250.20 Question

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augie47

augie47

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From posting in another thread I find I have a question on interpreting 250.20(B) in regard to a SDS
....
(B) Alternating-Current Systems of 50 Volts to 1000Volts. Alternating-current systems of 50 volts to 1000 voltsthat supply premises wiring and premises wiring systemsshall be grounded under any of the following conditions:
(1) Where the system can be grounded so that the maximumvoltage to ground on the ungrounded conductorsdoes not exceed 150 volts
(2) Where the system is 3-phase, 4-wire, wye connected inwhich the neutral conductor is used as a circuit conductor
(3) Where the system is 3-phase, 4-wire, delta connected inwhich the midpoint of one phase winding is used as acircuit conductor

Would a 208/120 system with n XO terminal in which the neutral was not used as a circuit conductor be required to be grounded? (1) above would indicate "yes" but (2) above might lead one to say "no" unless (2) applies to system over 150 volts to ground.
 
You only need to meet one of the three conditions so for 208Y/120 you would meet (1) whether you used the X0 or not.
 
The section states that only one needs to apply.
In your example, 208Y/120, (2) and (3) do not apply but (1) does. Nothing further to consider.

Sent from my XT1585 using Tapatalk
 
infinity said:
For a 240/120 volt transformer it would apply also.
Click to expand...
3 phase ? (hi-leg) I would appear to me that (1) would not apply since you do have a maximum voltage above 150 to ground and (3) would only apply if you used the midpoint.
 
infinity said:
For a 240/120 volt transformer it would apply also.
Click to expand...

I respectfully disagree,

When you ground a 240/120 delta 3 phase transformer you would have 208 volts to ground on the "high leg" therefore Item 1 would not apply. So if you are not using the grounded conductor as a circuit conductor you can have an ungrounded Delta 240/120 transformer.

Chris
 
augie47 said:
3 phase ? (hi-leg) I would appear to me that (1) would not apply since you do have a maximum voltage above 150 to ground and (3) would only apply if you used the midpoint.
Click to expand...

raider1 said:
I respectfully disagree,

When you ground a 240/120 delta 3 phase transformer you would have 208 volts to ground on the "high leg" therefore Item 1 would not apply. So if you are not using the grounded conductor as a circuit conductor you can have an ungrounded Delta 240/120 transformer.

Chris
Click to expand...

Yes, you're both correct I should have clarified by saying it would not apply due to the high leg (1) or it would apply if you used a grounded conductor (3).
 
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