here is the setup you have several ac units all 480 volt 3 phase each unit pulls 22 amps, the runs are over 100 ft. we are running inch and a half 1 1/2" EMT inside that we are running 36 wires all #10 thhn now I am being told that I only have to derate my wires to 80 per cent?
Would you guys run this many wires in there and is this correct for derating ,I think it needs to be dropped to 40 per cent according to the derating table ,but these guys are trying to tell me that is for heating purposes only Ihave been looking at tarticle 310 on adjustment factors any feed back or am i ok at using 80 per cent

Doc,
If the units have an actual load of 22 amps the ampacity of the wire must be 27.5 amps. The ampacity of a #10 THHN in a conduit with 35 other current carrying conductors is only 16 amps. You must apply Table 310-15(b)(2)(a). The required wire size is #6 if you place all 36 conductors in the same raceway.
Don(resqcapt19)

id run 1 conduit for every 2 units,i hope your not puting your stat wires in the same pipe also.remember ac units can run for long periods of time ...i would run #8's to feed them

Thanks for the confirmation guys I have been arguing this for 2 days with my boss but due to him hiring a electric contractor and we have a journeyman on staff and they both say 310 is for heat only and since # 10 is really good for 40 amps they can still run all that wire and put the 22 amp load on it,what is sad in this whole situation is that 2 young guys are torn between believing me or the 2 guys with the liscense .As for the T-stat wires it would not surprise me if they do run them in it.I never try to argue the code but sometimes you have to so I will go at my boss again tomorrow and show him this,sure glad he is a good guy

doc,
The required derating in Table 310-15(b)(2)(a) is for heat. Every current carrying conductor produces heat and the more you put in the same raceway the more heat you have. When you limit the current that is permitted to flow in each conductor you reduce the heat produced. In many cases you also have to apply the correction factors for high ambient temperature at the bottom of Table 310-16 in addition to the derating required by 310-15(b)(2)(a).
Don

Doc,

A quick look at table 310-15(b)(2)(a) shows that there is a serious derating penaly when you hit the 10th current carrying conductor.

Besides that, it is a serious pain in the butt to deal with that many conductors in one conduit.

Just think, nine #10's each in 4 runs of 3/4" EMT. Lot easier to bend, pull wire, etc and probably cheaper (material) than the 1 1/2" conduit.

Tom

Thanks again for confirming what I have been telling these guys along with my boss,Don I even threw in the fact that there is a correction factor involved because a lot of this wiring is on top of the building where the sun is hitting it. Tom that is what I suggested in the first place which got us at ends with each other,if one wire in all of that is bad it can melt the whole bundle and boy when I said that the arguing started.NOW HERE IS a dumber move at every 4 ft roughly they are now tapping those 36 wires together. Am I the only one that works with people with a lisc that does this type of work ? don't understand how a person can just throw his knowledge away and do shoddy work

Besides derating, just for ease of use we always went for the next up on conduit size. Thhn always wants to twist depending on the length of the run. It just makes life much easier on the electrician with the the next size and the cost dif is worth it to me. Just passing on an idea.

This was a long time ago but we ran 4" conduit to a magnetic mixer in a steel mill, used a 10 ton crane to pull it around 40'. I know crazy, we used max NEC to fill the conduit and we knew we would break some conductors. I just don't like going by the recommended every since then. Even 1/2" maxed is a real pain.

I must agree with Resistor on the max fill.



also, if you tape 'em together they will snarl up instead of pulling past each other.

Sparky, we had to tape them in groups, and taper them, and added soap. It was still a mess and the crane was lifting some of the foundation. Yikes! We never tried that again.

BTW, these were control wires.

[This message has been edited by Resistor (edited 07-14-2001).]

Taping is good to keep them from curling & nesting. BUT.. cut each band of tape as it enters thepipe.

Redsy,

That sounds like a great idea. I recently saw bundles of 1/2 pvc conduits that were bundled together with a sort of clingy plastic "tape" It was very easy to wrap and unwrap and wouldn't leave any gummy residue, maybe something like that would be even better?

Bill

I don't quite get that Redsy and definitly don't get the following comment from Bill. sorry guys.

Resistor,

Welcome to the Forum!

I think Redsy was talking about taping the wires together to keep them from going wild (crossing, tangling etc.) before they can be pulled into the conduit. And he suggested taking the tape off as right before it enters the conduit.

I was just suggesting something else I'd seen that would keep the wires together and come off easier.

