Conduit Question from "Another Forum"

[HMF]

"Questions on conduit sizing and install

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I am wiring in my phase converter. I have a couple of questions about using conduit and would like some advise and opinions.

When the house was built, I had the electrical contractor install a 100 amp sub panel in the garage. It is an oversize 3 car that will serve as my shop and is attached to the house. The panel face is flush with the drywall and the depth of the box is in the wall.

I went to the local electrical supply place and bought a 2011 NEC book, and I think I am tracking on everything OK, but I want everything to be done right the first time so I am seeking some advise.

I have an American Rotary 15 hp RPC. American Rotary says to use 4 ga copper wire for the supply. I am good with that, but it means I will need to run the supply wires through conduit as I can only find 4 ga copper in single stranded wire.

My converter panel will ideally be about 12 feet from the sub panel to get things laid out they way I would like them. Both panels will be mounted on the same wall, a straight run with no corners, windows, doors or anything between them. The garage is complete, so I think it would be very difficult to run EMT conduit through the studs (2x6 BTW).

Here are some questions. What I came up with sizing the conduit came out to 1" EMT. That was 3 wires, THHN 4 ga. A buddy of mine said I need 1 1/4 conduit. I think bigger would be better and I don't mind spending the extra money, but I am thinking 1 1/4 might be a little harder to work with.

How would you guys go about this? This is what I am leaning toward. Should I come out of the sub panel, (behind the drywall) with EMT conduit, come straight down and come out of the wall at the bottom near the floor, 90 degree it and run along the surface of the drywall until I am under the panel, junction box it and then go up into the bottom of the RPC control panel. The panel will be surface mounted of course.

A second option that I kicked around with my buddy is to use flexible metal conduit and bore holes in the studs. Keep everything behind the drywall, come into the control panel from the back so nothing is visible on the surface.

It looks to me like the flexible metal inside the wall would be in compliance with code. Also, it looks to me like with the 3 mentioned 4 ga wires I can still use 1" conduit. I kind of like this option, but what type of connector would I need to use to come through 1/2" drywall and attach to the back of the box?

Sorry this is so long winded. I just want to make sure you have a good picture of what I am doing.

Bottom line questions.

Is 1" conduit large enough for 3 conductors of 4 ga THHN? Is this true for EMT and flexible metal? If I bore holes in the studs I would rather stay with 1" as long as it is large enough. Would you guys go up to 1 1/4" even if the 1" is large enough?

What is the best method of transitioning conduit from behind drywall to a surface run so that it is done correct and also looks clean.

Is a 12 foot run of flexible metal conduit inside a wall acceptable? What would be the correct way to attach the flexible metal to the back of my control panel allowing for the thickness of the drywall?

What would be your preference if you were doing this?

Thanks."

 

[flutedchamber]

1 1/4 rigid plastic conduit will work for your 3 #4 THHN conductors. So will a 1 inch, but it will be tight.

For a clean transition use premade 45* ells and inspection type 90's. Support it every 4 feet with clamps. I like pinch clamps.

That's out of my 2005 book. Check the tables in the back of your 2011 book under rigid nonmetallic conduit.

Because #4 copper is so much fun to work with, put the wires thru the conduit BEFORE you glue the connections together, especially the sweeps and inspection 90's.

 

[Hawkeye]

Up here, 1" conduit, whether metal, plastic or flex, isn't legal for 3 #4 wires. 1 1/4" is minimum. You are limited to no more than 40% conduit fill. Keep in mind that you will also need a ground wire if you use flex or plastic conduit. EMT is allowed as a ground if properly installed.

Having said that, I would use #4/3 NMD90 cable. It is the same construction as the Romex wiring in your house. Similar to your range cable (in newer houses), but larger. Does Home Depot sell that kind of thing down there? If not, ask at your local wholesaler. Some of them will sell to 'civilians'.

Happy wiring.

Mike

 

[flutedchamber]

[quote author=Hawkeye link=topic=2648.msg27038#msg27038 date=1316987809]
Up here, 1" conduit, whether metal, plastic or flex, isn't legal for 3 #4 wires. 1 1/4" is minimum. You are limited to no more than 40% conduit fill. Keep in mind that you will also need a ground wire if you use flex or plastic conduit. EMT is allowed as a ground if properly installed.

Having said that, I would use #4/3 NMD90 cable. It is the same construction as the Romex wiring in your house. Similar to your range cable (in newer houses), but larger. Does Home Depot sell that kind of thing down there? If not, ask at your local wholesaler. Some of them will sell to 'civilians'.

Happy wiring.

Mike
[/quote]

Wow..what a difference. According to my 2005 NEC book you are allowed in conduit in open air an 80% fill rate...under all but high temperature conditions. I've tried getting three #4 in a once inch PVC conduit..you need a shoehorn.

 

[PeterHaas]

Re: Conduit Question from "Another Forum"

In the US, we generally go by the NEC unless the local AHJ (authority having jurisdiction) overrides the NEC with local rules.

