Disconnect Door Interlock

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k947

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Pa
I see door interlocks on disconnects where the disconnect must be in the open (off) position in order for the door to be opened up and allow access to the interior. I can not find any where in the 2008 code where this is required. Is it a NEC requirement, UL or NEMA ? Also, where would I find that standard ? I have looked at various places and cannot locate it in writing anywhere.

Thanks for your help

Kermit
 
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Gregg Harris

Senior Member
Location
Virginia
Occupation
Electrical,HVAC, Technical Trainer
k947 said:
I see door interlocks on disconnects where the disconnect must be in the open (off) position in order for the door to be opened up and allow access to the interior. I can not find any where in the 2008 code where this is required. Is it a NEC requirement, UL or NEMA ? Also, where would I find that standard ? I have looked at various places and cannot locate it in writing anywhere.

Thanks for your help

Kermit
Click to expand...

Try UL 508A
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
k947 said:
I see door interlocks on disconnects where the disconnect must be in the open (off) position in order for the door to be opened up and allow access to the interior. I can not find any where in the 2008 code where this is required. Is it a NEC requirement, UL or NEMA ? Also, where would I find that standard ? I have looked at various places and cannot locate it in writing anywhere.

Thanks for your help

Kermit
Click to expand...
Why would you NOT want a door interlock on a main disconnect? Any decent electrical safety program, which IS now required by OSHA, must include a provision that prevents access to live electrical equipment by unqualified people. That's what that mechanism accomplishes.
 
K

k947

Member
Location
Pa
Gregg Harris said:
Also look at NFPA 79 article #5 and 6
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We do want door interlock. A piece of equipment came into the customer without an interlock and we said it came in wrong. Now we have to have documentation for the owner that it is wrong and we are trying to find where it is in writing that a door interlock is required.

Thanks
 
G

Gregg Harris

Senior Member
Location
Virginia
Occupation
Electrical,HVAC, Technical Trainer
k947 said:
We do want door interlock. A piece of equipment came into the customer without an interlock and we said it came in wrong. Now we have to have documentation for the owner that it is wrong and we are trying to find where it is in writing that a door interlock is required.

Thanks
Click to expand...

What is the piece of equipment?
 
M

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Jraef said:
Why would you NOT want a door interlock on a main disconnect? Any decent electrical safety program, which IS now required by OSHA, must include a provision that prevents access to live electrical equipment by unqualified people. That's what that mechanism accomplishes.
Click to expand...

Then why do most have a "defeat mechanism" that only takes a screwdriver to open it with the switch closed? Just curious. I'll bet even unqualified folks can use a screwdriver.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
meternerd said:
Then why do most have a "defeat mechanism" that only takes a screwdriver to open it with the switch closed? Just curious. I'll bet even unqualified folks can use a screwdriver.
Click to expand...
The accepted issue there is that one must have a tool in their hand, which makes it a WILLFUL effort to open the enclosure with the power still on. You can't accidentally open it in trying to steady yourself, or casually open it just out of curiosity while walking by.

The NEC is a little loosey-goosey on this, but there are generalized requirements for preventing casual access. Check out 110.34.C, 430.232. Not exactly condemning the omission of door interlocking, but it does imply that it must be safely done.

But NFPA 79 however is very clear.
5.3.1.4 Supply circuit disconnecting means mounted within
or adjacent to the control enclosure shall be interlocked with
the control enclosure in accordance with 6.2.3.

6.2.3.1 Each disconnecting means mounted within or adjacent
to a control enclosure that contains live parts operating at
50 volts ac (rms value) or 60 volts dc or more shall be mechanically
or electrically interlocked, or both, with the control enclosure
doors so that none of the doors can be opened unless
the power is disconnected. Interlocking shall be reactivated
automatically when all the doors are closed.
Click to expand...

NFPA79 is the Electrical Safety Standard for Industrial Machinery. So if your equipment is not considered "industrial machinery", they may be able to make an argument for their omission. However, any AHJ could decide otherwise and you might be left holding the bag.
automatically when all the doors are closed.
 
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