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Joined: Jun 2004
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Such matters are decided by the Fire Marshall in most jurisdictions.

It's not to be found in the NEC.

Other building codes may address it.


Tesla
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Building inspectors here determine egress illumination, both day/nite, occupied/unoccupied, and emergency. Determinations are based on the 'Use Group' & occupancy of the structure. Also, if the path is used by other occupants of the structure in multi-tenant occupancies.

It is also a 'design' issue; to provide illumination for security reasons.



John
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Thanks, that's kinda of what I thought. In the rest of my explanations, I'll just make a recommendation that if they want to save on ballast etc.. they install some unswitched lighting. I'll try to come up with the simplest way to remedy their problem. Of course the simplest short term way is just to replace the bad emergency ballast, but the chance of overheating the #12 wires, ballast and the bulbs may become a problem later. I still haven't presented it all to them yet:)

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I know the effects of voltage drop will shorten the life of the ballast etc., but what is your opinion of the damage to the wires and possibility of fire hazard in this situation. This will be a very involved job to change any of the wiring. I need my facts together before I present them to the customer. They will be taking my word for this, since there is no one knowledgable at these offices.
Thanks again. Steve

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Steve:

IF the circuitry is #12 and has a 19 amp load, eventually (real world) there could be heat damage to the insulation, leading to a L/L, L/N, or L.G short. Understand, 'long term'.

You may want to stress the fail rates of the e-ballasts units ($$$) and the possibility of fines ($$$$) from the local fire officials as a reason to correct the issues. Our Fire Official has a violation book with a lot of $$$$ fines.

Scott35 probably has facts on the heating issues that are more in depth than my 'street' version.



John
Joined: Mar 2011
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Originally Posted by HotLine1
Steve:

IF the circuitry is #12 and has a 19 amp load, eventually (real world) there could be heat damage to the insulation, leading to a L/L, L/N, or L.G short. Understand, 'long term'.


I saw reference to this earlier, but can't see the reasoning why since #12's are rated for 25 amps, they should be fine loaded to 20 amps indefinitely.

The devices connected to it may not be, but the wire will be fine with the full load heat.

Last edited by Vindiceptor; 11/02/11 04:38 PM.
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Vin:
Yes, by the chart, but it is max 20 amp OCP! Now, this being a continuous load, comm lighting; that's down to 16 amps max load.

As mentioned within this thread by others; the design intent may have been 277 volt, and there was oversight by the installer & others it seems.

Yes, as I implied #12 will survive, perhaps for a long time, but...it is not compliant.


John
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Originally Posted by HotLine1
Vin:
Yes, by the chart, but it is max 20 amp OCP! Now, this being a continuous load, comm lighting; that's down to 16 amps max load.

As mentioned within this thread by others; the design intent may have been 277 volt, and there was oversight by the installer & others it seems.

Yes, as I implied #12 will survive, perhaps for a long time, but...it is not compliant.


Ahh, but #12's are compliant.

OCP has no bearing here on the #12's, their allowed ampacity is still 25 amps regardless of OCP and 80% of 25 is 20, so compliant they are, as long as the circuit ampacity doesn't exceed 20 amps (connected).

The OCP IS overloaded though whether by accident or design (unless it is fully rated, doubtful).

Last edited by Vindiceptor; 11/02/11 06:27 PM.
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Vin...

We're not allowed to use the 25 Amp rating for this calculation. It must start at 20 Amperes.

The 25 Amp rating can only be used for derating calculations such as multiple conductors and WRT certain motor load calculations.

One aspect of this that is normally overlooked is that these branch conductors are typically installed where shedding heat is not favorable. ( It's a lot warmer up high and when sandwiched within walls. That's why the Code kicks in an extra derating.)

Another aspect is economics. Taking the conductor up to its limit is VERY poor economics for the building's owner.

In all of the commercial contracts that I've dealt with it has been mandatory for the EC to bump up all homeruns to #10 ... and to #8 for site lighting runs when specified.


Tesla
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Tesla:

Thank you!


John
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