For "old work", and particularly for type TW (thick PVC insulation), or WW-II era Type RW (thick rubber insulation) three #4s requires a 1-1/4" conduit.

However, on an upgrade using thinner nylon-jacketed THHN, three #2s can fit in the same 1-1/4" conduit.

#4 was popular in the old days of 60 or 70 amp services, but almost all codes since the 1950s have required a minimum 100 amp service, with an exception being applied if the residence was all-gas, and has no electric cooking, heating or cooling, in which case one might get away with a 40 amp service.

These days, 200 amp services are almost always found, and 1-1/2" or 2" conduit is used, particularly for #4-0 copper-plated aluminum services.

Personally, I would never use an aluminum service. Sure, the utilities can handle it, and they have all the specialized crimping tools and anti-oxidation goop, but once that aluminum passes through your weather-head, it is your responsibility, and you are at the mercy of the installer to perform an aluminum-friendly installation.

 

[Tony Wells]

Re: Conduit Question from "Another Forum"

Here, on service entrance, they require copper 24" outside the weatherhead, where they they crimp to their aluminum service drop, which of course, is in open air, so they get by with a little smaller cable than they require for us.

 

[PeterHaas]

Re: Conduit Question from "Another Forum"

"Because #4 copper is so much fun to work with, put the wires thru the conduit BEFORE you glue the connections together, especially the sweeps and inspection 90's."

Well, #2 copper (125 amp service) is even worse.

Codes generally frown on inserting wiring materials before the entire conduit run is made up and tied down.

I had no particular trouble pulling a new 3 x #2 THHN service when a storm felled a tree right on my weather-head and shorted-out one of the line conductors to the 1-1/4" rigid conduit. The weather-head was fused into molten metal.

The 3 x #2 Cu (all insulated, as is now required) was an "upgrade" from the original 2 x #4 Cu (insulated) + 1 x #4 Cu (bare).

Took me only four hours to perform the "upgrade in place", and my service equipment was already rated for 125 amps, so I got a bump from 60 amps to 125 amps for almost no money.

Of course, the "on call electrician" wanted $1,500, and the city expected a permit to be taken, but they could not get to me for five days as it was at the beginning of a National holiday.

When the city FINALLY got back to me two days after the holiday, I cordially told them that the "problem" was found on the PG&E side of my service and that PG&E had "fixed" it.

Actually, all PG&E did was check my work at the meter socket, check my work at the weather-head, and then do a "turn on". Oh, yes, they also upgraded my service drop from #6 to #2, at my friendly suggestion.

My total cost: about $40 (forty dollars), plus a cold drink for the PG&E lineman, whom I assisted doing the service drop.

 

[Tony Wells]

Re: Conduit Question from "Another Forum"

I'm out on an REA, so I can get away with a little more DIY, and no permits.....but for new install when I remodeled 20 years ago I put in 2" rigid and 4/0 4/0 4/0 2/0 for 200 amp service. This with about 175 feet to the pole pig from the old 125 amp service. It took a year of griping about brownouts to get them to plant a stick in my yard and hang my very own transformer. And I got a new 2/0Al drop of about 50 feet. ALl no charge....I was finally happy.

 

[PeterHaas]

Re: Conduit Question from "Another Forum"

"Here, on service entrance, they require copper 24" outside the weatherhead, where they they crimp to their aluminum service drop, which of course, is in open air, so they get by with a little smaller cable than they require for us."

Mine was a budget job (but a high quality job just the same) as my "budget" was what little cash I had in my wallet (banks closed on account of a national holiday and cash machines mysteriously out of cash).

I carefully measured for the three #2 Cu conductors, and I was able to get black and also white from the local retailer who just happened to be open on the Sunday for four hours.

I left about 3' outside of the weather-head and the PG&E lineman cut that down to suit himself, about 1-1/2', I think. Then he crimped-on three #2 Al conductors. All using purpose-built compression tooling. Hydraulically applied.

That service will last me the remainder of my lifetime, I'm pretty sure, although if I win the lottery I plan to build a four storey residence with a full basement (for my shop) and install a 400 amp service.

 

[DMS]

Re: Conduit Question from "Another Forum"

I notice the original question was posted a while ago, but there is still activity, so maybe you are still working on things. I am not an electrician, but I just finished a garage remodel, and spent a lot of time making sure I did it right.

First thing, I am pretty sure that flex conduit in the walls is a big no-no per the NEC. I would go with 4 awg NM cable through the walls to a 4x4 junction box, then from there to armored cable (also called MC or FMC) to your converter. You can run conduit, but you will need to transition from your sub-panel to the wall surface. If you do conduit, my Ugly's book says you can fit 4 4awg THHN wires in 1" EMT. I believe this is 40" fill rate. Bigger conduit always makes for easier pulls.

The largest wire I pulled when I did my garage (other than the 1/0 SER cable for the main feed) was a 6awg for my welder. This was through 3/4" conduit and over about 30 feet, 4 bends. With a fish tape, some lube, and someone pushing on the other end, it was not very difficult at all.

Good luck whatever you decide.

-Matt