Generator

[wmeek]

I have a customer wanting to hook up a 250KW generator mounted on its own trailer. The Service on the building is a 800A 277/480v with a manual transfer switch. I have never done this type of installation. The generator output at 277/480 is 376A. I am not sure what type of wiring method is best to use. If I was to use an MC what size would be needed and how would be the best way to install it. Everything is outside and generator is about 20 feet from the transfer switch.

Thanks

 

[wxstevens]

I'm wondering, since it is on a trailer, will this be a "hook it up as you need it" type set-up or permenantly parked?

 

[zbang]

Is this a permanent installation? A trailer-mounted genset suggests not. Wiring methods will differ if it's temporary. Beware of where the MBJ is located. Is it a 3 or 4-pole transfer switch (solid or switched neutral)?

You'll find some good info about this by searching these forums.

 

[wmeek]

This is a 3 pole Transfer switch no switched neutral. The unit has been jacked up on some trailer jacks and is to be there permanent. I was thinking I would run parallel 3/0 to generator as it will only put out 376A at 480/277V and run to manual transfer switch. I do not think the code will allow to bond the neutral at generator, but to use the bonding and grounds at the transfer switch.
If it needs to be installed as a portable unit what size and type of wire would u use.

Thanks

 

[iwire]

Temp or permanent the grounding, bonding, wire sizing are all the same. The only thing that could change would be the wiring method.

With a 3 pole transfer switch the neutral must not be bonded at the genset.

 

[iwire]

Temporary basis
Feeder 4#500mcmthwn-cu

I am willing to bet two sets of 4/0 in the same raceway will be less expensive and easier to terminate.

 

[wmeek]

I know the building service is Parallel 500MCM and is 800a Service. But the generator is only rated for 480/277 at an output of 376A. Thats why I was thinking to run parallel 2 1/2" PVC conduits and and converting to sealtight and run parallel 3/0 thwn conductors. Is this not code compliant. Even if the the generator is on wheels, but lifted off the wheels (Tires Removed ) and blocked up wouldn't that pass for permanent installation. I am thinking that.
Also wouldn't I need to run an equipment ground in the PVC conduits.

Thanks

 

[wmeek]

Ok I am having difficulty trying to design this generator project. The service on the building is a 277/480 3phase 800a. The generator that customer has is a switchable voltage type, with a 800A breaker installed on unit an at 277/480V will put out 376A. The generator is the type that is on its on trailer. Customer has jacked the trailer off the ground and removed the tires. The manual transfer switch is already installed with the service on the building. If I come out of the generator with parallel 4/0 in 2 1/2" conduit to transfer switch would this be code compliant. The breaker that is installed on gen is a 800A non adjustable.
Not sure if you can feed a 800A transfer switch with a 400A feed from generator. I am feeling this would be a standby system. I appreciate any help. I am not good at designing this type of installations.


Thanks

 

[augie47]

The conductors are protected by the overcurrent device and must be sized accordingly.
To me, there is a fly in the ointment if you have a generator as the 250kw doesn't work out for your 376 amps and an 800 amp breaker at the generator does not fit the output specs.
In any event, your conductors from the generator should be sized by the generator OCP and an equipment grounding conductor based on that OCP should be included in the run.