Thread: Voltage Drop

I know I should know this and I read it in one of these post a long time ago. I did a search on this site but could not find it. What is the max voltage drop allowed on any given branch in a home. Does the IRC address this and if so where?

Thanks in advance guys!

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From the 2002 NEC. (bold is mine)- 210.19 Conductors — Minimum Ampacity and Size.- - (A) Branch Circuits Not More Than 600 Volts.- - - (1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.- - - - Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.- - - - - FPN No. 1: See 310.15 for ampacity ratings of conductors.- - - - - FPN No. 2: See Part II of Article 430 for minimum rating of motor branch-circuit conductors.- - - - - FPN No. 3: See 310.10 for temperature limitation of conductors.- - - - - FPN No. 4: Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation. See 215.2 for voltage drop on feeder conductors.

It is in several places in the NEC, Richard posted one of them.

However, FPN means Fine Print Note, and a Fine Print Note is not enforceable.

Originally Posted by Jerry Peck

It is in several places in the NEC, Richard posted one of them.

However, FPN means Fine Print Note, and a Fine Print Note is not enforceable.

True... a FPN is not enforcable. I think the question was not about code, but it was more about "what is the max voltage drop allowed on any given branch in a home."

No. The IRC does not (that I know of) specifically address max voltage drop.

rr

So what is the enforceable voltage drop for residental. Or what do you guys call out as to much drop for standard loads in residential receptacles.

Reason being is my Ideal tester I use on occassions showed 12% at some of the farthest runs but I don't have a bench mark to go from.

Sorry by the time I got that last post out about enforceable Richard replied...........

Originally Posted by Richard Rushing

True... a FPN is not enforcable. I think the question was not about code, but it was more about "what is the max voltage drop allowed on any given branch in a home."

While I will agree with you on that, I will disagree also - because the question said, and you repeated in the quote "allowed", which implies something that "allows" or "dis-allows" something, and, in this case, that would be the NEC, and FPNs are not considered to be 'part of' the code, which is why they are not enforceable. Thus, if not considered 'part of' the code and thus unenforceable, FPNs may not "allow" or "dis-allow" anything.

Which brings us back to the use of the word "allow".

Originally Posted by Mike Schulz

So what is the enforceable voltage drop for residental.

There is none.

Or what do you guys call out as to much drop for standard loads in residential receptacles.

Reason being is my Ideal tester I use on occassions showed 12% at some of the farthest runs but I don't have a bench mark to go from.

I always noted if in excess of 5%, and made a much bigger deal about it if in excess of 8% and made a big deal about it if in excess of 10% (I've found as high as 43% as some GFCI devices which (apparently) did not reset making proper contact.

Also, AFCI breakers tend to create a little voltage drop in those circuits, unlike GFCI breakers.

I always recommended using #12 AWG as a minimum size instead of using #14 AWG - because #12 *cannot be backstabbed* into devices like #14 can ... and that (backstabbing) appears to be the greatest single cause of voltage drop (other than using runs which are just plain too long and voltage drop is created in the length of wire in that circuit).

quote=Jerry Peck

"Also, AFCI breakers tend to create a little voltage drop in those circuits, unlike GFCI breakers."




Boy... that's putting it mildly. AFCI's create between 10-12% regularly (at least what I've seen).

rr

Originally Posted by Richard Rushing

Boy... that's putting it mildly. AFCI's create between 10-12% regularly (at least what I've seen).

I believe you would find that the voltage drop of a circuit with an AFCI *and* with *no* back stabbed devices would not be that bad.

I regularly found 9-17% before AFCIs came in. Whenever the electrician would go back and pull the wires from the backstab holes and put them under the screws, the voltage drop would drop by an average if 2-3% *per device* in series which was also backstabbed. That means if there were 6 receptacle outlets in the master bedroom, you could see a 12-18% reduction in voltage drop.

The best evidence of that was (other than when the electrician would change them to prove me wrong, only to end up proving themselves wrong) is when you have 6 receptacles in that same master bedroom and the voltage drops might be 3%, 5%, 4%, 9%, 6%, 2% as you went around the room. There is no doubt that the 9% one is voltage drop at its backstab connection, and that 4%, 5%, and 6% are up because of their backstab connections.

