Excessive Voltage Drop

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#1

Originally Posted By: sramos
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For those of you who take these measurements with a circuit analyzer like SureTest, how do you right up your findings? What threshold do you use? 5%, 10%? Do you call it a safety issue? Further investigation?

–
Steven Ramos


EnviroVue Home Inspection


866-541-2883

#2

Originally Posted By: bbadger
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The NEC does not consider voltage drop a safety issue as evidenced by the lack of requirements to control or limit it.


The only mentions of voltage drop in the NEC are fine print notes which are not code but suggestions or information.

Quote:
Conductors for feeders 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, will provide reasonable efficiency of operation.


Voltage drop caused by excessively long circuits will not start a fire.

Voltage drop caused by loose connections is another issue and could be a fire hazard.

The suretest can not tell the difference between the two, my suggestion is if you use the sure test use it to compare readings from one circuit to another.

If one circuit has radically different readings then another IMO that circuit would be suspect.

UL requires utilization equipment to operate with 10% under-voltage. But this is the total under-voltage of the utility and the premises wiring.

Between the service panel and the outlet it would be good to keep the voltage drop to less than 5%.

--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN
#3

Originally Posted By: tschwalbe
This post was automatically imported from our archived forum.


I think it can tell the differnce but i could be wrong. Wouldnt a circuit with bad connections have higher resistance than just a long circuit?

#4

Originally Posted By: sramos
This post was automatically imported from our archived forum.


Thank you for your reply Bob. When you say radically different readings between circuits, do you mean between outlets on the same circuit (i.e. two outlets in the bathroom).


Next question, in the absence of proper labeling at the service or distribution panel, how can you be sure the any receptacles are on the same circuit?

With respect to resistance, the Suretest does measure resistance. However, I beleive it measure the entire circuit not just that receptacle. I guess could use both measurements to ascertain where a high point of resistance begins, if you new which receptacles where on the same circuit?

--
Steven Ramos
EnviroVue Home Inspection
866-541-2883

#5

Originally Posted By: bbadger
This post was automatically imported from our archived forum.


tschwalbe wrote:
I think it can tell the differnce but i could be wrong. Wouldnt a circuit with bad connections have higher resistance than just a long circuit?


Yes it will, but that is no different to the suretest then the resistance from a long wire run.

--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN
#6

Originally Posted By: bbadger
This post was automatically imported from our archived forum.


sramos wrote:
Thank you for your reply Bob. When you say radically different readings between circuits, do you mean between outlets on the same circuit (i.e. two outlets in the bathroom).

Next question, in the absence of proper labeling at the service or distribution panel, how can you be sure the any receptacles are on the same circuit?

With respect to resistance, the Suretest does measure resistance. However, I beleive it measure the entire circuit not just that receptacle. I guess could use both measurements to ascertain where a high point of resistance begins, if you new which receptacles where on the same circuit?


All those point you make are valid IMO.

Without knowing the layout of the circuit it is tough to pin down answers.

If I had two outlets near each other on the same circuit I would expect the VD to be close to the same for each, if it was different I would suspect loose connections.

That said in my job I would tan pull the outlet out and check it out. HIs are in a tougher position you want to be able to give an accurate report without pulling the devices. That is asking a lot of anyone.

I think some other HIs should answer this thread (like you asked ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif) ) that use the suretest and describe how they report the readings.

I was mostly trying to explain the NECs position on VD.

Personally I hate voltage drop, I oversize wires quite often to combat voltage drop.

Anything with a motor has reduced power when run with voltage drop.

--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN