Running Conduit?

[JoeyD]

Did you know you can not run more than 3 current carrying cables in one piece of conduit? I just learned this as we were looking to increase our knockout size on our new top secret transformer. No point in having a 2" knockout if you can only legally pull 3 wires through it!! Just thought I would share to all you information junkies!!

[Mike M]

Holy crap. I was just completely impressed with the conduit I saw at FOLD in Orlando, that came with the new CAST transformers. I figured, great, just put all the wires up one big conduit.

Great info, Joey, thanks.

Is that an NEC thing? Must be. Not a manu or product issue, but an installer issue.

[Supper Grassy]

Joey nice pic in yor sig.

[JoeyD]

Mike, yes it is an NEC thing, I can dig it up if others want to dispute it.....

Thanks Supper Grassy, we're going to shoot this job one more time and work out some of the hot spots but yeah its coming out nice!! Believe it or not the lighting isnt done!!

[stumpjumper]

The only stipulations I'm aware of concerning the number of current carrying conductors in conduit is that if you have more than 3 then you have to derate your wire ampacity according to the charts in the code book. Without dragging out my code book I believe the charts are in section 319.

[JoeyD]

Alright stumpjumper, your gonna make me get that damn NEC book out again...First off you are correct about having to deregulate the wire if you run multiple current carrying cables in one piece of conduit. Thanks for helping me clear this up!!

So here it is......

NEC Article 310.15 2 (a)?
.........More than 3 current carrying conductors in a raceway or cable. Where the number of C-C Conductors in a raceway or cable exceeds 3, or where single conductors or multiconductor cables are stacked or bundles longer than 24" without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in table 310.15(B)(2)(a). Ea. C-C conductor of a paralleled set of conductors shall be counted as a c-c conductor.

So in a nut shell table 310.15(B)(2)(a) says......

if you have 4-6 C-C Cond. you can only use 80% of that cables rated ampacity..so if using 12ga that would be 12amps I believe.

7-9 C-C Cond. you can only use 70% of the cables rated ampacity....

and so on and so forth.......So you can run more but now you have to de regulate the cable quite a bit! In our opinion it is better to just use 2 or 3 smaller conduits and run no more than 3 in ea. of them.

[stumpjumper]

My calculation on no. 12 comes out to 16 amps. at 80%. It's a question of which is the most economic on whether to use more runs of smaller pipe or bigger pipe and derate the wire. If the individual loads are less than the derated wire ampacities than bigger pipe is usually cheaper.

[JoeyD]

You have to de regulate the wire to 80% anyway even if you run only 1 wire, I think once you run it into a conduit with 4-6 you have to deregulate it again which would bring it to 12amps. This seems stupid but I think it is correct because as you run more wires in one conduit the heat builds. In most cases I think we are just fine with the way it has been done, but as many of you know at any time an inspector can call you out on the stupidest of things, and it goes by their interpetation which this is exactly how it was interpeted to me by the NEC expert I spoke with.

[stumpjumper]

No you don't derate the wire until you get above the 3 energized wires, and nuetrals are counted as current carrying conducters. You also must take into account the different temperture ratings of the wire type. Such as THN rated as a 70 degree C. wire and THHN rated as a 90 degree C. wire. The derating table columns are titled "More than 3 current carrying conductors in conduit". And you're right on about the inspectors, I argued interpertations of the code book with them for 25 years, it's like mud wrestling with a pig. There is I believe a paragraph that states branch circuits should not be loaded at more than 80%, but to my knowledge this doesn't affect the wire ampacity rating and should not fiqure into the calculation.

[Firefly Prof. Lighting]

I hate a lot of small conduits running into my trannys, I like one big one, it is so much cleaner. Thanks a lot, you just ruined my day. Why did I have to look at this thread, now I will have to do it correctly.:cry:

[irrig8r]

Has anyone ever considered more of a "pedestal" design for transfomers as are commonly used for freestanding irrigation controllers?

In other words, instead of a need for separate conduits, then just one "cabinet" with a locking hinged door that goes all the way to the ground, and the TF sitting on top... kinda like these from Superior, Irritrol, AquaConserve and Rainmaster...

http://www.superiorcontrolsco.com/products/sterling_ped.jpg

http://ecx.images-amazon.com/images/I/21CGS3J2K4L._AA280_.jpg

https://www.aquaconserve.com/images/et16usp_med.gif

http://www.rainmaster.com/DWG/500502B.gif

[JoeyD]

Could be a cool idea Gregg. We could build a 5000w unit that would power all lights on the job. Run voltage taps from 11 all the way to 30v then you could power up lights anywhere you want on any size property....you may be onto something!!!

[TXNSLighting]

I like that idea!

[irrig8r]

If you would seriously consider this Joey, keep in mind that they usually sit on a poured concrete base. You could either run sweep ells though the concrete and into the cabinet, or leave an opening at the bottom to pull wires through.

But I think I might have a better idea:
Design it to mount to a precast concrete Christy box. Get them to make one for you to your dimensions w/ SS bolts and wire openings already cast in place...

An electrician could pull line voltage to a receptacle inside the cabinet, and the whole think could be locked up nice and secure.

Not sure how this would perform in areas where they have frost heave... or whatever they call that, but it would work in a lot of places. Set it in a bed of gravel....

Of course, if it was in the middle of hardscape then you could run lots of conduit to it...

[JoeyD]

This is a very cool idea Gregg. I a going to make sure we toss this idea around on Friday at our product meeting!!!

Thanks!!

[Mike M]

While you are at it, get a nice stainless steel bar stool for it, too. Some foot pedals for effects.

[irrig8r]

While you are at it, get a nice stainless steel bar stool for it, too. Some foot pedals for effects.

Mike, I don't think your clients would have any reason to confuse it with their outdoor refrigerator.... for one, they wouldn't find any cold beer inside.

(But why foot pedals?)

My idea was to leave more space for wiring, and to secure cables, power cords and receptacles all in one locking cabinet.

Obviously not for every job. But quite possibly appropriate for some larger ones. Think bigger Mike.

[JoeyD]

Hey Gregg, so coincidentaly I go to Nate and say Gregg Cantanese had a cool idea we should toss around. So I explain and show him your post, he laughs and says follow me. So we walk into his office and there stands one of those irrigation control boxes like you posted above. He said I got one from a local supplier about a month ago. You know what they say, great minds think alike! I will keep you posted as to how the development goes!

Joey D.

[NightScenes]

When it comes to conduit, you also need to look at the fill chart. larger conduits allow for more current carrying conductors.