loads in the example.

04012008, 10:58 AM #52
Re: Too much for 200A
Here's a quote from Paul Dickerson (a NACHI member) that explains it very well.
Lets follow the electrons. For 1/120th of a second, 200 amps will flow into the panel through Leg A, the same 200 amps will then flow through the 120V loads connected to leg A, the same 200 amps will then flow to the neutral bus, the same 200 amps will then flow through the 120V loads connected to leg B, then the same 200 amps will flow out of the panel through leg B. Then the current reverses and takes the same path backwards. It is all the same electrons.

04012008, 11:27 AM #53
Re: Too much for 200A
I'm not going to pick sides; I'll just try to explain what I believe to be true, in very simple terms.
power = watts = volt amperes = volts X amps
Absent a fault in the system, and neglecting very small losses due to heat, power leaving the transformer is equal to the power returning back to the transformer.
In a 120/240V threewire "single phase" residential wiring system, the 120 V coming in on the A leg from the transformer, and the 120 V coming in on the B leg from the transformer are 180 degrees out of phase with each other.
With your 200 amp main breaker installed, you can pull 120 V at 200 amps (24 kw) from the transformer on the A leg. At the same time, you can pull 120 V at 200 amps (24 kw) from the transformer on the B leg, for a total of 48 kw. 240 V branch circuits are formed by tapping into both the A & B bus bars in the panel, after the main OCPD.
If you pull 48 kw off of the transformer you must send 48 kw back to the transformer. Some goes back out of phase to what's coming in on the A, some goes back out of phase to what's coming in on the B, and if there is any unbalanced current, it goes back on the shared neutral. If the loads on A & B are perfectly balanced, there should be no current flowing on the shared neutral back to the transformer.
It should be possible to hook up four 120V loads each drawing 100 amps of current from the transformer at the same time without blowing the 200 amp main if they are balanced on the A & B. The power draw from each of those loads is 12 kw, or 48 kw total.
You can't equate amps to power without also specifying the voltage at which the amps are being measured. In this example you are in fact pulling a total of 400 amps off the transformer at 120 volts (48 kw). If you throw clamp meters on the service conductors you should measure 200 amps at 120 volts on the A, 200 amps at 120 volts on the B, and none on the neutral.
Unbalance that 48 kw load and you'll blow the main on whichever leg is trying to pull more than 200 amps at 120 volts (24 kw). The main OCPD will not let you pull more than 200 amps at 120 volts through either the A or the B legs.
If the system is wired and working properly to stabilize the voltage, you shouldn't measure more than 200 amps at 120 V (referenced to ground) on any individual conductor that runs from the transformer to the main OCPD as long as the duration is less than the trip point of the OCPD. This should be true whether the load is balanced or unbalanced.
Last edited by Brandon Chew; 04012008 at 12:05 PM.

04012008, 12:35 PM #54
Re: Too much for 200A
Jerry what you show with your pump is from phase A to the grounded conductor the power supply (4/0) in my example is allowed 200 amps there are two power supply's phase A and phase B the main is only passing 200 amps per phase but there are two phases of 200 amps each. If I were to connect phase A with two 100 amp loads 120 volt phase A would carry 200 amps and the grounded conductor would carry 200 amps no overload now add phase B with two 100 amp loads 120 volt phase B would carry 200 amps and in theory the grounded conductor would balance at 0 amps.

