Code Question of The Day

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Friday, May 7, 2021

Question:

2 days 8 hours ago

Hello Paul,

Thanks for the comment. The question was only seeking the "required overcurrent protection for the transformer," not the conductors supplying it or connected to the secondary side of it. Section 450.3 provides the general rule. There is an informational note following that section that refers to 240.4, 240.21, 240.100 and 240.101 for protection of the "conductors." So you are on the right track, that the transformer once protected in accordance with the NEC, often requires additional conductor protection rules to be applied, such as Section 240.21 which you mentioned in the follow up. Often this is achieved using the same overcurrent protective device.

Thanks for participating. 

?

Thursday, May 6, 2021

Question:

3 days 8 hours ago

Hello,

On a commercial service a contractor removed a de-rated aluminum neutral and replaced it with copper THHN of proper size. That made the hot legs, aluminum, and the neutral, copper, in a pipe mast. Is this allowed in the NEC? The local utility has said that they would not hook it up like this. I'm wondering if it would be allowed in a different situation.

Thanks,

Adam Rumpf

?

Friday, May 7, 2021

Question:

2 days 8 hours ago

Hello Paul,

Thanks for the comment. The question was only seeking the "required overcurrent protection for the transformer," not the conductors supplying it or connected to the secondary side of it. Section 450.3 provides the general rule. There is an informational note following that section that refers to 240.4, 240.21, 240.100 and 240.101 for protection of the "conductors." So you are on the right track, that the transformer once protected in accordance with the NEC, often requires additional conductor protection rules to be applied, such as Section 240.21 which you mentioned in the follow up. Often this is achieved using the same overcurrent protective device.

Thanks for participating. 

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