Grounded B Phase sub panel - Electrician Talk - Professional Electrical Contractors Forum

luby104 · 09-22-2010, 10:02 PM

This is a 240v Grounded B Phase sub panel in an older manufacturing facility. I am not familiar with this type of service. Any comments are welcome

There are only 2 pole QO breakers used in this panel
for A & C phases. If a three phase 240V circuit is needed,
a two pole breaker is used for the black and the blue wires, and the red wire is taken directly from the B bus bar. If a single phase 240V circuit, then a 2 pole breaker
is used with the black and blue wires only. The red B phase wire is not used. It's seems similar to a 220V residential setup with a grounded neutral.

The scary part is that the electricians that added some equipment a month ago, put a 3 pole breaker in the panel. (I might add that the motors on that equipment keep burning up.) I don't think that a 3 pole breaker should be in that panel.
Does anyone agree / disagree?

**frenchelectrican** · 09-23-2010, 12:38 AM

Quote:

Originally Posted by luby104

This is a 240v Grounded B Phase sub panel in an older manufacturing facility. I am not familiar with this type of service. Any comments are welcome

There are only 2 pole QO breakers used in this panel
for A & C phases. If a three phase 240V circuit is needed,
a two pole breaker is used for the black and the blue wires, and the red wire is taken directly from the B bus bar. If a single phase 240V circuit, then a 2 pole breaker
is used with the black and blue wires only. The red B phase wire is not used. It's seems similar to a 220V residential setup with a grounded neutral.

The scary part is that the electricians that added some equipment a month ago, put a 3 pole breaker in the panel. (I might add that the motors on that equipment keep burning up.) I don't think that a 3 pole breaker should be in that panel.
Does anyone agree / disagree ?

That is a major issue if someone did use the 3 pole breaker on CGD then they are nuts and I know few electricians are not really famuair with old school corner grounded delta system they look simauir to single phase but it is NOT !!!.

Merci.
Marc

Jlarson · 09-23-2010, 12:44 AM

Yeah a 3 pole on a corner ground delta system feeding 3ph equip. ain't going to end well. Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. So put in a 2 pole and land B on the bus bar and I bet the motor issue will hopefully be solved.

**frenchelectrican** · 09-23-2010, 12:53 AM

The only surefire way you can tell which phase is correct is get your voltmeter to read phase to ground and find which one is correct so like phase A to Ground is 240 volts while Phase C is 240 volts to ground that is correct and phase B should be complety ZERO volts any other voltage then you have issue there.

If that the case go to the main loadcentre or disconnect switch and make a note and read voltage and go from there.

If someone did install the true triphase load centre on CGD then you have to skip every third one and you will have to mark it down say CGD that will give them a head up.

I gave you the answer on the other topic in this forum about the breaker itself.

Merci.
Marc

Jlarson · 09-23-2010, 12:59 AM

Quote:

Originally Posted by frenchelectrican

The only surefire way you can tell which phase is correct is get your voltmeter to read phase to ground and find which one is correct so like phase A to Ground is 240 volts while Phase C is 240 volts to ground that is correct and phase B should be complety ZERO volts any other voltage then you have issue there.

If that the case go to the main loadcentre or disconnect switch and make a note and read voltage and go from there.

If someone did install the true triphase load centre on CGD then you have to skip every third one and you will have to mark it down say CGD that will give them a head up.

I gave you the answer on the other topic in this forum about the breaker itself.

Merci.
Marc

Sometimes you see (or at least I do) a single phase panel with A and C landed and B is on the bar. If it was a 3ph panel board and A,B,C are landed on the lugs, then a 3 pole breaker "would work" technically for a 3ph load.

**frenchelectrican** · 09-23-2010, 01:03 AM

Quote:

Originally Posted by Jlarson

Sometimes you see (or at least I do) a single phase panel with A and C landed and B is on the bar. If it was a 3ph panel board and A,B,C are landed on the lugs, then a 3 pole breaker "would work" technically for a 3ph load.

Yeah I have see that as well but not very often in that fashon for CGD but I know it can work with tripole breaker due it have common tripping mechesaim but the biggest killer is to properly grounded and bonded with subpanels with CGD that kinda eyeopener if ya not prepared.

Merci.
Marc

Toronto Sparky · 09-23-2010, 03:18 AM

I've been in the trade for 40+ years and I've never seen a grounded delta setup myself.
Sure it would trip me up too..

