Thread: Subpanel

Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?

Mark

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Mark,
It's going to depend on the wire size to the 100 amp panel. If they are # 8 you have 40 amp. I don't think you can stick a #2 wire into a 40 amp breaker without cutting out half the strands in the conductor.

Originally Posted by Mark Schniers

Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?

Mark

First, you do not have a sub-panel, you have two "panels", and both are to be wired the same. I am presuming that your "main panel" (which is simply also a "panel") is not actually "service equipment" as "service equipment" is wired differently than "panels" are wired.

With that clarified, ...

You stated the pole barn was fed off a double pole 40 amp breaker, which means the pole barn has 40 amp rated FEEDERS supplying it.

Thus, you could have a 60 amp, 100 amp, or even a 200 amp panel in the pole barn and be okay as you are not going to get more than 40 amps through it because of the double pole 40 amp breaker supplying it.

You would have a problem if the panel in the pole barn was only rated at 30 amps as then the panel would be rated less than the overcurrent protection protecting it - and that would not be good.

You have a maximum potential of 40 amps per leg at that panel. The panel may be rated higher and most likely is however the 2 pole 40 amp breaker is limiting the potential to 40 amps per leg.
Tony Dolce
Meade Electric
Phoenix electrician affordable repairs and installations electrical service in Phoenix

Originally Posted by Tony Dolce

You have a maximum potential of 40 amps per leg at that panel. The panel may be rated higher and most likely is however the 2 pole 40 amp breaker is limiting the potential to 40 amps per leg.
Tony Dolce
Meade Electric
Phoenix electrician affordable repairs and installations electrical service in Phoenix

No. That double pole 40 amp is limiting the current to 40 amps TOTAL, not "per leg", i.e., you will NOT be able to get 40 amps "per leg" or 80 amps total from that double pole 40 amp breaker.

The best way to think of it is like this: 40 amps out from one breaker to the feeder conductor to the pole barn panel through whatever is running out there, then back into the pole barn panel to the other feeder conductor to the other 40 amp breaker ...

... 40 amps TOTAL ... the SAME 40 amps in each leg ...

... now reverse that current flow, and reverse it again, reversing the current flow 60 times per second.

" You would have a problem if the panel in the pole barn was only rated at 30 amps as then the panel would be rated less than the overcurrent protection protecting it - and that would not be good."

Why, would that be a problem?

Originally Posted by Rick Cantrell

" You would have a problem if the panel in the pole barn was only rated at 30 amps as then the panel would be rated less than the overcurrent protection protecting it - and that would not be good."

Why, would that be a problem?

Rick,

Because the overcurrent protection for that panel is 40 amps.

You are not allowed to use a panel with a smaller rating than its overcurrent protection rating.

Higher rating, yes, lower rating, no.

Ok, help me understand this.

It's OK to have, 125, 150, or 200 amp service feed a 200amp service panel with a 100 amp main breaker.
And
It's OK to have a 20 amp circuit and breaker power a 60watt light.

But, it's not OK to feed a panel with a 30amp main breaker from another panels 40amp breaker.
I think I worded that right.

Originally Posted by Rick Cantrell

Ok, help me understand this.

It's OK to have, 125, 150, or 200 amp service feed a 200amp service panel with a 100 amp main breaker.

Yes, because the main breaker is on the load side of the service entrance conductors PRIOR TO the service equipment's bus bars.

The only thing NOT protected by the 100 amp main breaker, then, are the service entrance conductors themselves.

Question: With that 200 amp service equipment, what would you need to do to the service entrance conductors if the main was replaced with a 200 amp main?

Answer: The service entrance conductors would need to be replaced with ones which had a minimum rating of 200 amps.

But, it's not OK to feed a panel with a 30amp main breaker from another panels 40amp breaker.

Actually, that is exactly the same, except when not service entrance conductors the overcurrent protection is on the line side of the feeders (with a few exceptions not applicable here).

With service entrance conductors the overcurrent protection on on the load side, at the service equipment, OUTSIDE the building or structure, or, "as close as possible to the point of entrance" of the service entrance conductors INSIDE the building or structure.

