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Transfer Switch for my Onan


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Old 03-07-2012, 06:31:45 PM
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BigBlockChev BigBlockChev is offline
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Default Transfer Switch for my Onan

I am looking at a used transfer switch for one of my Onans either the 15KW MDJF single phase or the 15KW JC three phase nat gas ( which can be configured as 10KW single phase). The switch is a US built Winco model # UE200ATS-4B/D. which translates into a 200A three phase mid 80s vintage unit. So it is big enough since I only have a 100A single phase service. I am trying to determine if I can use it since it is three phase. My working theory is that if I disable the voltage sensing on 2 out of the 3 phases it should work , leaving 1 set of contacts to switch the neutral as well. The guy is only looking for $50 to get the switch out of his hair so you can see why it would be interesting to take a stab at it. Ideas, comments anyone? Cheers Dan
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Old 03-07-2012, 07:07:17 PM
Wayne 440 Wayne 440 is offline
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Default Re: Transfer Sw for my Onan

I do not recommend using that switch (or any other not specifically designed for the purpose) to switch the neutral. Generally, the neutral is disconnected after and connected before "hot" leads. BAD things often happen when that timing is not adhered to.
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Old 03-07-2012, 09:24:47 PM
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Default Re: Transfer Sw for my Onan

I just looked at the schematic provided with the switch and it appears that the neutral is left connected between the two sources and the hot leads are switched. I am assuming that this is acceptable. I was a bit confused as one of the manual transfer switches that I looked at made for Briggs and Stratten by cutler hammer or someone used two standard three pole breakers to effect the switching action. It had a mechanical interlock between them. One pole of the breaker was labeled neutral. It did not appear to me that there would be any way to alter the sequence of connection timing between the hots and neutral. You throw the breaker and they all go together. Am I missing something here? Cheers Dan
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Old 03-07-2012, 10:00:29 PM
Wayne 440 Wayne 440 is offline
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Default Re: Transfer Sw for my Onan

I have never seen the Briggs and Stratton switch, so all I can say is that I would not have designed it in that way. BAD things can happen if the neutral is open for any length of time while the hot leads are connected. I have seen 120 volt devices fail in spectacular fashion during such an event. Research "open neutral" if you want to see what can happen.
Here is one example - http://www.mikeholt.com/mojonewsarch...s~20030409.htm
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Old 03-08-2012, 11:03:22 AM
Dave Edmonds Dave Edmonds is offline
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Red face Re: Transfer Switch for my Onan

Had the neutral go open on a 3-phase circuit (actually, 3 circuits that shared a common neutral) that had quite a few high-wattage incandescent lamps on the various circuits. Some got VERY bright for a short while, then burned out; the rest burned dimly until the bright ones burned out. Thank goodness there were no inductive loads (motors, etc.) on the circuits, or we would have spent some REAL money!
Dave Edmonds
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Old 03-08-2012, 01:21:52 PM
Power Power is offline
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Default Re: Transfer Sw for my Onan

One pole of the breaker was labeled neutral. It did not appear to me that there would be any way to alter the sequence of connection timing between the hots and neutral. You throw the breaker and they all go together. Am I missing something here? Cheers Dan

Per code, switching the neutral is necessary for a separately derived system. It is not on a standby system.
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Old 03-08-2012, 04:19:38 PM
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Default Re: Transfer Switch for my Onan

Thank you , excellent answer. I have gotten the message regarding switching the neutral. Just have to mull over the ATS itself since I actually only need a 1ph switch. From the schematic it appears the only difference between the 1Ph and the 3ph units is a phase failure circuit hooked to L2 , which should be possible to delete. L1 and L3 appear to be identically configured. in both cases. Further thought is necessary. Cheers Dan
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