Voltage Drop

They are a nice tool, aren’t they. Been using one since 1985-6; doesn’t have the digital voltage read out on it though and it **does not **want to die so I can buy a newer version.


Not to put your feet to the fire or anything but the WHY the voltage drop is the person who is fixing the issue - They do the math

The person who is finding the problem is just the messenger

If I plug in a 1000 watt heater into any outlet and see 10% voltage drop that tells me that 100 watts going up in smoke somewhere and it could be 99% at one bad connection.

No math on this problem – This is a true safety issue

Not long ago I had the honor of a beer with a retired home inspector – He was sued once in 30 plus years in the profession.

Two children died in a electrical fire – He had inspected it and had NOT done a voltage drop test. He had not noted any major electrical problems. He stated that it was a 100 amp service and that some of the outlets were painted. He did not pull the front off the breaker box. (He does not like electrons)

He recommended upgrading if additional ckts we needed since all the breaker slots were used.

He walked because the parents were trying to heat the home with some electric heaters because the gas had been turned off for 6 months do to non payment and winter set in.

The fire started in master bed room outlet behind bed. Electric heater was the only load. Parents down stairs watching TV

Home was a rental - Guess who had to write the check - Guess who was very sad about the death of two small children that he could have perhaps prevented – Can you say HI??

While I hate SureTest I will say that it is a standard of our profession and that we should use it. (or something like it)

I do not use a SureTest but I do test for voltage drop on some outlets if I feel that there might be a problem. Same thing with the three light tester and switches. Test not all just a representative number


I will simply say this…Unless you know the situation and are clearly aware of the loads being served or locations being served…be very careful about making statements regarding Voltage Drop .

While some issues of Voltage Drop can be a sign of other issues, poor terminations, excessive runs, excessive draw and so on it is important that if you make a statement in regards to Voltage Drop that you clearly understand when it is acceptable and when it is not.

Much of the equipment we use today works on a very wide range of voltage swings or ranges if you may…I believe greg eluded to this earier but I did not read all the posts.

Example: if you have a long run and the calculated load upon the given circuit will not exceed a given number…thus works within the acceptable range then voltage drop is not really an issue.

When you use a suretest on the SAME circuit with it’s given 12A,15A or 20A settings…you are maxing the load specs on that line…so without going into ALOT of detail because to be honest I have a headache today…you have to know the loads and connected issues associated with the voltage drop.

Would you consider 8A on a circuit with acceptable voltage drop under 3% fine…but then use a sure test and use the 15A setting and then it jumps to say 7-8% as a defect…well you have to know the circuit and whats going to be on it…really gets more detailed and exactly why I always say if you are going to do voltage drop…do it as an extra service…charge for voltage mapping so the client knows which receptacles have the potential for it if placed with larger loads nearing the MAX of the circuits ability…so they know in the future what they should plug in here or there…but not as a defect issue…an added bonus or sale item…

Really…it is SO important to know how to use a SureTest properly…I offered to do a course and even online it to show all the ins and outs of it, how to use it to check devices and so on and I got too much flack saying it was " OVER " the SOP…like Infrared and other things arnt…but alas I gave up on it…


Good post - Don’t give up just educate people who want it - even if they are just educators

I am glad that we are no longer using gas lights and candles

As homes become more complex (smart homes) our skills will have to come up a level or two or inspections will have to be referred to a different profession



This old dog is always ready to learn new tricks.

I can promise you one thing…with Minds like Mike, Greg and Peter to name few( and others as well ) around as well…PICK THE BRAINS of knowledge anytime guys…

The higher ups have NO idea how blessed they are to have people here like those guys wanting to help HI’s learn…


I have a 15 amp circuit that has 12 outlets, 11 receptacles and one light.
Each of these receptacles is rated at 15 amps and to load them to 80% would be a 12 amp load each. This leaves me a combined possible load of 132 amps.

Should this be called out as a possible danger???

I load one of the receptacles to 12 amps, how much more can I load the circuit before the overcurrent device will open???

Listen to me very carefully and stay away from the voltage drop issues. In the end it will end up costing you work.

And the issue is the heater not the voltage drop.
We must remember that the voltage dropped across any load is going to be equal to the applied voltage so across this heater there will be a voltage drop that is equal to the voltage applied from the circuit.

