Voltage drop as part of inspection

Can anyone provide more recent info on Voltage Drop and it’s inclusion in an inspection/report?Seems while it is outside the SOP, many Inspectors are performing this test. Seems what i have read on the postings here are many years old- any more recent comments on Voltage Drop - I am a new inspector in waiting- on a ride along a couple days ago, the inspector plugged in device to test for Voltage drop- his take was that if he found more than 2-3 receptacles showing a 10 volt drop he would call that out- comments?

Ken, I never tested for voltage drop and I know some do on some houses.

I didn’t because I didn’t want to go beyond the SOP in that area, on every inspection. YMMV

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never have never will…not my job


If you are going to be commenting on voltage drop please understand and be prepared to back up everything you state in relation to the guidance of this article:

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Nope. I exceed the SOP at times but I stay in it for this.

Voltage drop compensation is not required by the NEC so unless you’re using it as a tool to find faulty wiring IMO it’s better left untested.

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Thanks for all the replies-,greatly sppreciated

Do you consider conductor not sized for VD part of “faulty wiring” ? (ex. remote 15 amp outdoor receptacle installed 250’ from the panel using #14 wire)

Come on guys let’s answer the OP question.
Yes you can do it. Absolutely and like the others have said is beyond the SOP. I did a drop voltage test in my own home. And I found a significant drop in my master bathroom circuit.
Yes you can do it. But it’ll take you a lot longer to do a comprehensive home inspected if you do

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IMO if it’s installed correctly and not an NEC violation it’s pretty hard to call it faulty. It may be a very poor design but it’s outside of the purview of the NEC.

I’ll leave the reporting to you professionals as you see fit.

I agree, it’s one of those things where a home inspector can go beyond the code, if they feel comfortable doing so. If I was buying a house, I would want to know that the electrician used the least expensive (size wise) conductor and as a result there could be voltage drop related issues (if the issue is not related to poor or faulty wiring) depending on the load.

On a rare occasion I will check an outbuilding 100 feet from the house wired with 10 gauge wire from the main breaker in the house, typically done by the homeowner.

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Just curious what exactly will that test tell you and how would you report it?

I just use one of the online voltage drop calculators to determine the maximum distance the wire could run at maximum amp rating for the wire size. I will look at the electrical panel to see what the circuits are being used for and make a determination if usage is likely exceed the amp rating based on distance. If they only have one light in a small shed I may not say anything, however if the outbuilding is large enough for a garage or workshop I may add the following comment: “The shed/outbuilding has a limited capacity for electrical appliances based on the service wire size and distance. Some motors and sensitive electronic equipment may be damaged due to voltage drop, if the service wire is too small and/or too long. Before adding additional electrical appliances have a qualified electrician determine if the service wire needs to be upgraded.”

Sometimes you find an idiot that has a 50 amp welder plug on the wall with a 30 amp service he buried out to the shed. In that case voltage drop is not the issue, just the homeowner and too much HGTV. Just call it out to have a qualified electrician inspect the electrical system and make any necessary upgrades or repairs.


Randy Mayo, PE


Mobile: 573-201-8162

Email: rmayo@rlmengineers.com | Website: www.rlmengineers.com





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Thanks Randy, I was just wondering how you would present this as a PE. IMO you would have greater latitude to generate an opinion regarding VD when compared to an HI. I think that for the HI this could be a slippery slop that is in most cases not reportable.

Would someone please send me the cliff notes from Randy’s post?
Aadd set in quickly.

If the feeder conductor is too long or too small you could have problems. :smile:

My thoughts exactly Inspector Larry.Yep!. I told her that last night…Huh?..Yes!

Master Inspector Roy, are you bragging again :kissing:

Yes Sir Inspector Joseph !
Da truth is da truth… :innocent: