Voltage Drop

[Larry D. Kage]

Originally Posted by rdawes

I for one, am not trying to do an electricians job but it doesn't take an electrician to go "wow, it's a long way from the panel to this bedroom" and then plug my SureTest into the outlet and see that it shows 22% voltage drop due to the long run of #14 wire and multiple backstabbed outlets in series. I then can suggest that qualified electrician be used to assure that it's really OK or to get it fixed. That gets the monkey off my back and lets me feel better about the situation.

Ron, I think Roy's point was that there was no monkey on your back to begin with...

but the way I see it...if it lets you feel better about the situation, and you want the additional role, then go for it.

[Dan Bowers, CMI]

I always get a long laugh hearing agents tell how an inspector with his/her brand new SureTest checked the outlets at a home inspection they were on - found a 7%-10% voltage drop and recommended calling out an electrician for electrical review, etc. AND the electrician called the HI a nincomboob.

The buyer ran away from the sale - the agents lost $18,000 commission.

The agents then go on to tell how they're passing the inspectors name around at sales meetings to alert other agents so they can keep this inspector out of any of their sales transactions.

Gosh life is humorous.

[rdawes]

A. I won't call out a 7-10% voltage drop but when it hits 12-15% I do.

B. Once when I called out several outlets with 15-22% drops, I got a call from an "electrician" who said he measured the voltage at the panel at 120 volts with his meter so there was "no problem". I spent 10 minutes trying to explain to him how to test for voltage drop. Not sure if he got his license in a cracker jack box or what or if he really had a license. Anyway somtimes the nincompops are right.

C. I don't try and please realtors.

[Mike Whitt]

Originally Posted by rdawes

A. I won't call out a 7-10% voltage drop but when it hits 12-15% I do.

Originally Posted by rdawes

C. I don't try and please realtors.

Here we have a problem.

What method are you using to come up with the voltage drop?

If you are using a voltage tester and coming up with a difference in voltage in a house the problem is something different than voltage drop due to the length of the circuit.

A simple calculator can tell you what the voltage drop is for a given circuit.
Using this calculator and the load of a voltage tester of let’s say one tenth an amp we can see that the voltage drop on a 15 amp circuit installed with #14 NM cable would need to be at least 6716.82 feet to have a 3% drop.

As you can see the meter is not enough of a load to make a difference in the voltage in a normal house.

If you are finding a 15% difference in the circuit of a house using nothing more than a voltage tester then there is a serious problem with the circuit and it is far more than a simple voltage drop due to the size of the conductor.

The formula for voltage drop can be found here
As we all can see one of the major players of voltage drop is the load on the circuit (twice the resistance of the conductor times the load or amperage times the length of the run)

It would be better to call out a difference in the voltages of a circuit as something else other than a “Voltage Drop”.
As a contractor the first thing I am going to ask for in the event of a HI calling out a voltage drop is the math he used. No math equals no voltage drop.

[rdawes]

As I said in post #15, and verified by your calculator, about 75 ft. of #14 wire will have a 5% drop at 15 amps. Hence the previous comment that long runs (much greater than 75ft) of #14 are a problem. I use a Suretest which puts a load on the circuit and calculates the voltage drop under load. Measuring the voltage under no load proves nothing.

The Suretest measures the voltage no load, then puts a momentary 12 amp load on the circuit, measures the voltage again with the load, then calculates the % voltage drop at 12 amps, extrapolated to 15 amps, and extrapolated to 20 amps. That takes about 3 seconds for the tester to perform. I use the 15 amp value as that is what the outlets are rated for.

[Brian A. MacNeish]

Originally Posted by rdawes

The Suretest measures the voltage no load, then puts a momentary 12 amp load on the circuit, measures the voltage again with the load, then calculates the % voltage drop at 12 amps, extrapolated to 15 amps, and extrapolated to 20 amps. That takes about 3 seconds for the tester to perform. I use the 15 amp value as that is what the outlets are rated for.

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.

[Richard L. Bennett]

Mike

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

rlb

[Paul W. Abernathy]

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....

[Richard L. Bennett]

Paul

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

rlb

[rdawes]

Paul,

This old dog is always ready to learn new tricks.

[Paul W. Abernathy]

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.......

[Mike Whitt]

Originally Posted by rdawes

As I said in post #15, and verified by your calculator, about 75 ft. of #14 wire will have a 5% drop at 15 amps. Hence the previous comment that long runs (much greater than 75ft) of #14 are a problem. I use a Suretest which puts a load on the circuit and calculates the voltage drop under load. Measuring the voltage under no load proves nothing.

Originally Posted by rdawes

The Suretest measures the voltage no load, then puts a momentary 12 amp load on the circuit, measures the voltage again with the load, then calculates the % voltage drop at 12 amps, extrapolated to 15 amps, and extrapolated to 20 amps. That takes about 3 seconds for the tester to perform. I use the 15 amp value as that is what the outlets are rated for.

Wow!!!

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.

Originally Posted by rbennett

Mike

Originally Posted by rbennett

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

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.

Originally Posted by rbennett

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.

Originally Posted by rbennett

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??
rlb

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.

Originally Posted by pabernathy

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 ...

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.

[Paul W. Abernathy]

Originally Posted by rbennett

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??

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?

[rdawes]

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.

[Paul W. Abernathy]

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....

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.....