transformer disconnects

[Brian Kemp]

300KVA transformer primary 480/3phse. secondary 208Y/120V. Primary from 400A 480V breaker located on mezzanine within 20 feet, access by ladder. Do I need a disconnect on the primary side? Also, must there be a disconnect on the secondary side before the load?

 

[petersonra]

300KVA transformer primary 480/3phse. secondary 208Y/120V. Primary from 400A 480V breaker located on mezzanine within 20 feet, access by ladder. Do I need a disconnect on the primary side? Also, must there be a disconnect on the secondary side before the load?

I think that the 400A CB can probably serve as the disconnect for the transformer.

I do not think that in general you are required to have a secondary disconnect. As a practical matter, you will probably run it to a panelboard with a main to meet the requirements for OCPD on the secondary side. So you will end up with a potential secondary disconnecting means even if it is not required.

 

[kwired]

300KVA transformer primary 480/3phse. secondary 208Y/120V. Primary from 400A 480V breaker located on mezzanine within 20 feet, access by ladder. Do I need a disconnect on the primary side? Also, must there be a disconnect on the secondary side before the load?

Primary disconnecting means - see 450.14.

Secondary - how about we just say the secondary conductors are more less considered feeder taps, and you will need to comply with 240.21(C) exactly what you need for protection will depend on application conditions, but a 208/120 secondary will almost always need overcurrent protection, conditions mentioned in 240.21(C) may allow variances in how long those conductors may be before they have to hit an overcurrent device though.

 

[Brian Kemp]

transformer disconnects

Ok, so since the secondary side will be to a main lug only 800A panelboard, a fusible disconnect before the panel would provide a suitable protection.

 

[Brian Kemp]

transformer disconnects

Also, the distance between the transformer and secondary load is less than 10 feet.

 

[iwire]

I think that the 400A CB can probably serve as the disconnect for the transformer.

I do not think that in general you are required to have a secondary disconnect. As a practical matter, you will probably run it to a panelboard with a main to meet the requirements for OCPD on the secondary side. So you will end up with a potential secondary disconnecting means even if it is not required.

Starting I beleive in 2011 they added a requirement for a primary side disconnecting means in sight of the transformer. They also have an exception if you label the remote location and provide a spot to lock it off.

Going from memory so take it for what it is.

 

[Brian Kemp]

transformer disconnects

Thanks for the help gentlemen.

 

[kwired]

Starting I beleive in 2011 they added a requirement for a primary side disconnecting means in sight of the transformer. They also have an exception if you label the remote location and provide a spot to lock it off.

Going from memory so take it for what it is.

It is all in 450.14 that I mentioned before.

here it is:

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 location. 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.

The reference to 110.25 was a change in 2014.

No actual printed exception there -just a requirement to do it one way or the other.