I bought an old Army Corps of engineers 30kw 3 phase genset with Hercules
DD298ER 6cyl motor.
The numbers on it say GE 5SJ4324Y2Y6
stock no 6115 976 8982
I want to use it to back up my main power on my ranch. I have 240V single
phase service coming in from Southern Calif. Edison.
My main panel is 100Amp single phase.
Genset has a busbar of 12 leads which can be reconfigured for 120/208
240/416 or 120volt delta .
Right now the 120/208 has been chosen. I measured 217V no load coming out.
There are 3big split bolt connectors coming out and one smaller one which
appears to be the neutral or ground. Right now, 125v is measured from this
point to each of the big split bolts.
I decided to use one phase to power the whole house less the well pumps
and put the well pumps on the second phase. That is because the amps per
phase is listed as only 57 amps in this configuration and I figure I since
the pumps take 9 amps each running and there are two of them, that this
would leave more amps available to power the house on the other phase. This
leaves the third phase not connected to anything(open circuit.) as a spare.
I bought some transfer panels(double pole double throw) and have brought
the well pump 30amp dp breaker wires out to a separate 60a transfer panel
and connected it to one of the phases of the genset. the other phase I put
into the 100amp main breaker and a 100 amp transfer panel.
I am a retired electrical engineer but my specialty was microwave and
antenna design and not power engineering.
Is this setup ok or do I have to install more equipment?
I don't think you can do this without a big transformer. The problem
is that the 120VAC on either side of neutral on your utility power is
180 degrees out of phase from each other. This allows you to get
240VAC by using the two hot leads.
With a 3 phase system, the phase difference is 120 degrees (or 240
degrees). So, even though you can get 120VAC between two delta taps,
you won't also be able to get 240VAC by using taps from two different
If you try to do everything on just one delta winding, then you can
only draw 10Kw from the generator.
First, you need a building permit to do this. If anything happened your
insurance company could easily disclaim your filing based on not having the
service inspected. (And of course, if anything is wrong, they would be able
to tell you.)
As far as you have gotten so far, you will need to identify the transfer
equipment as to exactly what it is (fire dept. requires.) Also permanently
identify the second panelboard as being used for emergency use. Make certain
the transfer equipment and secondary main disconnects are rated as service
equipment (prob 6000 amperes should be Ok, but your local AHJ may require
larger.) The standby service overcurrent breaker must disconnect all phases
if one phase opens.
You should be able to get 120 v between the A and C phase (the smaller
centertap is between the A and C phases, B phase is the High Phase and is
required to be colored orange.) Between the tap (neutral and either A or C
should give you 120 v (your measuring 125 v with no load). What's critical
is make certain you bond the neutrals together (neutral from Edison and the
tap or smaller connector).
Make absolutely certain you get a release from your local building
department for this.
Thanks for the responses.
Am a little confused about the neutral situation. I just got through
talking to a retired electrician and he told me you have to disconnect the
neutrals from the mains and make sure they are not connected to the genset
in any way. I figured he was right since when I tried to throw the transfer
panel switch for the pumps the particular breaker on the SEP tripped. Right
now, all the neutrals are tied together for everything. No equipment was
I will be checking more wiring and all that. It may be that I might have
to use just the one phase for entire backup and forget about the other
Yes, the mains are basically two phases 180 degrees out of phase and I
neglected to .consider the effect of that on my pumps. Not sure if it will
mess them up.
I was also concerned that trying to pull loads on two of the phases which
are not necessarily balanced would mess up the genset, but the electrician
told me it wouldn't.
Will be trying to find the manuals for the genset and study up a bit more
on multiphase power before trying another smoke test.
"Dennis" < email@example.com> wrote in message
OK, thanks for the info. I did some more searching and troubleshooting and
most of the crisis seems to be over.
I did find a wiring error in the pump subpanel which explained why the
breaker tripped when I turned on backup power. This has been corrected.
There is a voltage regulator adjust control on the 208 tap which all you
have to do is turn to get it to advance to 240 volts. I did find out about
reconfiguring the 12 leads in what is called a zig zag connection and
another connection called double delta which is balanced but the genset is
derated about 83 per cent when this is done.
Finally, I found I did not have to switch the neutral of the mains out
when on backup power. All the neutrals are bonded together and I can switch
back and forth with the transfer panels now.
I made a mistake saying the mains were two phases 180degs out; they are in
fact called split phase and the two 120v to ground legs for each pole are in
Thanks to all for the help.
"nospam" < firstname.lastname@example.org> wrote in message
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