# RMC/IMC thread engagement length



## MDShunk (Jan 7, 2007)

At one time I had a nice laminated note of thread engagement lengths for all the sizes of RMC/IMC conduit. Handy for knowing how much to add before you chopped it off and threaded it. It’s slightly different than plumbing engagements, since plumbing is tapered thread fitting to tapered thread pipe, and electrical is straight thread fitting to tapered thread pipe. I remember 1/2” pipe was 1/2”, 3/4” pipe was 5/8”, and 1” pipe was 3/4”, but I don’t remember the rest. Anyone have a link to a chart like this or know the rest off the top of your head?


----------



## Southeast Power (Jan 18, 2009)

MDShunk said:


> At one time I had a nice laminated note of thread engagement lengths for all the sizes of RMC/IMC conduit. Handy for knowing how much to add before you chopped it off and threaded it. It’s slightly different than plumbing engagements, since plumbing is tapered thread fitting to tapered thread pipe, and electrical is straight thread fitting to tapered thread pipe. I remember 1/2” pipe was 1/2”, 3/4” pipe was 5/8”, and 1” pipe was 3/4”, but I don’t remember the rest. Anyone have a link to a chart like this or know the rest off the top of your head?


It would be interesting to know if that measurement is the depth of 5 threads in each of the pipe sizes.

Page 4:
www.ideadigitalcontent.com/files/11508/GalvanizedRMC_catalog_11-JMC-0037_061812.pdf


----------



## splatz (May 23, 2015)

from http://www.jgbhose.com/technical-reference-literature/normal-engagement-length.asp

Thread Size	"A"
1/8" 1/4"
1/4"	3/8"
3/8"	3/8"
1/2"	1/2"
3/4"	9/16"
1"	11/16"
1-1/4"	11/16"
1-1/2"	11/16"
2" 3/4"
2-1/2"	15/16"
3"	1"
4"	1-1/8"
5" 1-1/4"
6"	1-5/16"
8"	1-7/16"
10"	1-5/8"
12" 1-3/4"


----------



## Southeast Power (Jan 18, 2009)

Im not sure of the measurement or for other trades but our requirements are 5 threads maybe due to the introduction of metric measurements:

This section requires that metric threaded entries shall have a specified class of fit of 6g/gH and that a minimum required number of threads are engaged based on the Group Classifications. 
The section was rewritten for clarity in the 2017 NEC® however certain aspects remain unclear. 

The intended requirement is that the *thread engagement shall be no less than 5 threads made up wrenchtight for Groups C, D, IIB, and IIA* and no less than 8 threads made up wrenchtight for Groups A, B, IIC, and IIB +H2. 

*This metric fit Class is similar to the unified straight thread Class 2 fit. *The end-user does not need to be concerned with this class of fit where the product is listed. This requirement is controlled between the equipment manufacturer and the listing agency.

I have no idea what the 8 thread requirement is for. 

https://www.emerson.com/documents/a...ents-of-articles-500-516-of-nec-en-518452.pdf


----------



## glen1971 (Oct 10, 2012)

I usually just measure a factory end on a new stick, then write it down near the bender/theader for that job.. It's also one of those things, if I was running 2" every day, I could tell you.. But when you don't do it every day, it is no where near the front of my memory..


----------



## bill39 (Sep 4, 2009)

MDShunk said:


> At one time I had a nice laminated note of thread engagement lengths for all the sizes of RMC/IMC conduit. Handy for knowing how much to add before you chopped it off and threaded it. It’s slightly different than plumbing engagements, since plumbing is tapered thread fitting to tapered thread pipe, and electrical is straight thread fitting to tapered thread pipe. I remember 1/2” pipe was 1/2”, 3/4” pipe was 5/8”, and 1” pipe was 3/4”, but I don’t remember the rest. Anyone have a link to a chart like this or know the rest off the top of your head?


I've never even heard this term before but you have my attention. Are you talking about the threaded length on a factory piece of rigid conduit? And is this just so you'll know how far to thread a pipe in the field?


----------



## glen1971 (Oct 10, 2012)

bill39 said:


> I've never even heard this term before but you have my attention. Are you talking about the threaded length on a factory piece of rigid conduit? And is this just so you'll know how far to thread a pipe in the field?


I believe he is talking about how much to add to a measurement if you measure the edge of a fitting, like an LB.


----------



## TGGT (Oct 28, 2012)

glen1971 said:


> I believe he is talking about how much to add to a measurement if you measure the edge of a fitting, like an LB.


I think he's just trying to match factory thread length. I do the same thing. Some guys run the pipe all the way to the face of the threader making the length too long which is terrible for spinning into couplings or even condulets without locknuts.

Sent from my SM-G930T using Tapatalk


----------



## Lone Crapshooter (Nov 8, 2008)

From THE AMERICAN ELECTRICIANS HANDBOOK 9th addition

Found this on page 9-29 table 67 STANDARD CONDUIT DIMENSION OF THREADS
EFFECTIVE LENGTH OF THREAD INCHES
1/2 .53
3/4 .55
1 .68
1 1/4 .71
1 1/2 .72
2 .76
2 1/2 1.14
3 1.20
3 1/2 1.25
4 1.30
4 1/2 1.35
5 1.41
6 1.51

Hope this was helpful

LC


----------



## MDShunk (Jan 7, 2007)

Lone Crapshooter said:


> From THE AMERICAN ELECTRICIANS HANDBOOK 9th addition
> 
> Found this on page 9-29 table 67 STANDARD CONDUIT DIMENSION OF THREADS
> EFFECTIVE LENGTH OF THREAD INCHES
> ...


That is it. Thank YOU!


----------



## Southeast Power (Jan 18, 2009)

Lone Crapshooter said:


> From THE AMERICAN ELECTRICIANS HANDBOOK 9th addition
> 
> Found this on page 9-29 table 67 STANDARD CONDUIT DIMENSION OF THREADS
> EFFECTIVE LENGTH OF THREAD INCHES
> ...


Wow,
You must have a slow modem. :biggrin:


----------

