Two Service Lines

[buzzp]

Are there any gotcha's I should be aware of while supplying a large facility with two services (480V/277 2000kVA and 1500kVA)? I am keeping them isolated and will have the appropriate signage, etc as required and appropriate grounding/bonding. I just want to make sure I haven't overlooked anything. Any gotcha's I should watch for? Thanks

 

[ScottyUK]

Are the two supplies synchronous, or more exactly could they ever be non-synchronous? You can get some abnormally high interphase voltages if one system slips relative to the other. Most occasions it won't be a problem but it could come as a nasty surprise for a user or maintenance worker if supplies from both sources were present in the same area. Check any dual-supplied loads are OK with it too - most are.

 

[marks1080]

interlocks interlocks interlocks. Assume operators will make mistakes and don't let them make really bad ones.

 

[buzzp]

They are both utility supplied sources (delta - Y transformers)so they are in phase. I plan to supply power by area to reduce the possibility of using both sources on one piece of equipment. Since they are in phase, I don't believe there is any real danger if they cross wired the two sources later on when they retrofit the facility or upgrade, etc. This is my biggest concern since both sources are fed from the same distribution point. Since the Y configured secondaries are grounded (separately but within 20' of each other), if they use the a phase from one source and b and c from the other, I think they will measure line-neutral due to the ground connection if they measure b - a or c-a. Would you agree?

On the interlocks, what could I interlock to prevent such a cross wiring? Maybe you misunderstood the question or I wasn't clear enough on my first post.
Thank you.