Voltage Increase

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chrisreisinger79

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Location
Grand Rapids, MN, USA
My supervisor at work had an interesting question. Some background information first:

1) Residential service, 220VAC
2) 4 120VAC Circuits, 15A each
A) #1: Refrigerator
B) #2: Microwave
C) #3: Stove, Fan, TV, Other General Purpose Receptacles
D) #4: Lighting

The question is: When the microwave is turned on (Circuit #2), the fan spins faster (Circuit #3) and the lighting gets brighter (Circuit #4). He checked voltage on Circuit #3 and noticed an increase from 120VAC to 137vac. To his knowledge each circuit has its own neutral back to the panel. This just started happening as well. What could cause this?
 
Have him check the voltage on the other leg to see if it decreases.
It does sound like a neutral problem from the description.
 
retirede said:
Bad service neutral connection.
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To clarify this for your future reference, the cause will be a high resistance connection or possibly and open ANYWHERE along the neutral toward the utility transformer after the affected loads share that common neutral.
 
Take Jumper's advice and disconnect all electronics or anything that has a digital display. It's a bad neutral. Either at the MB panel, the meter, the service head or on the utility pole.
 
I heard back from my supervisor this morning. Here is what he had to say:

"Good voltage off the pole, 121 on one leg and 122 on the other leg. In the Main Panel, voltage fluctuates between legs depending on what's energized."

I took that as depending on what leg is enegized, he's seeing an increase in voltage on the opposite leg.
 
180124-1124 EST

chrisreisinger79:

I have discussed precise locations to measure voltage at in some other thread. Go search for it.

Make voltage measurements directly on the wires, not terminals, entering the main panel. It is clear you have a neutral problem.

If the big change in voltage occurs on these wires, then the problem is before the main panel. If not, then the problem is within the main panel or after.

You can use two 25 W or smaller incandescent bulbs for testing instead of a meter(s). Bulb size is to reduce brightness for looking at.

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180124-1157 EST

Is your supervisor a lit school person like music major, english major, or business school? Your last question comes from someone that has no electrical knowledge.

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chrisreisinger79 said:
My supervisor wanted me to ask another question in relation to this. How is the circuit completed without a neutral to return? Does it use the other leg and if so, how?
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With no neutral back to the source but still connected together at the panel, you ultimately end up placing the loads on opposite "legs" in series with 240 volts. The more mismatched those loads are the more serious the voltage differential becomes. You will have low voltage across lower resistance loads and high voltage across high resistance loads. A good neutral stabilizes the volts of each load to near 120.
 
This graphic is for a MWBC, but it applies to a service also.

index.php
 
gar said:
180124-1157 EST

Is your supervisor a lit school person like music major, english major, or business school? Your last question comes from someone that has no electrical knowledge.

.
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I don't know his background beyond he has PLC training. We've had other discussions about the function of a neutral before and I've had trouble explaining clearly the nature of the neutral in relation to balanced/unbalanced loads. Thanks everyone for the help.
 
180124-1345 EST

PLC training means nothing relative electrical knowledge, and may not mean much relative to logical circuits.

Putting people in supervisory positions does not make much sense if they know very little about what they supervise.

.
 
chrisreisinger79 said:
My supervisor wanted me to ask another question in relation to this. How is the circuit completed without a neutral to return? Does it use the other leg and if so, how?
Click to expand...

See post #12. Your voltage fluctuations are due to a lost (or very nearly failed) service neutral. Where the exact failure is, you'll have to track it down - could be the service neutral in the panel, in the meter, in the run or a bad splice at the weatherhead or the pole.

Normally, a 120V circuit uses a hot and a neutral to complete the pathway. A 120V circuit on the opposite leg does the same, just 180* out of phase with the first. A MWBC, or service drop, uses 2 hots with one neutral. This neutral carries the imbalance of the currents between the legs, and voltage stays at 120V. If that neutral is lost, instead of having 2 120V circuits in parallel, you now have a single 240V circuit with the loads in series. If there is a difference in the resistances of those loads, the voltages across those loads will differ. You will still have 240V total, but maybe, as you found, 137V on one leg - the other would have ~103V.

Do not use any 120V loads until you find and repair the break in the service neutral. That is the bottom line and the bare minimum you need to understand at this moment.

ActionDave said:
Your supervisor needs to turn off the main and call an electrician before he burns up all the appliances in his house.
Click to expand...

retirede said:
Bad service neutral connection.
Click to expand...

Little Bill said:
Have him check the voltage on the other leg to see if it decreases.
It does sound like a neutral problem from the description.
Click to expand...

Strathead said:
To clarify this for your future reference, the cause will be a high resistance connection or possibly and open ANYWHERE along the neutral toward the utility transformer after the affected loads share that common neutral.
Click to expand...

Ditto x6
 
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