IMC vs Rigid

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I'm looking for feedback from users of intermediate metal conduit. Some interests include:

- Real cost savings of IMC compared to rigid?
- Ability to resist physical damage compared to rigid?
- Workability - Is there any drawbacks for the folks who are installing IMC?
- Durability - How does it stand up to the elements and/or corrosive environments (compared to rigid)?
- Safety - It is approved by the NEC for use in hazardous areas, but in your opinion, is it as safe as rigid?

Thanks for any feedback that you may have concerning these questions.
 

Pullnwire

Senior Member
Location
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Electrician, Business Owner, SME and Trade Instructor
I have run quite a bit of rigid and IMC moslty 3-4"...

IMC is MUCH easier to work with, just from a weight standpoint. If you are working off a ladder, lift or trying to get into an existing trapeze like I was most of the time, you will appreciate this. THreading is the same. Bending, need a little patience with a multi shot bender. Its not as forgiving as GRC. But, it you are using factory elbows, thats a non issue I believe its as safe in a C1D1 location. THe code is concerned about the amount of threads engaged in the connection.

Just my opinion
 

Fulthrotl

~Autocorrect is My Worst Enema.~
I have run quite a bit of rigid and IMC moslty 3-4"...

IMC is MUCH easier to work with, just from a weight standpoint. If you are working off a ladder, lift or trying to get into an existing trapeze like I was most of the time, you will appreciate this. THreading is the same. Bending, need a little patience with a multi shot bender. Its not as forgiving as GRC. But, it you are using factory elbows, thats a non issue I believe its as safe in a C1D1 location. THe code is concerned about the amount of threads engaged in the connection.

Just my opinion

it's approved for cl1 div1, so that is about as durable as it gets... i'd say it's a bit more crushable than RMC, but
unless you hit it with a forklift or backed an 18 wheeler into it, i doubt you'd know the difference.

explosion proof is five full threads of engagement. does not have to be made up tight to be explosion proof.

i've ran it on racks in refineries, off extension ladder and such, and in big sizes, there is a significant time savings.
where i've had to do intricate bending, i've substituted a piece of GRC for there, so it doesn't get flattened, and
moved along......

two guys running 4" grc, up high, after a while, your speed does decrease significantly.... like the second half of
the day... :-/

something i've been using lately in smaller sizes is aluminum rigid conduit...... won't work in all occupancies, but
geez, it's lighter than a popcorn's flatulence. (put proper word in to keep from post being deleted, i hope)
 
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Thanks

Thanks

Thanks for the feedback guys - exactly what I was looking for. I am planning to have some IMC installed on a project in the next 2-3 weeks to see how it compares to rigid. I already have pricing for the materials, and it is a fairly significant savings. The electricians seem to be pretty interested too, especially when you are installing 3-4 inch conduit, due to the reduced weight. I just hope it works out well.

Thanks again for your replies!
 

ron

Senior Member
Thanks for the feedback guys - exactly what I was looking for. I am planning to have some IMC installed on a project in the next 2-3 weeks to see how it compares to rigid. I already have pricing for the materials, and it is a fairly significant savings. The electricians seem to be pretty interested too, especially when you are installing 3-4 inch conduit, due to the reduced weight. I just hope it works out well.

Thanks again for your replies!

Why not go to EMT?
 

Fulthrotl

~Autocorrect is My Worst Enema.~
500.8(E) requires both "wrenchtight" and a minimum of 5 theads full engaged.

i stand corrected... i just remembered the crouse hinds guys demo on explosion
proof with using threaded cover j boxes, and how five threads was enough to
prevent explosion, even if not made up wrench tight... the whole thing is that
the amount of thread engagement allows the explosion inside the
box to cool below the flash point of the surrounding atmosphere before it
escapes... it's a heat sink.

he did a really cool demo with propane, and the explosion was contained with about two
full turns on the box cover....
 

don_resqcapt19

Moderator
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Location
Illinois
Occupation
retired electrician
I don't think it is a heat sink function that provides the cooling to the escaping gasses. It is a result of the pressure drop.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
I don't think it is a heat sink function that provides the cooling to the escaping gasses. It is a result of the pressure drop.

i never bothered to analyze it... the person teaching the certification class said that
was the purpose behind the pressure flange on a bolted enclosure, to provide
enough dwell time for the flame front to cool as it escaped from the enclosure...

but, the law of an expanding gas losing temperature as it expands might
cover that as well... if you have a bezillion pounds of pressure inside a vessel,
and it's escaping to ambient pressure, then it would cool as the pressure
drops across the threads, or pressure flange, or expansion valve in an A/C
unit, for that matter....
 
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