Residential........emt vs romex

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tallgirl said:
I think you're looking at more than 2000' of THHN, unless that's 2000' x 3 wires. And even then you're wrong :)
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Wasn't his 1000' just for material cost comparison for rx vs. emt? What am I missing?
 
Yes, the figures are just for cost comparison.

If you have 1000' of RX on hand, you will not be actually installing 1000'. Some will be scrap. some will be for tails (RX has that pesky ground wire), etc.

Some for the pipe job, 10% wasted pipe, 5% wasted wire, etc.

My numbers showed 2000' #14 THHN, NO installed EGC..etc.
That's w/o any consideration to appliances, pulling EGC's for things AC condensors, etc.
 
I know that the Chicago area requires conduit, but what about using MC cable instead of EMT? I would think they would allow this and this would save a lot of time.


I read through this thread quick so sorry if someone already covered this.
 
big vic said:
So you suggest I tell them their Electrical is going to be over $200,000
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I already told you my suggestion in post [#4]:
celtic said:
If this is an area that you have little or no expertise in, I would inform the customer of such and simply refuse to price it.

I would give them the RX number, ask them to "shop around", and call me at a later date - even if your number is not accepted.
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Keep in mind, 3/4" EMT loaded with #10's as home runs will greatly reduce your labor costs.
 
I wouln't be suprised if the conduit bids were right in line with your original NM bid.


Edit to add: To clear up an earlier statement, FMC, AC and MC are all used to fish feeds in exsiting closed walls and ceilings, just no long open feeders.
 
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j_erickson said:
Wasn't his 1000' just for material cost comparison for rx vs. emt? What am I missing?
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:: whew! ::

I was thinking about the number of times I've been in a much smaller-than-4000-sqft house and used more than 1,000' of Romex. I was starting to think I'm a really wasteful pig.
 
Relax Julie....it was just to toss some numbers on the board :)

I can't imagine actually using all 14 and 1/2 anyway ;)
 
big vic said:
So you suggest I tell them their Electrical is going to be over $200,000
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Big Vic, this does sound like a lot for a house but what if it were a wood framed banking facility. What's the difference? What would you charge for a commercial job where they wanted all EMT ( no MC )?

I would try to sell them on metal boxes and MC cable for about triple the normal cost then use conduit for the home runs only ( run along the bottoms of the joist). If you sell it right this could be a real money maker.

They end up with the added safety, you end up with the added money.
 
iwire said:
~ never mind installing EMT 24" at a time through the studs.
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Bob, a trick I picked up on the other forum last time a guy from Chicago was hangin' round was that if you pull a stud out (32" open), and you can lightly wax your holes a 10' stick of 1/2 will have enough spring to it that it will make it whole into a wall. I tried it - it works..... I didn't even realize I had been doing it the same way on tin can studs forever - just never thought it would work in wood. You do have to put the stud back though ;)

Otherwise they do an aughfull lot of notching - that I would never be able to get away with here..... And a lot of up-and-over. I have also heard that dropped lids are a popular item there too.

Celtic, there is no real benifit of #10's in 3/4", (max is 10 THHN as opposed to 9 12's in a 1/2") the real benifit starts at 1" and 1 1/4" (16 or 28 @ #10)
 
e57 said:
Celtic, there is no real benifit of #10's in 3/4", (max is 10 THHN as opposed to 9 12's in a 1/2") the real benifit starts at 1" and 1 1/4" (16 or 28 @ #10)
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But what about derating? After 20 CCC's the ampacity of a #10 drops to 18 amps.
 
20 and less #10 (40A) @ 50% (20A) @ 90C.... Thats one run of 1 1/4" vs. two of 3/4". And if loading at 80% (16A or more correctly 125 percent of the continuous load. Still 16A on a 20A per 210.19(A)(1)) ;)

Let's say 1 1/4" as an example:

Or 20 or < #10 (35A) @ 50% (17.5A max) @ 75C - Still one run vs. two.

Or 28 or less #10 (40A) @ 45% (18 max) @ 90C

Or 28 or less #10 (35A) @ 45% (15.75 MAX) @ 75C.... (but only loaded to 15.75A)

27 conductors is 18 3-wire circuits.... in one 1 1/4" or for those of you... 28 CCC's as 14 2-wire...
or 15 conductors in a 1" = 10 3-wire circuits or for those of you... 16 CCC's as 8 2-wire...

