# Transformer disconnect



## ecelectric (Mar 27, 2009)

My buddy has been called to install a transformer for a machine shop and asked me about the disconnect location, so here I am . He is installing a 150kva transformer for a machine the shop just purchased , the owner would like the transformer to be located near the machine rather then the electrical room . The trans will be protected by a breaker in that room . So aside from his disconnect for the equipment he was wondering if he had to have a disconnect for the primary side as well? The electrical room is not with in site in case that matters . I'm mainly a residential guy so im of no help . Thanks in advance


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## Pete m. (Nov 19, 2011)

*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 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.

Pete


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## ecelectric (Mar 27, 2009)

Would this be relevant to a dry type trans


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## Pete m. (Nov 19, 2011)

ecelectric said:


> Would this be relevant to a dry type trans


As I see it, yes. It's under part I of 450 which is titled "General Provisions".

Pete


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## ponyboy (Nov 18, 2012)

Is your buddy an electrician? Frankly, the requirements for transformer disconnecting means are the simplest part of a transformer installation. 


Sent from my iPhone using Tapatalk


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## macmikeman (Jan 23, 2007)

Like Pete pointed out, it can be remote as long as it is lockable. Also not mentioned is some installations you can use the circuit breaker serving the primary as your disconnect so long as the primary feeders and secondary turn ratio meets certain requirements also. What you won't be able to do so easily is hide away your secondary overcorrect protection, normally the secondaries are limited to ten feet in most cases before an overcorrect means must be provided. I'm making the assumption your client does not want to look at the disconnects. A panel served by a main overcorrect device is pretty common on the secondary side of a transformer. A feeder to the machine can be run from that. If looks are important. Myself, I prefer disco's on each side of the xfmr, and fused ones at that. Or molded case breakers in housings.


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## telsa (May 22, 2015)

150 kVA is a huge transformer for just one machine tool. 

May I surmise that the equipment is a European import ... and that you're shooting for 400 VAC ?

%%%

BTW, dry type transformers do not tolerate nasty conditions well. :no:


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## Pete m. (Nov 19, 2011)

I'm glad Macmikeman chimed in because he brought up some other, more important, considerations.

To the OP... make sure your friend doesn't get article 450 and 240 confused when dealing with a transformer installation.

Simply stated article 450 deals with protection of the transformer and does not consider the conductors feeding or being fed by the transformer.

For conductor protection look to article 240.

With careful design you can marry the two: transformer and conductor protection. Then your friend will also want to consult article 250.

Pete


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