With feeders, there is no requirement to keep them outside the building or structure as they are ALREADY protected on their line side.

It's OK to have a 20 amp circuit and breaker power a 60watt light.

Yep.

Because you are not even attempting to protect the 60 watt light, heck, make it a 4 watt night light ... the breaker is to protect the *circuit conductors* ... WHETHER OR NOT ... ANYTHING is plugged in or connected to them.

Hopefully I helped explain why?

Originally Posted by Jerry Peck

No. That double pole 40 amp is limiting the current to 40 amps TOTAL, not "per leg", i.e., you will NOT be able to get 40 amps "per leg" or 80 amps total from that double pole 40 amp breaker.

The best way to think of it is like this: 40 amps out from one breaker to the feeder conductor to the pole barn panel through whatever is running out there, then back into the pole barn panel to the other feeder conductor to the other 40 amp breaker ...

... 40 amps TOTAL ... the SAME 40 amps in each leg ...

... now reverse that current flow, and reverse it again, reversing the current flow 60 times per second.

Wrong:
40 amps x 120 volts = 4800 watts
40 amps x 240 volts = 9600 watts

9600 watts divided by 120 volts = 80 amps total or 40 amps per leg.

Originally Posted by Tony Dolce

Wrong:
40 amps x 120 volts = 4800 watts
40 amps x 240 volts = 9600 watts

9600 watts divided by 120 volts = 80 amps total or 40 amps per leg.

Nope, not quite, but you are getting there (I hope).

You need to understand what you are saying.

There IS ONLY 40 amps flowing through EACH breaker, and it is the SAME 40 amps which flowed through the other breaker.

This is what you said:

Originally Posted by Tony Dolce

You have a maximum potential of 40 amps per leg at that panel. The panel may be rated higher and most likely is however the 2 pole 40 amp breaker is limiting the potential to 40 amps per leg.
Tony Dolce
Meade Electric
Phoenix electrician affordable repairs and installations electrical service in Phoenix

There is THE SAME 40 amps flowing through Phase A as there through Phase B, and that one and only 40 amps is at 240 volts.

When you get to the bus bars, which is not what we are talking about, we were talking about the double 40 amp breaker protecting the pole barn panel, you then and only then can use the 120 volts calculation.

Okay, let's go back to Electrical 101:

40 amps at 240 volts = 9600 watts

That is what is at that double pole 40 amp breaker and that is what is at that pole barn panel.

Agreed?

40 amps at 120 volts at each bus bar = 4800 watts each bus bar

That is what is available at EACH bus bar at that pole barn.

Agreed?

There are TWO bus bars, to you have 4800 watts + 4800 watts = 9600 watts.

Agreed?

Question: How many amps are flowing through each section of that double pole 40 amp breaker?

Answer: 40 at maximum draw.

Question: How many amps is flowing through that double pole 40 amp breaker?

Answer: 40 amps maximum draw.

Agreed?

If not, what am I not explaining where you agree and understand?

Originally Posted by Jerry Peck

Nope, not quite, but you are getting there (I hope).

You need to understand what you are saying.

There IS ONLY 40 amps flowing through EACH breaker, and it is the SAME 40 amps which flowed through the other breaker.

This is what you said:


There is THE SAME 40 amps flowing through Phase A as there through Phase B, and that one and only 40 amps is at 240 volts.

When you get to the bus bars, which is not what we are talking about, we were talking about the double 40 amp breaker protecting the pole barn panel, you then and only then can use the 120 volts calculation.

Okay, let's go back to Electrical 101:

40 amps at 240 volts = 9600 watts

That is what is at that double pole 40 amp breaker and that is what is at that pole barn panel.

Agreed?

40 amps at 120 volts at each bus bar = 4800 watts each bus bar

That is what is available at EACH bus bar at that pole barn.

Agreed?

There are TWO bus bars, to you have 4800 watts + 4800 watts = 9600 watts.

Agreed?

Question: How many amps are flowing through each section of that double pole 40 amp breaker?

Answer: 40 at maximum draw.

Question: How many amps is flowing through that double pole 40 amp breaker?

