15% voltage drop

[ingeniero]

There one branch in my home that is downstream of a GFCI that has a voltage drop of 15%

The home inspector who inspected the home when I moved in said that this branch could possibly overheat causing a fire.

When i called an electrician, he said not to worry about it.
Is this something that I should be concerned about?

Thanks,
Concerned Homeowner

 

[charlie b]

Re: 15% voltage drop

It might be a problem, but let?s be clear about our use of terms. Are you saying that the voltage drops by 15% (e.g., 18 volts out of 120) from the beginning to the end of this one branch circuit? Are you therefore also saying that the voltage on every other branch circuit in the house is close to the same voltage as the beginning point of this one problem circuit? If so, I would say that you do have a problem, and should contact an electrician for help (perhaps a different person this time, or at least ask the first electrician to give you a clearer explanation of his opinion). The National Electrical Code suggests (without establishing any requirements) that if the voltage drop along a branch circuit is less than 3%, the circuit should function well.

Much depends on the nature of the load. What does this circuit serve? How did you (or some other person) discover that there was a 15% voltage drop? Was the load running when the measurement was made?

 

[tonyi]

Re: 15% voltage drop

Originally posted by ingeniero:
There one branch in my home that is downstream of a GFCI that has a voltage drop of 15%

The home inspector who inspected the home when I moved in said that this branch could possibly overheat causing a fire.

When i called an electrician, he said not to worry about it.
Is this something that I should be concerned about?

Thanks,
Concerned Homeowner

15% is a lot. Some things you might plug into it may not work right (ex. computers with a cheap power supply). If you plugged some heavy draw thing in (like a space heater), the wire would get pretty warm.

Its probably #14 wire and run a LONG way from the panel right?

[ October 03, 2003, 01:47 PM: Message edited by: tonyi ]

 

[ingeniero]

Re: 15% voltage drop

The circuit with the 15% drop serves a bathroom where the GFCI is located at well as exterior outlets at the rear of the home. (a LONG way from the panel)

(other branches in the home have less than 10% drop)

The inspector used an Ideal ST 1D Circuit Analyzer to measure the drop. The house was vacant when the inspection was done, though I don't know what load was running on the circuit when the measurement was made, I would imagine it was small.

 

[charlie b]

Re: 15% voltage drop

Something here is not making sense. You can have a couple hundred miles of very small cable, but have no (or very little) load, and the voltage drop could be from 0 to 1%. So if the inspector is measuring 10% with no (or very little) load, then I surmise that he was not taking the measurements correctly. As I said before, 3% is a large value for voltage drop, and 1-2% is more typical, so 10% - 15% is extraordinarily large.

As a side issue, are you sure that there are loads outside that share a circuit with a bathroom? That might be a violation of NEC 210.11(C)(3). You might want to verify this.

 

[bennie]

Re: 15% voltage drop

These analyzing type meters are causing a lot of mis-understanding about voltage drop.

Remember that voltage drop is a result of I x R.

Measure the voltage at the end of the longest 15 amp circuit with no load. Then apply a 15 amp load at the end, and measure voltage across the load. If the circuit is 191 feet in length, the drop will be 18 volts.

There is two ways to prevent a high voltage drop. One is larger wire. The other is to install panels closer to the load.

 

[BAHTAH]

Re: 15% voltage drop

As Bennie pointed out these testers can cause problems when checking for VD. If this is the tester that comes to mind (Ideal Sure Test) the voltage drop is measured by the meter assuming a 12,15 or 20amp load. I think in reality your drop will depend more on what these outlets are actually used for than what the inspector is telling you. You may do better to have an electrician measure the drop under an actual load.

 

[don_resqcapt19]

Re: 15% voltage drop

You also have to remember that when you are using one of these plug-in testers, that you are measuring the voltage drop from the utility source to the receptacle that is under test. Was a test made at a receptacle very close to the panel? If so what was the drop there? For the actual voltage drop on the branch circuit, you can subtract the voltage drop at the panel from the one at the remote receptacle.
Don

 

[tonyi]

Re: 15% voltage drop

Originally posted by charlie b:
As a side issue, are you sure that there are loads outside that share a circuit with a bathroom? That might be a violation of NEC 210.11(C)(3). You might want to verify this.

This is apparently a common configuration (at least in Florida) depending on the vintage of the place. There's about 850 places in my mom's development wired this way - all circa 88'-89'. GFCI requirements were somewhat in flux and the 20A dedicated bath stuff we have today hadn't been nailed down yet. Someone running tools outside and a hair dryer in the bath is almost a guaranteed trip in these bogus setups.

 

[iwire]

Re: 15% voltage drop

SOP (standard operating procedure) while I was doing condos 83 to 87 was 14 awg from panel to the closest bathroom, use a GFCI there come off the load side to the other bathroom and then hit one or more exterior outlets.

