240 volt 3 phase 3 wire service

[captaincrab55]

So basically I skip 2, 5, 8,11,14....................... when using this setup. 1/3 of my panel is dead in the water. My 240v overcurrent protection should be 2 pole.

This is a 3 PHASE system that requires 3-pole Breakers...... You will need a separate single phase service for general lighting and power... The POCO in & around Baltimore, Md still has that type of 3 Phase power in limited areas. It's gradually being phased out.. Knowledge of the system is also limited. I've seen Engineered drawings just last year that were goofed up because the engineer didn't understand what 3 Phase system he was dealing with... It will power 3 Phase kitchen equipment with heating elements too, but must be labeled for 3 phase/240 volts...

....

 

[winnie]

I'm with Trevor(Infinity) on this; there are inconsistencies in the original post, and these need to be resolved in order to help resolve Chris'(aelectricalman) questions.

The first is the '3 phase available' '3 phase not available' issue.

The second is the statement that A and C phases are brought to the panel with a neutral, and that B phase is jumpered to ground.

I believe the Pierre is making correct guesses given the above confusion; but until what the POCO is supplying is clarified, then they are guesses.

Chris: there is a system called corner grounded delta. The full 240V is available between all three conductors, and the system may be used to supply 3 phase loads. Loads may be connected between any of the legs; the grounded leg is a fully useable current carrying conductor. The only difference is that the leg is held at ground potential.

The grounded phase leg may be left without OCPD, or it may be protected by OCPD given the specific requirements for OCPD on a grounded conductor. Thus corner grounded delta may be fed to a three phase panel, and all breaker spaces used.

You may use a panel that looks like a single phase panel, with breakers only on the two ungrounded legs, and still feed 3 phase loads. The panel looks like a single phase panel, with two phase bus bars and a 'grounded conductor' bar, however there is a critical difference: the panel will be rated for the different voltages. Normal 240V single phase panels and breakers are rated for 240V leg to leg, but only 120V leg to ground. You would need a panel that was fully rated for 240V.

If you use a three phase panel, you also need to confirm that it is fully rated for 240V to ground, and not 'slash' rated 240/120V.

A serious inconsistency is that if you have a grounded phase leg, you _cannot_ also have a grounded neutral. But if you have a neutral in a 240V system, you are required to ground it. So the statement about bringing in A, C and Neutral , but then grounding B leg is quite confusing.

-Jon

 

[Pierre C Belarge]

These do not completely show the panel terminations, but it may help some who have not seen this before.

 

[iwire]

if you have a grounded phase leg, you _cannot_ also have a grounded neutral.

Well actually you can ..... but that is commonly called a short circuit.

 

[aelectricalman]

Just to let you all know, it is a corner grounded 240v 3 phase 3 wire system. There is no neutral, but I am still confused about 1 thing. I only bring 2 ungrounded wires from the POCO? Do I need to create my equipment ground for this grounded leg from my GEC and Water Ground or is it derived at the transformer by the PoCo? Basically do I need to bring in three or two wires from the transformer?

Thanks for the help for everyone who chipped in. I guess I am too young to have common knowledge of this system. I have never seen it and I know 10 year Masters who have not seen it, so I really thank you all for your input.

 

[jrannis]

I believe you have the option of NOT grounding the corner of that delta system. I think that might make better sense to the person that comes in behind you to service the equipment or to do some troubleshooting.
Or you could feed a delta wye 240/ 120/208 transformer with that setup and help eliminate future confusion.

 

[ptonsparky]

One way of doing it. Hope it helps a bit. All the standard disclaimers apply.

If you decide on a transformer ie 240 to 240/120 for lighting & recepts, you will need to mark your grounded & EGC conductors differently to identify which system the originate from.

 

[jim dungar]

Just to let you all know, it is a corner grounded 240v 3 phase 3 wire system. There is no neutral, but I am still confused about 1 thing. I only bring 2 ungrounded wires from the POCO? Do I need to create my equipment ground for this grounded leg from my GEC and Water Ground or is it derived at the transformer by the PoCo? Basically do I need to bring in three or two wires from the transformer?

Thanks for the help for everyone who chipped in. I guess I am too young to have common knowledge of this system. I have never seen it and I know 10 year Masters who have not seen it, so I really thank you all for your input.

For all intents you need to treat this grounded phase conductor the same way you have always treated any other grounded conductor( which have always been neutrals). You can not use the ground as part of your normal current carrying path, you need a separate conducotr from the utility transformer and needs to be identified as white or grey. Watch out for any CT can, the utility usaully grounds the "C" phase but you need to install it in you new gear as the B phase.