Could you give some references to this case as I would like to incorporate it into some of my classes? Being that most electric heaters have resistive elements the amount of voltage would not be a factor in the heating of the conductors in the circuit. The heater would simply emit less heat at the lower voltage and the amount of current being drawn would not be adversely affected.

Listen to what Paul is saying here. I don’t like going out to a house and shooting down the Home Inspector’s report but sometimes this is just what I do.
The HI has a very important job to do and one that should be done with professionalism and not whims.

Hey Fella,

In this case I would not think the issue was the heater itself unless it caused the fire due to placement. In this case I would venture to say the wiring was old, poor connections possibly under the load of a 1000W heater quite possibly caused a connection that was weak or poor to heat up and in the end caused the fire.

Having a load like this on a circuit with a poor connection, bad breaker with a poor gap or similar can lead to exactly what you have stated but not so much in regards to the voltage drop issue…sounds to me like more of a older wiring or poor connection issue…

Having excessive voltage drop in an example heater like that will simply result in well…less heat as if the OCPD works properly it would have protected the conductors…provided that was done right but it sounds like the person did not pull the panel which I would hate to defend in court personally…

Just some thoughts on it…would have liked to be the investigator on that one as I have done it quite a few times here in VA…on specific things…any idea what the final conclussion was in the report?

Hypothetical case: Suretest measures 15% voltage drop at 15 amps. 75 ft of #14 wire accounts for 5% of the 15 leaving 10% of the drop to some other part of the circuit. Again hypothetically let’s assume worst case and say it’s all at a poor contact on a backstabbed outlet. And assume that an electric heater is plugged in rated at 15 amps.

For the wire: 5% of 120 volts is 6 volts and 6 volts X 15 amps is 90 watts. 90 watts evenly distributed thru 75ft of 2 conductor wire is not a big deal temperature wise.

For the backstabbed outlet: 10% of 120 volts is 12 volts and 12 volts X 15 amps is 180 watts. 180 watts in a small space can get very hot. I have 120 watt soldering iron that does a good job at getting quite hot.

Again, all that is worst case but it’s worst cases that make for tragedy. HIs who don’t want to do voltage drops with Suretest are fine and within all known SOPs. Some HIs want to go just a bit further. If I find a 15% drop at an outlet, I’m going to recommend that an electrician at least pull the wires out of the backstabs and wrap them under the screws. That usually clears it up. If the electrician says I’m a nincompoop and won’t do it then so be it.

Probably a good point to make Ronald along with that is this…you guys need to ERR on the side of safety and not be concerned with what “I” or another electrician might say in regards to personal shots…in the end your client is paying you to be their SAFE eyes…

Now…I wont go into rights and wrongs…but when you gain additional knowledge of the proper aspects of " Voltage Drop " which I personally have a passion that you all SHOULD…in fact I feel electricity is taken WAY too light within this association in the past year or so…

point being…GET all the education you can, learn what voltage drop means to circuits other than just assuming a full load is being applied…understand the diversity of electricity…learn it’s habits, it natures and it;s desires…yes Electricity has a desire also…to get back to it’s WOMB…don’t we all…:wink:

In the end…there is a REASON why NACHI has the best inspectors in the world…quite frankly it is because of these boards…the people who care and the inspectors LIKE YOU GUYS who have the passion to learn.

We NEVER know it all…I strive to learn something new every day of my life and I work hard at it…today I am reading a book on advanced vectoring for Transformers…why because I want to learn MORE…More…MORE…

The day I think I know it all is the day I am ready to retire…I would have then LOST my passion and desire to move forward…

YIKES…I just read my previous post and I sound like some freakin GHANDI or something today…man I need more coffee

That’s a shame. I have a Suretest and would have looked forward to such a course.

I don’t think knowing information beyond the SOP makes a inspector more likely to go beyond the SOP. Certianly some would but I think most are inteligent enough to knwo what to say and what not to say. I hope i’m not wrong? -o<

Perhaps courses like the one Paul A proposed should simply require that the inspector pass the SOP quiz first.

I just stumbled aqcross this thread and have found it to be very interesting and educational reading ! Here are a few thoughts…

  1. Way up the list there was a short discussion about the wisdom of having a couple of driveway lights at the end of a fairly long run of #14. I’m surprised that no one pointed out that the voltage drop due to the long run matters only to the extent you wish to be able to see the light burning. An incadescent bulb will operate quite safely on any voltage at or below its rating - it will just keep getting dimmer as the voltage decreases.:mrgreen:

  2. Voltage drop, as mentioned above, can be a function of many factors, each of which has to be understood and properly evaluated before declaring a ‘safety’ defect.

