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Discussion Starter #1
So I'm doing a side job and the coustmer had asked me to replace old rusty panels n breakers for new shiney ones!! So here is my main question. With a 240v corner grounded delta (b phase) so I need a special panel and breakers specifically for grounded deltas .. or will the normal 240v 3 phase panels and breakers from the supply house work?
Been to like 4 supply houses and when I mention corner grounded delta .. it's like they never heard of it before.
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Not sure what you mean by “normal”.

Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground.On a 240V 3 phase grounded delta system, the voltage to ground is 240V from 2 of the poles. So all of the breakers you need to use on there must be “straight 240V” rated, no slash in the rating. Those are available, but will be more expensive.

So I take it this system has no 120V loads, or there is a separate transformer for those? Unusual in this day and age. Might be worth looking into an upgrade to a 240/120 3 phase 4 wire system.
 

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Discussion Starter #5
Not sure what you mean by “normal”.

Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground.On a 240V 3 phase grounded delta system, the voltage to ground is 240V from 2 of the poles. So all of the breakers you need to use on there must be “straight 240V” rated, no slash in the rating. Those are available, but will be more expensive.

So I take it this system has no 120V loads, or there is a separate transformer for those? Unusual in this day and age. Might be worth looking into an upgrade to a 240/120 3 phase 4 wire system.
The shop has 2 services.. it's a old shop that a new tenant moved into .. it has a 240 grounded delta and a 120/240 service for recpts. I got the info on the straight 240 breakers. Thank you. Will a normal 240v 3p panel work also
 

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The shop has 2 services.. it's a old shop that a new tenant moved into .. it has a 240 grounded delta and a 120/240 service for recpts. I got the info on the straight 240 breakers. Thank you. Will a normal 240v 3p panel work also
Yes it will.

Depending on the available fault current, you might be able to use a single phase panel and treat the grounded phase like a neutral. But the AIC rating on the breakers is often lower than what's stamped on them.
 

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Yes it will.

Depending on the available fault current, you might be able to use a single phase panel and treat the grounded phase like a neutral. But the AIC rating on the breakers is often lower than what's stamped on them.
I was thinking to do it right the B phase should be un-switched. Would using the neutral bus suffice?
 

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Is the OP saying he has a corner grounded Delta or a grounded Delta? Post #1 and then Post #5. I try very hard to stay away from corner grounded Delta systems. My understanding is that there are no 3 pole breakers used. Only two pole including the main.
 

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Discussion Starter #10
Is the OP saying he has a corner grounded Delta or a grounded Delta? Post #1 and then Post #5. I try very hard to stay away from corner grounded Delta systems. My understanding is that there are no 3 pole breakers used. Only two pole including the main.
It's a corner grounded delta .. and the old panels hanging up do infact have 3 pole breakers
 

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3 Pole breakers are perfectly fine to use for 3 phase induction loads. Certain drives or equipment may not like it If they need a reference from each phase to ground or only a certain Maximum voltage on each phase if there are MOVs. Only the B phase with the higher voltage will require straight rated breakers. Induction two pole or 3 pole loads will be fine in any location. Most 3 Pole circuit breakers are straight rated.
 

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Bilge Rat
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I was thinking to do it right the B phase should be un-switched. Would using the neutral bus suffice?
It should, just like a 120/240 single phase neutral except this is a 240/240 3Ø system.

I've only seen 2 or 3 of these, one was 240 the others were 480. All of them used 2 pole breakers.
 

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Bilge Rat
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There's a single pole 15 in the pic, that would seem more like a high-leg system. Corner grounded would be all 2 or 3 poles.

On the other hand, back when this panel was installed, they did some pretty strange things........lol.

what voltage do you have from the top screw of the main to ground, like the panel metal or conduit metal. Also what voltage from the middle screw and the bottom one, each to ground.

If it's a corner-grounded system, you'll have 240 on 2 of them and 0 on the other. If it's a high-leg system, you'll have 120 on 2 of them and 208 on the third one.
 

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Discussion Starter #15
There's a single pole 15 in the pic, that would seem more like a high-leg system. Corner grounded would be all 2 or 3 poles.

On the other hand, back when this panel was installed, they did some pretty strange things........lol.

what voltage do you have from the top screw of the main to ground, like the panel metal or conduit metal. Also what voltage from the middle screw and the bottom one, each to ground.

If it's a corner-grounded system, you'll have 240 on 2 of them and 0 on the other. If it's a high-leg system, you'll have 120 on 2 of them and 208 on the third one.
Thanks for catching that sorry clicks the wrong picture by mistake
151431
 

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Discussion Starter #16
There's a single pole 15 in the pic, that would seem more like a high-leg system. Corner grounded would be all 2 or 3 poles.

On the other hand, back when this panel was installed, they did some pretty strange things........lol.

what voltage do you have from the top screw of the main to ground, like the panel metal or conduit metal. Also what voltage from the middle screw and the bottom one, each to ground.

If it's a corner-grounded system, you'll have 240 on 2 of them and 0 on the other. If it's a high-leg system, you'll have 120 on 2 of them and 208 on the third one.
Also idk y a single pole 15 is in there but but from a,b 240 b,c 240 c,a 240.. a,g 240 b,g 0 c,g 240
 

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240.22 Grounded Conductor.
No overcurrent device shall be connected in series with any conductor that is intentionally grounded, unless one of the following two conditions is met:
(1)The overcurrent device opens all conductors of the circuit, including the grounded conductor, and is designed so that no pole can operate independently.
(2)Where required by 430.36 or 430.37 for motor overload protection.
So three pole circuit breakers are fine, but not three pole fused disconnects. Not unless you put a dummy fuse in the grounded conductor.
 

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No doubt, it's a 240 corner grounded system.

You can use any 3Ø panel or a single phase one.

I don't know about any other manufacturers, most likely they're all the same but the Square D 2 pole breakers are limited to 5000 amps interrupting current on a corner grounded system. The 3 pole ones are whatever is stamped on them.
 

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From your voltage readings, this is a corner grounded system. These are common in many areas on industrial facilities.

Details, some of these are already mentioned:
You must use 240 volt rated breakers and panels- NOT slash rated 240/120 breakers or panels.
Fuses should not be installed in the grounded conductor.
While you can use 2 pole breakers and use a "neutral" bar for the grounded phase, this could cause some real problems for the less knowledgable folks later on.
Normally the fault current will be higher on a corner grounded system, as any fault is phase to phase.
 

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Discussion Starter #20
From your voltage readings, this is a corner grounded system. These are common in many areas on industrial facilities.

Details, some of these are already mentioned:
You must use 240 volt rated breakers and panels- NOT slash rated 240/120 breakers or panels.
Fuses should not be installed in the grounded conductor.
While you can use 2 pole breakers and use a "neutral" bar for the grounded phase, this could cause some real problems for the less knowledgable folks later on.
Normally the fault current will be higher on a corner grounded system, as any fault is phase to phase.
Thanks for all the help trying to find panels the same dimensions is the problem now. So I don't have to re fab all the pipe work that is alrdy there. Thanks for all the info I appreciate it very much. Keep on sparking everyone
 
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