Transformer disconnects?

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Nickarus

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At some point in my education, I believe I read NEC Section 110.58 and burned into my memory that ALL motors and transformers should have a disconnect/breaker located on the primary/supply side of the equipment within sight, for safety reasons.

I realized this week that that section is specifically for "Tunnel Installations over 600 Volts, Nominal" (the header for this section - doh!).

That said, my current understanding is that transformers do not require, by code, a disconnecting means on the supply side within sight of the transformer.

HOWEVER... Is it still a smart idea from a safety perspective?

When a transformer needs servicing, perhaps it isn't a big deal to find the disconnecting means elsewhere in the building... but do transformers fail in dangerous ways that would make an electrician think "WHERE THE HECK IS THE DISCONNECT?"

Thanks in advance =)
 
charlie b

charlie b

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Required? No. Good idea for safety reasons? I suppose so. But keep in mind that disconnecting means are not intended to be operated as an emergency shutoff. If a transformer were on fire, it would be really nice to walk a few feet over and turn off the power by operating a breaker or disconnect. But nothing requires us to have that ability.
 
augie47

augie47

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not trying to negate the possible advantages of a disconnect being close-by, but your statement:"When a transformer needs servicing" did make me grin. Purely a guess on my part, but ones based on many years experience. I would think 95% of the dry-type transformers in service today have never needed servicing and wont until removed from service.
 
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Nickarus

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augie47 said:
not trying to negate the possible advantages of a disconnect being close-by, but your statement:"When a transformer needs servicing" did make me grin. Purely a guess on my part, but ones based on many years experience. I would think 95% of the dry-type transformers in service today have never needed servicing and wont until removed from service.
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This is the sort of perspective I needed =).

I suppose I'm trained to always plan for the worst case (the 5%) when it comes to safety concerns, but it sounds like this isn't something I should be paranoid over when designing systems.

And Charlie, I believe you hit one of the roots of my issue with this... I generally think of disconnecting means first as a "emergency shutoff" safety feature, then secondarily as a means of servicing equipment (like tinkering with a motor). It sounds like I need to revisit this and think "backwards:" "Servicing means" first, then sometimes as an "emergency situation" device.

Thanks very much!
 
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petersonra

petersonra

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Northern illinois
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engineer
augie47 said:
not trying to negate the possible advantages of a disconnect being close-by, but your statement:"When a transformer needs servicing" did make me grin. Purely a guess on my part, but ones based on many years experience. I would think 95% of the dry-type transformers in service today have never needed servicing and wont until removed from service.
Click to expand...
and I suspect that many transformers that might need an emergency shutdown are situations where you would want the disconnect some distance away. :)
 
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