To measure- or not to measure- voltage drop

See any inaccuracies in this?

                 **Voltage drop observations:******

****1. An increasing number of inspectors are testing for voltage drop. There are informational-only notes in the NEC **(215.2 (A)(4) **suggesting that conductors sized to prevent a voltage drop exceeding 3% at power, heating and lighting loads (or combinations of those loads)… and

  1. That preventing a maximum voltage drop exceeding 5% on both feeders and branch circuits to the farthest outlet…

…will provide reasonable efficiency.


  1. This means on any particular circuit, voltage measured at a device like a receptacle or connection to a load that consumes power, such as a motor, a heating component, or lighting component should not be more than 3% lower than the voltage measured on the same circuit at the OCPD. The OCPD may be located at a service panel, or a distribution (sub-) panel.

  2. This means on any particular circuit, voltage measured at the outlet farthest from the service should not be more than 5% lower than the voltage measured on the same circuit at the OCPD in the service panel.

NEC: Some equipment will operate satisfactorily at a greater voltage drop and some may not tolerate as much as a 5% voltage drop. The 3% and 5% numbers are suggestions, not NEC recommendations. The NEC does not consider all voltage drop beyond these levels to be a safety concern.

Measuring voltage drop exceeds the Standards of Practice of all home inspection organizations.

Reasons to do it:
· Inspectors may perform this type of measurement in order to gain a business advantage over competitors who don’t perform voltage drop measurement,
· It’s possible by measuring voltage drop to identify conditions that may indicate a potential fire danger (such as a bad electrical connections).
· It’s possible by measuring voltage drop to identify conditions that may damage sensitive electronic equipment (such as voltage significantly lower than 120V.

Reasons not to do it:
Inspectors who measure it become responsible for the accuracy of their measurements and how they report their findings, and so open themselves to increased liability. Making mistakes in measuring voltage drop or improperly describing the gravity of a voltage drop has, in the past, cost inspectors future work.

I think a large amount of inspectors are not qualified to do this and can see difficulties if they are taken to court.

When I left the electrical trade I also dropped my Electrical license to avoid getting involved with things like this.

I think they should get some legal advice on doing this .

I have been checking for this for over a year to get a bearing on what is out there and I hardly ever see anything less than 5%. Normally I find the average drop is 10% on every single home.

Is this for your use or do you put it in the report .

Are you an electrician ??

As I said to get a bearing on to understand it. No I don’t put in report. It seems the low voltage is more from the stab locks.

I wouldn’t want to signup for voltage drop measurements with in the home. Besides, In the electrical trade voltage drop is usually associated with longer runs of wire to remote buildings…detached garages, sheds and the like.

Pretty good discussions here:


It seems everyone in this thread wants to measure voltage drop with connected loads of some kind which creates more resistence. To measure voltage drop (as a problem) shouldn’t everything be unplugged from the circuit? in order to get the true voltage drop (which I imagine will be higher these days with all the stab-loks being used on devices) the circuit should be clear of all loads. What the customer plugs in down the road is their deal. I may be wrong.

Looks to me like we have a few who are not electricians and they have a hate on for
stab-loks .
I think most of you guys should do home inspections and write your reports.
Going ouside of the existing SOP methods of inspections could come back to haunt you .

This could be a good course for some of you .

I wired houses for a few years and we didn’t use the stab loks, boss wouldn’t let us and I have played around with this and my personal opinion is the that the stab loks are the problem.

Service brand wouldn’t affect voltage drop, which would typically be connected to overly long runs or poor electrical connections. Maybe other problems too.

Second hand information is not always the best way .
Facts are what you should follow.
Well I have a Stab lok in my home and I am not changing it .
I made my Living as an Electrician for many years never managed to play around with it .
Took proper training and many follow up courses to stay up too date , two brothers both also qualified Electrician’s .

Cause could be lots of different things.


Interesting can you please show us some different reason’s for voltage drop.

Kenton, I’m curious, where did you get this info from?

If doing this test is a liability increase, what difference is there when measuring the Delta T of an HVAC system with a thermometer?

If you are liable for voltage drop calculations, just what are you liable for? A service call by an electrician?

Unlike using a thermometer to test HVAC, measuring voltage drop is mathematical just like ohms law.

He every so often finds things or dreams them up .
He sure can get us looking and thinking .
I do not always agree with him but it sure is better then what some others do on this forum.
Thanks Kenton… Much appreciated… Roy

14 awg copper over 50ft. = >3% voltage drop.

I have not seen in the SOP where we should be doing voltage drop testing.
Just think if the home inspectors is being asked questions on a court case .
Now my Inspector you did a voltage drop test during your inspection.
I see there is a 42 circuit panel did you do all circuits or just some .
Now this I am sure can lead to much longer inspections and things being done by none electricians . I did not see where you got calculations from .

Roy, I just spent that last two days in court… $$$$

My purpose was to convince the jury that a home built to code is “not” OK.
That home inspection has limitation, exception and exclusions.
That me, a HI can talk about and collect information in accordance with ASTM and numerous other engineering standards.

Like the building code, HI Scope of inspection is a minimum standard.
You can not build a “Quality Home” just to code specs., nor can you provide a quality home inspection just to “SOP”.

On numerous occasions I was asked by the defense, after I provided "what could be the cause of an issue (which was creating an obvious “problem”), did you look inside to verify this?

“If I looked inside I would have obliterated your clients ****up.”

I have “nothing to prove”.
I report what I see. Document what I see. Form an opinion based upon education and experience (only when you ask). It’s your job to figure the rest out.

As I left the court room, I asked my client if he was “Happy”.
He said he was very happy.

I am “Happy” to deposit his check…