250.30(A)

[ZCBee]

"(A) Grounded Systems. A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non?current-carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper. "

Does the "not" clause above relate to all three listed conditions? Is this read as:

1. ...shall not be connected...,
2. (shall not) be connected to equipment...
3. (shall not) be reconnected...?

If the negative applies to all conditions listed, is this normal convention in the NEC?

Is a bonding jumper then required or not required in a single phase 480V to 120V transformer setup to supply control circuit power. Can the bonding jumper, the grounded conductor, and the grounding conductor all be one source such as a ground bar for the 120V system? Or, in this situation, should a grounded conductor from the source be run with the 3 phase ungrounded conductors?

Thanks again for the help.

 

[ZCBee]

"
Is a bonding jumper then required or not required in a single phase 480V to 120V transformer setup to supply control circuit power. Can the bonding jumper, the grounded conductor, and the grounding conductor all be one source such as a ground bar for the 120V system? Or, in this situation, should a grounded conductor from the source be run with the 3 phase ungrounded conductors?

Thanks again for the help.

If the second condition is true, where is this specified?

 

[wirenut1980]

The transformer secondary would be another separately derived system. It is permitted to bond the grounded and grounding conductors there again. You would not need to run a grounded conductor with the ungrounded conductors to the transformer.

So I suppose the "not" would apply to all 3 of your conditions.

 

[ZCBee]

The transformer secondary would be another separately derived system. It is permitted to bond the grounded and grounding conductors there again. You would not need to run a grounded conductor with the ungrounded conductors to the transformer.

So I suppose the "not" would apply to all 3 of your conditions.

OK, so I have a 20A, 480V branch that is for heating equipment. If the control transformer is considered a separately derived system, how is 250.30(A) interpreted then? Am I reading it incorrectly or am I missing the exception in my situation? It states:

"(A) Grounded Systems. A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non?current-carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper.

 

[wirenut1980]

OK, so I have a 20A, 480V branch that is for heating equipment. If the control transformer is considered a separately derived system, how is 250.30(A) interpreted then? Am I reading it incorrectly or am I missing the exception in my situation? It states:

"(A) Grounded Systems. A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non–current-carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper.

I could be wrong, but it sounds like you think bonding the grounded and grounding conductors at the control transformer secondary will result in current flowing on the equipment grounding conductor on the primary side of the transformer. This is incorrect. Under non-fault conditions, the secondary grounded conductor current will only attempt to flow back to the control transformer, which is it's "source." If I am wrong in my thinking, please let us know more specifically what your concern is.