Well finally ran into something interesting at work. not the same old MC and PVC. This vintage 1960's service is supplied by POCO at 240V 3phase 3wire corner delta. And from a pad mount XFMR!! I always thought those went back to pole tops. Anyway, the contractor has Sq D service equipment. I think it's a QED type, this is by phone call. According to Sq D bulletin QED boards are listed for use on corner grounded systems. Has anyone hooked one of these up recently or at all??? I'm curious about the bonding provisions for the grounded phase. Are they right there just as in a 4 wire board??? Is there an extra part or kit you need to order. I want to be able to tell this guy some good info. I am going to look at it tomorrow. Thanks guys
-------------------- Larry LeVoir Inspector City of Irvine,CA
Can't say that I have dealt with one of these systems lately (within the last 2-3 years), but between the mid 1980's and Y2K (year 2000), I dealt with a few here and there. The more "Common" System in the "Old School Days" I ran across, was the Ungrounded 3 Wire Delta.
I have some Schematics + data in the Technical Reference section, which may be of assistance to you + the E.C.
Scott35 Great stuff on the diagrams. I don't know what I'm going to find when I go there. They will be useful to explain the system to the electrician. I hope the existing premises wiring was done correctly.
Scott(electure) Yeah, Who would of thought in super clean Irvine
I have seen it a couple times for pumping stations. A quick glance might have you thinking this was regular single phase. You are right about the equipment tho. Everything must be 3p rated and for the applied voltage. The grounded conductor, a phase, is still white and you have your EGC green or bare. You can have all 2 pole breakers as long as they are 3p rated. Other than the equipment listing issues it is not that confusing. Just remember there is no downsizing of the "neutral" (one of the few times when that term is inappropriate for a grounded conductor)
Re: 3wire 3 phase grounded service#60907 01/13/0610:55 AM01/13/0610:55 AM
Everything must be 3p rated and for the applied voltage.
Some standard single phase equipment is listed for use on corner grounded delta systems. There is no need for overcurrent protection in the grounded phase. Also, many forget that the rules in Article 200 apply to the grounded conductor in this system. Don
Does the equipment need to be specifically rated for 3 phase service? Or is it sufficient that the equipment be rated for the voltage to ground?
As an analogous question: is a common 240/120 single phase residential panel suitable for use when supplied from two legs plus the neutral of a 208Y/120 supply? Or does it need to be labeled for that application?
240.85 Applications. ...A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1–3 <phase> to indicate such suitability.
[This message has been edited by gfretwell (edited 01-13-2006).]
The sw/board turned out to be labled for 3phase 3wire, but no had provisions for bonding B phase. It appeared to have been ordered incorrectly. Sq-D's bulletin on this(see above post) specifically mentions to specify grounded B phase when ordering. I was also dismayed to see a glaring violation of 408.3(A)(2) on Sq-D's part. Equipment ground buss located at the top mere inches away from unguarded service buss bars. The contractor is trying to convince POCO to supply as ungrounded delta. I don't know if POCO is allowed to do this or will do it. If so, that will solve one problem.