Secondary XFMR ocpd

[PCN]

If a transformer is feeding a panel with a main breaker, could that breaker be considered the secondary protection?

Or do I still need an OCPD at the transformer where the conductors orginate.

( none of 240.21 (C) 1 thru 6 would apply)

Thank you

 

[raider1]

What do you mean that none of 240.21(C)(1) through (6) applys?

The transformer secondary conductors need to have overcurrent protection that complys with 240.21(C). That overcurrent protection can be a main breaker in a panelboard provided that it complys with 240.21(C). If the breaker in the panel does not meet any of the sections in 240.21(C) then you must add an additional overcurrent protective device to protect the transformer secondary conductors in accordance with 240.21(C).

Chris

 

[PCN]

Chris, What I was trying to say is we don't meet the criteria to allow primary protection only.

Thanks for the response.

 

[raider1]

Your welcome.

Chris

 

[augie47]

PCN, Look at 240.4(F) to see the conditions that allow the transformer primary overcurrent to protect the secondary conductors.
That said, if you are supplying a panelboard, you must also satisfy 408.36

 

[Pierre C Belarge]

Generally, the secondary disconnect/overcurrent protection should be either 10 or 25 feet of conductor length (not raceway) from the transformer. The conductor length includes the conductor from the termination point in the tranformer, to the termination point in the disconnecting means.


It is rare that the primary protection of dry type power transformers used indoors will provide the proper secondary protection necessary.

 

[PCN]

Thanks guys, very helpful.