Transformer Secondary

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Jimmy7

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Boston, MA
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Electrician
I just received a set of drawings for a project where on one floor a 150 Amp 208/120 volt MLO panel is being fed from a 45kva 480 to 208/120 transformer. Shouldn't this panel have overcurrent protection? I believe article 240.21 pertains this, but does not apply to this situation. Would I be correct?
 
I think that overcurrent protection is required for the transformer secondary, the transformer secondary conductors, and the panelboard. It could all be the same physical device. it does not have to be part of the panelboard.
 
petersonra said:
I think that overcurrent protection is required for the transformer secondary, the transformer secondary conductors, and the panelboard. It could all be the same physical device. it does not have to be part of the panelboard.
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Yes, not providing it is a mistake I'm seeing quite a bit of lately. :slaphead:
 
An update to my previous post, I met the engineer on the job who states that it doesn't need a MCB, because it was within 10' of the transformer. As a result, I've been talking to others in the field in order to try to understand this. I've heard so many different reasons why secondary protection isn't required in certain situations, for instance NEC 450.3(B). Regardless of the reason, doesn't 2017 NEC 408.36(B) require panels that are supplied through a transformer to have overcurrent protection. There is an exception to this article which references article 240.21(C)(1) which doesn't apply to this installation. What do you think?
 
Jimmy7 said:
An update to my previous post, I met the engineer on the job who states that it doesn't need a MCB, because it was within 10' of the transformer. As a result, I've been talking to others in the field in order to try to understand this. I've heard so many different reasons why secondary protection isn't required in certain situations, for instance NEC 450.3(B). Regardless of the reason, doesn't 2017 NEC 408.36(B) require panels that are supplied through a transformer to have overcurrent protection. There is an exception to this article which references article 240.21(C)(1) which doesn't apply to this installation. What do you think?
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One common mistake is not realizing that 450.3 is only about the transformer, and says nothing about the conductors (or the panelboard).
 
Jimmy7 said:
I met the engineer on the job who states that it doesn't need a MCB, because it was within 10' of the transformer.
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I think that engineer needs a lesson on "Charlie's Rule." He (or she) is remembers that there is a "10 foot rule," but did not bother to read it before making that statement.

I agree with David: that engineer is wrong.

 
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