Cloths dryer overload

[Jraef]

"An appliance tech is a waste of money." Assuming this is a residential dryer, yes this is a power supply issue rather than dryer. Dryer motors are 120vac and around 5-8 amps. running. Had a very similar call at a home (120/240 residential 200 amp service). The end result was a bad neutral at the pole.

Had a similar one a couple of years ago, it was a corroded meter socket jaw. Under normal household loads, the resistance in the jaw was insignificant, but when the AC or the dryer came on, it caused a severe voltage drop. I had troubleshot everything else, called the utility to check their lines. They pulled the meter and found the bad socket jaw.

 

[gar]

211215-2123 EDT

I would approach this as follows:

I would measure voltage on the main panel input wires directly on the wires. Thus, not on the lugs. This is done with generally little load on the panel. Measure line to line, each line to neutral, and neutral to some outside earth point.

I would use two devices for voltage measurement. One a digital meter with 0.1 V resolution on a scale that reads at least somewhat over 260 V. The other is two 15 W 120 V incandescent bulbs. The bulbs will slightly flicker on a 2 V change at around 120 excitation. Loading one phase will cause a light dimming on that phase, and slight increase in voltage on the unloaded phase. Do a measurement at the main panel when the drier starts, and after the heater turns on. If there is indication of excessive voltage change at the main panel determine its cause.

This same test can performed on the output side of the breaker for the drier at the main panel. If a problem shows up at the main panel find out where.

If no major problem appears at the main, then do the same tests at the drier.

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[Pat75]

Are there any other large loads that produce the same situation on the panel?
I had a call 30 years ago that I never forgot. A table saw in a garage caused the entire house to dip way beyond tolerable, to the point other items would shut down due to voltage drop. I went through every possible scenario in troubleshooting that I could do, with no reason for it other than the power company. I called for a trouble truck from the poco, guy shows up and without testing ANYTHING at the meter,, says its impossible for it to be their problem because he just finished checking the
XFMR and its fine.
I asked him to pull the meter ( in our area electricians aren't "supposed" to pull it). He does as I ask and to our surprise he finds a knockout slug from the original installation which had fallen between a lug and the meter can. The paint prevented a dead short. He pulled it out and presto problem is gone.
I'm not saying that is your problem, but it wouldn't surprise me if it is on the PoCo side.

 

[Hv&Lv]

Are there any other large loads that produce the same situation on the panel?
I had a call 30 years ago that I never forgot. A table saw in a garage caused the entire house to dip way beyond tolerable, to the point other items would shut down due to voltage drop. I went through every possible scenario in troubleshooting that I could do, with no reason for it other than the power company. I called for a trouble truck from the poco, guy shows up and without testing ANYTHING at the meter,, says its impossible for it to be their problem because he just finished checking the
XFMR and its fine.
I asked him to pull the meter ( in our area electricians aren't "supposed" to pull it). He does as I ask and to our surprise he finds a knockout slug from the original installation which had fallen between a lug and the meter can. The paint prevented a dead short. He pulled it out and presto problem is gone.
I'm not saying that is your problem, but it wouldn't surprise me if it is on the PoCo side.

IMO that particular situation wouldn’t be a POCO issue, as the HO owns the Meterbase. (At least around this area anyway)
The POCO may have to pull the meter, but that’s as far as it goes. The slug was the HO issue

 

[gar]

211218-1446 EST

I have now reread the first post, and several others. Really there is not much need to look at what happens at the dryer other than it is a convenient location to measure current. The problem is not at the dryer.

The dryer is fed directly from the main panel, and there is no mention that any of the other devices that show a voltage variation are on this same breaker.

Therefore, with the given information the problem is certainly not with the dryer or its own circuit.

The problem is somewhere that is common to the dryer, and the other circuits.

Some other considerations ---

There is enough information to indicate that the motor is 120 V, not 240.

What kind of instrumentation, and in what mode, is being used that you can see a 50 A pulse on the instrument?

Only a meter such as a Floke 87 in 1 millisec mode would produce a 50 A reading if the pulse width was short as is expected. On my dryer I can not get a 50 A reading until I use the 1 mS mode. A long duration starting current implies very low supply voltage. I am now inclined to guess that you have a high resistance in the very input part of your main panel, or a power company problem.

So a voltage measurement of each input phase on the input wires relative to neutral during dryer startup using both the meter and 15 W bulbs is needed.

If both phases drop in voltage at dryer startup, then the problem is in the power company transformer, or before it.
If one voltage drops, and the other rises, then it is a neutral problem.

.

 

[gar]

211219-1154 EST

I have now brought my scope up from the basement to my first floor laundry room.

There isn't much load in the dryer drum. There are some dried clothes. Both the current and outlet voltage are monitored by the scope. Sync is from the current channel. Nominal voltage is 123.7 from the scope. Obviously not 0.1 V resolution. The scope uses an 8 bit converter.

Voltage change at the outlet 123.7 dropping to 120.2 during motor starting. This is a change of 3.5 V and would correlate with the visual change of the 15 V incandescent,

Peak current was 50 A, and lasted nearly constant for 225 milliseconds ( 1/4 second ) until the centrifugal switch opened. This converts to 35 A RMS.

Very similar to my unloaded motor at my bench. Time to dropout is longer because of the inertia load. If the dryer had a larger heavy load of clothes, then inertia would be greater and time to dropout longer.

Results with Fluke 27, and 87.

87 MAX in MIN-MAX AC ...... 16 A, 16 A
87 in PEAK AC ..................... 40 A, 40 A, converted to RMS these are 28 A

27 MAX ................................ 14 A, 15 A

Note: for this duration of pulse the 27 and 87 are fairly close. But on my bench test motor the difference between the 27 and 87 is much greater because of the shorter pulse duration.

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