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Derate this........ #77897
07/20/01 11:39 AM
07/20/01 11:39 AM
Jim W  Offline OP
Junior Member
Joined: Jul 2001
Posts: 7
I agree the code teaches derating, but in real world practice I have seen many ignore it. I mean you would have to run multiple conduits for simple things like wall outlets ect. Matter of fact in code class many working electricains were just as shocked as I was by how much you must derate. Looking backwards at that point I saw several projects not derated admittley out of my own ignorance, the wire fill for conduit is useless when you cross it with the derating table, your wires are rated down so much long before the fill is reached (when dealing with smaller conductors #14-10#).
That said on any future designs I will derate for safetys sake!, but I to tryed explaining this to my boss and it was just easyer to run 2" emt and stuff it full. Sorry guys but thats what happened and does happen. Like I say I now know better.
Also running seperate conduit for control wiring is like pulling teeth.
When I talk about control wiring I mean, from thermostat to relays and so on, I know its good to put them in a seperate conduit yet..., I work commercail, radio, tv, broadcast stations, better yet run the suckers in the open much quicker if below 60 volts throw them across that false ceiling. Strap them to the outside on the emt along with the cat 5 ! Ha Ha Ha.
Ive seen 2" emt stuffed with 30 wires no derating.
Like I say the fill tables are a joke, if you derate why would you fill that conduit up? You would not. Run 10 3/4" pipes instead that way you can have 3-6 wires in a stick. Ha Ha would'nt that look nice. And remember you can not use conduit to support conduit! Those 10 pipes be hanging all over the place!
Little off the wall tonight but you get the idea, about what a shock these derating tables are.

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Re: Derate this........ #77898
07/20/01 05:02 PM
07/20/01 05:02 PM
gpowellpec  Offline
Joined: Dec 2000
Posts: 127
Irving, Tx USA
I came up doing industrial work. Did a lot of Motor Control Centers in my younger days and wondered why the motor feeders were all run in individual conduits (RGS or Aluminum) instead of trunk runs. When I came to the requirement for derating due to number of conductors in raceway while studying the Code it became obvious. By the time you upsize the conductors to run one trunk for a number of circuits, then upsize the conduit for the oversize wires you will have a lot of money in extra copper, and the larger sizes of conduit increase in price at a greater proportion than the volume does. Not to mention the labor for the extra weight of the copper and conduit. And fittings. How many 3/4 inch LBs can you buy for the price of one 2 inch LB?

Re: Derate this........ #77899
07/20/01 07:17 PM
07/20/01 07:17 PM
electure  Offline

Joined: Dec 2000
Posts: 4,280
Fullerton, CA USA
There certainly is a point of diminishing returns on the "pipe stuffer" method.
Jim, I think one of these days your boss will get burned by an inspector, or worse.
If one of his jobs cooks, and he loses $$, maybe he'll wake up.
. Best of luck to you, & kudos for trying to do the right thing.

Re: Derate this........ #77900
07/20/01 09:49 PM
07/20/01 09:49 PM
sparky  Offline
Joined: Oct 2000
Posts: 5,372
the diligent sparky, or so i was told, that meets the code MINIMUM eats best.

your boss eats best Jim.

but just for now....

in my idealistic fanatsy 5 star NEC inspectors will be hiding behind every corner to take him down.


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