hookup of 3phase genset as home backup


I bought an old Army Corps of engineers 30kw 3 phase genset with Hercules DD298ER 6cyl motor.
The numbers on it say GE 5SJ4324Y2Y6
Jetta power stock no 6115 976 8982 mfg 1964
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?
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If your single phase pumps are designed for 240 volt, I wouldn't use the 208 volt tap. Your phases are 1-2, 2-3, 1-3, so if you are using two of them as single phase, you are doubling up on one leg, so it does limit the capacity. You may be better off to connect it as a Delta, and just use the single phase 120-240 volt taps

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It looks like most of the crisis is over. It turns out that there is a voltage regulator knob control which if you turn, you can vary the voltage on the 208 tap up to 240. I have worked the pumps off backup power now for the first time and all appears ok. I did find a wiring error at the pump subpanel which explained why that breaker tripped at the SEP when I first tried all this. Also, I did not have to disconnect the neutrals of the mains and backup power; I can switch between the two entirely at the transfer panels. A lot of good came of all this as I have learned a lot more about 3 phase power and backup generators. Thanks for everybody's help.
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don paolino
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desperado wrote:

If it's a 12 lead reconnectible alternator, there is a "zig zag" configuration used to get single phase power. I don't recall the connection sequence offhand, but you should be able to find it online somewhere, perhaps the Kohler or Onan sites.
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Agreed. 12 lead generators can be set up in a number of 3 phase and single phase and voltage configurations including 120/240 volt single phase to match your current house system. If you can locate the wiring diagram, it will simplify tying into the house wiring. I have one and it is set up this way.

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thanks for the response. I will keep looking for the wiring diagram for the 120/240 before giving it the smoke test.
Right now, only 3 diagrams are printed on the bus bar panel.
I forgot to mention that all the neutrals of both genset and mains are connected together. I just got thru talking to a retired electrician and he said that is a no no. Got to disconnect the neutral of the mains when working off backup genset. This explains possibly why, when I did try to throw the transfer switch on the pumps, that the breaker in the main panel tripped to this particular circuit. All equipment is still ok. I will put in a separate switch to switch out the neutral to the mains when on backup. I was also worried about being unbalanced loads in each phase I am using, but the electrician said that wasn't a problem. I will educate myself a bit more about transfer panel setups before throwing any more switches and am also trying to find the service and operator manual for this particular genset. Thanks
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don paolino
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desperado wrote:

Here is the "zig zag" low voltage 120/240V single phase connection diagram for a 12 lead generator:
http://www.marathonelectric.com/generators/connect/14X00903.pdf
I wouldn't worry about the solid neutral at this point, it's unlikely to be the source of the problem and it is not always required to be switched. The vast array of commercial transfer switch gear with solid neutrals wouldn't exists if it was.
Pete C.
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"Pete C." wrote:

Oh yea, you also have to derate slightly when in a "zig zag" configuration:
"You can estimate the Zig Zag power rating by dividing the three phase power rating by 1.2. i.e. 58,000 W / 1.2 = 48,333 Watts (single phase Zig Zag)"
Pete C.
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Thanks Pete. I was going to try and search for this zig zag on Google. Sure saves me a lot of time. Will back off on neutral switch for the moment and check recheck all box wiring. I will have to translate the zig zag diagram field connections into the specific bus bars on my genset but I think I can do that since there is a schematic printed on a brass plate on the control panel doors. I was thinking if that didn't work I might be better off going to transformer configuration, but that could get expensive and still might be tricky as I don't know how to spec the transformer. OK on the derate. looks like 25kw. I would think that would be enough in an emergency situation. If things get tight I have a couple of smaller sets I use in the field to power small hand tools and motors, so I think I am ok.

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