Voltage Drop Unexplained

Old 06-10-03, 07:06 AM
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Voltage Drop Unexplained

Different (unrelated) Issue:

When my wife and I purchased a new house in Chicagoland, IL two years ago our home inspector found that there was 15% voltage drop from the fuse box in the basement to most of the outlets on the second floor of our house. The first floor has a very slight voltage drop but nothing to be alarmed about.

What's even more interesting is that when an outlet on the second floor is disconnected from the box in the wall, such that it is "dangling" by the wires, there is no voltage drop. It only seems to happen when the outlet is properly screwed into place.

Our builder and two electricians have spent hours trying to figure out what the problem is and have been unsuccessful. Furthermore, the head electrician (owner of the company) offered to pay for the cost of someone to fix the problem but only if the problem could be fixed. He won't pay for someone to inspect the situation and tell us that there is no problem.

Furthermore, the builder does not believe the issue is a problem and even if it is a problem he thinks it is too minor to worry about. I of course what the wiring to be correct but am I over worrying about this situation? Is it OK to leave as-is and put the situation to bed? Or does it need to be corrected and why? Also, does anyone have any suggestions what could be causing the problem?
Old 06-10-03, 09:17 AM
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Voltage drop

Furthermore, the builder does not believe the issue is a problem and even if it is a problem he thinks it is too minor to worry about
Not sure if my math is right but the way I figure it is , 120v with a 15% voltage drop leaves you with 102v at the receptacle.(120x.15=18) (120-18=102) yes this is a problem. Thats assuming you have 120v at the source (it could be as little as 110v which would leave you with 95v at 15%) where I come from 5% is the max voltage drop. If you are in Chicago then the house is Probably done in conduit. Therefore one solution is to pull larger wires from the panel to the receptacles. The fact that the position of the receptacle determines the ammount of voltage drop tells me that there is a bad splice or broken solid conductor. Most residential wiring is solid wire and if it were knicked during installation it could break inside the insulation causing a poor connection.

Hope this helped
Old 06-10-03, 09:43 AM
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Thank You & Follow-Up Question

Thank You very much for your resonse - it is very helpful. I appreciate you taking the time to share your knowledge & experience.

If you wouldn't mind, I'd like to understand your perspective of why this is a problem. If in fact the voltage on the second floor is between 90v - 100v, why is this a problem? What are the risks?

And what do you recommend to correct it? Do we need to pull the wire on the second floor until we find the problem?
Old 06-10-03, 10:05 AM
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It will be necesary to test this circuit with a load on the circuit and reading the voltages with an acurrate analog meter, a meter with a needle that deflects across the scale.

If there is a 2 ohm resisitance in the Branch-Circuit wiring, a load of 1 amp will result in a V.-D. of 2 X 1 = 2 volts. If the load is 12 amps the V.-D. is 2 X 12 = 24 volts so connect a load of this approx. value to the circuit.

Dis-connect the wires from the receptacle that seems to indicate a problem and locate the Black/White pair that "feeds' 120 V. into the outlet-box. Re connect the receptacle to the "feed-in" pair only and plug a 12 amp load into the receptacle and read the voltage across the device terminals.If you read 100 volts at the device terminals and 120 volts at the fuse/breaker terminals then there's a loss of 20 volts in the wiring between the panel and the outlet.------Good Luck!!!!
Old 06-10-03, 11:26 AM
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Voltage drop cannot occur without current flow. So the questions are: what is drawing the current that causes the voltage drop, where is it connected, and how much current is it drawing? Answer these questions and you'll be a lot closer to the solution.

If you are measuring voltage drop in the absence of load, then you are either using a defective test instrument, are measuring phantom voltage, or are misusing the test instrument.
Old 06-11-03, 05:11 AM
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If they are saying there is a voltage drop due to the fact that the outlets upstairs are only around 90-100volts.... then their logic isn't quite correct..... obviously if pulling out one device fixes the problem, it's not voltage drop, it's bad connetions.... most likely a bad neutral connection in that outlet you had to dangle.
Old 06-11-03, 05:49 AM
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The outlet in question seems to be where the problem is. I would try nutting the wires together with no outlet. See what happens. Now try pushing the wires around in the box. See if you can make the problem occur. Could be a damaged wire in the wall. Perhaps the drywallers damaged it outside the box. Perhaps the box clamp is too tight and pinching the wires. I you have to, pull the box and invesitgate inside the wall.

New thought.
You said Chicagoland. You probably have conduit. Find the other end of the wires and pull them out of the conduit. Might have been damaged or knicked during the initial install.
Or perhaps the problem is one of the adjoining boxes and pushing the wire into the box is pushing it out the other end of the conduit and messing with another connection.

You could also try a thermal imaging camera. A voltage drop that high should be generating heat somewhere.
Old 06-11-03, 04:17 PM
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More Than One Outet

The problem we are experiencing happens to be every single outlet on the second floor other than bathroom outlets. We have 3 bedrooms, each with 2 outlets and all 6 are having this problem.

We tested the main lead running to the second floor and it did not seem to have any problems.

I like many of the suggestions that were brough forward and I'm going to look into these possibilities - thank you all that have responded !!
Old 06-12-03, 09:30 AM
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Is it possible its not a volatage drop but a poor ground makeing it look like a voltage drop ?
Old 06-15-03, 04:39 PM
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Just a thought about your problem. If you have alot of electronic equipment in your house, such as florescent lights with electronic ballests or other high speed switching devices, tv's vcr's, computers ect....you may be creating a harmonic imbalance on the neutral side of your service. This would make the neutral carry excessive current which when you measure it at an outlet you will notice a lower potential voltage between the hot and neutral throughout your house. The bathroom outlets are on GFI's and would be isolated from the rest of the houses neutral load, explaining why you do not have the same voltage drop in your bathrooms. To check this get a good quality clamp on amp meter and put it on the service feeders neutral conductor. If you have a 200 amp panel the current on the neutral should be at the very most about 60% of 200 amps. To really figure out what is going on with your service you need to connect an oscillacope to the service conductors and look for a higher frequency that 60hz. This will pinpoint the harmonic problem. Anyway I hope this helps you out and good luck with the contractor. They never think a problem is that big and try to worm out of fixing anything that may cost them a few bucks....

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