Answer: 40 amps maximum draw.

Agreed?

If not, what am I not explaining where you agree and understand?

Wrong:
Phase a has A 40 amp potential and phase B has a 40 amp potential. Yuell get it! Lets make this simple. A 15 amp single pole breaker has 15 amps available - 2 seperate 15 amp single pole breakers each have a capaciety for 15 amps each. Now instead of using a 2 pole breaker lets say we have 2 single pole 15 amp breakers one on top of the other, basically the same thing without the common trip. How much power does each breaker allow. Right 15 amps each or each leg. A 3 pole breaker would mean each leg has the maximum capicety of 15 amps per leg. Remember the perpose behind the breaker, it's to protect or limit the amount of amperage that can flow over a wire. Each wire is sized and rated to safely carry only so much power. Because a 2 pole breaker protects 2 wires it limits the total amount of available amperage per each individual wire. Hence a 2 pole 15 has #14 wires, a 2 pole 20 has #12 wires, a 2 pole 30 has #10 wires. Are you starting to get this most basic concept or should I continue. Each wire is protected individually for 40 amps in the forementioned question thus there is a total of 40 amps available on each leg or 80 amps total.

Two breakers stacked on top of each other are out of phase by 180º.

When they wired my garage, they used two "hot" wires (one to each breaker) and one neutral.

Originally Posted by Tony Dolce

Wrong:
Phase a has A 40 amp potential and phase B has a 40 amp potential. Yuell get it!

Jeez, I can't believe I am explaining this to an electrician ...

"Potential" is VOLTAGE, not current (amps).

We are discussing AMPS, not voltage.

There is a maximum of 40 amps which will be allowed to flow through that breaker on either phase of the breaker (provided the breaker is operating properly and provided we all realize that the 40 amps is not exactly 40.000 amps and then it trips, but for the discussion underway, "40 amps" is sufficient to use for where it trips).

Each wire is protected individually for 40 amps in the forementioned question thus there is a total of 40 amps available on each leg or 80 amps total.

No ... no ... no ... there is only 40 amps TOTAL available THROUGH that double 40 amp breaker ... 40 amps on each leg - if you try to pull 80 amps through that breaker it had better trip.

Here is a question for your electrical knowledge: You walk up to a house with a 200 amp main service disconnect ... does that house have 200 amps available or 400 amps available.

I am pretty sure that every home inspector here knows the answer, do you?

There are some that think 200a @ 240v is the same thing as 400a @ 120v.
It is not.

There are some that think 200a @ 240v is the same thing as 400a @ 120v.
It is not.

400Amps @ 120V....imagine the size of the conductor!

Originally Posted by Jerry Peck

Jeez, I can't believe I am explaining this to an electrician ...

"Potential" is VOLTAGE, not current (amps).

We are discussing AMPS, not voltage.

There is a maximum of 40 amps which will be allowed to flow through that breaker on either phase of the breaker (provided the breaker is operating properly and provided we all realize that the 40 amps is not exactly 40.000 amps and then it trips, but for the discussion underway, "40 amps" is sufficient to use for where it trips).



No ... no ... no ... there is only 40 amps TOTAL available THROUGH that double 40 amp breaker ... 40 amps on each leg - if you try to pull 80 amps through that breaker it had better trip.

Here is a question for your electrical knowledge: You walk up to a house with a 200 amp main service disconnect ... does that house have 200 amps available or 400 amps available.

I am pretty sure that every home inspector here knows the answer, do you?

200 amps per leg is what's available. And don't be be such an arrogant little man - you'll start to learn this way.

Originally Posted by Tony Dolce

200 amps per leg is what's available. And don't be be such an arrogant little man - you'll start to learn this way.

Now answer the rest of my question.

You are showing your arrogance, and lack of knowledge, by answering ONLY PART OF the question.

*I* asked: "Here is a question for your electrical knowledge: You walk up to a house with a 200 amp main service disconnect ... does that house have 200 amps available or 400 amps available."

Answer the last part - I made it red text so you would make sure not to "miss it" this time.

I see you took your electrical contractor signature off, why?

