Secure Fastening and Support of RMC 344.30(A) and (B)

[cowski]

I'm looking at some short runs of RMC from a motor to a junction box.

Do 344.30(A) and (B) imply that all runs of RMC must have at least one clamp (even if the run is less than 3')? They seem to...

It seems like very short runs of unsupported rigid were allowed briefly with 344.30(C) which was added in 2008 and then removed in 2011.

Is RMC considered securely mounted when it's threaded into a junction box that's been bolted down? (i.e. the junction box is secure and the conduit is not being used to support the junction box).

Or are there any other sections of code that modify this? Is there any leeway for when flexibility is required? In my case the motor is mounted to a plate that is adjustable. There is a flexible coupling between the motor and junction box.

 

[cowski]

I should add that I'm using rigid in a hazardous area (CID1 and CIID1) so articles 501 and 502 would apply as well if there are any modifying conditions there.

Thanks very much in advance for your thoughts.

 

[cowski]

I think this boils down to the definition of "securely fastened" in 344.30(A). I don't see a definition for "securely fastened" in article 100... I don't think I can argue that the threaded connection alone is "securely fastened". We're going to add a support so the conduit can be clamped.

I think in the future I'll start using MC-HL cable with Crouse-Hinds Terminator TMCX connectors. I'm in an industrial environment with limit access... The AL covering will probably resist corrosion better than the galvanized rigid in our very wet environments.


I'm going to review the conditions required for MC-HL in hazardous areas. I don't think I could justify harsh duty cable. But MC-HL may be ok...

 

[JoeStillman]

You had me at "RMC from a motor." Never mind the support, what about the vibrations? The stuff in your picture looks a lot more appropriate.

 

[don_resqcapt19]

You had me at "RMC from a motor." Never mind the support, what about the vibrations? The stuff in your picture looks a lot more appropriate.

Most all of the factory skids for Class I locations that I have seen, had the motors hard piped.

 

[cowski]

You had me at "RMC from a motor." Never mind the support, what about the vibrations? The stuff in your picture looks a lot more appropriate

Hah. Right. There's always a 12" flexible coupler on the rigid as it enters the motor junction box...


I should have posted this in the hazardous area thread (sorry mods).

 

[don_resqcapt19]

Hah. Right. There's always a 12" flexible coupler on the rigid as it enters the motor junction box...

View attachment 2571215
I should have posted this in the hazardous area thread (sorry mods).

The cost of those is very likely the reason the factory built skids for Class I locations have almost always had the motors hard piped.

 

[macmikeman]

GRC-- secured withing 3 ft of box or termination. Supported at 10 ft intervals minimum.

 

[kwired]

GRC-- secured withing 3 ft of box or termination. Supported at 10 ft intervals minimum.

Hah. Right. There's always a 12" flexible coupler on the rigid as it enters the motor junction box...

View attachment 2571215
I should have posted this in the hazardous area thread (sorry mods).

I think the question is more of a general code question than a hazardous location question.

Three feet within boxes or other termination has always been fine, then somebody thought they had to mess with this some and it made absolutely no sense to do so.
If you have a 30" piece of 4" GRC between two cabinets what is going to move it that isn't also going to damage any support you put on it along with one or likely both cabinets in the process?

Even 1/2" piece of GRC in same situation is taking a pretty good beating and still holding up.

 

[don_resqcapt19]

I think the question is more of a general code question than a hazardous location question.

Three feet within boxes or other termination has always been fine, then somebody thought they had to mess with this some and it made absolutely no sense to do so.
If you have a 30" piece of 4" GRC between two cabinets what is going to move it that isn't also going to damage any support you put on it along with one or likely both cabinets in the process?

Even 1/2" piece of GRC in same situation is taking a pretty good beating and still holding up.

The proposal that resulted in a rule that was only in the 2008 code made perfect sense.

There is nothing in the code that permits the raceway terminations to be the required support. The language as currently found in the NEC requires a support for ANY length of raceway.

The code making panel does not seem to understand what the rule actually says.

They read it like most inspection authorities read it...that is no supports required when the raceway is 36" or less in length, but that is not what the language says.

There have been a number of PIs after the 2011 code to fix these rules, but all have been rejected by the CMP. Some of them would have added specific language that said where the raceway is 36" or less in length, that the conduit termination shall be permitted to serve as the required support.

I agree that support is not needed for short lengths of non-flexible metal raceway, and see a need for the code language to clearly state that.

Right now, it is a rule that is probably only enforced where the inspection authority encounters an obnoxious electrician.