Voltage Drop at outlets on a Custom Residential Home

[Downtown1121]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold. The electrician who wired this house for me has wired 10+ homes over the years. They used 12 gauge wire in 20 amp circuits and 14 gauge wire in 15 amp circuits.

I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop. As I understand it, the voltage drop only occurs when you max out the circuit and there are few items using the max power of the circuit...

 

[PaulMmn]

Was there anything plugged in while he took his measurements??

What is the voltage the power company is supplying??

 

[charlie b]

I don't know anything about the specific meter you named. But I seriously doubt that your average homeowner knows enough to be able to set up a test, using such a meter, that would reliably give you the voltage that would be present under full loading conditions. This is likely to turn out to be a non-problem. But, sadly, the burden of proof is just as likely to fall upon your shoulders. Good luck with this one.

 

[K8MHZ]

 

[Dennis Alwon]

The 5% threshold is not a requirement but rather a recommendation. Informational notes are not enforceable-- and you are correct that there is rarely a full load on circvuits

Informational Note No. 4: Conductors for branch circuits as
defined in Article 100, sized to prevent a voltage drop exceeding
3 percent at the farthest outlet of power, heating, and lighting
loads, or combinations of such loads, and where the maximum
total voltage drop on both feeders and branch circuits to the
farthest outlet does not exceed 5 percent, provide reasonable
efficiency of operation. See Informational Note No. 2 of
215.2(A)(1) for voltage drop on feeder conductors.

 

[ptonsparky]

You need to know what the voltage is doing at the panel during theses tests.

What problems is the customer having other than he has a nice new toy?

 

[Jamesco]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold. The electrician who wired this house for me has wired 10+ homes over the years. They used 12 gauge wire in 20 amp circuits and 14 gauge wire in 15 amp circuits.

I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop. As I understand it, the voltage drop only occurs when you max out the circuit and there are few items using the max power of the circuit...

~

CT70-EN-V8.2-4/12 4Operation Overview The CT70 AC Circuit Load Tester can test outlets or circuits under load for proper wiring, reverse polarity, and the presence of a ground. The CT70 uses a simple menu-driven display to allow the user to quickly see line voltage, voltage drop under full load, ground-to-neutral voltage, and line impedance. The GFCI testing utility is performed separately per UL-1436, disrupting the flow of electricity if a functioning GFCI is present. Note: To avoid the buildup of heat during load testing, allow at least 20 seconds to elapse between tests. In addition to the safety benefits, this will allow the meter to maintain its stated accuracy during repeated tests.

http://www.extech.com/resources/CT70_UM.pdf

About 15 years ago I called for an electrical final inspection and when the inspector showed up he had some kind of a meter in his hand. He said I got a new toy that will check an unloaded branch circuit for voltage drop, (VD), at the point the outlet is connected to the branch circuit. He said do you have some time to see how it works?

He first plugged the device into a wall outlet where we were standing. The outlet tested fine. He then asked if I knew where the last outlet was located on the circuit. I did a quick look on the prints and we went to the location of the outlet. Again the circuit tested fine. The inspector did a few other random tests in the area and again all tested fine.

The next time I called him for a final he had the meter with him again. I said I see you are still carrying your expensive new toy? He replied yeah, but now I have to ask for permission to check for (VD) on a circuit.

At that time one of the biggest commercial/Industrial contractors in the metro called the inspector's boss and complained about the inspector checking for VD on his jobs. The contractor said, which is true, calculations for VD are not mandated by the NEC. I said I bet a lot of the outlets you tested failed on the branch circuit VD test didn't they?

 

[infinity]

The voltage drop could be 10% and the NEC still doesn't care. Unless the contract stated that the home was to be wired for no more than 5% VD he'll have to live with it or pay to have remedied.

 

[ron]

As mentioned, the testing gives unrealistic unenforceable results.

It is drawing 12, 15 and 20A and checking VD. Keep in mind, even for non-dwelling, we only use 1.5A as a recorded load for general purpose recepts.

NEC doesn't have enforceable language regarding VD.

Most adopted Energy Codes have enforceable VD language, but most aspects don't apply to residential.

 

[480sparky]

I had an inspector try one of those meters on a hotel I was getting a final on. He'd plug into each receptacle and say, "Oops.... 7 percent." "Nope, 6 percent." "This one's good, 3 and half percent." "Gotta redo this one..... it's 8 percent." "You're gonna have to rewire all these with 10."

Funny thing was, he want back and did them again, and got different readings.

 

[hbiss]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold... I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop...