Bill

U guys ever use any 'quick-pull' for this sort of stuff?
http://www.cliffordvt.com/howtopull.html

Resistor,

When pulling multiple smaller stranded wires ,as the length and number of wires increases ,so does the likelihood of forming a rat's nest on the floor.
One way to prevent this is, after a certain number of wires(4, 5, 6?) are laid out, wrap a ring of tape every so often(15,20 or so ft., depending on wire size&length.) You may end up with 2 or more bundles. This really helps, but as the tape approaches the conduit, cut it off so if you have to pull more wires in the future, you won't hook the tape.

Well,yesterday {16 jul} i took these to fine outstanding electricians and seated them at a table and told them to explain why they thought the derating and adjustment was not needed I had the code book with me nearly fell out of my chair when they went to conduit fill table and told me that if I would use this table and never put more wires in it than what it says the fill is then I never had to derate and as long as I never went over 100 ft. I went back to 310 and ask ok what is the purpose of this one shurgged his shoulders and walked away and the other one says that is a hard article to explain and odds are you will never use it if you use the conduit fill tables ,never could get either one of them to explain the purpose of the derating table and the adjustment. I give up on these 2 but did show it to my boss and think he may have done a little calling around THANKS GUYS FOR ur patience with us of less knowledge

Doc,

It sounds like your guys are not too sharp when it comes to the NEC. In the hands-on world derating is something that may not be realized as important, or as a factor at all until there is a failure or a conduit too hot to touch and someone goes looking for an explanation.

Bill

First off, Thanks Bill.

Second, It's been a long time since we did the job I mentioned. Now I understand what ya'll meant, I can't remember if we removed the tape or not, although that would be pretty obvios when you know there is binding.

We did pretty much the same thing Redsy mentioned but we were usng 4" conduit and running around #12 stranded [control wiring](sorry, don't remember the exact type wire) so we taped more than 5 wires in a bundle or we would have had another mess, but taped mess.

I love this site and come here to learn about the codes in reality. My Father was licensed, so I didn't need to be since we worked together. Don't mean to bum you out but my father got lung cancer, and I wasn't going to waist his short time he had, with him trying to tutor me on the NEC.

So now I'll figure it on my own, (in other words I'm workin' on the test) or with help from other sources like this place. So I'm glad this place is here. Thanks for the site!


[This message has been edited by Resistor (edited 07-18-2001).]

Doc,

Those clowns missed out on a free and valuable lesson, but due to their reluctance to care or listen, will never realize how rarely this type of an opprotunity comes around!

My guess is that the only time the derating items will become serious to them is when they see the effects of it on something they installed.

Kind of a basic thing we all have learned in Code classes and in the field - why they can't grasp it is something for a high priced shrink to figure out

Scott SET

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.

Not for industrial use, matter o fact it's common. If your replying to my comments, we were running from a control room not a box. Also, I never saw an inspector in industrial except OSHA.

I agree with Redsy and Resistor. I too work in an industrial setting and we tape wires in bundles to avoid rat's nests but cut the tape before it enters the conduit(right at the mouth of the conduit). I also have never seen an inspector on an industrial maintennance job only the boss who knows less aboout electrical work than my 18 year old daughter!! We have to run the low voltage (120 volts or less) in a seperate conduit from the high voltage (480 volt 3 phase)wiring.

Thanks SCOTT,
guys tell me if I'M wrong here but what i think is the conduit fill tells you that yes you may stick 36 # 10 wires in an 1 1/2 " emt it does not say that you can use them at full amp load so that is why you derate them
if those # 10 wires were running 500 foot and only pulling 2 or 3 amps then it says you can stick all 36 in there now if u are not sure about the amperage then the derate table tells you how many amps you can safely put to each wire takes out the guessing of you over heating the wiring am using these numbers as examples only dont have book at hand.
Have worked in 3 locations where an inspector showed up now in 2 of the 3 locations 2 of the inspectors mostly turned their head on most items but one was tougher than a boot and he would tell you " I may be wrong by code but until a judge tells me I'M wrong you either do it my way or you stop work "
AS for running mixed voltages in the same conduit I know it is legal but it is just something I do not do and have taught guys that have worked for me to not do it and if the case arises where they have to at least run BOY for the 277-480 and red black and blue for 120 240 also white for the 120/240 and gray for 277/480

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.

[This message has been edited by Jim W (edited 07-20-2001).]

I don't know all the details of your project, but with the over whelming number of branch circuits in one conduit, it might be time to consider running a feeder to a distribution panel located central to your loads. Bring the overcurrent devices closer to the loads being served.

STU,
now did u read all of the post on here these guys dont even know what derating is and now u want to suggesrt they run a feeder and add a panel YOU do want me to be hung from a light pole dont you HA HA ,
I made all kinds of suggestions to these two fine outstanding gentlemen and got no where with them,but can you imigine if they put a feeder and panel over there then we would be running a 100 wires out of there before they were done ,they really think that the closer to the panel and the bigger the conduit the more wires they can stick in