# Transformer Disconnect



## RePhase277 (Feb 5, 2008)

Hawk said:


> Question is: There is a 400A breaker in the switchgear feeding a Transformer on the second floor. (480/120-208, 800A) Does there need to be a disconnect switch (non fused) on the primary at the location of the transformer for servicing?


I say yes. I don't know a code reference right off hand, but I know that disconnecting means isn't covered in article 450. But I have never installed a transformer that was remote from its supply without a disconnect. To me, it is like any other piece of equipment. It needs a disconnect within sight and within 50'.


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## william1978 (Sep 21, 2008)

No...............


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## william1978 (Sep 21, 2008)

Just on the secondary side within 25'.


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## raider1 (Jan 22, 2007)

I agree with William, no.

A transformer requires primary overcurrent protection in accordance with 450.3. This overcurrent protection for the primary of the transformer does not need to be within sight of the transformer.

An overcurrent device will likely be required for the secondary conductors either within 10 or 25 feet in accordance with 240.21(C)(1) through (6).

Chris


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## RePhase277 (Feb 5, 2008)

But when this thing is on boiling smoke and hopping around, do you really want to have to run down two flights of stairs to kill the power? I think the right thing to do, whether it is required or not, is to have a primary disconnect if the tranny isn't in the same room with the panel that feeds it.

Now, if this is an existing installation, I wouldn't go trying to insert a disco.


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## bobelectric (Feb 24, 2007)

I wouldn't want to be a hero.That's why they want main breakers or fusible protection .I'm running to safety.


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## Hawk (May 12, 2009)

I know over current protection is not required at the remote electrical room. I am referring to service disconnect means. Like InPhase277, I have always included the disconnect, usually because it is on the drawings. This remote is a small two story building, but "what if" it was a large department store or multilevel office space. I have searched and cannot find where a disconnect is required. It seems odd.


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## william1978 (Sep 21, 2008)

It does seem odd, but it is not required. Put a disconnect in if you would like, but it isn't required. Installed one a few years ago and the disconnect was about 500' away.


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## raider1 (Jan 22, 2007)

InPhase277 said:


> But when this thing is on boiling smoke and hopping around, do you really want to have to run down two flights of stairs to kill the power? I think the right thing to do, whether it is required or not, is to have a primary disconnect if the tranny isn't in the same room with the panel that feeds it.
> 
> Now, if this is an existing installation, I wouldn't go trying to insert a disco.


To me a transformer is no more likely to have an issue than a panelboard, I don't really see a need for a disconnect within sight of a panelboard or a transformer.

Again there is no NEC code section that requires a disconnect within sight of a transformer.

Chris


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