Definition of "locked"

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paddyp

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Dear friends

We are designing a medium voltage electrical junction box for an outdoor industrial application, and we're arguing amongst ourselves whether a 1/4 turn cam lock as commonly used on electrical cabinets would meet the requirements of Article 110.21, part D of NEC 2008:

Doors and covers of enclosures used solely as pull boxes, splice boxes, or junction boxes shall be locked, bolted, or screwed on.

Strictly speaking, these cam locks render the door "locked" because a special key is needed to open them. In my opinion, however, it's too easy to open these locks without the key (using a pair of pliers for example), so we will add a facility for a padlock or even a mechanical interlock. The question becomes academic, but would 1/4 cam locks be considered sufficient for this kind of application?

I look forward to reading your comments.

Best regards
 
I would say a lock is a lock, who is really going to try to break into this junction box anyway? and if they were determined to get into it by bypassing the lock by jacking with it with a pair of pliers, they would probably pry off a hasp with a claw hammer also. I have never had to lock a junction box, but if I was concerned about someone messing with it, I would probably just use some tamper resistant screws.
 
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It appears that the real requirement is that you need some type of tool to open the box. I think the 1/4 turn cam lock would meet the requirement just as well as a screw or bolt.
 
The following if from 110.31(D) and all the highlighting is mine. "Where exposed to physical damage from vehicular traffic, suitable guards shall be provided. Nonmetallic or metal-enclosed equipment located outdoors and accessible to the general public shall be designed such that exposed nuts or bolts cannot be readily removed, permitting access to live parts. Where nonmetallic or metal-enclosed equipment is accessible to the general public and the bottom of the enclosure is less than 2.5 m (8 ft) above the floor or grade level, the enclosure door or hinged cover shall be kept locked. Doors and covers of enclosures used solely as pull boxes, splice boxes, or junction boxes shall be locked, bolted, or screwed on."

The last sentence seems to apply as you stated in your original post since the highlight parts I pointed out only apply to equipment. If I am not mistaken, the NESC and the NEC are basically the same on this issue.

I know that the NESC doesn't apply to you. However, the NESC requires two means of locking medium voltage equipment. Normally, a penta-head bolt is the first method where it is recessed or a guard is built up around the head. The second method is a padlock that is normally locking the cover as well as blocking access to the penta-head bolt.

Remember that you said this is medium voltage so you are dealing with voltage levels that are greater than 1 kV, but less than or equal to 69 kV. In my opinion, you should do the same as we are required to do for equipment even though it is not required. :smile:
 
Firstly, to those who have responded, thank you very much for taking the time to do so - greatly appreciated! :smile:

Charlie, you indicate that NESC doesn't apply to us, but since we will be supplying this equipment into the US market, maybe it does? To be honest, I had never heard of NESC until today, so it looks like I may need to invest in some more literature...
 
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