When is it necessary to install a disconnect for a transformer?

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jonny1982

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Does anybody know when it would be necessary to put a disconnect in for a transformer? Can the breakers from the panels count, or are there situations when a disconnect is needed?

Thanks
 
jonny1982 said:
Does anybody know when it would be necessary to put a disconnect in for a transformer? Can the breakers from the panels count, or are there situations when a disconnect is needed?

Thanks
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Untill 2011it wasn't. It still isn't if you put a label on the transformer telling folks where the breaker that feeds the transformer is.
 
The disconnect can be the circuit breaker as long as long as the location of the device is labeled on the transformer and the provisions for disconnecting means as prescribed in 110.25 are followed.
 
While the primary disconnect is most often the OCPD for the primary and can be located anywhere as long as there is a sign at the transformer giving the location of the disconnect, the rules in 240.21(C) for the protection of the secondary conductors almost always results in a secondary disconnect (OCPD) within 25' wire feed of the secondary termination points in the transformer.
 
Just want to verify something.

Just want to verify something.

The city I mainly work in is still working under the 2008 NEC. As long as I label the transformer with the location of the breaker or disconnect - I do not need a disconnect on the primary side of the transformer.
 
Just want to verify something.

Just want to verify something.

Let me give you some more info. I have a 277/480 V MDP on the exterior of the building. They have added a 277/480- 120/208 Step Down Transformer on the roof to feed some equipment. We will install a disconnect on the secondary side of the transformer but i want to know if the breaker in the MDP is an ample disconnect if i label the transformer with the location of the breaker in the MDP.
 
Under the '08 Code, there is no requirement for a primary disconnect means or labeling.
As noted above, later Codes did add requirements.
The requirement for secondary disconnect (over current device) is determined mostly by the transformer secondary rules in 240.21(CF). In most cases you are limited to 25 ft of secondary conductors prior to an overcurrent means.
You might also check 250.30 for your grounding requirements.
 
If you don't put a disconnecting means within sight of the transformer,not only does the location of the remote disconnecting means have to be marked on the transformer,the disconnecting means at the remote location has to be "Lockable" also.

<JAP>
 
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