lights flickering when dryer is running

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atsparky

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I recently did a basement and installed a new dryer, now the lights on different circuits are flickering only when the dryer is running. It is a 240v dryer and have checked the connections, changed the breaker on both dryer and lighting circuits. I have also moved the dryer breaker to the top of the panel just in case and checked all neutral connections.

Has anyone seen this before any help would be appreciated.
 
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Thanks,

I checked it out but the dryer keeps changing it's amperage pull as the heat cycles on and off and pulls around 11amps medium and from 4 to 22amps nothing that indicates this flickering should happen. I'm thinking that it might be a main breaker or service issue. The voltage at the panel bounces around when the dryer is running and when the dryer is turned off it stays at the same voltage.

I'm going back now with a helper to do some more tests and get exact readings on all sides of the breakers and meter socket.
 
090425-1702 EST

Provide some values for the voltage change. Do this across the 240, and from neutral to each hot line. Also measure neutral voltage at the main panel to the ground rod at the transformer location if possible.

.
 
Ok here are some voltage measurements :

Before I turn on the largest lighting circuit which is drawing 10.9 amps

Phase A 120v
Phase B 119.2v

After I turn on the lighting circuit breaker

Phase A 120.6
Phase B 117.1

Then when I run the dryer

Phase A 118.1 but constantly bouncing up and down over a 1.5voltage
Phase B 114.5 also constantly bouncing up and down over a 1.5 voltage

This voltage reading is the same at the line side and the load side of the main breaker and also the same at the line side of the meter socket

the reading accross the 240 was 232volts

I also run the dryer off the line side of the main breaker to eliminate if the breaker was causing impedence
Thae transformer is not in view of the property and must be up the block.

I could only see one copper ground large enough to be either to the water or the ground rod, could not locate the end and could not find the ground rod location. The panel is on the first floor with a full finished drywalled basement. I checked the access for the water meter and only found an old type ground with mc covering it jumping the meter..

Do you think if I installed a ground rod it would eliminate this, I'm now worried that the previous electricain didn't install one as I also found that he wire nutted the under cabinet lights in plain view under the cabinets so this considered I think he may have taken a short cut to the closest water pipe and left it at that.

Thanks again for all your help
 
090415-1811 EST

atsparky:

You are showing less voltage change on phase A than B.

When the dryer was on 118. + 114.5 = 232.6 correlates well with the measurement across A to B of 232.

I do not know if your lighting breaker was only on phase B and how much its current was. Suppose the lighting load was equal on both A and B, then the greater drop on B would imply a high resistance on B compared to A.

On the other hand the lighting load causing phase A to increase in voltage by 0.6 V implies that the lighting is mostly, if not all, on phase B.

If you can try, then the following experiment:

1. Use a 1500 W or thereabouts test load.
2. Turn all loads off except a small light, maybe a CFL. This light is to provided light to observe your measurements.
3. With no load, except the small light, measure your line to neutral voltages.
4. Connect the 1500 W load to phase A, and measure both phase to neutral voltages.
5. Repeat 4 but with the 1500 W load connected to phase B.
6. Report the results.

From your previous data I expect you will see a greater drop on phase B.

.
 
090415-1839 EST

atsparky:

On my 200 A system tonight with a 1500 W load I get the following results:

With the voltmeter on the opposite phase from the load I got less than 0.1 V change from the load. This was the same for either phase combination. This meant that my neutral impedance was less than 0.1/12 = 0.008 ohms.

The voltage change on the side with the load, not thru the breaker or outlet with the load, was about 0.6 V. This means that the impedance of the transformer (center tap to hot line), hot wire, meter, and main fuse was about 0.6/12 = 0.05 ohms.


Assume a maximum of 5000 W for a dryer. This is 5000/240 = about 20 A.

Your 11 A and 2.1 V was about 2.1/11 = 0.19 ohms if all 11 A was on phase B. At 11 A and 0.6 V, the neutral change, the resistance of the neutral is about 0.6/11 = 0.05 ohms. Therefore the hot side is about 0.19 - 0.05 = 0.14 ohms.

Probably not out of line with what you might expect. If we assume 0.28 ohms for the 240 impedance and 20 A, then total 240 drop would be 5.6 V at dryer full power. 120+119.2 = 239.2 and 118.1+114.5 = 232.6, and 239.2 - 232.6 = 6.6 V. Not grossly out of line with my calculation based on estimated impedances. However, the difference in drop on the two sides is confusing.

The measurements with a specific load shifted from one side to the other may help understand what is going on.

.
 
not a loose wire being vibrated, it's on a few lighting circuits but I haven't been back to the house since, told them to put a call into the electric company and have their end checked first, then i'll proceed with further investication if they find nothing.

I'll let you all know what the outcome is.
 
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