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IMC vs RMC #53384 06/22/05 09:19 PM
Joined: Jun 2001
Posts: 21
VOLTS Offline OP
What are the difference between IMC & RMC. I have an electrical contractor telling me there is no difference. I have always spec'd RMC in an explosion proof area. I know the Code states IMC is legal, But I was always taught RMC was stronger and had better grounding of interferance for control circuits using 4-20ma. I would like to stay with RMC what would be a good argument not to use IMC?

Work Gear for Electricians and the Trades
Re: IMC vs RMC #53385 06/22/05 09:30 PM
Joined: Aug 2003
Posts: 1,374
Ryan_J Offline
IMC is less expensive and can be used in all areas that RMC can be used. I am also told that it is stronger, but I have never read anything on that. IMC also has a bigger cross sectional area and is easier to bend.

I would not install RMC unless I was forced to.

Ryan Jackson,
Salt Lake City
Re: IMC vs RMC #53386 06/22/05 10:01 PM
Joined: Jan 2004
Posts: 615
Jps1006 Offline
I have always found IMC much stiffer and more difficult to bend. I always opt for RMC because it is easier to bend.

Re: IMC vs RMC #53387 06/22/05 10:33 PM
Joined: Aug 2003
Posts: 1,374
Ryan_J Offline
Really? I haven't bent either of them in about 6 years or so, so I might not be remembering properly. [Linked Image]

Ryan Jackson,
Salt Lake City
Re: IMC vs RMC #53388 06/22/05 10:43 PM
Joined: May 2003
Posts: 2,876
e57 Offline
IMC has a thinner wall, and more tempered/stiffer, not sure why.

RMC is slightly thicker, weighs more, less tempered, but seemingly about the same to bend. Costs a penny more.

Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: IMC vs RMC #53389 06/23/05 12:44 PM
Joined: Nov 2000
Posts: 2,148
resqcapt19 Offline
I agree that IMC is much stiffer and harder to bend and thead than RMC. I have also seen problems with the IMC breaking at the threads on the 1/2 and 3/4" size. This is caused by the reduced wall thickness of this conduit. There is very little strength left after you cut the threads.

Re: IMC vs RMC #53390 06/23/05 09:19 PM
Joined: Mar 2001
Posts: 2,056
Redsy Offline
I used a fair amount of IMC and GRC in hazardous locations including 4-20 mA control circuits and VFDs. Never noticed a diffrence in EMI or RFI problems in one over the other.
Although lighter in weight the IMC was indeed harder to bend, and keeping the shoe tight against the pipe for an accurate radius was difficult even at the 3/4" size. I would avoid using it for hand bending.

Re: IMC vs RMC #53391 06/24/05 10:39 AM
Joined: Jul 2004
Posts: 9,558
gfretwell Offline
From an RF standpoint a wrap of properly grounded metal window screen is as effective as RMC. The difference is physical protection.

Greg Fretwell
Re: IMC vs RMC #53392 06/24/05 01:53 PM
Joined: Jun 2001
Posts: 21
VOLTS Offline OP
Thanks for the feed back.

Re: IMC vs RMC #53393 06/24/05 07:29 PM
Joined: Jul 2002
Posts: 680
walrus Offline
I prefer working with IMC, lighter and easier to bend IMHO. Never had a problem with it breaking underground and Maine frost can break anything. My suppliers don't stock it anymore though so I use RMC all the time now anyway. What are people paying for 3/4 rigid, last time I checked it was 17 bucks a stick up here??

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