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110/220V safety questions



Quoting Steve Roys <sroys-at-umabnet.ab.umd.edu>:

> I have a pair of 30A contactors that I want to use in my 220V 
> control cabinet.  The problem is that the power to the cabinet
> is going to be from a 3-wire 220V outlet (2 hot and a ground),
> and the relay coils are energized by 110V.  I have been told 
> that I should have a 4-wire circuit if I wanted to use a single
> side of the 220V line to get 110V at any appreciable current, 
> but am I going to have problems if I just wire the relays up so
> I use one hot side and the ground of the 220V to get the 110V 
> needed to energize the coils, or should I do something else. 

Since we are talking about relay coils I would just go ahead and 
wire one side to your juice and the other to your third wire
ground. I have done exactly that in my 240 volt power cabinets
for years and never had a problem, I also run pilot lamps, the
red panel illumination light, etc., in the same way. The fourth
wire solution simply brings in another neutral wire, which is
common to the third wire you already have. If you ran three wire
in through EMT conduit your conduit should be bonded to the
breaker box and meets code requirements for a dedicated ground in
some wiring installations. I have done it both ways and never had
a problem, but you will never find a poor connection in any of my
60 cycle work.

Richard Quick


... If all else fails... Throw another megavolt across it!
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