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Old 04-30-2012, 02:22 PM   #1
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switch phases and the machine worked correctly


This is a bit beyond a DIY job, but some of you know that I just opened a new laundromat. In doing so I took 10 dryers we had in storage for 2 years and installed them at the new location. They are gas, but of course the controls are electric. The fan motor is 240/208-120v. The timer is 120v. All the relays in the timers are 120, no transformers. When we hooked everything up after two days of operation the customers complained that the time on the controls did not match their watch. To our dismay the timers were counting down at twice the normal rate, ie. buy 6 minutes you only get 3 minutes. This is crazy because all ten worked fine at the old location and now they are all counting down double time.

I tinkered with the ground wire and even removed the ground to see if it would change. Nothing. I switched 120v hot phases and it solved the problem. I rewired back to original and the problem returned. I was stunned. I then opened the sub panel and traded the two hot feeder wires from the main with each other to make the opposite phase and the problem on all ten dryers went away.

We wired the building 120/208Y, 4 wire + ground. Our old location was 240v delta 4 wire + ground. Why would it do this? I am really surprised this happened. I need to call the timer manufacturer because their engineer was stumped, also and had no idea why the timers were doing this.

What did we miss?

David


Last edited by n175h; 04-30-2012 at 04:35 PM.
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Old 04-30-2012, 02:35 PM   #2
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switch phases and the machine worked correctly


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Some of you know that I just opened a new laundromat. In doing so I took 10 dryers we had in storage for 2 years and installed them at the new location. They are gas, but of course the controls are electric. The fan motor is 208/240. The timer is 120v. All the relays in the timers are 120, no transformers. When we hooked everything up after two days of operation the customers complained that the time on the controls did not match their watch. To our dismay the timers were counting down at twice the normal rate, ie. buy 6 minutes you only get a quarter. This is crazy because all ten worked fine at the old location and now they are all counting down double time.

I tinkered with the ground wire and even removed the ground to see if it would change. Nothing. I switched 120v hot phases and it solved the problem. I rewired back to original and the problem returned. I was stunned. I then opened the sub panel and traded the two hot feeder wires from the main with each other to make the opposite phase and the problem on all ten dryers went away.

We wired the building 208y/120. Our old location was 240v delta with a stinger leg. Why would it do this? I am really surprised this happened. I need to call the timer manufacturer because their engineer was stumped, also and had no idea why the timers were doing this.

What did we miss?

David
The ground would have nothing to do with this. Your building is three phase? You do have a neutral, yes?

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Old 04-30-2012, 02:38 PM   #3
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switch phases and the machine worked correctly


You stumped me. Timers usually rely on the 60Hz line frequency for time keeping so I have no idea how switching phases would affect them. Is there possibly something on the one phase that is introducing noise to affect the timer operation?
Did you measure the voltage on each phase?
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Old 04-30-2012, 03:09 PM   #4
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switch phases and the machine worked correctly


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You stumped me. Timers usually rely on the 60Hz line frequency for time keeping so I have no idea how switching phases would affect them. Is there possibly something on the one phase that is introducing noise to affect the timer operation?
Did you measure the voltage on each phase?
Yes, we checked with a volt meter--120v hot to neutral, 120v hot to ground, 208v across the phases.

Give me an example of what would introduce noise into the phase. No other problems in the building. All 3 phase equipment running fine. All other single phase equipment both 240/208 working good and all other 120v stuff ok, except we are having some trouble with the video camera feeds to the DVR that we have not solved yet.

David
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Old 04-30-2012, 03:35 PM   #5
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switch phases and the machine worked correctly


I suspect there is something funky about the way your system is wired (DUH, I know) but I can't deduce what it is without more information. I'm trying to envision ways of obtaining a 120Hz signal from a 60Hz system. Is the building service from the utility 120/208Y, or are there transformers serving this equipment? You mention 240V equipment; how is it powered from this service? Are the dryers single phase or three? Are other dryers of the same model not having this problem? If so, what's different?
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Old 04-30-2012, 03:36 PM   #6
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switch phases and the machine worked correctly


From my experience (and I admit I have never worked on a 3-phase hi leg system), you cannot just take equipment from a 3 phase 240V system and plug it into a 3 phase 120/208V system without some sort of rewiring of the equipment.
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Old 04-30-2012, 04:16 PM   #7
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switch phases and the machine worked correctly


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I suspect there is something funky about the way your system is wired (DUH, I know) but I can't deduce what it is without more information. I'm trying to envision ways of obtaining a 120Hz signal from a 60Hz system. Is the building service from the utility 120/208Y, or are there transformers serving this equipment? You mention 240V equipment; how is it powered from this service? Are the dryers single phase or three? Are other dryers of the same model not having this problem? If so, what's different?
AEP assured me it is 120/208Y. No transformers in the equipment. Dryers are single phase with the motor spec plate labeled 240/208-120. No other dryer models are on the premises.

