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Old 11-15-2011, 01:26 PM   #1
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Default Single phase genset feeding 3 phase panel

I am looking at a job that has a 120/240 delta feeding a 100a 3phase panel. The customer wants to hook in a 120/240 single phase residential generator into the panel for standby radio transmitter operations. Two questions, and I wouldn't see a problem with this but am looking for comments, - 1. Could I feed a 3phase panel with a single phase if I moved the loads around?All loads are single phase, panel congfig is- 1 2p60a and 3-sp20a , the the panel is loaded pretty light and 2- Why is there such thing as a residential genrator and are they ok for use on commericial?

Thanks
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Old 11-15-2011, 01:29 PM   #2
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Quote:
Originally Posted by 220wire
I am looking at a job that has a 120/240 delta feeding a 100a 3phase panel. The customer wants to hook in a 120/240 single phase residential generator into the panel for standby radio transmitter operations. Two questions, and I wouldn't see a problem with this but am looking for comments, - 1. Could I feed a 3phase panel with a single phase if I moved the loads around?All loads are single phase, panel congfig is- 1 2p60a and 3-sp20a , the the panel is loaded pretty light and 2- Why is there such thing as a residential genrator and are they ok for use on commericial?

Thanks
If it's 120/240, all your 120volt loads are probably already only using two phases without rearranging anything.
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Old 11-15-2011, 01:33 PM   #3
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Do you want to cover your ass and make some money?

Install a MLO panel for your generator branch circuits.
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Old 11-15-2011, 01:36 PM   #4
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Do you want to cover your ass and make some money?

Install a MLO panel for your generator branch circuits.
I want the whole panel to be on the standby ATS there's one there already. Why would I need another?
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Old 11-15-2011, 01:51 PM   #5
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I want the whole panel to be on the standby ATS there's one there already. Why would I need another?
Just use the 30hase ats and only feed two legs of it from gen. Be careful though, if there's 30hase motors and contactors, they could energize b phase through the motor windings.
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Old 11-15-2011, 01:55 PM   #6
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will do
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Old 11-15-2011, 06:41 PM   #7
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Originally Posted by mcclary's electrical

Just use the 30hase ats and only feed two legs of it from gen. Be careful though, if there's 30hase motors and contactors, they could energize b phase through the motor windings.
You need to install a separate panel for 1 phase loads or put in phase loss relays for any 3 ph equipment. No ones gonna turn the 3 ph stuff off in time.
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Old 11-18-2011, 02:50 PM   #8
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I am looking at a job that has a 120/240 delta feeding a 100a 3phase panel. The customer wants to hook in a 120/240 single phase residential generator into the panel for standby radio transmitter operations. Two questions, and I wouldn't see a problem with this but am looking for comments, - 1. Could I feed a 3phase panel with a single phase if I moved the loads around?All loads are single phase, panel congfig is- 1 2p60a and 3-sp20a , the the panel is loaded pretty light and 2- Why is there such thing as a residential genrator and are they ok for use on commericial?

Thanks
I had this very same question for a similar application many years ago and got this answer from my best code expert. No, it is would not be installed as approved by the manufacturer. See 110.3 especially (B).
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Old 11-19-2011, 08:17 PM   #9
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The only way i can see this working is if the three incoming phases
are paralleled on the generator side of a transfer switch.
And any true three phase loads such as motors
would be isolated by the transfer switch.
So that way there is no way any one could try to use a
three phase load on a single phase feed.
Now I know you said there is no three phase loads currantly,
But in the future someone who doesnt know the limitations
of the system could try to use three phase loads.
And this is were you will run into problems.
I think the term is "IDIOT PROOFING".
all possible, but not easy or cheap,
And I am not sure if codes would like a set up like this !
Too many chances of future troubles.
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Old 11-19-2011, 09:16 PM   #10
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It would work fine since the third delta leg is worthless anyway. Not sure if it's compliant but how about jumping one pole to the third phase on the transfer switch and spacing the 2 pole breakers so they'd recieve 240 volts upon transfer.
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