From: David Cole (DavidCole@tk7.net)
Date: Thu Oct 23 2003 - 01:35:25 PDT
The electronic devices that state 120 vac probably won't live long at 208
vac. Transformers running at 240 vac instead of 208 vac are a different
story. It really depends on how much of a load is being placed on the
transformer at the higher voltage than the lower voltage. They will really
only burn out if they flow excessive amounts of current. If that doesn't
happen at the higher voltage, then you are probably going to be ok. It's
tough to answer your question without understanding the circuitry. However
a clamp on ammeter might be useful to determine the currents that are
flowing through the transformers. You can also use buck-boost transformers
to alter voltages slightly to allow 208 volt devices like air conditioners
and flourescent lights to run properly with a 240 volt supply. I have also
used buck-boost transformers to bump up voltages from 240 to 277 to use
commercial lighting fixtures salvaged (cheaply) from industrial plants.
Since they are used as auto-transformers, they don't have to be large to
bump the voltage up and down significantly.
Here is an article on using buck-boost transformers.
http://www.acmepowerdist.com/ael11.html
Dave
>>>>>>>>>>>>>>>>>>
On Wed, 22 Oct 2003 21:20:08 -0700, patrick jankowiak <eccm@swbell.net>
wrote:
> 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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-- Dave
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