Originally Posted by Jerry Peck

Now answer the rest of my question.

You are showing your arrogance, and lack of knowledge, by answering ONLY PART OF the question.

*I* asked: "Here is a question for your electrical knowledge: You walk up to a house with a 200 amp main service disconnect ... does that house have 200 amps available or 400 amps available."

Answer the last part - I made it red text so you would make sure not to "miss it" this time.

I see you took your electrical contractor signature off, why?

OK you want to play word games. Each leg has a total of 200 amps available. This means if either leg pulls over 200 amps the common common trip will trip both legs but since each leg has 200 amps available there is a total of 400 available amps available. Lets make it simple for you. Heres an experment for you to try, just don't hurt yourself. Take a 15 amp 2 pole breaker and wire in 2 outlets. Use one hot terminal on the breaker for each outlet so it is 120 volts. Now plug in an 1800 watt hair dryer to each outlet, the breaker does not trip because there is 1850 watts at each outlet of 15 amp each. Thus 15 amp per leg or 30 amps total. Your turn hero.

Originally Posted by Speedy Petey

There are some that think 200a @ 240v is the same thing as 400a @ 120v.
It is not.

Same amount of power
120V x 400A = 48000 watts
240V x 200A = 48000 watts

Based on single phase 120/240volt

Tony,

I'll make it REAL SIMPLE FOR YOU ...

... so, ... you are saying that is a 400 amp service?

Yes or no?

Originally Posted by Jerry Peck

Tony,

I'll make it REAL SIMPLE FOR YOU ...

... so, ... you are saying that is a 400 amp service?

Yes or no?

No it's a 200 amp service 120/240 volt single phase. Now let me make it simple for you. If we go back to our original 40 amp 2 pole breaker feeding a sub panel can you run 4 -18 amp 120 volt devices at the same time without tripping the breaker. Yes or no? It's a simple caculation.
40amps x 240 volts = 9600 watts
9600 watts divided by 120 volts = 80 amps. got it????

Originally Posted by Tony Dolce

No it's a 200 amp service 120/240 volt single phase.

BINGO!

You are now making headway.

That is a 200 amp service BECAUSE there is ONLY *200* amps available.

Now let me make it simple for you. If we go back to our original 40 amp 2 pole breaker feeding a sub panel can you run 4 -18 amp 120 volt devices at the same time without tripping the breaker. Yes or no? It's a simple caculation.
40amps x 240 volts = 9600 watts
9600 watts divided by 120 volts = 80 amps. got it????

Okay, jeez - back to square one again,

Go back to the service discussed above, that 200 amp service, now change 200 amps and put in 40 amps, ... think ... slowly if it helps ... how many amps is that "service" to that pole barn ... think hard now ...

Ready for the answer yet? 40 amps.

THE SAME AS THAT 200 amp service.

If you need me to, I will draw it up for you and label it, being as you are an electrician I am hoping I will not need to do so in crayon.

I may do this for the others, but *I KNOW* the others do not need this done in crayon, they are working with pencils and pens now, which they are using on their thesis work.

Tony,

See if this helps.

If not, well ... I would not want to have you as an electrician, that is for sure ...

Your a slick one....nobody questioned if it was a 40 amp or 200 amp service. I said that a 40amp 2 pole breaker provides 40 available amps on each leg. You said no. Oh and the reason I don't put my website on every post is I'm not a little spammer if ya know what I mean. P.S. humble yourself a little and and the other kids will want to play with you. You can even share your finger painting supplies.
Have a great day! Tony

Originally Posted by Tony Dolce

Your a slick one....nobody questioned if it was a 40 amp or 200 amp service. I said that a 40amp 2 pole breaker provides 40 available amps on each leg. You said no. Oh and the reason I don't put my website on every post is I'm not a little spammer if ya know what I mean. P.S. humble yourself a little and and the other kids will want to play with you. You can even share your finger painting supplies.
Have a great day! Tony

Tony,

This is the first post in which you are not insisting that there is 80 amps there ... does that mean you now understand?

you never answered my question. Can you run 4 18 amp devices at 120 volts at the same time thru a panel that's feed with a 40 amp 2 pole breaker.