As you can see the way to address this with your customer is to tell them that there is no threshold, no maximum voltage drop requirement specified anywhere in the Code. Further, the maximum voltage drop will be exhibited at the farthest receptacle in the circuit when the full current rating of the circuit is being drawn from that receptacle. It's not likely that that's going to happen very often.

-Hal

 

[nizak]

How many of us here have encountered a homeowner who's concerned with voltage drop?

Sounds like someone is coaching them.

 

[growler]

I don't know anything about the specific meter you named. But I seriously doubt that your average homeowner knows enough to be able to set up a test, using such a meter, that would reliably give you the voltage that would be present under full loading conditions. This is likely to turn out to be a non-problem. But, sadly, the burden of proof is just as likely to fall upon your shoulders. Good luck with this one.

Actually you would have to be pretty dumb not to be able to use one of these testers. The directions are very simple and they are easy to use. They are known as circuit analyzers and all you need to know is to plug it in and which buttons to push. Easy as pie.

Understanding the information gathered by using this device is a different matter. If you can get a close estimation of the length of the wire the voltage drop reading is normally really close to what a calculation of voltage drop should be. If you calculate 5% and read much higher (say 10-20%) then it's time to start looking for a bad or loose connection.

 

[480sparky]

How many of us here have encountered a homeowner who's concerned with voltage drop?

Sounds like someone is coaching them.

Or they've watched too many YouToob videos.

 

[roger]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold. The electrician who wired this house for me has wired 10+ homes over the years. They used 12 gauge wire in 20 amp circuits and 14 gauge wire in 15 amp circuits.

I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop. As I understand it, the voltage drop only occurs when you max out the circuit and there are few items using the max power of the circuit...

Tell the H.O. that these type meters measure voltage drop from the utility transformer to the point in the circuit where the meter is connected and since you have installed per the NEC requirements the POCO needs to move their transformer closer to their house or even put it inside their house if need be.

BTW, welcome to the forums.

Roger

 

[oldsparky52]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold. The electrician who wired this house for me has wired 10+ homes over the years. They used 12 gauge wire in 20 amp circuits and 14 gauge wire in 15 amp circuits.

I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop. As I understand it, the voltage drop only occurs when you max out the circuit and there are few items using the max power of the circuit...

Was there any wording in the contract that suggests a minimum voltage drop? If not then IMO the homeowner doesn't have a complaint. If he wanted a minimum voltage at full load on that outlet, then he should have stated so in the contract. It's not an NEC compliance issue.

 

[electrofelon]

I have a customer (homeowner) that is testing the outlets in their house with a meter from Extech (CT70) for voltage drops. This meter is showing many outlets over the 5% threshold. The electrician who wired this house for me has wired 10+ homes over the years. They used 12 gauge wire in 20 amp circuits and 14 gauge wire in 15 amp circuits.

I'm a little out of my element here and was looking for some help in how to address their concerns about voltage drop. As I understand it, the voltage drop only occurs when you max out the circuit and there are few items using the max power of the circuit...

I would (more politely than this) say "who cares?" Does he run a bunch of air compressors all day or heat is house with plug in space heaters? His giant TV is only going to draw a few amps.

Hope he doesnt find out his 200 amp service is a scam since the POCO is using a 25KVA tranny.... :roll:

 

[480sparky]

I would (more politely than this) say "who cares?" Does he run a bunch of air compressors all day or heat is house with plug in space heaters? His giant TV is only going to draw a few amps.

Maybe he's going to start a grow operation.

 

[Downtown1121]

Follow Up Question

Follow Up Question

Thank you everyone for the insight you are providing.

At what point would voltage drop start negatively impacting things in a house?

On residential construction, what code determines the size wire that is required for different circuits?

Is there a code that says there is a maximum, unacceptable voltage drop?

Does a voltage drop of 14.8% on the last outlet in a 15 amp branch circuit using 14-2 wire, with 6 outlets, concern you?

If one expects there home to be wired to the recommendations in the NEC, then any voltage drop over 5% is unacceptable. Why would the NEC publish this recommendation?

 

[hbiss]

At what point would voltage drop start negatively impacting things in a house?
When they stop operating properly.

On residential construction, what code determines the size wire that is required for different circuits?
The NEC.

Is there a code that says there is a maximum, unacceptable voltage drop?
We've already covered that- no.

Does a voltage drop of 14.8% on the last outlet in a 15 amp branch circuit using 14-2 wire, with 6 outlets, concern you?
Yes it would. It indicates a problem.

If one expects there home to be wired to the recommendations in the NEC, then any voltage drop over 5% is unacceptable. Why would the NEC publish this recommendation?

A home must be wired to the minimum requirements of the NEC. Recommendations within the NEC are just that- recommendations, and are not required to be followed.

-Hal