To measure- or not to measure- voltage drop

This is so great we can have a discussion with out getting upset and all will learn things .
Unfortunately many have hurt our Forum and many great inspectors have left and others frequent this forum very seldom.
I do wish things improve and we get back to what we had a few years ago.
Thanks for being the way you are David … Much appreciated … Roy

I am sorry if this is too blunt. Spending 16 hours with defense lawyers and their tunnel visioned “experts” I have little latitude for unspecific facts.

When people start talking liability, you really have little clue what your up against.

What the hell difference does it make if I attended kindergarten?


Started looking at the SureTest manual, then Googled “measuring voltage drop” which brought me to these two MB discussions:


In one of those MB discussions, an inspector said he’s lost work because he made a mistake in measuring voltage drop.

I’m taking the NFPA online course on NFPA-70, and the InterNACHI Electrical course. The NFPA course makes a point of saying that 215 A4 is only intended as a design suggestion, not a rule, which is not made clear in the InterNACH course. As I go through the InterNACHI course I’m making notes for possible updates, changes, or additions, and running them past you guys, in additon to using what I know that I know, and what I can find online and in the NEC and IRC.

Gotcha. You do realize this thread is 8 years old, right?…82/index2.html

Yeah. Still, seemed like some things worth reading, and if no dates were given, from the content, seems like it would be hard to tell it was that old.
The only NEC book I have access to right now is NEC 2002, although I believe NFPA membership gives me access to the 2014 version online. I’m involved with the basics, and I don’t think they’ve changed much in 8 years.

Voltage drop is dependent on load. The greater the load the greater the voltage drop.

I believe people are talking about back stab, not just one style of FPE breaker.

The NEC doesn’t require VD compensation (with a few exceptions) for a reason. Now if your VD tester can find other problems then go for it but to put a 15 or 20 amp load at the end of a normal circuit and find a greater than 3% VD is a waste of time.

If that’s the case measuring voltage drop is Way beyond “the basics” as far as home inspections/inspectors are concerned.

Or as Robert put it in post 27-

It’s only way beyond the basics, if it’s way beyond you.

Right now measuring voltage drop is in the course worded in a way that implies that the NEC has a rule stating that anything over 3%/5% is excessive. I’m just trying to clarify for those who don’t know that it’s not a rule and not that simple. Newer inspectors are going to see measuring voltage drop mentioned and if they don’t know better, think they’ll do a bang up job and offer some extra value by measuring voltage in a few places with some instruments that give just enough information to be dangerous.
The alternative is to not mention testing for voltage drop at all and, it’s not a totally basic course.

I asked if anyone saw any inaccuracies in my original post. If anyone wants to post something better than what I put in my original post, feel free!

Now we’re on post 30 and not one answer to the question, or suggestions for improvement, just a bunch of opinions. ](*,)

Not needed .
A waist of time.
Not much of a concern with modern installations .
Many are not qualified to do these Readings .
This is just another method of extending the time needed to do an inspection .

In general, I agree with you , but David Anderson does them, Jeff Pope does them, they both seem to see some value in it, but their level of knowledge is a lot more advanced than a lot of inspectors. And you’ve been an electrician! I’m just trying to write something accurate.

This is an interesting discussion. I need to sit down and write a few things out on paper to get it straight in my head. Absent that cause I am laying here in bed with a tablet and concentration is near impossible while my wife is watching TV. Thinking out loud here and probably making a mistake.

Power in watts = voltage * current (amps)
Watts / amps = volts
Watts / volts = amps

In DC its volts = current * resistance < but what does it matter right?

OK so to look at it the only (real) constant is, 120volts 60Hz AC supplied at the service panel. Am I right?

It could be a 15A or 20A circuit, but that is simply the rating of the circuit, with … Well maybe this constant 14 or 12 gauge wire regardless of 20 foot or 20 miles (exaggeration of course).

So the suretest could simply measure the volts AC and calculate the percentage. But surely its smarter than that. It puts a load on the circuit and measures both the voltage and the current right?

I think I am missing something simple to understand this. But my biggest question is how to decide the current rating to test. 15 or 20 amps? Sure if it is a kitchen it should be on 20.

I guess I need to really study up on this.

I think there is value in providing Voltage drop testing as a service. But I need to get my head wrapped around it fully to see the value. There are two models of the suretest meter that I have used, one is just as fast as your typical outlet tester and you kill two birds with one stone so to speak. The other model takes several painful seconds to give a reading. Probably 80 % of receptacles on a house bigger than 500 square foot are over 5% drop.

I just did a house today that had fans running in the rooms and I tested the duplex plug next to the fan with and without the fan running and got the same reading. So the answer is " the fan placed very little load…" Well the client embarrassed about the house started vacuuming, I took the opportunity to test outlets on the same circuit and found it made no difference. Most vacuums pull a lot of amps. For me I’m thinking the way to look at it is if on the same circuit one outlet has a considerable biggest voltage drop, Ben we have a receptacle problem. But yesterday I had a kitchen that would pop the gfci while doing a suretest droptest at only 15 Amps while giving me an average reading something like 5.6% drop. Other outlets on the same circuit didn’t pop the gfci and had higher voltage drop.

So I am back where I started.

I do not do this in all houses. But sometimes you have a 7k house with the main sub-panel on one side of the house, running 14 awg to the 3rd floor bonus room at the other.

I ask: what are using this room for?
Often it is an offie with lots of equipment.

Just the fact that it is more than 50 ft away is enough for me. But to get a builder to do anything, you have to prove your facts.

Joseph, the values you need is voltage, amperage, resistance of the conductor to get voltage drop.

That makes sense. Seems like when, why, and how to measure voltage drop, and how to report on what you find could be a mini course in itself, but I’m not qualified to write it. I HATE electrical. I’ve found it to be by far the most difficult system to understand.

Not to start an arguement but I have found voltage drops as high as 15 to 19% that were only 15 feet away from a panel as I am sure you have to.

With what load?

Tested with an amprobe Insp-3 circuit analyzer. Turns out two were bad receptacles, I knew the electrician. As far as the others I don’t know what happened, didn’t know who the electricians were.

In my honest opinion, a voltage drop test is beyond the scope of a home inspection and beyond the skills of the average home inspector. I would not perform this as part of a HI.