You first have to answer my questions: The last one being basically the same as the first one - are you still saying that there is 80 amps in that pole barn panel supplied through a double pole 40 amp breaker, similar to what my drawing depicts.

It really is an easy question, in fact, it is a "Yes." or "No." answer.

Surely that is not too difficult for you, is it?

We ALL make mistakes, and I say I do frequently.

NOT saying you did when you made such an obvious one is not accomplishing anything.

1st I have to, no I asked you first - ARROGANT. I'll answer it for you. Yes you can run 4 - 20 amp circuits at 120 volt off a subpanel feed with one 2 pole 40 amp breaker. You do the math, I'm done with you. Good luck and good riddance.
P.S. I would'nt want you for my home inspector anymore than you would want me for your electrician, bad attitude - arrogant.
P.S.S. try to quite spamming every post I'm sure you have a link by now.
Have a great day!

Originally Posted by Tony Dolce

1st I have to, no I asked you first - ARROGANT.

I will agree that you are the arrogant one, that is for sure.

First ... YOU ... INSIST there is 80 amps in that 40 feed to the pole barn.

Then ... YOU ... try (though not insisting) to tell us there is 400 amps in that 200 amp service.

Finally ... YOU refuse to acknowledge that you were wrong on BOTH accounts AND you try to change the subject direction of the discussion away from your errors ...

If THAT is not "arrogant" I don't know what is.

Man up to it Tony, admit there is not 80 amps in that 40 amp feed and that there is not 400 amps in that 200 amp service.

I'll answer it for you. Yes you can run 4 - 20 amp circuits at 120 volt off a subpanel feed with one 2 pole 40 amp breaker.

Sigh ... you really have no idea what you are talking about, do you?

And you are ... what was that ... oh, right "an electrician".

I will try to explain it to you in r-e-a-l s-i-m-p-l-e terms:
a) if there is a 2-pole 40 amp breaker and a 3-wire cable (as defined in the original post) there is 240 volts at that pole barn panel
b) you have tried to add the neutral to make it a 4-wire cable to allow for your incessant chattering about 120 volts, so, on your behalf ... I let that slide because you still DID NOT KNOW what you were saying
c) whether there is 240 volts or 120 volts / 240 volts at the pole barn panel supplied by a 2-pole 40 amp breaker you WILL NOT GET 80 AMPS there
d) no way, no how

You do the math, I'm done with you. Good luck and good riddance.

So instead of learning how to do the math CORRECTLY you are leaving? Bye.

P.S. I would'nt want you for my home inspector anymore than you would want me for your electrician, bad attitude - arrogant.

And apparently one with more knowledge about electrical than you the electrician.

[qutoe]P.S.S. try to quite spamming every post I'm sure you have a link by now.[/quote]

See, the difference is you don't even know what you are talking about there either.

I have not, like you did, put my web site where it would be pinged, you did because, I guess, you think it would make your web site "enhanced" in some way.

On the other hand, I have not put my web site where it will be pinged, I put it in my signature, like many of us do, so people can go there when and if they want to. Unlike pinging to try to get an automatic hit.

[quote=Mark Schniers;97354]Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?

Jerry's post
"You stated the pole barn was fed off a double pole 40 amp breaker, which means the pole barn has 40 amp rated FEEDERS supplying it"

Now more than a few people might be confused.The original post mentioned 2x40amp breakers and Jerry mentioned 1 double pole 40amp breaker.

Now is it 2x40amp =2 x 120volt and each leg protected by 40amp or 1 x 40amp=240volt?
would the two 40amp legs,if the wires were spliced in a box now be 80 amp?

or ?

[quote=Michael Garrity;97723]

Originally Posted by Mark Schniers

Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?

Jerry's post
"You stated the pole barn was fed off a double pole 40 amp breaker, which means the pole barn has 40 amp rated FEEDERS supplying it"

Now more than a few people might be confused.The original post mentioned 2x40amp breakers and Jerry mentioned 1 double pole 40amp breaker.