Of course, I've also seen where those receptacle outlets averaged 16-18% around the room and only improved to about 6% when under the screw terminals - because of the length of wire in the circuit.

Just because someone makes a meter that says "X" it does not necessarily mean anything. Voltage drop is such an example of a 'factoid;' that is, a fact that may have absolutely no meaning whatsoever.

If all the voltage drop occurs at one point, there might very well be a problem. If it is gradual over the entire run ... well, that's simple physics.

The final voltage is relevant. A circuit supplying 132v ... not unheard of in new developments, or near the PoCo transformer .... you can have an 18% drop, and everything will work fine. Yet, if you're only getting 110v ... again, quite possible in an older part of town ... even a 3% drop puts you below the NEMA specs for most things - you're going to be damaging equipment.

Also relevant is the actual load. If the load at the end of the run draws but 5 amps, testing the circuit with a simulated 20 amp load will not give you any relevant information. Naturally, with general purpose convenience circuits, one cannot really say what the loads will be .... but testing to 'worst case' is something for engineers to fret over, not the inspector.

IMO, those testers might have some value in the context of troubleshooting or quality control .... but have no place in the HI's work. The information they provide is useless without being put in context ..... and, frankly, can be only described as 'electrical work.' As such, it is beyond the competence of anyone but a licensed electrical contractor / master electrician to offer an opinion.

Thanks for all the replies, it was quite helpful.

Originally Posted by John Steinke

Just because someone makes a meter that says "X" it does not necessarily mean anything. Voltage drop is such an example of a 'factoid;' that is, a fact that may have absolutely no meaning whatsoever.

Quite to the contrary.

If all the voltage drop occurs at one point, there might very well be a problem. If it is gradual over the entire run ... well, that's simple physics.

Yeah, and that's why voltage drop is supposed to be factored into the calculations - to avoid that physics problem.

The final voltage is relevant.

Quite the contrary.

Also relevant is the actual load.

Yes and no. The actual load will create a varying voltage drop based on the actual load, and, as the load changes (no load in a dwelling is going to be consistent 24/7) the voltage drop will change.

The PERCENT voltage drop at the circuits rated ampacity is what is important as a circuit MAY BE USED as its rated ampacity, thus ...

... testing the circuit with a simulated 20 amp load will not give you any relevant information.

... testing the circuit at rated ampacity provides very relevant information about the ability of the circuit to perform as intended.

IMO, those testers might have some value in the context of troubleshooting or quality control .... but have no place in the HI's work.

And in my opinion no HI should work without one, least they run across the work of an electrician who either does not know about voltage drop, or maybe simply does not care (there are many of both out there).

The information they provide is useless without being put in context ..... and, frankly, can be only described as 'electrical work.' As such, it is beyond the competence of anyone but a licensed electrical contractor / master electrician to offer an opinion.

I've known many HI who have the knowledge and background to explain what, why, and how voltage drop is to a "electrical contractor / master electrician". Many of them just do not understand it and its consequences and thus take no steps to reduce it.

On the issue of testing for voltage drop, we will have to agree to disagree.

On the issue of competence, it's not out opinion that matters. "Competence" is very strictly defined by law ... if you don't have the license, you are, by definition, not competent. Period. It matters not how smart, educated, or experienced you may be. No license, no legal competence.

"Electric work" requires and electrical contractors' license. You might as well argue that HI's could write drug prescriptions.

Originally Posted by John Steinke

On the issue of competence, it's not out opinion that matters. "Competence" is very strictly defined by law ... if you don't have the license, you are, by definition, not competent. Period. It matters not how smart, educated, or experienced you may be. No license, no legal competence.

Quite to the contrary.

A "license" does not mean you are "competent", it only means you are legally allowed to perform the *WORK*.

"Electric work" requires and electrical contractors' license.

*YOUR* license says you can perform the electrical work.

*MY* license says I can inspect electrical work.

*YOU* perform the electrical work, *I* will inspect the electrical work.

I found this old post but found it very interesting because voltage drop is telling on how the circuit is performing.

