I got a call today from dry cleaners he wants to add new washer. it is three phase 240 volt the panel is 200 amp three phase corner grounded the listing in the panel 120/240 volt single phase or 240 volt three phase delta.the panel has two bus bars and grounded bar. the breakers in the panel are two pole 240 volt rated two wires to the bus and one wire to the grounded bar. can i add the new washer the same way ?
delta
- Thread starter domnic
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kwired
Electron manager
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- NE Nebraska
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- EC
If straight 240 volts is all that is needed - you can likley do this. If it needs a "neutral" or has other instructions prohibiting it from being connected to such a system then no. If VFD's are involved they may not play well with that source, but you said there wasn't any drives.
Don't forget the grounded phase is a current carrying conductor and you need to run a separate equipment grounding conductor with your circuit. That conductor should be white or gray and be treated like the neutral is on a system with a grounded neutral. It is not a neutral but is a "grounded conductor".
One real good example why NEC uses the term "grounded conductor" instead of "neutral" in places like this where people have confusion why NEC doesn't use the term "neutral" .
Don't forget the grounded phase is a current carrying conductor and you need to run a separate equipment grounding conductor with your circuit. That conductor should be white or gray and be treated like the neutral is on a system with a grounded neutral. It is not a neutral but is a "grounded conductor".
One real good example why NEC uses the term "grounded conductor" instead of "neutral" in places like this where people have confusion why NEC doesn't use the term "neutral" .
Curious..
Can you tell us a bit about the electrical system such as is this the service and how are 120 v loads addressed. HOw large a facility ?
Again, just curious. I don't ever recall a 240v corner grounded delta on a small
service/facility.
Can you tell us a bit about the electrical system such as is this the service and how are 120 v loads addressed. HOw large a facility ?
Again, just curious. I don't ever recall a 240v corner grounded delta on a small
service/facility.
kwired
Electron manager
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- NE Nebraska
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- EC
I have never encountered 240 volt corner ground, but would think that limited load applications (not so much limited VA as much as limited to single load or single load and limited accessories) would be ideal place to use such a service. Something like a pumping station would be a good example.
We used to have 480 volt corner ground services for irrigation services, but 480 volts to ground and farmers that don't understand it are a bad combination. 277 to ground is bad enough with unqualified people frequently messing with it, but AFAIK all corner ground "services" are now gone in this area.
ggunn
PE (Electrical), NABCEP certified
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- Austin, TX, USA
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- Consulting Electrical Engineer - Photovoltaic Systems
I was wondering that as well. 120V loads would have to be serviced through an isolation transformer, wouldn't they?
kwired
Electron manager
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- NE Nebraska
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- EC
That would be the most common method I would guess. There probably are facilities that had corner grounded supply for long time that maybe have a second service feeding them that has 120 volts available. Some places POCO's maybe only will give you one "service" and if you need different voltages you need to derive them from what you have. NEC doesn't limit number of services we can have if they have different characteristics like different voltage, number of phases, frequency, etc.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Something is not right here, or this is a very old system, from back in the days when the NEC did not exist...
Those two statements CANNOT coexist in the same system, at least not now. There may have been a time, long before I ever got in the Electrical Business, when you could have legally fed a 3 phase load from a corner grounded system panel with a 2 pole breaker and a grounded conductor. But that has been illegal for as long as I know now, the code requires that all current carrying conductors have an OCPD on them, and in a corner grounded delta system, a 3 phase load will have current being carried on all 3 conductors, regardless of the fact that one of them is at ground potential. If it was installed prior to that code requirement, it may be grandfathered in, but you will not be able to add any 3 phase circuits to it.
So bottom line, this is going to depend on whether or not the new equipment is 3 phase or single phase (you never said). If it is 3 phase, and the installation is really like this, then legally, you will not be able to add it to that panel.
kwired
Electron manager
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- NE Nebraska
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- EC
I rarely disagree with you but I think I do disagree here. That grounded phase is no different then a grounded neutral in a system most are more familiar with when it comes to whether or not overcurrent protection is necessary. It can be run through a three pole breaker that opens simultaneously with the ungrounded conductors, but it can not go through a fuse as you can blow the fuse of the grounded conductor and still have the ungrounded conductors energized.
Now not all two pole breakers will be rated for use on such a system particularly those rated 120/240 volts, but that is a listing issue for that particular breaker not a code issue prohibiting use of a two pole breaker for a circuit from a corner grounded source.
You may also find single phase panels that are not listed for use with corner grounded delta - again a listing issue more then a code issue.
texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
Well, it is rare for Jraef to make a wrong call, but I gotta agree with you here.
Judging from the OP comment that this building has a 120/240 service and a 240 corner grounded service this sounds like a place such as Philadelphia area where they still have some stuff like this.
To the OP-I would make sure the manufacturer is OK with this as not all modern equipment is OK on a corner grounded system for a number of reasons.
- Location
- Connecticut
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- Engineer
I gotta agree with kwired as well.
I think the relevant sections would be 240.21 for ungrounded conductors and 240.22 for grounded conductors.
I think the relevant sections would be 240.21 for ungrounded conductors and 240.22 for grounded conductors.
texie
Senior Member
- Location
- Fort Collins, Colorado
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- Electrician, Contractor, Inspector
Here is a good white paper from Square D on this subject: http://static.schneider-electric.us...n/Molded Case Circuit Breakers/2700DB0202.pdf.
While I don't see these system too often, I usually find all kinds of violations due to all the details required to make these systems compliant as pointed out in this SqD document.
While I don't see these system too often, I usually find all kinds of violations due to all the details required to make these systems compliant as pointed out in this SqD document.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
I'm confused. In a 120V distribution system (as in a residence), the neutral is grounded and current carrying but does not require OCPD. What's the difference?
In a corner grounded delta system, a ground fault on the grounded conductor would not trip the OCPD. What would be the point of having it?
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- Placerville, CA, USA
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- Retired PV System Designer
I think that the consensus is that jraef's statement was wrong.
Now in the case of a three phase delta motor load with external overload protection there needs to be an overload sensing mechanism in the grounded conductor as well as in the ungrounded conductors since the grounded conductor is current carrying, but that does not affect which conductors the OCPD (or indeed the overload) needs to interrupt.
(In the case of a wye wound motor, the neutral is not normally current carrying and so does not need an overload sensor.)
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Nice of you all to think that I rarely make mistakes, but you are all mistaken on that...
I made one here. It's undoubtedly another case where I was taught that oh so long ago but never challenged it, and because there is nothing inherently unsafe about using a 3 pole breaker on a corner grounded 3 phase system, I never had reason to. I thought I had read it later though. Now that you all challenged me, I looked again and I think I must have read 430.36 / 37, but that is for over LOADS, not OCPDs.
Mea culpa :ashamed1:
I made one here. It's undoubtedly another case where I was taught that oh so long ago but never challenged it, and because there is nothing inherently unsafe about using a 3 pole breaker on a corner grounded 3 phase system, I never had reason to. I thought I had read it later though. Now that you all challenged me, I looked again and I think I must have read 430.36 / 37, but that is for over LOADS, not OCPDs.
Mea culpa :ashamed1:
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