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#205562 03/07/12 04:49 PM
Joined: May 2007
Posts: 55
U
Up2code Offline OP
Member
Existing 600 amp/3 phase/120-208/ 4 wire/ Y service panel board contains an existing 3 pole 400 amp fused switch.

Phase A & Phase B of this 3 Phase, 3 pole 400 amp fused switch have been "double-lugged" to feed...
(2) seperate 200 Amp/120-208 single phase main breaker feeder panels. (The double lugs on this 400 amp fused switch have been approved for the conductors.)

Both SETS of Feeder conductors from 400 amp fused switch (which does have 400 Amp rated fuses) to EACH 200 amp feeder panel are 3/0 THHN copper.

Question #1) Is this setup a NEC violation?

Question #2) Would having Phase A & B feeding one feeder panel AND Phase A & C (out of this 3 pole 400 amp fused switch) feeding second feeder panel make any difference, as far as NEC is concerned??

Confused because in the past, previous AHJ would allow on RESIDENTIAL...
a 400 amp meter base only (no outdoor service disconnect)... to be double-lugged on load side of meter base, with 3/0 copper, to (2) separate 200 amp service panels, as long as outdoor disconnects were not required, due to distance, etc.

Joined: Jan 2001
Posts: 1,044
Tom Offline
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As far as I can tell, you are in compliance as long as you meet the tap rules regarding distance.

Q2- since this is 120/208, no difference at all.

Last edited by Tom; 03/07/12 05:37 PM.

Few things are harder to put up with than the annoyance of a good example.
Joined: May 2007
Posts: 55
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Up2code Offline OP
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Thanks Tom.

Conductors meet conditions of section 240.21(B)(2), so all is well. For some reason, I have a hard time remembering this tap rule. Suppose because I don't run across it that often.

Joined: Jun 2004
Posts: 1,273
T
Member
Did you actually check the voltages?

'Cause the Service might be our old classic: the 4-wire, center-tapped 240 VAC delta.

Double-lugging off of the A & B legs would then give you twin 240/120 single phase panels...

Leaving the Main Panel to support 3-phase loads at 240 VAC: A,B,C.

If the Service was truly 208Y120 the impulse would be to split half the daughter load onto A&B and then B&C.

Just sayin'.


Tesla
Joined: May 2007
Posts: 55
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Up2code Offline OP
Member
Tesla, no I did not check the voltages.

I will ask the electrical contractor to verify when I return today. Tag on existing switchboard did say 208Y120. As electrical inspector, I shouldn't "suppose" it is or isn't a certain voltage.

Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
If the panelboard is marked 120/208 and it is connected to 120/240, will you write that up as a violation? I've had to do so a couple of times when electricians have used "loadcenter" grade panels. At least one manufacturer (Cutler Hammer) has 3 phase panels with plug on breakers listed for 120/208 only, if you want a 120/240 3 phase, you have to step up to a bolt on breaker.


Few things are harder to put up with than the annoyance of a good example.

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