So..this system is like a regular single phase panel but the grounded phase is landed on the (so called) Neutral bus?

A three phase motor would be tied into a two pole breaker plus a feed from the (so called) neutral bus?

**frenchelectrican** · 09-23-2010, 03:40 AM

Let me throw couple photos how it describe .,

This is one part and let me throw other part.

If someone else have more diagram please do post it here.

As you can see why you have to be extra carefull with CGD system as I mention above it can get ya if not watching the grounded and grounding conductors. { espcally with subpanels that where the trouble start }

Oh yeah they do come in both 240 or 480 volt verison.

Merci.
Marc

**frenchelectrican** · 09-23-2010, 03:43 AM

Quote:

Originally Posted by Toronto Sparky

I've been in the trade for 40+ years and I've never seen a grounded delta setup myself.
Sure it would trip me up too..

So..this system is like a regular single phase panel but the grounded phase is landed on the (so called) Neutral bus?

A three phase motor would be tied into a two pole breaker plus a feed from the (so called) neutral bus?

I kinda figure that some of the guys never see that before and mutter " WTF " .,,,

Yeah simauir to single phase panels but a big gotcha is you have to be aware with supply set up { it can trick ya if you are not watching or check the voltage with volt meter to make sure }

And to answer your last question Oui { Yes } it been done like that.

But not very many places still have CGD anymore they are slowly dropping out for safety issue.

Merci.
Marc

varmit · 09-23-2010, 05:20 AM

I work on corner grounded delta systems quite often. CGD systems are quite common on older industrial facilities. Almost all of these use 3 pole breakers for 3 phase loads and appear, to the eye, as a wye system. You must always use a meter to know for sure. I also see many CGD systems with fuses in all 3 phases. This, of course, is a code violation, but a very common violation. There are also several ungrounded Delta systems in use in this area. ALWAYS USE YOUR METER TO KNOW WHAT YOU ARE DEALING WITH.

As to the OP question about the motors failing: If the motors are 3 phase, and connected to all 3 phases, and the motors are wired for the proper voltage, it would make no difference if the system was CGD or wye. If they were 120 volt, they would of course burn up. If the motors are 240 volt single phase, connection to any 2 phases, grounded or not, would work.

If the OP is saying that this is a single phase panel, with the "neutral" bar used as the "B" phase buss, on a 3 phase system, then you COULD NOT use a 3 pole breaker to power a 3 phase load as this would put two lines of one of the phases on the circuit.

Bob Badger · 09-23-2010, 05:36 AM

Quote:

Originally Posted by varmit

I work on corner grounded delta systems quite often. CGD systems are quite common on older industrial facilities. Almost all of these use 3 pole breakers for 3 phase loads

That is because they used 3 phase panels, but you can also use single phase panels using the 'neutral bar' for the grounded phase.

When using single phase panels use of a three pole breaker would be wrong and provide only two legs to the motors.

Code wise the grounded phase should be white, it should not be switched unless it is switched at the same time as the other legs.

brian john · 09-23-2010, 06:23 AM

Quote:

Originally Posted by Bob Badger

Th.

When using single phase panels use of a three pole breaker would be wrong and provide only two legs to the motors.

gs.

And that will fry motors in short order.

Also shouldn't the "B" phase grounded conductor be white,

hardworkingstiff · 09-23-2010, 06:53 AM

Quote:

Originally Posted by brian john

Also shouldn't the "B" phase grounded conductor be white,

Quote:

Originally Posted by Bob Badger

Code wise the grounded phase should be white, ....

I think so.

raider1 · 09-23-2010, 10:49 AM

Quote:

Originally Posted by brian john

And that will fry motors in short order.

Also shouldn't the "B" phase grounded conductor be white,

Quote:

Originally Posted by hardworkingstiff

I think so.

Yes, the grounded conductor of a corner grounded system must be identified either white or grey the same as any other grounded conductor.

Chris

Vintage Sounds · 09-23-2010, 05:05 PM

Quote:

Originally Posted by Toronto Sparky

I've been in the trade for 40+ years and I've never seen a grounded delta setup myself.
Sure it would trip me up too..

Does this mean it's unlikely that I would run into a delta system, doing work around Toronto? I was hoping to see one sometime.

Bob Badger · 09-23-2010, 05:09 PM

Say your factory is 600Y/277 and someone brought in some 230 volt 3 phase motors, a delta / delta transformer set up as grounded delta would be a quick and easy solution.