If you see drop then you are most likely seeing resistance.

Like Jerry says I can tell when circuits have been back-stabbed, I can then pull one cover and verify my reading. So far I am batting a 100% on that diagnosis.

You're dipping your toe in possible liability territory. If you stay true to the generalist licensing of a Home Inspctor, you're OK w/ voltage appears low, substantially less than normal or symptoms observed are consistent with low voltage. If you cite specific voltages, like say 92 volts or calculate a 12% voltage drop explaining only 5% is allowed, your equipment, ( meter ), and it's documented calibration could come into play. Since you likely have no calibration documentation, IMO it's best to stay generic.

Garry, I understand your opinion. I have never used any specific readings. I use it as a general guide then verify. I have yet to have it not be a back-stabbed circuit.

Originally Posted by Garry Blankenship

You're dipping your toe in possible liability territory. If you stay true to the generalist licensing of a Home Inspctor, you're OK w/ voltage appears low, substantially less than normal or symptoms observed are consistent with low voltage. If you cite specific voltages, like say 92 volts or calculate a 12% voltage drop explaining only 5% is allowed, your equipment, ( meter ), and it's documented calibration could come into play. Since you likely have no calibration documentation, IMO it's best to stay generic.

Garry,

"You're dipping your toe in possible liability territory."

I disagree. Addressing voltage drop is not any more than (and is likely much less than) to create liability than any other part of the house you check things.

That 'going beyond the SoP creates liability' is an old wife's tale passed on by home inspector schools who are training new home inspectors and do not want to actually train the home inspector in anything more than the 'generalities' of home inspection.

The easiest way to address voltage drop, and I did it ALL THE TIME, was to state 'voltage drop measured 15.8% with a SureTest (give model number)'.

I have a setup I made which I plug into a receptacle and plug two heat guns into receptacles in my setup. I read the voltage with a meter, turn one on high, then the other I adjust to get the amp reading I want on my clamp-on ammeter, then read the voltage again. Then it is just a matter of doing the math.

I use that whenever someone does not believe the SureTest, and the results are *always* *worse* than the SureTest because now I am heating the circuit up at full rated amps.

It pays not to distrust the inspector - distrust the inspector and one will regret the results of the supporting documentation which comes next.

Jerry, I had a conversation with a trial lawyer on this specific topic about exceeding standards.

He said like you allude to is that you should no more liability and most likely less liability.

There is a lot of keep between the lines mentality out there. If I have the knowledge to provide more information then I will provide it.

Robert,

I am looking at voltage drop and resistance as an indication of the circuit wiring. More times than not it is the use of back-stabbed receptacles causing resistance on series wiring.

I have seen issues with this wiring. As the system ages it develops more resistance.

My view is that back stabbed receptacles are an issue. I have seen scorched neutrals and other issues with them.

I can follow a circuit throughout the room and see the voltage drop from one receptacle to the next.

I have them in my house and in the process of swapping them out.

On another note in older wiring systems where you have no ground available or in limited places you may find bootleg grounds.

Here is a good article from ideal on this-

http://www.idealindustries.com/media...20circuits.pdf

Originally Posted by Don Hester

Robert,

I am looking at voltage drop and resistance as an indication of the circuit wiring. More times than not it is the use of back-stabbed receptacles causing resistance on series wiring.

I have seen issues with this wiring. As the system ages it develops more resistance.

My view is that back stabbed receptacles are an issue. I have seen scorched neutrals and other issues with them.

I can follow a circuit throughout the room and see the voltage drop from one receptacle to the next.

I have them in my house and in the process of swapping them out.

On another note in older wiring systems where you have no ground available or in limited places you may find bootleg grounds.

Here is a good article from ideal on this-

http://www.idealindustries.com/media...20circuits.pdf

I think I totally agree w/ you on stab lock terminations being bad. In particular wiring through receptacles rather than splicing out to them. Don't necessarily agree with the correlation to voltage drop and definitely think it's all too much info. for a report. Further; not in agreement w/ J.P. on the too much information. Once you have established yourself as an expert, ( specific voltage readings and voltage drop calcs do this), you are subject to a much higher level of scrutiny. The client needs an electrician anyway. Why bother sharing info. a client would not understand, but a lawyer can use as fodder ? If you do end up in a dispute, save that info. for your benefit rather than providing it in advance to a law smith to complicate your life.