And you can also apply 240.4 B to Lighting and "Fastened" in place Appliances or the like. (as thats pretty much all that is left after condition #1) All could be 20A CB's. Recepticals too in a dwelling via 220.3(10)

(B) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
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Also heres a neat example from the handbook commentary...
Example
A commercial office space will require fourteen 277-volt fluorescent lighting circuits to serve a single open office area. The office area lighting is assumed to be a continuous load, and the office ambient temperature will not exceed 30?C (86?F). Each circuit will be arranged so that it has a computed load not exceeding 16 amperes. The selected wiring method is Type MC cable, 3-conductor (with an additional equipment grounding conductor), 12 AWG THHN copper. Each individual MC cable will contain a 3-wire multiwire branch circuit. To serve the entire area, this arrangement will require a total of seven Type MC cables bundled for a distance of about 25 ft, without maintaining spacing between them where they leave the electrical room and enter the office area.
Determine the ampacity of each circuit conductor in accordance with 310.15, applying Exception No. 5 to 310.15(B)(2)(a) to account for the bundled cables. Then determine the maximum branch-circuit overcurrent protection permitted for these bundled MC cables.
Solution
Step 1.
To apply Exception No. 5, first determine the quantity of current-carrying conductors. According to 310.15(B)(5), equipment grounding conductors are not counted as current-carrying conductors. According to 310.15(B)(4)(c), fluorescent lighting is considered a nonlinear load, so the grounded conductor of each Type MC cable must be counted as a current-carrying conductor.

7 cables X 3 conductors each = 21 CCC

Because the quantity of current-carrying conductors exceeds 20, a 60 percent adjustment factor is required by 310.15(B)(2)(a), Exception No. 5.

From table 310.16, #12 THHN = 30A
30A X .6 = 18A

Step 2.
Determine the ampacity of each current-carrying conductor due to these MC cables with more than 20 current-carrying conductors being bundled.
Because the actual computed load is 16 amperes of continuous load, 210.19(A)(1) is applicable. The conductors must have an ampacity equal to or greater than the load before the adjustment factor is applied. Because the ampacity of the conductors after the adjustment factor is applied is 18 amperes, no further adjustment is necessary and the conductors are suitable for this installation.
Step 3.
Finally, determine the maximum size of overcurrent protection device permitted for these bundled MC cable branch circuits. Section 240.4(B) permits the use of the next higher standard rating of overcurrent protection device. Therefore, although the conductors have a computed ampacity of 18 amperes, a 20-ampere overcurrent protective device is permitted. In addition, and of significance, the 20-ampere overcurrent protective device is in compliance with 210.20(A), given that the actual 16-ampere continuous load would require a 20-ampere overcurrent protective device, based on the listing of the overcurrent device.
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But either way if the area is not kind of wide open.... working with 1 1/4" will be pretty much a hassle, then two 1/2" might as well be the choice. No real math to do and you can just use #12's with three 3-wires.
 
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For any of you that recommended to stay away from EMT to ruff a house if your not use to it, you are correct. However, in the same vane, if I had to ruff a house in NM, I would be COMPLETELY lost.

They both have thier own style of installation, and tricks on the trade. There was even a post against using the conduit as the ground. I am here to tell you that this is a COMMON occurance and done EVERY DAY here. Unless it is a spec of the job, then you dont get a ground wire. You can debate this all day, however this is within code and thats how its done.

I ONLY do homes in EMT. If you would like to see any pictures of a home ruffed in EMT send me your email address and I will send them your way.

I would post them here but I dont have a clue how to do that. For a home thats about 3800 square feet the costs are coming in at about $15,000 - $17,000. There are too many variables to give you a better price, but this puts you in the ball park.

We also dont allow PVC for the services either. They need to be in rigid conduit as well. Were not big on plastic anything here. Some things just done change................
 
e57 said:
And I thought my area was writing thier own code.... :0
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Nyc used to have a simular restriction years ago,no more than 7 conductors in conduit.Also no 4 wire bx,No NM.To me it was a union thing but we can`t go there can we :)I`ve been doing residential for 20 + years and can`t see where there is a reason to use EMT over NM,other than add ons down the line.

I figure 1 ft. of 2 wire for every sq ft of home,then 3 wire is about 1/3 the sq. footage per ft. of wire.It is not an exact measurement but it is really a close estimate.This covers about everything.
 
Having done plenty of both NM and conduit, both residential and commercial, it seems like a couple of well-placed subpanels might save on materials and labor, depending of course on the structure size and layout.

I've always been a fan of well-distributed power for both efficiency's and performance's sakes (and even economics). Due to load diversification alone, a feeder can reduce voltage-drop for otherwise-long home runs.

I see a savings in both materials and labor by using centrally-located panels for several circuit groups, and eliminating having to use derating and oversized conductors to attempt to reduce home-run conduit count.

In other words, why wouldn't some (i.e., large and spread-out) residences benefit by using smaller-scale versions of what is generally done in commercial/industrial work, and for the same reasons: economics and performance?
 
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Or 28 or less #10 (40A) @ 45% (18 max) @ 90C

Or 28 or less #10 (35A) @ 45% (15.75 MAX) @ 75C.... (but only loaded to 15.75A)

And you can also apply 240.4 B to Lighting and "Fastened" in place Appliances or the like. (as thats pretty much all that is left after condition #1) All could be 20A CB's. Recepticals too in a dwelling via 220.3(10)
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All receptacle circuits in the above calculations with one or more duplex receptacles would have to be sized at 15 amps. Rounding up to the next larger standard size for these circuits is not permitted.
 
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