Now is it 2x40amp =2 x 120volt and each leg protected by 40amp or 1 x 40amp=240volt?
would the two 40amp legs,if the wires were spliced in a box now be 80 amp?

or ?

As word in the original post:
]

Originally Posted by Mark Schniers

Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?

The IMPLICATION was that the two breakers were side-by-side and tied together, as many people say "2-40 amp" instead of "double pole", with the same meaning.

Now you are, I think, trying to tell us that the "100 amp breaker" in the original post is a "single pole breaker" because the poster did not specifically state it was a double pole breaker?

Me thinks you are trying to stretch things a wee bit far there.

So we shall let Mark (the original poster) clarify what was there, if Mark will come back and do so.

Mark,

1) Was the 2-40 amp breakers side by side like a double pole, or were they tied together with a handle tie to make a double pole breaker?

2) Was the 100 amp breaker a single pole or a double pole breaker?

I suspect that, if anyone was confused, it was limited to Michael (and very few others - if any others), but Mark can clear that up.

Quote:

Originally Posted by Mark Schniers
Branching off the main panel (200 amp) is a 3-wire cable protected by 2-40 amp breakers. This cable feeds a pole barn sub-panel with a 100 amp breaker. What is the rating of the sub-panel service?


The IMPLICATION was that the two breakers were side-by-side and tied together, as many people say "2-40 amp" instead of "double pole", with the same meaning.

Now you are, I think, trying to tell us that the "100 amp breaker" in the original post is a "single pole breaker" because the poster did not specifically state it was a double pole breaker?

Now you are the one that is confused.I asked a question.I did not state anything.I quoted Mark and you.You mentioned double pole not Mark, he said 2-40amp.Only Mark can tell us.Do not think too much Jerry ,I did not mention anything about 100 amp breaker.Just don't add mind reading to your CV and remember to take your pills and don't forget your nap.The facts Jerry ,just the facts

Originally Posted by Michael Garrity

I did not mention anything about 100 amp breaker.

The facts Jerry ,just the facts

I KNOW *YOU* did not, which was my point ... MARK DID, and you were quoting Mark ...

So, what I was stating was "The facts Jerry, just the facts.", i.e., "The truth, and the whole truth, and nothing but the truth", while you were only stating one part of the facts, or only half of the truth, which was all truth, but not the whole truth.

The facts, Michael, just the facts, and ALL of the facts, not just part of them.

I can read, and write, and I can read the entire thing, and even write the entire thing, while you ... it seems you are having a problem with me writing "the entire" wording as you only wanted part of that wording ... seems to me as it is you who may have trouble reading.




Which is why I said only Mark could answer those questions.

Gentlemen! I would gladly clarify but at this point (7 days later) I do not have specific recall. I believe as I wrote the original post it was referring to 2 40- amp single pole breakers feeding a double pole 100-amp breaker.

Thanks for all the clarified confusion.

Originally Posted by Mark Schniers

I believe as I wrote the original post it was referring to 2 40- amp single pole breakers feeding a double pole 100-amp breaker.

Mark,

You've really done it confused us now ... two single pole breaker, not attached with a tie handle (you did not say they were attached with a tie handle) feeding a double pole breaker ...

BUT ... was there a neutral for 120 volt / 240 volt or 240 volt only? I know you said you do not recall, but do you have a photo of the pole barn panel with the cover off?

Hi Tony,

I'm glad to see someone else understands electricity and power.

Jerry will never change and he can't do math. 4 x 20 does NOT = 80 in Jerry's world. I had this same discussion with Jerry before that ran over 200 posts and he still couldn't understand.

He is too obsessed with the fact that it is the same amp in each leg to understand that the same amp can power 2 loads at 120v on a 240v circuit.

Originally Posted by Tim Voss

He is too obsessed with the fact that it is the same amp in each leg to understand that the same amp can power 2 loads at 120v on a 240v circuit.

You really believe that, don't you???

While this is true in a 120/240v circuit, such as a dryer or other appliance with both 120 & 240v loads, it is NOT true in a straight 240v load.
A straight 240v circuit can power ONE load only, NOT 2.

20A @ 240v is NOT the same as 40A @ 120v.