Electrician Talk banner
1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
I am working on a project where a city bought a large (300 amp) trailer mounted generator to use to provide power during outages to their many sewer lift pumps through out the city. These lift stations are all outdoor services with manual transfer switches that have receptacles for connecting a generator. These services vary in size from 20 amps of load to 200 amps of load. Some are three phase and some are single phase.

The generator has several outlets from the factory mounted to it with built in over current protection. There are two 120V outlets and three 50 amp single phase outlets. The generator has a switch that will change the voltage from 480 volt to 240 volt three phase and also to 240/120 single phase. It has lugs for large cables to connect directly to the 300 amp breaker.

I am mounting a weather proof load center that mounts on metal unistrut to the frame of the generator. It has several 3 pole breakers for the different amperage requirements of the different lift stations. Each breaker is connected to a cord that terminates through a strain relief and has a cord end that mates with the receptacle mounted on the different lift stations.

A few of the single phase lift stations will be powered by a 50 amp cord that plugs into one of the 50 amp receptacles that came originally on the generator.

Problem I have is the generator comes with the neutral bonded to the generator frame. I planned on keeping the load center unbonded (ground and neutral separate). All of the transfer switches on the many different lift stations are 3 pole and do not transfer the neutral (grounded) conductor. So I am trying to figure out how to connect with out paralleling my ground and neutral wires feeding from my load center to the lift stations. I can not separate the bond at the generator due to the outlets mounted (and needed) on the generator (can I?). The city does not want to pay for replacing all of the transfer switches. Can I eliminate the ground wire and use the neutral alone? Since I will be bonded on both ends. This type of connection would be grounded the same way as a utility company would (bonding at tansformer and again at service).
 

·
Senior Member
Joined
·
13,020 Posts
I don't see a way to avoid it and remain compliant. If you can't/won't remove the neutral/ground bond on the generator, and your transfer switches don't switch the neutral, then you would have two neutral-ground bonds on your system when you plug it in. One of 'em has to go.

We did a job like this for a city a few years ago. Make sure to double check phase rotation on all the stations so when the generator gets plugged in you aren't running backwards. Might change from one to the next but you can swap phases in the transfer switch or inlet.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #3 ·
Thanks for the reply erics37. I was planning on checking rotation at all of the lift stations.

Is there any reason that I would need to leave the ground and neutral bonded at the generator? If I separate, wont it cut the ground fault path on the ground (grounding) wire back to the coils of the generator?
 
1 - 7 of 7 Posts
Top