04012008, 12:58 PM #55
Re: Too much for 200A
It is still NOT "equivalent to 400 amps". It would be, as Brandon explained, hopefully better than I have been, "equivalent" to 48,000 watts ... but that gets into interchanging the terms "watts" and "amps" again, which I also tried to explain, and Brandon also explained.
Technically there are 200 amps flowing within the 240V source but we were trying to use the system as an example to show that you can use it as only a 120V system and get FOUR 100 amp loads to operate without tripping the 200 amp breaker.
I hope you do agree that the power cost to run four hundred amps of 120V loads is the same as 200 amps 240V because it really is.
Anyone that did not learn something from this thread is not being honest with themselves. I know I have learned how to also view the weird setup we were discussing as a 240V system even though we were using only 120V loads in the example.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 01:09 PM #56
Re: Too much for 200A
Bruce,
Paul almost has it right.
This:
Should read as follow:
Lets follow the electrons. For 1/120th of a second,
1) 200 amps will flow into the panel through Leg A,
2) the same 200 amps will then flow through the 120V loads connected to leg A,
3) the same 200 amps will then flow to the second set of 120 volt loads connected to the first set of 120 volt loads,
4) the same 200 amps will then flow to leg B,
5) then the same 200 amps will flow out of the panel through leg B.
6) Then the current reverses and takes the same path backward. It is all the same electrons.
As set up for our discussion  *no* current will flow on the neutral bus or neutral conductor.
Now, in the photo I posted with the extra 10 amp load, another 10 amps will be flowing through the neutral conductor and the top phase leg, which we can call Leg A. Which makes 210 amps, which will likely trip the breaker (which is why I put it there, to help show that "400 amps" would trip the breaker as even "210" will trip the breaker  but that "400 amps" discussion now seems to be history, as well it should be).
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 01:14 PM #57
Re: Too much for 200A
First, no neutral current will flow in the neutral when there are those four 100 amps loads being discussed.
Second, you do not have "two phases of 200 amps each", you have 'two phases with the same 200 amps in each' ... therein lies the big difference.
Thinking there are *two* sources of 200 amps leads one to think there is 400 amps. Understanding that there is only one source, with two legs, which have *the same* 200 amps in them, hopefully allows one to understand that there is only 200 amps.
Sometimes electricity is difficult to understand, that is why I switched to using the water example  virtually everyone understands water flow, not everyone gets electrical current flow.
My water example would be representative of DC, for AC, simply switch the supply and return hoses 120 times per second (I figured it would be easier to understand without complicating matters with 'switching the supply and return hoses 120 times per second' ).
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 01:46 PM #58
Re: Too much for 200A
This is getting a little silly, but I'm going to stick by 100+100+100+100 does indeed = 400
Physics doesn't lie, so if Power = Volts x Amps and I have 240v x 200a then I also have 120v x 400a
I can wire up a 99% efficient AC to AC voltage converter (transformer) that will transform my 240v x 200a service into 120v x 396a to run those 2 giant 200amp 120v loads I have. I really do have the equivalent of 400amps. But I don't need to, because the utility company has already given me a 120v neutral tap.
It's true you will never see more than 200 amps on any given wire (unless you use the transformer mentioned above), but the amps ARE additive, even though they are the same amps. That is because the same amps are going through two 200a 120v loads, so they are doing twice the work as one 120v load. Thus, they are "equivalent" to 400amps at 120v.

04012008, 02:51 PM #59
Re: Too much for 200A
Another way to look at it is as a wave on a oscillascope. You have two waves of the same amplitude but peaking at opposite times of each other thus cancelling each other out. At no point can Phase A and Phase B become an additive value.

04012008, 03:59 PM #60
Re: Too much for 200A
The way I see it is that the power company charges by the KW. So if you have a 200 amp 240 load your cost will be for 48 KW.If you have two 200 amp 120 volt loads you are still paying for 48 KW. Your cost for each load will be the same and both loads can be fed from the same 120/240 volt single phase pane with a 200 amp main breaker.

04012008, 05:01 PM #61
Re: Too much for 200A
Yes, "100+100+100+100 does indeed = 400", HOWEVER ... you do not have "100+100+100+100", you only have "100+100" and that does indeed = 200
Physics doesn't lie, so if Power = Volts x Amps and I have 240v x 200a then I also have 120v x 400a
You do have 240 volts X 200 amps. but you do not have 120 volts X 400 amps.
You have 120 volts X 100 amps four times, but you do not have 400 X anything.
(sigh)
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 05:14 PM #62
Re: Too much for 200A
Actually, what you have is *one* waveform, simultaneously in Phase A and Phase B.
The current flow in Phase A and out Phase B for 1 120/sec, then flows in Phase B and out Phase A for the next 1 120/sec, then it repeats that process for the next 2 120/sec. At this point in time, 1/60 of a sec later, you have completed one cycle, one waveform which rises from 0 to +170 then drops to 0 to 170 then rises back to 0.
Think of the water hoses being switched 60 times a second, what you are describing would be both water hoses being used on at the same time, creating no potential difference and thus no flow (voltage is potential, which is what creates current flow).
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 05:16 PM #63
Re: Too much for 200A
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com

04012008, 08:48 PM #64
Re: Too much for 200A
Now I'm not sure what you are saying. You say I have 120v x 100a x 4. Yes, I agree. But you also say I have "100+100=200", don't agree.
What about this? Can I light 400 1amp 120volt light bulbs with my 200amp 240volt service?

04022008, 06:31 AM #65
Re: Too much for 200A
Tim,
This is the difference in how you are saying it.
You are saying 100+100+100+100=400 (if they were added up that way, you would be correct, but they do not add up that way).
What you really have is 100+(that same 100 goes through the next load)+100+(that same 100 goes through the next load)=200
What about this? Can I light 400 1amp 120volt light bulbs with my 200amp 240volt service?
That would make 1+(that same 1 flows through the next lamp)+the same thing 199 more times=200
______________ Phase A < 1 amp current flow

1 amp Lamp

______________ Neutral 0 amp current flow

1 amp lamp

______________ Phase B > 1 amp current flow
Add as many pairs of lamps as you wish, there will be an additional 1 amp current flow per pair of lamps wired that way. 200 pairs of those lamps would = 200 amps.
Add one single lamp between Phase A and Neutral and there will be an additional 1 amp current flow, this will be the same for each single lamp added between a given Phase A and Neutral.
Now add a single lamp between Phase B and Neutral and that will 'pair up' with one of the single lamps on Phase A and Neutral not adding any current flow  all it will do is take 1 amp from the Neutral and run it through Phase B  same 1 amp though.
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
www.AskCodeMan.com
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