Cloths dryer overload

[DuaneL]

There is a cloths dryer at a clients house that is powered directly from the 200amp load center. #8-3 romex from a 30 amp 2p breaker to a four prong receptacle. When the dryer starts, lights dim a bit and the TV turns off but comes right back on. Checked the voltage, ground , neutral…. All the usual suspects.
I First went to the panel and checked the torque on all of the terminals including the main and neutral. Repaired a neutral crimp connector on the pig tail where it attached to the terminal strip on the dryer. Checked amperage on both legs. One jumped to 50 amps then settled at 20-22amps. The other leg had 0 at first but after 5-10 seconds showed 20 amps. Could something internally be causing this problem?

 

[Dennis Alwon]

You may have a loose terminal from the power company or somewhere before the breaker. I guess it is possible the breaker is bad. I would take the breaker out of the panel and make sure the bus stabs on the panel and breaker are not burnt.

 

[DuaneL]

Dennis.
Yes. I did pull the breaker. Everything looks good. I did advise the customer to call an appliance tech to look at the dryer. Just to rule out any questions as to where the problem originates. Thanks for your input!

 

[Dennis Alwon]

Didn't the dryer have a neutral? if so then you shouldn't have the same voltage an both legs. One leg has the dryer motor and both legs will have the heat. Heater 240v Dryer Motor- usually 120v

There are units that are straight 240.

 

[petersonra]

There is a cloths dryer at a clients house that is powered directly from the 200amp load center. #8-3 romex from a 30 amp 2p breaker to a four prong receptacle. When the dryer starts, lights dim a bit and the TV turns off but comes right back on. Checked the voltage, ground , neutral…. All the usual suspects.
I First went to the panel and checked the torque on all of the terminals including the main and neutral. Repaired a neutral crimp connector on the pig tail where it attached to the terminal strip on the dryer. Checked amperage on both legs. One jumped to 50 amps then settled at 20-22amps. The other leg had 0 at first but after 5-10 seconds showed 20 amps. Could something internally be causing this problem?

I agree with Dennis. The 50 Amps you are seeing is the motor starting. The heating element comes on after the motor starts. The readings you are seeing is probably normal.

The reason the lights dim is because the #8 wire allows a lot of current to flow when the motor starts and starves the rest of the house for a few seconds.

 

[Dennis Alwon]

The dryer is a 230 V circuit. I don't see how you could have 50 Amps on one leg and zero on the other. Where is that 50 Amps going?

If there is a neutral then some would be going to thru the neutral for the motor however something isn't right

 

[DuaneL]

Didn't the dryer have a neutral? if so then you shouldn't have the same voltage an both legs. One leg has the dryer motor and both legs will have the heat. Heater 240v Dryer Motor- usually 120v

There are units that are straight

Yes, it has a neutral. What you said about the motor and heat explains why one leg would show amperage at start up, and the other showed amperage after a few seconds when the heat started. Correct?

 

[petersonra]

If there is a neutral then some would be going to thru the neutral for the motor however something isn't right

I was editing while you were typing.

 

[DuaneL]

If there is a neutral then some would be going to thru the neutral for the motor however something isn't right

It spiked at 50 at start up then dropped.

 

[petersonra]

It spiked at 50 at start up then dropped.

that is probably the motor starting. but it seems like a lot for a small motor like that.

 

[DuaneL]

that is probably the motor starting. but it seems like a lot for a small motor like that.

That was my thought as well.

 

[gar]

211129-1135 EST

DuaneL:

You lack the best tool with which to make your measurements, a scope.

However, there are some things you can determine with some simple instruments, and loads. However, an ordinary indicating instrument, such as a Simpson 260 or 270, Fluke 27, or 87, is not well suited to measure sort time drops in voltage. A 15 W tungsten filament incandescent is useful for detecting shortime voltage drops. The 15 W is to reduce the brightness that you are looking at. You start to see flicker at around a 2 V drop. The light bulb is a qualitative means, but a fast responder.