  3. If we are going to test voltage drop, should such testing be limited to 15a receptacles? I would be more concerned about the circuit feeding the electric stove, or other high load devices.

  4. If we, not as engineers, but as Home Inspectors, are going to check for voltage drop using SureTest or other devices, how many receptacles and circuits should we test? I would hate to have stand up in court to try and explain why I only tested a few convenient “representative” locations, when the one behind the bed caused the fatal fire.

Overall, to me it is a ‘slippery slope’ that I don’t think most home inspectors are prepared to tackle. Of course, all this is JMHO.:wink:

I know Paul replied to this already but I must also comment.

While extremely sad, this case has NOTHING to do with the topic at hand of voltage drop. This is a black and white case of parents looking for ANYONE to blame for something terrible that happened. I guess the HI was the easiest target. I would think the LL would be the most responsible.


Yes, you are correct, the LL was the person that took it in the shorts. He did not rent a home that was electrical safe

Sorry but I do feel that this is on thread of voltage drop (ShureTest would have probably found it)

The parents also should have payed the gas bill and so it goes

BUT the HI did not flag the home as being needing of a good electrician.


Yes, you are correct as I understand the story outlet heated up IR loss went up (voltage drop), then more heat, then the bed sheets, curtains and then the up went the upstairs



The HI in question is from Michigan and now works in our county as a code officer. He was very active with Great Lakes ASHI. I have learned a lot from him. Some day I will get the story revised without the beer so you can use it. I assume that you instruct electricians

Look at it this way - current = IR loss (voltage drop) = heat = more resistance = more heat = a problem if we don’t dissipate the heat

At this time you do not know my background and I do not know yours so if you don’t tell me yours I will not tell you mine

Now that we have a clean page

I am sure that you understand that somewhere a breaker would trip with 12 outlets with 12 amps of load on each unless we were using some very large wire and a big breaker. Rating and usage are two different things.

Yes, the heater is the problem not the voltage drop. It should not have been used.

Please remember that the applied voltage at the heater went down (Voltage Drop) because of the bad outlet and other resistance issues. When the voltage went down at the heater it cooled down a little thus its resistance went down a little and it pulled more current making the problem worse

As a matter of note I do not like ShureTest

It only loads the Ckt for a short time which does not allow a bad connection to heat up like it would with normal use with something like a space heater or iron etc. If allowed to heat up the resistance would go up and the VD would get worse.

I am always willing to come to the site to work with a system professional that has a problem with my findings

No I do not test voltage drop in all cases and never on “wired in” equipment

Too hard to get to terminals and they don’t pay us for the extra time

No I do not test all outlets - It is hard to find all of them - move all the junk and not break some old pot on top of something. (my back is not a strong as it was a few years back)

Real simple if it is bad report it – if the system professional does not agree – you still reported it

This idea of looking for VD will cost us work sounds like a realtor. I work for my client. If the home need a good electrician and he makes very good money he should buy me the beer

Just like some of the other “looking” that some of us are doing (thermo imaging camera) Standby here comes thermo imaging of the electrical system under load




Get educated and start testing for Voltage Drop

ShureTest not my first choice but who is in second place?


Can you tell me why we should be testing for voltage drop?

… Cookie

I use a Suretest because I didn’t know of a comparable product from someone else. Is there?

Using the $10 3 light tester in an outlet takes 1 second, using the Suretest takes 3 seconds. Not a big time increase. Each inspector makes their own choices.


Look at your own home

What can you test for and that you could correct that you can not see that would hurt you, your loved ones, and your home??

Smoke detectors
CO detectors

How about VD to show up a bad connection in a junction box

Ever see the inside of a breaker panel that had a high resistance connection that caught fire and hurt the home?

VD shows problems - it is easy to test for -

If you were buying a home would you like someone to test for VD?

The cost is low and it does show problem

I just don’t like the ShureTest way of doing it

Maybe someone from ShureTest needs to give me a sales pitch

My home was built in 1925 and has been electrically updated many times

It is not as big of a mess as when I moved in and I know I have problems to the point that when we go on vacation I kill all breakers except the refrigerator and a few lights on timers

I have replaced over 75% of every wire

VD was a very large problem