3 pase corner grounded delta
- Thread starter domnic
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big john
Senior Member
- Location
- Portland, ME
Make sure you have the correct breaker per 240.85: A slash rated breaker is not designed to interrupt L-L voltage with a single pole.
Also remember if you pick the grounded phase then all the rules of article 200 and 240.22 apply: Really common to find misidentified and fused grounded conductors on corner deltas.
Also remember if you pick the grounded phase then all the rules of article 200 and 240.22 apply: Really common to find misidentified and fused grounded conductors on corner deltas.
Good advice.
3 phase drlta corner ground
3 phase drlta corner ground
THE service is fed from PO to a two pole disconnect hot legs fused. grounded leg Is not and bonded to the disconnect .then goes to 3 phase panel with three phase 200 amp main breaker. so I will be ok to use any two legs for my two pole 240 volt single phase AC ?
3 phase drlta corner ground
THE service is fed from PO to a two pole disconnect hot legs fused. grounded leg Is not and bonded to the disconnect .then goes to 3 phase panel with three phase 200 amp main breaker. so I will be ok to use any two legs for my two pole 240 volt single phase AC ?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Yes, noting the above posts caveats.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
If you are concerned with feeding the AC with 240V with one ungrounded and one grounded conductor versus 240V from two ungrounded conductors, don't be.
The AC will run with either set up. As long as it gets 240V it is happy.
The AC will run with either set up. As long as it gets 240V it is happy.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I would agree but I might add that this would be OK for the 1 phase equipment in the OP's case. If he was going to supply a 3 phase load with a 2 pole breaker, then a breaker marked 1 phase-3 phase would be required.
The other thing I would say is that, while this is often overlooked, all devices, panelboards, etc. must be rated for use on a corner grounded system. There is not much available these days as corner grounded systems are going by the wayside.
- Location
- Massachusetts
Do you have a code section to look at?
I've always thought it fell under 408.58 and 110.3(B)... but every time I bring it up, others say in essence, it is not so. :blink:
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
You are correct.
In fact, UL has 'special' listing requirements for corner-grounded equipment.
Don't forget to also quote 240.85.
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Here is a link to some weird manufacturer that agrees with you. Go figure.
http://static.schneider-electric.us...n/Molded Case Circuit Breakers/2700DB0202.pdf
- Location
- Illinois
- Occupation
- retired electrician
And the grounded conductor is covered by all of the rules, including the identification rules, found in Article 200. I don't think I have every seen a grounded phase system that complied with those rules.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
As Smart$ said, I cite 408.58, but also 110.3. And as Jim Dungar mentioned, I am aware that UL has a requirement for this. I always thought the reason for this was to prevent, say, a person from using a 120/240 garden variety "load center" on a 240 volt corner grounded system that is not rated for 240 volts to ground.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The issue is usually not the panel, if a 3-phase version is available like with QO load centers, but the common 2 pole breakers are almost always a concern.
big john
Senior Member
- Location
- Portland, ME
There may be another caveat I'm missing, but I believe the intent of that section is to be sure that no single breaker pole is opening a voltage higher than it is designed for, the same as how you can't use a slash-rated breaker on a high leg delta.
So if you have a 120/240V breaker, it means no pole is rated to interrupt current at higher than 120V and that both poles together would be capable of opening 240V. In a corner ground, suddenly any single pole becomes 240V-G and the interrupting ability of that pole will be severely reduced.
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