| Re: [GMCnet] Generator [message #325667 is a reply to message #325664] |
Thu, 02 November 2017 17:30   |
Richard Denney
Messages: 920
Registered: April 2010
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Senior Member |
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Each leg of 240-volt service carries 120 volts with respect to neutral, and
240 volts only with respect to the other hot.
If both hots on a 50-amp plug are fed from the same 120VAC source, then the
two buses are in phase. If they are fed from a 240VAC source, the two sides
are out of phase.
It's true that a 240VAC supply is accustomed to carrying very little on the
neutral, since each hot is the return path for the other. But there are
240VAC appliances that have 120VAC circuits in them (clothes dryers are a
common example) and will return some current on the neutral. But one has to
be careful to find wiring that provides enough neutral conductor to carry
everything. The usual appliance pigtail has #8 on the two hots and #10 or
even #12 on the neutral.
A 6000-watt Onan is 6000 watts at 120VAC, which is 50 amps at 120VAC. That
hot output is wired to both hots in a 50-amp receptacle (as supplied in the
early coaches), in parallel. The maximum that can be drawn is 50 amps,
total of both buses. A 50-amp receptacle at a park is 240 volts, but the
coach will still only draw up to 50 amps total of both legs (actually, 40
amps total from a 120VAC source--20 amps on each bus, as equipped by GM).
So, the neutral never has to carry more than 50 amps (er--40). When I
installed a new 50-amp pigtail, I got one that had #8 wire on both hots and
the neutral (and the safety ground)--not the common type but still readily
available. My pigtail reaches my power opening only, but I no longer use
the generator receptacle, and have instead installed a 50-amp transfer
switch.
I could split my two hots and feed them from separate receptacles because
they are not wired together anywhere in the coach. But they would be
sharing a neutral and that would absolutely trip every 120VAC GFI device,
which demands that the neutral current be identical to the hot current.
Rick "who uses a 50-amp extension cable from Camping World to reach the
pedestal, or a 30-amp cable plus an adapter which is usually plenty" Denney
On Thu, Nov 2, 2017 at 4:58 PM, John Phillips
wrote:
> Johnny,
> It depends.
> Case 1: If you have 120-volt devices on both sides of the split you will
> need an adapter to feed 120-volts to both sides of your 50-amp cord. The
> 50-amp neutral wire becomes a weak point but the probability of you putting
> more than 50-amps is quite low.
> If you can move all your load to one side of your split you only need to
> power one side of the 50-amp cord with an adapter but you will be limited
> to 40-amps of 120-volts
>
> Case 2: No problem. 240 volts with each side of the split the split getting
> 120 volts 180 degrees out of phase with each other. The neutral wire will
> carry the difference current between the two busses.
>
> On Thu, Nov 2, 2017 at 1:18 PM, Johnny Bridges via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> My coach has a split bus breaker box with one side of the 50A cord fed to
>> each. Given there are no 240V appliances it it, doesn't matter whether
> it's
>> plugged into 240 or 120.
>>
>> --johnny
>>
>> --
>> 76 26' Eleganza(?) with beaucoup mods and add - ons.
>> Braselton, Ga.
>> "I forgive them all, save those who hurt the dogs. They must answer to
> me
>> in hell" - ol Andy, paraphrased
>>
>>
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>
>
>
> --
>
> *John Phillips*
> _______________________________________________
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--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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