David
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Old 04-30-2012, 04:22 PM   #8
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switch phases and the machine worked correctly


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From my experience (and I admit I have never worked on a 3-phase hi leg system), you cannot just take equipment from a 3 phase 240V system and plug it into a 3 phase 120/208V system without some sort of rewiring of the equipment.
The dryers are labeled 240/208-120 single phase on the motors (Marathon motors). No field wiring change is required for 240v to 208v. It is required for 120v, however. We have them wired 240/208. The timers are 120v only and only require milliamps to operate. The timers do four things--count quarters, countdown time, switch the fan relay, and switch the gas valve relay.

The washers are labeled 240/208v 3phase. They come field wired for 240v with a specific placard designating, "use enclosed jumper to change to 208v). We did that as soon as they were installed. No problems with them at all. Washers did not require a neutral. Dryers do require a neutral for timer controls.

David

Last edited by n175h; 04-30-2012 at 04:27 PM.
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Old 04-30-2012, 04:31 PM   #9
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switch phases and the machine worked correctly


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Old 04-30-2012, 05:36 PM   #10
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switch phases and the machine worked correctly


stupid question probably but from what your saying you have a 3 phase system in your laundromat with a 240v subpanel running off it. So at the subpanel you have only 2 phases out of 3? I've done 12 years of industrial/commercial/new construction and tenant work on 3 phase systems and i've never seen that one pulled off before. Oddly enough by switching the two hot legs of the circuit you have in effect just reversed the direction of the motor no. Maybe this has something to do with it. I've never installed any industrial dryers before but i would imagine that they would have to be hardwired and the two legs would have to be installed the right way. Just to throw an idea out there for the super theory minded what if he for instance had the A phase and B phase. wired one way they would be 90 degrees out of phase, wired the other they would be 180 degrees out of phase. Just a thought.
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Old 04-30-2012, 05:56 PM   #11
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switch phases and the machine worked correctly


Given a 3 phase panel with three hots and a neutral, or a single phase panel with two phases of a 3 phase system and a neutral, if you take any two wires you will have a single phase power source.

A single phase motor (with two wires or terminals) does not care whether the power source came from a 3 phase system or a single phase system, provided that the voltage is correct.

But a 240 volt motor that requires the neutral and also both hot wires will not work properly given two hot wires of a 208 volt system along with the neutral.
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Old 04-30-2012, 06:38 PM   #12
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switch phases and the machine worked correctly


Ok, I've been over this in my mind over and over and the only other question I can ask is how you know that the timers were running correctly when they were previously installed.

Is it just because no one complained?

The part that throws me is how swapping two legs of a single phase service would have any affect what-so-ever. Swapping 2 legs of a three phase service would result in the motor spinning the opposite direction.

Are there 10 separate breakers for these 10 dryers?
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Old 04-30-2012, 06:56 PM   #13
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switch phases and the machine worked correctly


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Given a 3 phase panel with three hots and a neutral, or a single phase panel with two phases of a 3 phase system and a neutral, if you take any two wires you will have a single phase power source.

A single phase motor (with two wires or terminals) does not care whether the power source came from a 3 phase system or a single phase system, provided that the voltage is correct.

But a 240 volt motor that requires the neutral and also both hot wires will not work properly given two hot wires of a 208 volt system along with the neutral.
The motor doesn't require a neutral unless it is field wired for 120v. All ten motors are wired 240/208. The problem was in the timer, not the motor. I could take the timer out and pigtail the hot and neutral control wires and plug it into a wall plug if I wanted, drop a quarter through the coin slot and it would count down time.

David
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Old 04-30-2012, 07:01 PM   #14
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switch phases and the machine worked correctly


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Ok, I've been over this in my mind over and over and the only other question I can ask is how you know that the timers were running correctly when they were previously installed.

Is it just because no one complained?

The part that throws me is how swapping two legs of a single phase service would have any affect what-so-ever. Swapping 2 legs of a three phase service would result in the motor spinning the opposite direction.

Are there 10 separate breakers for these 10 dryers?
The timers are supposed to blink once per second as they count down, ie. 60 blinks per minute. You could set your watch by it. They were blinking 120 times per minute before the swap, now they blink 60 times per minute

I'm with you about the wire swap, makes no sense to me since it is a sub panel, single phase two leg circuit fed from a 3 phase main panel. I just tried the swap out of desperation, and it worked. And yes they are on 10 separate 20 amp two pole breakers.

David
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Old 04-30-2012, 07:07 PM   #15
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switch phases and the machine worked correctly


If you wanted to get crazy, you could figure out which phase the timer was being powered by then trace it back to the main panel and move the breaker for the subpanel to the "good" phase and the one not currently in use. I don't know what that would do except possibly narrow down what is going on.

If you move the sub main to the good and not currently used phases, you could then swap the phases to see if you could replicate the problem. If you can't, then there is something up with that one phase.

I don't know if you even care anymore now that you got it working, but its intriguing me.

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