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 Post subject: Control Cabinet Lighting
PostPosted: Tue Apr 01, 2008 6:33 pm 
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An engineer I work with tells me that due to arc flash codes, I can not put 115 VAC lights in my control cabinet and feed them from a source outside the cabinet (i.e. the lights would still be on when the main 460 VAC cabinet disconnect was off). Is there some area of the code that would deal with this issue or does anyone have an experience with this?


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PostPosted: Wed Apr 02, 2008 5:41 am 
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Location: Charlotte, NC
I cannot think of a major issue with a separately fed 120 vac cabinet light and I doubt that the code folks would expect you to work in a dark de-energized enclosure. The fact that the light is fed from a different and possibly smaller ie. limited source could imply no arc flash hazard with the circuit anyway. I would ask for clarification from your guy. Makes me wonder what level of PPE would be required to change a light bulb? I can see the cartoon already.....3 guys in full flash gear, one to hold the bulb and two to turn the chair!

I guess your guy might be saying that as long as the light is energized the enclosure has not been placed in an "electrically safe" condition? If so, leave the light out of the enclosure, plug a drop light into the same 120 vac source and hang it in the enclosure when you are working. Am I missing something here?

Alan


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PostPosted: Wed Apr 02, 2008 10:04 am 
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You are correct. He says that, per code, you need ppe to change a light bulb. With regards to the control cabinet, he says that if any power is on inside the cabinet, that the PPE for the cabinet must be based on the largest risk (i.e. the 460 VAC input), even if the main cabinet disconnect is off. He wants to put a bunch of lights outside the cabinet, which is more expensive and very inconvienent.


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PostPosted: Wed Apr 02, 2008 4:27 pm 
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If the 460 is not live in the cabinet at all, and verified, ie. "electrically safe" then I don't see how you could need to be concerned with an arc flash from that source. After all, the purpose of de-energizing the gear is to eliminate the hazard. If this is the case then I would have to disagree with your guy's opinion. Maybe we can get someone else to show us what we are missing.

Do you still have exposed and live bus in the gear that would qualify as the work being done inside a PPE required boundary? If this guy is saying that you need PPE to change a light bulb, then something else must be going on here.

Anybody else have an opinion?

Alan


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PostPosted: Thu Apr 03, 2008 6:45 am 
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I believe NEC requires a label to indicate that the cabinet has power from two sources. As for Arc Flash, as long as you wire the light with no exposed terminations, which I doubt you would do today anyway, then when the 480 is off you have no live work parts. There is nothing to say you can't have energized 'insulated' circuits in the cabinet. IE, you could stick your bare hand with no arc flash into a cluster of insulated wires in a wireway - should you choose to.


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PostPosted: Fri Apr 04, 2008 8:18 am 
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PPE to change a bulb?

Article 100 of the 70E contains Definitions. Among them are those for "energized", "exposed", you get the idea. The definition for "exposed (as applied to live parts)" in Article 100 is "Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated or insulated".

The 70E goes on to define the flash protection boundary as "an approach liit at a distance from exposed, live parts....". If your light doesn't have parts that are "exposed" while they are "live", or vice versa, you can change the bulb in your underwear. Assuming of course that you aren't operating inside the flash protection boundary of some other nearby device.

As far as the other issues you have described, I can't imagine why your engineer would assert that you can't have a light inside the enclosure powered by a separate source. Ask him where in the code he found this reference. He may giveyou the standard engineer answer "Because I'm an engineer and you're not" but don't let him get away with it. I believe he's mistaken.


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PostPosted: Fri Apr 04, 2008 9:24 am 
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PPE to change a bulb?

Dave,

Thanks for the input. I totally agree and it should go without saying that a "because I said so" answer from an engineer, tecnician, electrician, or anyone else.....except of course maybe the boss should never be accepted as reason. One would hope that the main focus of any site review will be to improve safety as necessary, insure code compliance, and allow folks otherwise to do their jobs without unnecessary restrictions and cost to the client.

While I agree that a placard is often prudent for control power supplied from a separate source, this by itself does not imply that an arc flash issue exists with the installation, and I am not sure that a light bulb would require placarding.

Ya think I should go ahead and start working on the cartoon?

Thanks,
Alan


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PostPosted: Mon Apr 07, 2008 10:47 am 
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Shoot yeah!

Alan,

Is it gonna be Dilbert style? There was a Dilbert strip last week where the pointy haired boss asked Alice (one of the office women) to interview a job candidate. In the second frame she's asking the candidate why he left his last job, and his response is "I punched my boss".

In the last frame, Alice is in front of the pointy haired boss's desk where she says "He's exactly what we need."

Much funnier if you're looking at it rather than reading my account of it. But you get where I'm going...


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PostPosted: Mon Apr 14, 2008 6:05 am 
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I don't have anything really to add. If there is proper identification that there is two sources and the 480V source is electrically safe then the engineer you are talking to either doesn't know the situation (poor communication) or has pointy hair.

And for the strip Dave was mentioning, see below for your viewing pleasure


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