Phasing

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jmd445

Senior Member
Is there a 'norm' to wiring a building to the respect of rotation.

When the utility brings in the high tension feeders (34.5 kv in this case) labeled Bk-Red-Blue and every device down stream is labeled L1-L2-L3 / X1-X2-X3, etc. An we correctly follow L1 to A, L2 to B, L3 to C and so on. Would the rotation stay the same through out the facility?

Also, are the phases A-B-C (B-O-Y) are the normally CW or CCW rotation.

PS. If I were to rent a generator (I am, I need to take the existing out of service for repairs), is there a standard that phases A-B-C on the existing Cat genset would be the same rotation as phases A-B-C on another.

A confusing multiple level question. I hope I made it clear enough.

Jim
 

Paul B

Senior Member
There is no garentee, but you swap one pair of leads to correct the problem if it is wrong. I might not be understandiing your question correctly.
 

bdarnell

Senior Member
Location
Indianapolis, IN
Occupation
Retired Engineer
Typically, the rotation that you get from the utility is CW A-B-C. If you maintain that phasing throughout your facility, everything should be phased correctly.

If you connect a generator to the "hard wiring" of the building, I think that it's imperative that you connect a rotation meter to the generator prior to connecting it to the building wiring system. Verify your rotation before you energize the genset.
 

Zifkwong

Member
I do not think that there is a standard and if there is I never heard of it being enforced. If I knew the angular relationship - with respect to the utilities high side transformers - I would try to make it ABC, positive sequence, left to right or front to back.
 

Zifkwong

Member
Woops.


I just read the rest of your question. There is no common point of reference for your generator and the utility. Therefore, your A phase has no relationship to the utilities A phase - I would just verify rotation.
 

hockeyoligist2

Senior Member
Gen

Gen

Something i might add but doesn't relate directly to the question. I have ran into this several times with diesel generators. if something goes wrong with the control system on a diesel, and it will not turn off, most everyone thinks (i learned the hard way) that you disconnect the battery and it will turn off. I was wrong, the solenoid that shuts off the fuel has to have power to close it. a jumper can be used if it won't shut down, it is a normally open solenoid
 

eric stromberg

Senior Member
Location
Texas
I was on a job last summer where we were changing out a 500kVA transformer with a 1000kVA transformer. For the week that the swap was being made, we ran the system on an 800kVA generator. The company wasn't confidant in the generator and wanted to have a spare generator sitting there, just in case. I cranked up the second generator and checked rotation on it. Two identical generators. Same company, same everything. Different rotation.

Always check rotation. Never leave this one to chance.

Eric Stromberg, P.E.
 
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