Parallel Generators on One Day Tank

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elecshop

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Electrical Engineer
I am working on a hospital that was designed in 1985. Existing are two Onan generators 500kW each drawing fuel from the same 100gal day tank, which is piped to an exterior main fuel source tank. From that day tank, it looks like there is one line that goes to both generators, instead of each generator having its own return and supply fuel lines. Someone told me this is not modern day NFPA codes compliant, but I am not able to find this section of code - I scanned through 110, 99, and NEC. Has anyone encountered this before? I just want to confirm that this is not code compliant.
Thanks!
 
ron said:
If they share the same exterior main fuel source tank, I don't see it as much different to share a day tank if it works with available flow.
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Is it code compliant if both generators use the same supply line and return line from the day tank? Regardless of the exterior main tank.
 
I couldn't find anything in NFPA 99 or 110 that says they can't share the fuel pipe. Unfortunately, that doesn't prove it's not in there somewhere; but the PDF search function on the term "fuel" gives a good degree of confidence.

BTW, that 100 gallon day tank is pretty small for 2@ 500 kW. I estimate you have about 1-1/2 hours run time at full load.

I've heard that it is a good idea to run the returns right back to the main tank because the return fuel will be hot and the day tank can overheat. But yours has been in place since 1985 so I guess its not a problem. Probably burns up before it heats up.
 
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