Garry,

First off I have not ever been even close to anyone wanting to sue me.

The greatest protection from of a law suit, as they say, is good bedside manners.

I think you can provide valuable information to your client and do so in a manner that will both inform and most likely show your client that you are looking out for them which in turn usually means they will never think of suing you.

I think setting up proper expectations is always best.

Originally Posted by Garry Blankenship

I think I totally agree w/ you on stab lock terminations being bad. In particular wiring through receptacles rather than splicing out to them. Don't necessarily agree with the correlation to voltage drop and definitely think it's all too much info. for a report. Further; not in agreement w/ J.P. on the too much information. Once you have established yourself as an expert, ( specific voltage readings and voltage drop calcs do this), you are subject to a much higher level of scrutiny. The client needs an electrician anyway. Why bother sharing info. a client would not understand, but a lawyer can use as fodder ? If you do end up in a dispute, save that info. for your benefit rather than providing it in advance to a law smith to complicate your life.

Uhhh ... Garry,

"Why bother sharing info. a client would not understand, but a lawyer can use as fodder ?"

The clients DO understand that, they understand that better and easier than just some number off some test equipment such as a SureTest, they understand because THEY SAW IT.

THEY SAW the voltage was 123.8 volts, then THEY SAW the voltage dropped down to 105.2 volts, and THEY SAW what would happen when they plugged in their monster entertainment center.

And the BUILDER/SUPT SAW IT TOO.

"but a lawyer can use as fodder"

Yep ... against the builder ... not against the inspector.

What on earth makes you scared of providing information for YOU CLIENT to use against others.

What on earth make you scared that your client will use information which SHOWS THEM A PROBLEM ... against *you*?

I was in South Florida, where the attorney/population ration is probably the same as in California (Florida and California have the two highest ratios), no one down there was scared of providing information for their client, in fact, if anything, providing that information make one more comfortable as their client cannot say they did not know this and the inspector 'should have caught it' - the inspector 'did catch it and did report it'.

You seem to have succumbed to Old Inspector Lore (similar to Old Wives Tales ).

Originally Posted by Jerry Peck

What on earth make you scared that your client will use information which SHOWS THEM A PROBLEM ... against *you*?

You seem to have succumbed to Old Inspector Lore (similar to Old Wives Tales ).

The fear is not of the obvious, too much info, but of the more obscure, "too much info in that corner but no info over here, where the fire started".

If you hold yourself up as the expert who spends a whole day diagnosing the wiring, then you had better find all the problems all the time.
"It wasn't visible or accessible" won't protect you with your bag full of test instruments that you claim to be so good with.

Which you already know, but forgot.

Originally Posted by John Kogel

The fear is not of the obvious, too much info, but of the more obscure, "too much info in that corner but no info over here, where the fire started".

If you hold yourself up as the expert who spends a whole day diagnosing the wiring, then you had better find all the problems all the time.

Again, Old Inspector Tales.

Not even true for an electrician who spends the day there. Superman with his X-ray vision, yeah, MAYBE ... but not us mortals ... heck, even Superman is allowed to have an off day now and then. Why do you think we give Watson a break now and then?

Originally Posted by Jerry Peck

Uhhh ... Garry,

"Why bother sharing info. a client would not understand, but a lawyer can use as fodder ?"

The clients DO understand that, they understand that better and easier than just some number off some test equipment such as a SureTest, they understand because THEY SAW IT.

THEY SAW the voltage was 123.8 volts, then THEY SAW the voltage dropped down to 105.2 volts, and THEY SAW what would happen when they plugged in their monster entertainment center.

And the BUILDER/SUPT SAW IT TOO.

"but a lawyer can use as fodder"

Yep ... against the builder ... not against the inspector.

What on earth makes you scared of providing information for YOU CLIENT to use against others.

What on earth make you scared that your client will use information which SHOWS THEM A PROBLEM ... against *you*?

