From: patrick jankowiak (eccm@swbell.net)
Date: Wed Oct 22 2003 - 21:20:08 PDT
Since we are on about volts and amps and such, I have a fun question;
I bought a used 40KW generator and transfer switch for emergency power
at home. It's a 208-Y system but I am adapting it to 120/240VAC single
phase.
The automated transfer switch for my generator is designed for 208-Y,
that is, 120V from phase to neutral and 208V between phases. It has a
few contactors which have 208V coils, and two single phase
transformers which are rated for 208V.
I have rewired the genset's 12-wire alternator from 208-Y to 120/240V
single phase (going from Y to zigzag), and reconfigured the xfer
switch to not freak out on having only one phase to sense, but I am
still faced with the fact of having 240V mains voltage applied to
these items in the transfer switch which are rated at 208V. Some are
small electronic timers which plainly state 100-120VAC, and these run
off the 120V secondaries of the 208V power supply transformers.
The electrician says 208 and 240 are the same, and that 240 is really
220, and that the components will be ok.
I call "BS!" on this.
I know I have 240 at the mains, as I have measured it, and I know that
240 is 15% higher voltage than 208 resulting in a possible 33%
increase of dissipation of power in the components. Therefore, I am
leery about connecting the automatics of the transfer switch until I
am sure nothing's going to fry. OK for an initial test I am sure, but
beyond that..
It will be too expensive to change out the components, but I can
reduce the 240 to 208 with a small transformer, actually two small
transformers (one for line voltage sensing relays and power supply
input, and one for emergency power supply input).
Anyway, any opinions about the matter of running 208V single phase
items on 240V single phase?
Patrick
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