US standard , conduit pipe threads

[MBfreak]

Hi to all.

Can somebody please point me in the right direction on US standards for cable gland threads and conduit threads. In Europe we use "Pr" thread which is basically inches but called off in mm´s.

However, they do not match and I will have to make some US standard cable glands. Sizes are in the OD range 1 to 1,5 "

Best regards

Ola

 

[pattenp]

Are you referring to NPT (National Pipe Thread)? This is US standard.

 

[darkzero]

I believe it's National Pipe Straight (NPSM). Similar threads sizes & pitch as NPT but no taper. Not 100% sure though, I've never bothered to check, I just screw em together.

 

[Norcal]

I do believe that the conduit threads are 3/4" taper per foot but that may just be NPT as said above, rigid conduit threads are tapered, but the couplings are not.

Here is a copy & paste from the 2008 NEC.

344.28 Reaming and Threading. All cut ends shall be
reamed or otherwise finished to remove rough edges.
Where conduit is threaded in the field, a standard cutting
die with a 1 in 16 taper (3⁄4-in. taper per foot) shall be used.

FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe
Threads, General Purpose (Inch).

 

[hidollartoys]

It is NPT, not straight. I Know this 100% for sure.

 

[hh76]

rigid conduit is NPT (tapered), but rigid couplings, and most connectors for EMT are straight threaded.

 

[MBfreak]

Thanks for the replies.

I was under the impression that there was a separate standard for cable gland threads in the US also.
In Europe we have one, thread type " Pr "

Anyway.
One of the parts may be straight NPT or WP.
Outside dia is 7/8", inside 3/4" and has 14 TPI. I have run a 1/2" NPT tap thru, it was a bit stiff, but this may be due to a worn tap used at manufacturing in 1950.

The other part is off any thread table I have found.
Outside dia is 1 1/4" , inside 1 3/16 and 18 TPI. This is not even close to NPT, WP, UNC or UNF.

I may end up making and brazing in adapter parts.

Merry Xmas to all!

Ola

 

[walrus]

I doubt what you have is pipe thread, 7/8 would be close to OD of 1/2 pipe here in the states, slightly larger than actual OD of 1/2 pipe but ID would be 1/2. You have some thin wall tubing at least compared to pipe here in the states

 

[darkzero]

OP stated cable glands. In the US we usually call these strain reliefs. Since EMT connectors aren't actually strain reliefs I assumed he was referring to the connectors that screw onto squares/boxes. The threads on these connectors are not tapered. Even the connectors that screw into FMC aren't tapered. EMT is not supposed to be threaded so maybe the OP is talking about something else?


Here's an actual cable gland/strain relief that I installed my lathe. The thread on it was straight pipe thread but they're available in metric & other thread types too. Cable glands are used to prevent a cable from being pulled out & these type of fittings are not used with conduit (EMT compression fittings are similar but still have straight thread).

 

[Stuart in MN]

Cable glands are also called cord grips in the US. Here's a cut sheet for a Crouse-Hinds cord grip, they are plainly marked in the pictures as having NPT threads but I suppose other brands or models may be different. http://www1.crouse-hinds.com/crousehinds/newproducts/relatedinfo/FinalNCGsellsheet.pdf

 

[walrus]

Not sure how you'd get a threading die on a cord grip?

 

[MBfreak]

Hi Guys.
I have now learned that cable sealing glands do not have a US standard, at least not in the 40´s when the motors for the FUTURLINER body functions, such as opening doors, covers, were manufactured. I will dig out my TPI gear set ( used last time some 20 years ago) for the lathe and just make up parts to fit.
Best regards

Ola