I was in South Florida, where the attorney/population ration is probably the same as in California (Florida and California have the two highest ratios), no one down there was scared of providing information for their client, in fact, if anything, providing that information make one more comfortable as their client cannot say they did not know this and the inspector 'should have caught it' - the inspector 'did catch it and did report it'.

You seem to have succumbed to Old Inspector Lore (similar to Old Wives Tales ).

It's nor fear; just common sense. As I said earlier, the voltage appears low or the data is consistent with low voltage serves the client just fine. It is the specific numbers an calcs that are unnecessary and only serve as inspector chest thumping and increased liability exposure. These details can also be safely shared with the client in a verbal debrief. When a buyer become disenfranchaised with their purchase decision the real reason for that becomes irrelavent. The goal is to either get out of the deal or find some money in the purchasing food chain to ease the pain. A lawyer is hired and the search for a way out and/or some money ensues. The real reason is a neighbor from Hell, but the lawyer is working anything that can bring benefit to the client. [ Law Smith ]"how did you know the voltage was 99.8 volts ?", [ Inspector ]"I checked it with my Suretest meter and recorded the reading", [ Law Smith ]"when was your meter last calibrated ?" Where this goes is the same path as a speeding ticket and the radar gun used. If you cannot prove with documentation the meter was calibrated by a certified entity, that report info is rendered in-admissable and that possibly along with similar incidences creates enough factual doubt that the plaintiff wins. I have both seen and participated in this process in construction via both owner / general contractor disputes or a job site injury or death. The real problem or reason for injury, death, cost over-runs etc. may or may not be involved. The case becomes extracting money from any available pocket, regardless of merit or cause. Whether or not an inspector somehow harmed a clint does not matter. It is whether or not some law smith can convince a judge or jury his client was harmed by an inspector that matters. I do what I can to avoid being right, but broke.

Originally Posted by Garry Blankenship

It's nor fear; just common sense.

It's "common sense" that the more information you give the greater your liability is?

As I said, that is Old Home Inspector Tales, and it is against all "common sense".

I can report a lot of test values during an "inspection" that I can substantiate in court. These were the readings I took on this date and time under these circumstances-- do with them what you will. I'd like to see an attorney prove I did not measure a certain level of depressurization in Pascals at a specific point on a house, at a specific time. Really....You know, when I tested the air conditioning or heater to see if they ran, my ambient room temp in the room where the thermostat was at the height of the stat was X# degrees F. Prove it wasn't.

I can perform combustion analysis and prove my readings because I print them out in hardcopy. However, my biggest aid in documentation is taking pics of meter readings. I also take pics of my tape rule measurements.

I can take readings with my Sure Test to see if a certain outlet is suitable for a window air conditioner or blow dryer. I can also test the power to a furnaces to see if the power is suitable for an electronic ignition system.

Next we'll get back into that old discussion about if you own test equipment then you're obligated to use it all the time.

If the voltage drop in question will affect the safe and/or proper operation in a legally required standby system, a fire alarm system, and a few other instances, then that voltage drop issue is enforceable.

For those of you with IR cameras, does the voltage drop - resistance - also show up on the camera?

Originally Posted by Chris Weekly

For those of you with IR cameras, does the voltage drop - resistance - also show up on the camera?

With normal checking of voltage drop, no.

I was checking it with my setup once and noticed that the circuits were visible behind the drywall as the circuit wiring was actually heating up enough to affect the surface temperature of the drywall.

Later, without doing a voltage drop test, at a conference where I was trying out and showing my infrared camera, I found several circuits in the main conference room which were hot enough to show through the drywall. I thought I might of a photo or two of that effect but I don't.

Anyone else with an infrared camera ever try to look at that? What did you see?

You just gave me an idea J.P..
I performed just diag/repair for a few years, some years ago. Got so good at it that I had to start charging a minimum fee just to go out (if I do say so myself ). When the circuit tracers evolved, it became child's play.
The one thing that I wish I had was x-ray vision.
Now for 'our' idea: If one used an adjustable load device, one could cause sufficient I squared R loss in a circuit and trace it with one of those new fangled infrared camera thingys!