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Joined: Mar 2005
Posts: 240
ok here is my question to the experts.
i wired a house which has long home runs about 130-150 foot. the master bed room feeds only the master bed room and the master bath, a home inspector(not electrical) has a tester which can apply 15 amps across circuit and gives a percentage of the volt drop. he says i have a 13% volt drop at that outlet. at that same plug i get 120 volts. when i turn every singe light and bath fan and plasma tv on i get a 112 volt reading on my tester.
i am aware of the 5% and reasonable operation, since entitre circuit would have to be on to achieve such volt drop.
i calculated th volt drop for the home run @
2kil/csa =
12.2 volt drop
following the FPN the max amount of #14 wire would be 50 foot
4.7 volt drop
i never calculated volt drops for a house before, have always tried to keep branch circuit to min opening count(12 on a fifteen amp circuit)am i missing something here?
are my calcs right and have i been trained and practicing excessive volt drops?
if 15 amp branch circuits are limited to such small footage you would need a sub panel every 50 foot. and as far as the load calcs and min circuits required go i have more than tripled them. bedroom draws 8 amps with that load i mentioned.
please help with comments and criticism.

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Joined: Jan 2005
Posts: 5,370
Likes: 1
Cat Servant
This is a difficult thread, where one must make a reply without getting passionate.

Just because someone makes a fancy meter (toy) that cranks out a number does not mean that either the toy or the operator are running the job.

Test results are meaningless without the ability to evaluate them. Neither the tester, nor the operator, can make those design decisions. They're simply not qualified.

One bit of information is useless, without being in context with much more information.

The 5% figure is a recommendation ... not a code requirement.
What is probably more important is the minimum voltage. NEMA standards typically call for equipment to operate at 10% under their nameplate voltage. For an appliance marked "120," this means that the appliance will operate at 106 volts, in a reasonable manner. If, under full load, you have 112 v, you don't have a problem.

Factors such as 'start up current' are not really relevant for a general purpose circuit; if it was for a specific appliance -say, an air conditioner- the matter is different.

Another cause of large voltage drop is bad connections. If the drop is pretty even across the circuits that is one thing; if most of it seems to happen at one device, then perhaps there is a problem that needs to be fixed.

For future jobs, you can reduce the problem by using a larger wire for home runs, or by using sub-panels. Voltage drop is something you need to consider. Yet, for all the fuss that has been made at the HI sites over voltage drop, I cannot help but wonder how the trade made is a century without those dang meters!

Joined: Feb 2003
Posts: 939
good point Reno ,, I will agree with you about the common sense with long run and my thumb of rules every 30 metre or 90 feet i useally upsize wire one size bigger or get subfeed panel to reduce the voltage drop depending on the design of the place.

but the HI [ home inspectors ] somecase the dont understand the system very clear at all and can get misunderstood it pretty easy.

Merci , Marc

Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

Joined: May 2002
Posts: 1,716
I would also add that to have any general lighting circuit in a dwelling unit loaded to 15 amps would be an extremely rare situation and this is one of the problems with this type of tester.

If it could apply say 4 to 8 amps it would be more realistic but I would say in my house most general lighting circuits (excluding the kitchen and bathroom) never see more than 2 to 3 amps in a normal day.


Joined: Apr 2002
Posts: 7,333
Likes: 7
Did anybody determine the available voltage at the main? Depending on the utility, time of day, time of year....available line voltage at the main may or may not be 120 exactly!

Joined: Dec 2003
Posts: 751
Many jurisdictions have adopted the ICC International Energy Conservation Code (IECC). For Commercial buildings, the IECC adopts the standard ASHRAE/IESNA 90.1. In section 8.2, feeders are limited to 2% VD, and Branch circuits to 3% VD.

One and two family dwelling wiring has no such requirement.

Joined: Jul 2004
Posts: 9,788
Likes: 14
I have always been a bit skeptical of the readings on the SureTest. This has to be a very short pulse and it may not actually be there long enough to get a real world reading. I would prefer to back this reading up using a real meter and a hair dryer. They will provide a steady load of around 12a (ignore that "1800w" number on the case. It is the same type of rating as the "5HP" air compressors with the 120v/15a plug)

Greg Fretwell
Joined: Mar 2005
Posts: 240
the nec makes reference in a FPN about volt drop, what is its intent? that at 100% of branch circuit is 5% or that at farthest point before plugging in is 5%? this is becomming a "he said /he said" issue between me and the contractor. this home inspector now brought in another electrician who supports his fancy meter and for few thousand bucks he will install a sub panel.
the same sub the contractor didn't want to pay for durring original construction.
i just cant get through to this home inspector that plugs are convienence and intended as such alarm clocks, lamps, tv's, vcr .... yada yada and whith all lights on this branch circuit the meter reads 112 volts
turn all lights off(master bath-tub,shower,fart fan,vanity,toilet fan/light) the meter reads 120 volts. where is this supposed volt drop? monday i will bring hair dryer and test as suggested by gfretwell, but i know with an 8 amp draw what the nuber already is since i tested the amps with all lights on.
please guys explain the intention of FPN to me.

Joined: Jan 2005
Posts: 5,370
Likes: 1
Cat Servant
The FPN does nothing more than remind you of an accepted guideline, or design goal.

So what is this voltage drop issue all about?
In the first case, it's about days past, where a 120v service might actually be delivering only 120 v to the customer. Lose a few more volts, and you no longer have the minimum 108 that a 120v appliance needs for proper operation. Of course, these days I quite often measure incoming voltages that are much closer to 130, than 120!

Secondly, a large voltage drop is a suggestion that there MIGHT be a problem. Far more than wire length, bad connections will cause such a drop.

It might be interesting to do the voltage drop test at the panel, as well as at the receptacle. Then, progress along the circuit, and see if the drop is gradual - or happens at one place.

If, even with the drop, you have more than 108 v at the receptacle ... and there is no mention of this testing in the contract ... I don't see a need for you to do any more. This time. What else you do is more of a business decision than anything else.

As mentioned earlier, a 'quick fix' would involve replacing the home runs with #10. Putting junction boxes in the attic, and replacing the bulk of the run, just might make everyone happy.

Otherwise, you've received a 'wake up call.' I'm sure you will forever consider voltage drop in your future work. Because, legalities aside, you can see where 'code minimum' and 'good design' are not the same thing.

As for the HI ... well, everyone has an opinion. Keep in mind that the HI is not the one licensed to do electric work - you are - so by definition you are qualified, and he is not. Keep in mind that he is not, in any way, the AHJ. He's just a spectator. You have no contractual relationship with him, and have no obligation to care in the slightest what he thinks.
If the customer is not happy, he can pay you ... and not hire you again. Or, future jobs will be planned / priced with this additional requirement in mind. Or, you can be NICE and accommodate him this time, for the sake of future business.

But the FPN has NO code significance, and is only a suggestion, without even the weight of the code saying 'may' or 'should.' It's NOT part of the code. This is explained in the very first pages of the code itself.

Joined: Jul 2004
Posts: 9,788
Likes: 14
HI in general is just a way to force a seller to lower his price. I guarantee the buyer doesn't want the voltage drop fixed, he just wants a credit on the price equal to the work the HI recommends.
I do see some silly discussions over on the NACHI BB trying to make mountains out of molehills. I suppose if you pay someone $300-400 to give you a 2 hour inspection they feel obligated to find "defects". They argued for a week over multiple ground wires in a single lug on a bus. They lose their mind if you don't reidentify a white wire on a romex used for 240v. You would think babies were dying all over the country from this "defect"

Greg Fretwell
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