emergency generator design
emergency generator design
(OP)
I am installing a new 50kw emergency generator for an existing office building. I am having trouble sizing the necessary wires for design. Inside the building there is an 80A emergency panel that will be wired to a 200A, 3phase, automatic transfer switch. The building uses 120/208V. The automatic transfer switch is wired to a 1200A Main Distribution panel as well. In design, I believe that the load breaker for the generator must match the size of the emergency panel, so it would be 80A/3p. I size the wire from the generator to the ATS for 80A. Do I size the wire from the ATS to the emergency panel for 80A as well? Now for the wire from the MDP to the ATS, I am not sure whether to size it for 200A or 80A? Right now I designed to have a 200A breaker in the MDP for the ATS and sized the wire for 200A. I was told that I do not need to size it for such a high amperage, so I am not sure what to do. I am sorry if this is really confusing to read, but I would appreciate any advice or recommendation of where to learn this design concept. Thank you.






RE: emergency generator design
Here is a site that might assist with sizing tbe gen.
http://www
RE: emergency generator design
RE: emergency generator design
Do it right. You never know when someone will decide to
add more load.
IMHO, there is no such thing as "too much generator". :)
Oversizing (within reason) takes care of all sorts of
annoying little problems.
<als>
RE: emergency generator design
I agree with you electrically.
Mechanically I have seen engine problems with two new sets that were oversized and had vendors representatives express serious reservations about two others. That said, I have installed quite a few sets that were oversized for motor starting duty.
Sometimes running a new diesel engine with a light load will glaze the cylinder walls. The engine will then pump its lube oil out the exhaust in a few hours. Typically the set shuts down on low oil pressure when there is not enough oil left in the crankcase.
I watch a new set for an hour or so for oil pumping. If a set starts pumping oil I set up a load bank for anywhere from a day to a week to make the engine work until the rings seat in.
I have never had to use it, but some mechanics will cure glazing by introducing a spoonful of Bon-Ami (Pumice powder) into the intake of a running engine.
A generator will not handle an over load nearly as well as a transformer. I see lots of sets running lightly loaded and once the rings seat in it's not a problem.
yours
RE: emergency generator design
What you've described is called "wet-stacking". It can really become a problem. However, if you do monthly maintenance runs, ie run the gen at full load with a load bank, then it becomes less of an issue.
Mike
RE: emergency generator design
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