With a 1500 W heater as a switched load at my bench I see a very slight flicker. Starting a small 1/3 HP 120 V mechanically unloaded induction motor I see a substantial flicker. Starting current lasts only about 6 cycles. My 1500 W heater is about a 12 A load.

I suggest you make voltage measurements at your main panel as well as at the dryer. At the main panel put your probes directly on the incoming supply wires. I am assuming here that we are dealing with a split phase system. Since there are some utility wires that are not real large, and have substantial impedance from the power company transformer to the main panel under consideration, then we can expect when you load neutral to one phase that there will be a voltage drop on that phase, and about 1/2 of that drop will show up as a rise on the other phase. For the 12 A heater load this drop might be in the range of 1 V.

Make the same kind of test at the dryer location, and report back your results.

.

 

[DuaneL]

211129-1135 EST

DuaneL:

You lack the best tool with which to make your measurements, a scope.

However, there are some things you can determine with some simple instruments, and loads. However, an ordinary indicating instrument, such as a Simpson 260 or 270, Fluke 27, or 87, is not well suited to measure sort time drops in voltage. A 15 W tungsten filament incandescent is useful for detecting shortime voltage drops. The 15 W is to reduce the brightness that you are looking at. You start to see flicker at around a 2 V drop. The light bulb is a qualitative means, but a fast responder.

With a 1500 W heater as a switched load at my bench I see a very slight flicker. Starting a small 1/3 HP 120 V mechanically unloaded induction motor I see a substantial flicker. Starting current lasts only about 6 cycles. My 1500 W heater is about a 12 A load.

I suggest you make voltage measurements at your main panel as well as at the dryer. At the main panel put your probes directly on the incoming supply wires. I am assuming here that we are dealing with a split phase system. Since there are some utility wires that are not real large, and have substantial impedance from the power company transformer to the main panel under consideration, then we can expect when you load neutral to one phase that there will be a voltage drop on that phase, and about 1/2 of that drop will show up as a rise on the other phase. For the 12 A heater load this drop might be in the range of 1 V.

Make the same kind of test at the dryer location, and report back your results.

.

Very interesting! I will let you know.
Thanks for the info.

 

[readydave8]

The reason the lights dim is because the #8 wire allows a lot of current to flow when the motor starts and starves the rest of the house for a few seconds.

Would it be different if wire ws 10 rather than 8?

 

[gar]

211201-0800 EST

readydave8:

A given motor has a locked rotor impedance. This is somewhat independent of current, at least over a reasonable range.

So if you have a reasonably stiff system feeding a home, then by lowering the impedance between the main panel and the locked rotor motor you will draw greater starting current with a larger wire between the main panel and the dryer.

.

 

[DuaneL]

Would it be different if wire ws 10 rather than 8?

From what I understand the dryer and wiring is 3 years old. And this just started Sunday evening.
So I doubt it.

 

[gar]

211201-0911 EST

Measurements on my little 1/3 HP mechanically unloaded 120 V motor are:

First sine wave peak current is 50 A ( about 35 A RMS ), and drops to 40 A peak at the 6th peak, and then centrifugal switch opens and peak current is 10 A. At my bench this produces about a 5 V peak change in voltage or 3.5 V RMS.

.

 

[gar]

211201-1724 EST

On a different load I expected a bigger light change of the 15 W bulb. Did not visually appear to happen.

This load was a 750 W tungsten filament photoflood. Peak current was about 100 A.

The bulb took about 6 cycles to reach its steady value of about 6.25 A RMS. But the decay is rapid.

The change in light intensity, from the 750 W tungsten bulb, of the 15 W bulb was less noticeable than from motor load.

.

 

[Hv&Lv]

I would check the voltage, not currents at the main when the dryer starts.
A dryer starting shouldn’t dim the lights. Check the voltage, rule out bad connections and/or neutral on your side, then call the POCO to check their side.
An appliance tech is a waste of money.

 

[micabay]

"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.