Ive got voltages at a 3 phase disconect reading A-B-C all saying 240 across them ok. When you go A & B to ground u get 240v. But on C Phase u get nothing, my meter says 3 volts to ground. Some one was telling me this was delta with a high leg, but I thought that one of the legs to ground would read something high like 300 volts. And the other legs were 120 to ground for lights. Does this make any sense?
3 Phase Delta?
- Thread starter vramp7
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- New Jersey
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- Journeyman Electrician
It's likely a 3 phase, 3 wire corner grounded Delta. The is no high leg in that system.
ptonsparky
Tom
- Occupation
- EC - retired
What colors do you use for any grounded conductor?
200.7(A)
200.7(A)
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Thanks for the info. That's interesting, looking at the website pics it says the HOT phase thats grounded should be grey. wouldnt that throw someone off thinkin that thats a nutrel for 120 circuits? the disconnect thats in now has fuses for all 3 phases an acording to the drawings, that should have no fuse just a buss link. If thats so, if u get 240 between the grounded phase what happens in a fault if the grounded phase isnt fused? does the other fuses trip? So if i touch with my hand the grounded 240v phase I should not feel anything right??
ptonsparky
Tom
- Occupation
- EC - retired
Think of a grounded delta system as you would the normal single phase service. The difference being the grounded conductor does not carry the imbalance of L1 & L2 and there are no line to neutral loads. Once that phase is grounded, you are at the same potential. Only thing different is the phase to ground voltage. Yours is 240v, we have some in this area at 480v to ground.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Disconnects on corner-grounded delta systems should not have fuse in the grounded conductor (unless the fuse is providing overload protection to a motor).During a fault condition the grounded conductor behaves just like any other grounded conductor.
Touching any grounded conductor can be dangerous, if there is current flowing on the conductor your body becomes a parallel path.
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
Is it possible that this was supposed to be an ungrounded system that has a fault?
-Jon
-Jon
It shouldn't, nothing should ever be taken for granted.
The fuse should be removed and replace with a slug.
This is really no different electrically than solidly grounding the center of a single phase 240 v winding to make a 120/240 v system. Until two points are contacted there is no hazard. If the grounded conductor is opened another hazard is introduced the same as opening the grounded conductor of a 120/240 v system.
It should, the same thing would happen in the above example of a 120/240 v single phase system.
Not until a second point of the system were touched at the same time.
Roger
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