Transformer disconnect

[MBLES]

Need to install a 480v to 240 transformer single phase and feed it from first floor panel. The line side is 480/277v to load side 120/240 single phase.
The transformer will be located on seveth floor. do i need disconnect one on each side of transformer in mechaniical room? the load side will feed a panel on a platform. do you think i would need another discoonect at the panel or the panel main breaker would be enough?

 

[infinity]

The primary disconnect does not need to be within sight of the transformer as long as it complies with the provisions of 450.14.

450.14 Disconnecting Means. Transformers, other than Class
2 or Class 3 transformers, shall have a disconnecting means
located either in sight of the transformer or in a remote loca-
tion. Where located in a remote location, the disconnecting
means shall be lockable in accordance with 110.25, and its
location shall be field marked on the transformer.

 

[augie47]

The load side would need overcurrent protection per 240.21(C).
The panel main will suffice if it meets the requirements of the above section.

 

[MBLES]

so you guys are saying. the transformer can set in mechanical room with no primary disconnect or secondary if the main breaker its feeding meets requirements.

 

[don_resqcapt19]

so you guys are saying. the transformer can set in mechanical room with no primary disconnect or secondary if the main breaker its feeding meets requirements.

There is no requirement for the primary OCPD or disconnect to be at the transformer. If you are using the current code, the transformer will require a sign or label tell the location of the primary disconnect. Without knowing the size of the transformer and the rating of the primary OCPD, I cannot tell you if the transformer needs secondary protection.

I can tell you that the secondary conductors will require protection per the rules in 240.21(C). In most cases, compliance with the secondary conductor protection rules, will require an OCPD no more than 25' wire feet from the transformer.

 

[electricalist]

The xfmr is a sds and if I understand it correctly,the secondary side would be the same as ser conductors where tap rules , 6 disconnecting means and mlo panels can be used as long as their requirements are met and in some cases the ocpd for the xfmr can be the ocpd for the secondary although I didnt fully comprehend to sizing .

 

[don_resqcapt19]

The xfmr is a sds and if I understand it correctly,the secondary side would be the same as ser conductors where tap rules , 6 disconnecting means and mlo panels can be used as long as their requirements are met and in some cases the ocpd for the xfmr can be the ocpd for the secondary although I didnt fully comprehend to sizing .

The transformer primary OCPD cannot be used to protect the transformer secondaries except for a single phase two wire to two wire transformer or for a 3 wire delta to 3 wire delta transformer. Those types of transformers are not near as common as single phase transformers with a 3 wire secondary or a transformer with a wye secondary.
I think the only provision for the use of a MLO is 240.21(C)(1) which limits the secondary conductor length to a maximum of ten feet.

 

[electricalist]

I'm trying Mr Don.
Hopefully not too bad. Its a lot to read and remember