single phase three wire panelboards

[bxny]

I have four (4) individual 120/240V, single phase, three-wire rated panelboards. However, the power source is 208/120, 3-phase, 4-wire. My loads require either 120V or are air conditioning units that are rated for both 208 and 240V. I think that I should be able to connect each of the above panels using 2-phase, 3-wire 208/120V (i.e. one wire from each of 2 phases and one neutral, giving 208V phase to phase and 120V phase to neutral). I would attempt to balance the loading on the transformer by connecting one panel phase A, phase B, neutral, and the next phase B, phase C, neutral, etc.
Am I on the right track here? Am I violating any codes?

 

[BJC]

1.) Yes
2.) Maby -Make sure there labeled correctly when installed. The difference in connecting something at 208 vs 240 is significant for some loads. Ten years from now someone needs to know. Vendors will label your panels 208/120 if you specify it to be so.

 

[alehman]

That's certainly thinking outside of the proverbial box. I don't think there's a problem with the letter of the NEC if the panels are properly rated and labeled. If these are service entrance panels, they must be installed in accordance with the six-switch rule and be grouped at one location. If they are fed from a transformer, you will need to take a close look at the rules for transformer overcurrent protection.

 

[mc5w]

What you are doing is what is known as a 3-wire network feeder. In large apartment buildings the service will be 120Y208 volts 3-phase with a 3-phase 4-wire house service to run heating system pumps and elevators. The house meter would usually be a form 14s or 16 s. The tenant feeders would use the neutral and 2 of the 3 phases. The tenant meters would form 12s which uses 2 stators because of the phase shift.

An alternate practice was to install a separate 3-phase house service and then put in 1, 2, or 3 single phase services for the tenants so that cheaper form 2s meters could be used for the tenants. All depended on who your electrical utility was.

 

[resqcapt19]

bxny,
Just remember that if you make this installation, that the grounded or neutral conductor is always a current carrying conductor for the purposes of applying the derating that is required for more than 3 conductors in a raceway or cable. 310.15(B)(4)(b)
Don

 

[jraef]

I agree with BJC and alehman. No problem, but labeling is crucial to this. Otherwise some poor schmuck in the future is going to ASS-U-ME that he has 240V using a 2 pole breaker and burn something up.

"Venditori de oleum-vipera non vigere excordis populi"

 

[mc5w]

Also, the current in the neutral will ALWAYS be 100% of the 120 volt loads that are running. If you have a reduced size neutral conductor or a junky neutral bus you could have problems.

 

[bxny]

Thanks to all for your help.
bxny