Are RMC Compression threadless couplings permissible to use in CL1/DV1 applications?

JsnBo

Member
Location
CA
Occupation
Electrician
Location: Chemical Fertilizer Plant
Access: Restricted to essential personal only. No public access.

I've scanned through Articles 500-506 and Article 344 looking for allowances to install my conduit. All conduit bodies, connection points, entry points etc. are all in CL1/DV1 compliance. The question is specifically about my conduit connections, basically looking for an allowable alternative to grc couplings in this setting.
 

JsnBo

Member
Location
CA
Occupation
Electrician
You will need to look at their Listing information. Most likely mfg catalog would have some as well.

Now think about why threaded fittings are used in those areas.
I definitely know why they're used (Not a newbie in the trade) the question was purely out of curiosity.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
With respect to the title of the thread, compare Section 501.10(A)(1)(a) for Division 1 with Section 501.10(B)(1)(1) for Division 2; i.e., the answer is no.
 

fbhwt

Electrical Systems Inspector
Location
Spotsylvania,Virginia
Occupation
Electrical Systems Inspector
Just looking at the new 2020 NEC and found this, 500.8(E)(1) Equipment Provided with Threaded Entries for NPT Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT-threaded conduit or fittings, listed conduit, listed conduit fittings, or listed cable fittings shall be used. All NPT-threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
Just looking at the new 2020 NEC and found this, 500.8(E)(1) Equipment Provided with Threaded Entries for NPT Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT-threaded conduit or fittings, listed conduit, listed conduit fittings, or listed cable fittings shall be used. All NPT-threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread.
So are conduit couplings going to switch to tapered threads? Will there be an identifiable difference in appearance? I anticipate a rapid correction to this.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
So are conduit couplings going to switch to tapered threads? Will there be an identifiable difference in appearance? I anticipate a rapid correction to this.
This a disconnect in the code that CMP 14 does not seem to understand. Conduit couplings are fittings and subject to the requirement you cited.

I don't think we have ever used tapered thread conduit couplings in the US. (unit the early 80s, the Canadian Electrical Code, required the use of tapered thread couplings)

Based on the fact that the couplings are part of the listed rigid conduit, CMP 14 says they are suitable for use in classified areas per the listing, even though they do not comply with 500.8(E)(1).

I don't have an issue with using the straight thread couplings in conduit runs in classified areas, but I do have an issue where one is used between an enclosure that is required to be explosion proof and the conduit seal for that enclosure as permitted by 501.15(A)(1) in the 2020 code. I can find no evidence that the couplings have ever actually been evaluated for for the purposes of containing the hot gasses from an explosion within the explosion proof enclosure.

The requirement for conduit fittings in classified areas to have tapered threads is not new, it has been in the code since at least 2002.
 

tom baker

First Chief Moderator
Staff member
Before I knew the difference I used an electrical coupling in a water line, which leaked.
Now think about why threaded fittings are used in those areas.
Exactly. In other words what are the purposes of the threads, why minimum of 5 threads, why do enclosures have flat ground surfaces, ? Once we understand that, then the reason RGS threaded can not be used will be clear.
 
Last edited:

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
I think it's time for "shark bite" type electrical fittings. They will be pricey but convenient for these type installations.

Roger
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Before I knew the difference I used an electrical coupling in a water line, which leaked.

Exactly. In other words what are the purposes of the threads, why minimum of 5 threads, why do enclosures have flat ground surfaces, ? Once we understand that, then the reason RGS threaded can not be used will be clear.
Compression couplings are acceptable in Division 2. That's why I cited Section 501.10(B)(1)(1) in Post #4.
 

paulengr

Senior Member
Before I knew the difference I used an electrical coupling in a water line, which leaked.

Exactly. In other words what are the purposes of the threads, why minimum of 5 threads, why do enclosures have flat ground surfaces, ? Once we understand that, then the reason RGS threaded can not be used will be clear.
If I remember that gives you a long enough flame path through the thread to cool the hot gas. It’s a natural labyrinth seal. Works just like NEMA 9/10 boxes.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I think it's time for "shark bite" type electrical fittings. They will be pricey but convenient for these type installations.

Roger
I did a little research on them. I would need to do much more research to see if they were suitable for Section 501.30. (Bonding is a BIG deal in both Divisions 1 and 2.) I would definitely question their suitability in Division 1 as a substitute for threading.
 
Top