local motor diconnects required per UL/NEC? 3

[dampflockomotive]

I can't find in NEC if I have to provide local disconnect means for 3-phase motors if MCC is in another building. Per CSA it is not required as long as you have proper lock-out features at MCC. Can anybody point me in the right direction? Thanks a lot.

 

[DRWeig]

Hiya Dampflockomotive,

Look at NEC 430-102(b). An exception permits non disconnect in motor vicinity as long as the disconnecting means for the controller is lockable in the "open" position.

That said, I disagree with it in your case -- a motor in a separate building from its controller really should have a disconnect nearby. They don't cost that much, and the NEC is a bare minimum. Put it this way, would you get yourself tangled in a motor drive, knowing that you could not visually verify that the power was off?

Let us know what you decide!

Best to ya,

Old Dave

 

[dpc]

I agree with DRWeig - the NEC exception allows the elimination of the local disconnect if the disconnect at the controller can be locked open - and I also agree that you might want to put in a local disconnect anyway. (Although I haven't checked to 2005 version yet)

Anytime the motor is a long distance from the controller, it's a really good idea to provide a local disconnect.

Imagine a worker when it's five minutes until quitting time deciding he doesn't really need to walk all the way back to the MCC to secure power to that pump or fan before he sticks his hand somewhere he shouldn't.

 

[RRaghunath]

I agree with dpc and DRWeig that the surest way to be safe is to have local disconnect for the motor.

A lockable emergency push button in the local to the motor with its contact wired in the motor breaker / contactor closing circuit does ensure adequate safety and may be a simpler alternative.

 

[dbaird]

I agree with all the above.

"Food for thought"-------> NEC 430-107. "One of the disconnecting means shall be readily accessible"

I don't consider located in another building as being "readily accessible"!!



David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[rbalex]

I'm not sure which edition of the NEC applies to your application; but, beginning with 2002, the 430.102(B) Exception is far less generous than it has been. You will need to make sure your application is covered by one of the two “conditions” noted in it.

Don’t count on condition (a) to cover you as much as you would like; despite FPN 1, “impracticable” virtually means “impossible,” so unless you can justify “increased hazard,” it probably doesn’t apply. Most industrial facilities don’t have adequately ” written safety procedures” to apply condition (b) either.

A local push button, lockable or not, is not acceptable. It is not a controller disconnecting means per the definition in 430.81(A) since it does not interrupt “motor current.”

I’m fairly familiar with these requirements. I was on Code Making Panel 11, during the 1996 NEC Edition and I’ve regularly been part of the ongoing debates since then.

 

[dpc]

rbalex is correct, the exceptions were tightened in 2002. I think most industrial facilities assume they fall under condition (b). Most have some type of written safety procedures, even if no one actually pays any attention to them.

I've attended safety workshops where the experts talked as if this entire exception had been virtually eliminated, but that's not how it reads to me. If the plant manager shows the AHJ a big thick safety manual, I don't think he is going to really question it too much further, especially since it has been an accepted practice for so long.

BTW, I agree that a local "Lock-out" pushbutton in no way meets local disconnect requirement. In many ways, these create greater hazards, by instilling a false sense of security.

 

[RRaghunath]

Thanks rbalex, I am educated.