Secondary disconnect

[jrventures]

In regards to our computer room power distribution units(PDUs), our equipment is built to, complies with and labeled as meeting UL 60950 standards. Typicalconfiguration is main CB, 480-Y208/120 transformer and then some combination ofoutput distribution breakers.

We have a local inspector who’s interpretation of the NEC2011 is that we have to have a CB on the secondary of our PDUtransformer (there is already one as a main ahead of the transformer). Hisreference is the code Article 240.4(F).

Nowhere in all the years of supplying PDUs with sometimes 8,12 … output breakers has this been raised an issue. Any guidance on where totake this discussion?

 

[charlie b]

For most installations that I would come across, the inspector would be right. You need to protect the secondary windings of a step down transformer, and the secondary conductors leading to the first downstream device, and the breaker upstream of the primary side of the transformer is not permitted to do that job. Sometimes, a set of breakers in close proximity, all connected to the secondary conductors of the transformer, can serve this purpose. However, if I understand your question correctly, the transformer is internal to a UL listed system. That puts it outside the scope of the NEC, and the inspector would therefore be wrong.

Welcome to the forum.

 

[petersonra]

However, if I understand your question correctly, the transformer is internal to a UL listed system. That puts it outside the scope of the NEC, and the inspector would therefore be wrong.

Is that really true?

Nothing in the code exempts such a transformer from the rules.

 

[dkidd]

As Charlie said

the transformer is internal to a UL listed system. That puts it outside the scope of the NEC, and the inspector would therefore be wrong.

 

[petersonra]

As Charlie said

where does it actually say that in the code?

I don't recall it ever saying that.

 

[dkidd]

90.2 Scope

From definition of premises wiring

Such wiring does not include wiring internal to appliances,
luminaires, motors, controllers, motor control centers,
and similar equipment.