Very confusing for the home owner when they trip the GFCI using a power tool outside, their first thought is not "let me check the bathroom outlet"

I did not like it, but the owner of the company did and it was his name on the job.

 

[dereckbc]

Re: 15% voltage drop

All, the Ideal Sure Test meter performs a number of opreations. When first plugged into the circuit it reads the open circuit voltage. Then it puts a 15-amp load between L-N ,reads the voltage between L-N-G. 3rd it puts a 15-amp load from L-G then re-reads the voltages between L-N-G and determines the percentage of voltage drop and circuit impedances.

Where an error can be introduced is if there is a upstream or downstream load. The meter will tell you if there is a load, but you have to look to see. Otherwise if used by a knowledgeable individual the meter is very accurate and useful.

So to the question at hand if the inspector was knowledgeable and used the meter correctly the reading was accurate. 15% is too high and needs to be examined. It could be an extremely long circuit, or there could be a problem.

 

[iwire]

Re: 15% voltage drop

Dereck, I am curious when it takes the no load reading does it store that value internally and then do the load test and compare the two readings?

Or does it simply expect the circuit to be 120 volts?

What I am getting at is the same thing Don was, at my house the utility voltage is low in summer it has been as low as 97 volts RMS (yes I complained) so how does the tester handle this?

Bob

 

[dereckbc]

Re: 15% voltage drop

Originally posted by iwire:
Dereck, I am curious when it takes the no load reading does it store that value internally and then do the load test and compare the two readings?

Or does it simply expect the circuit to be 120 volts?

What I am getting at is the same thing Don was, at my house the utility voltage is low in summer it has been as low as 97 volts RMS (yes I complained) so how does the tester handle this?

Bob

Bob the meter takes the reading initially before the load is applied, and again at the end of the load test so you can read it.

The trick is to cycle throug the menus and look at N-G voltage to determine is there is any othe loads on the circuit. If there is your results are invalid.

Another nifty feature is you can measure a connected load with the meter.

But to answer your second question it measures the actual voltage rather than assume 120.

If you would like e-mail me and I can walk you through some of the features like harmonic, PF, etc.

 

[karl riley]

Re: 15% voltage drop

I also use the SureTest circuit analyzer. I have never seen a 15% drop. It will measure the percent drop of the hot, grounded, and grounding conductors separately, so if the big drop is on only one conductor, that gives you a clue.

Karl

 

[brian john]

Re: 15% voltage drop

15% is a lot. Some things you might plug into it may not work right (ex. computers with a cheap power supply


While not a recommended operating voltage, PC's will and do function at this level.

 

[tonyi]

Re: 15% voltage drop

Originally posted by brian john:
While not a recommended operating voltage, PC's will and do function at this level.

Depends a lot on where you're at before losing the 15%. Some will accept as low as 90V, others 100V or more. If you're starting with a nominal 120V, no problem. I've seen areas where you're lucky to ever see much over 110V with frequent drops down into the 90's.

 

[dereckbc]

Re: 15% voltage drop

ingeniero, how long of a circuit is it one way in cable feet? To get 15% voltage drop and technically be no safety problem, the circuit would have to be a 14 AWG at 200 feet plus tested at 15-amps.

Typically residential readings are in the neighborhood of 2 to 8%.

 

[bennie]

Re: 15% voltage drop

The impedance of the branch circuit, must be added to the service feeder and transformer impedance, to calculate voltage drop.

The best way is to compare load and no load voltage at the end of the branch circuit. These testers perform that function.

The only problem is most circuits are not loaded to the maximum at the end, and the high numbers create questions of integrity.

 

[frenchelectrican]

Re: 15% voltage drop

really 15% voltage drop sound very serious.. but one thing i am puzzled with testers ( i dont have that kind of tester what you guys describeing ) and when put a load on and what is the duration during the load test?? a short burst or long burst like same idea when crank up electric motour simuiar to vacumm cleaner or hairdryer . typically my experince with voltage drop useally in 3 to 5 % range at end of run but main point is how far from POCO transfomer to breaker box then from breaker box to the most furthest oulet then deturmed the vd is ..


please do correct me if i am wrong on this one


Merci, Marc

 

[dereckbc]

Re: 15% voltage drop

Bennie & Marc, you do have to consider the impedances of the feeders and transformers during the test. In most cases these impedances are so small in caparison to the branch circuits it can be ignored. If in doubt, it is best to turn off all loads before making the test. This will keep the error under 1%. Note if you had something like a 50 amp service over a distance of more than say 150 feet then these impedance can come into play, otherwise you can ignore it.

Marc, the testers only put the load on for a few milli seconds. Just long enough for the meter to obtain a loaded reading.

But 15% is way to high and should be looked into by a professional.