250.22

[electrofelon]

For the purposed of 250.22, what is meant by an "ungrounded circuit"? Do they mean a circuit originating from a system that is ungrounded?

 

[texie]

For the purposed of 250.22, what is meant by an "ungrounded circuit"? Do they mean a circuit originating from a system that is ungrounded?

Not exactly sure I understand your question, but maybe an example will help. Look at 250.22(4). This is telling you that the secondary side of the transformer for a low voltage lighting system can not be grounded. The supply (primary side) to this transformer can be supplied from a grounded system (and most likely is required to be).

 

[electrofelon]

Not exactly sure I understand your question, but maybe an example will help. Look at 250.22(4). This is telling you that the secondary side of the transformer for a low voltage lighting system can not be grounded. The supply (primary side) to this transformer can be supplied from a grounded system (and most likely is required to be).

Ok right, that is what I thought. I think I am confused that they use the word "circuit" and not "system". I fully understand grounded and ungrounded systems and that seems to be the umbrella context for 250.22 so not sure why they didnt just stick with "systems not to be grounded".

 

[GoldDigger]

If you are just feeding, for example, a single set of lights and have no or only one OCPD fed from the transformer I guess it seems like overkill to call it a Separately Derived System instead of just a circuit.


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[electrofelon]

I think it is lame wording. Some of the items listed would be definitely be "systems" - with a panelboard and all.

 

[david luchini]

I think it is lame wording. Some of the items listed would be definitely be "systems" - with a panelboard and all.

These circuits would most likely come from electrical systems that ARE grounded.

The specific circuits would be isolated from the grounded system, and the circuits would be left ungrounded. See for instance in 503.155(A) "The power supply to the contact conductors shall be electrically isolated from all other systems..." or 517.61(A)(1) "...each power circuit...shall be isolated from any distribution system..."