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Old 02-17-2009, 09:10 AM   #1
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NEC omissions


If the NEC and the AHJ is silent on some issue, e.g., I don't know, like putting a small fan in a resi. panel to equalize CB temperatures by circulating the air in the panel, is anyone allowed to install this fan?

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Old 02-17-2009, 09:12 AM   #2
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no. NEC covers this by specifying that no device or material is to be used for a purpose not specified by its UL rating.

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Old 02-17-2009, 10:51 AM   #3
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no. NEC covers this by specifying that no device or material is to be used for a purpose not specified by its UL rating.
So far, so good.

http://www.nhpa40.org/b2b/pics/Computer_Fan.jpg
If this fan is UL listed to move air within a certain ambient temp, then it's OK to use?
I can't imagine UL anticipating every possible usage of their listed products (unless they have some catchall phrase that prohibits "other usage").
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Old 02-17-2009, 12:04 PM   #4
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Originally Posted by Yoyizit View Post
If the NEC and the AHJ is silent on some issue, e.g., I don't know, like putting a small fan in a resi. panel to equalize CB temperatures by circulating the air in the panel, is anyone allowed to install this fan?
Why would a fan like this be necessary? In a properly wired panel with good connections is there any substantial temperature rise? Maybe if it is very heavily loaded?
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Old 02-17-2009, 01:28 PM   #5
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Why would a fan like this be necessary? In a properly wired panel with good connections is there any substantial temperature rise? Maybe if it is very heavily loaded?
Jamie
It would not be needed. Cooling is not needed in a breaker panel.
It would void the testing and approvals of the panel not the fan. The panel is encolsed to contain any fire. The fan would let the fire out in the slim chance there was a fire. It would also fan it and make it more intense.
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Old 02-17-2009, 02:08 PM   #6
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A guy is having occasional breaker trips with an HVAC system. The fan, not vented to the panel outside, might let him squeak by by equalizing the hot breaker temp.
Another way would be to hand select breakers that trip on the high side of the tolerance band but that method is not too practical.

Design revision A; wire a NC overtemp switch in series with the fan.

Last edited by Yoyizit; 02-17-2009 at 02:10 PM.
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Old 02-17-2009, 02:25 PM   #7
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A guy is having occasional breaker trips with an HVAC system
He needs to diagnose and address the problem not treat the symptoms.

If you car leaks coolant, you don't duct tape a bucket under it to catch the fluid then pour it back in every day.
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Old 02-17-2009, 02:31 PM   #8
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Bad compressor valves, short cycling, installed the minimum vs. max OCPD?
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Old 02-17-2009, 05:52 PM   #9
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It's so infrequent and seems to have to do with the Aux heat having to come on with his 3C nighttime setback, that maybe 1 out of 5 breakers picked at random might work for him, but there is no practical way to do this experiment.

We'll see what clamp-on meter says.
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Old 02-17-2009, 08:45 PM   #10
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I thought this was a hypothetical question. I have to start reading more carefully!

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Old 02-17-2009, 11:10 PM   #11
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One of the local casinos I work at occasionally had a 2000 amp 480 volt breaker trip one day. Their solution was to remove the cover, and place a fan to blow cool air at the breaker. A few days later, me and 3 other guys were replacing a 1500KVA transformer. It weighed about 6000 lbs. It wasn't fun.

I build industrial control panels occasionally, most of them have some sort of cooling system. It can be a simple fan, or an A/C unit specifically designed for the purpose. The biggest problem I have with any type of fan in a control cabinet is dust getting all over EVERYTHING. Even if it's in a clean area, and filters are changed regularly, it still gets in.

The fans, etc. in the control panels are because there is heat producing equipment inside, not to keep a breaker from tripping. Sometimes, you'll see fans connected to large industrial panels, motor control centers, and such, that are installed in dusty environments. The fans are always outside, and their purpose is to maintain a slightly positive air pressure in the panels. This way, dust cannot get in. (It does anyway though, just not as much.)

It shouldn't be too hard to figure out why the breaker trips, and solve the problem once and for all.

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Old 02-17-2009, 11:21 PM   #12
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If the AHJ is silent on this scenario, they're dropping the ball. It should be prohibited unless both the panel and the fan are listed for use in conjunction with each other.

Just because the NEC doesn't expressly prohibit something doesn't mean that you can do it.
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Old 02-18-2009, 10:04 AM   #13
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It should be prohibited unless both the panel and the fan are listed for use in conjunction with each other.
I'm thinking no fan. . .thanks, folks. . .
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Old 02-18-2009, 12:33 PM   #14
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Computer fans are never UL listed.

Components can have the RU recoginized component mark, but never get a UL mark.
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Old 02-18-2009, 12:56 PM   #15
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I think the problem is solved. There were other loads on that same 100A breaker. Rewire!

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