tap rule ?????

[pgordon]

#1 , can I use a MLO panel on the secondary side of a transformer ?

#2 , can I tap a generator bus ( before the main gen breaker) and pipe over 25' to a breaker (in the generator enclosure)and then to a load bank connection ?

 

[petersonra]

#1 , can I use a MLO panel on the secondary side of a transformer ?

#2 , can I tap a generator bus ( before the main gen breaker) and pipe over 25' to a breaker (in the generator enclosure)and then to a load bank connection ?

In the general the answer to both questions is a qualified yes, IMO. Like many such answers though, the devil is in the details.

 

[JoeStillman]

#1 You can't feed an MLO panel from tap conductors. 408.36 requires the OC protection for the panel to be on the load side of the transformer.

#2 You might be able to make a case for article 240.21(B)(5) for the load bank conductors, if they are running underground.

 

[petersonra]

#1 You can't feed an MLO panel from tap conductors. 408.36 requires the OC protection for the panel to be on the load side of the transformer.

That was not the question he asked though. He asked if he could use a MLO PB on the secondary side of a xfmr. That is perfectly acceptable.

#2 You might be able to make a case for article 240.21(B)(5) for the load bank conductors, if they are running underground.

I had in mind 240.21(B)(6).

 

[iwire]

That was not the question he asked though. He asked if he could use a MLO PB on the secondary side of a xfmr. That is perfectly acceptable.

How would you protect the panelboard?

How would you protect the conductors between the transformer and the panel?

How would you provide the transformer secondary overcurrent protection if required? (And it generally is)

 

[charlie b]

Try it this way: You can use an MLO panel on the secondary side of a transformer. However, there must be an overcurrent protection device of some description (fused disconnect or enclosed breaker, to give two examples) between the transformer's secondary terminations and the panel's MLO terminations.

 

[iwire]

Try it this way: You can use an MLO panel on the secondary side of a transformer. However, there must be an overcurrent protection device of some description (fused disconnect or enclosed breaker, to give two examples) between the transformer's secondary terminations and the panel's MLO terminations.

Sure, but that does not seem to be the OPs question.

I would be willing to bet the OP would not be asking this question if they were going to use an OCPD ahead of the MLO panel.

 

[Smart $]

Let's backtrack these replies and say it is dependent on the transformer configuration and protection plus transformer secondary conductor protection. See 240.21(C)(1) and 408.36(B) Exception. Where both of those apply, it is conceivable to have an MLO panel connected directly to a transformer secondary.

 

[iwire]

Let's backtrack these replies and say it is dependent on the transformer configuration and protection plus transformer secondary conductor protection. See 240.21(C)(1) and 408.36(B) Exception. Where both of those apply, it is conceivable to have an MLO panel connected directly to a transformer secondary.

Conceivable sure, likely not so much.

As always the answer lies in the details which we do not have.

 

[augie47]

Let's backtrack these replies and say it is dependent on the transformer configuration and protection plus transformer secondary conductor protection. See 240.21(C)(1) and 408.36(B) Exception. Where both of those apply, it is conceivable to have an MLO panel connected directly to a transformer secondary.

Which exception to 408.36 would allow a panelboard to be connected directly to a transformer without a main disconnecting means ?

 

[david luchini]

Which exception to 408.36 would allow a panelboard to be connected directly to a transformer without a main disconnecting means ?

The exception is in 408.36(B). It permits the Primary OCPD which protects the secondary conductors of a delta-delta transformer, for example, to also protect the secondary panelboard.

 

[augie47]

The exception is in 408.36(B). It permits the Primary OCPD which protects the secondary conductors of a delta-delta transformer, for example, to also protect the secondary panelboard.

Amazing what one finds when they turn the page

So, as Bob states, the devil is in the details.