ECN Forum Forums General Topics of the Trade General Discussion Area Residental homerun

CJS, I don't think you fully understand derating and you're not alone. I have had this same discussion with several inspectors. You derate from the 90deg column. Take a closer look at the ampacity tables and you will see what IWIRE and Don are talking about. I agree with Don, EMT over PVC. PVC needs to be supported at closer intervals to avoid a sloppy saggy install. I always pull an EGC in my EMT and bond it in every j-box. I install a 14 lug ground bar in the pull boxes to avoid a rat's nest of grounds/wirenuts. MW branch circuits installed in this manner present no more of a hazzard than any other wiring system and in 99% of the circuits they eliminate the neutral as a current carrying conductor for derating purposes.

I also figure derating the same as the other guys, but I don't run shared neutrals, so I figure 4 circuits maximum in the conduit (counting the neutral as a current carrying conductor).

Why do you pull a ground wire in EMT, Fred?

Dave

Can you use pvc in the States as we can,t use it in houses up here in Canada and generally our rules are similiar.

CJS,


Why not?

I can think of many excellent reasons for using multiwire circuits:

1. Less labor.
2. 50% reduction in voltage drop.
3. 1 cable instead of 2.
4. 3 wires instead of 4 (assuming pipe).
5. Money saved as a result of 1, 2, 3 and 4
6. Less natural resources consumed

There are even more savings on 3-phase systems.

So why are they so bad?

Peter

[edited for typos]


[This message has been edited by CTwireman (edited 09-20-2004).]

Dave55, I pull an EGC in pipe every since I saw a hot wire loose in a j-box arcing around and NOT opening up the CB. It was a brand new school addition and the run of pipe was up through 30' of concrete block. Loose couplings or connectors, it only takes one, and your ground path is gone. I don't understand the aversion to MW branch circuits. I mark the neutrals in the panel to identify which 2 hot wires share them and I mark them in the pull boxes. I don't get why some electricians react to MW branch circuits like they would a live snake.

Thanks for the reply, Fred. I saw a loose connector with conduit hanging in the air in an attic once which also lost the ground.

I have no aversion to multi-wire circuits when properly installed and maintained by electricians. However, I've seen cases of homeowners and handymen moving the breakers around creating the possibility of an overloaded neutral. I personally don't feel the savings of 50 feet of 12 ga. wire is worth the risk of a fire down the road.

Dave

In answer to the original question, I use them occasionally. We are working on a very large residential remodel, 8,000 sq. ft. We ran the homeruns to the attic, and spread out from there. We usually run a lot of branch circuits so they are not loaded up so much, but we may put a bedroom, a closet lite (covered fixture of course!), and maybe a hall light or two on one homerun. This method keeps the number of conductors in switch boxes to a minimum.
WireWrestler

Dave55, I just don't subscribe to the "what if somebody down the road does..". The same guy who would indiscriminately move breakers around will probably replace a 20A with a 30A if his 4 plug-in heaters he's using to cure paint in his homemade autoshop paint booth keep tripping the 20A. I never ever fill a panel on a new install. My rule of thumb is to leave at least 8 spaces open in a 40 ct panel even if I have to set a 20 ct sub right next to it with empty pipes up and down out of it. I look at it from the viewpoint of "what if the next competent electrician needs to add a circuit and what if he's me?" If it's me I want it to be easy. If it's not me I want him/her to say "The original electrician was a saint!".

We should have a semi-detailed discussion thread regarding Derating and etc. per as many factors which may apply (ambient temperature, number of current carrying conductors per raceway, increased size of conductors for adjustments to various factors, which to count and when, yadda-yadda-yadda).

This information is quite easy to understand, yet is not well understood by some Persons in the Field.

Box fill is another issue to address.

These items are simple things to grasp, but if explained by me... well ... might be more difficult!


Scott35

BTW, if this post doesn't make too much sense (i.e. missing some key info.), I am "Rubber-Necking" between the Monitor / Keyboard, and the Angels / Seattle game!
Score as of the bottom of the 8th:
Ana: 4, Sea: 2

Also, there's some dude that has become increasingly more buzzed per inning!
Along with the increased intoxication, is an increased dB voice level; and a correspondingly decrease in proper English Speaking skills (Read: Slurred Gibberish is increasing exponentially!)


S.E.T.

p.s. Wanted to add the redundant EGC - as mentioned by Fred (adds a Grounding Conductor to EMT runs) is a very good idea, to assure the Electrical Bonding of Metallic Raceways + Equipment.

Me...

[This message has been edited by Scott35 (edited 09-21-2004).]

Scott
Got to love them Yanks!!!!
Sorry Bob.

Pierre

P.S. Oh ya ..., I agree that a good thread on conduit fill and ampacity adjustment would be a good idea, with box fill being separate, and then sizing of larger boxes next.