Unlisted NPT Couplings

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Wire-Smith

Wire-Smith

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Would any of you inspectors fail me for using hot dipped galvanized NPT plumbing pipe couplings with galvanized rigid conduit? I cannot find NPT conduit couplings(normal ones are NPSM (straight thread), if you know of any or have an idea of where i could get them please let me know. i know i could get a ul field evaluation, i think that is a waste, the couplings are ul listed for plumbing pipe, i know i could even get them listed for the use, just think that is a waste. And for the ones asking, i am using these for improved electrical connection at the joints and for water tight conduit, don't worry about telling me its a waste of time, you would be wasting your typing.

Thank you,
 
We just order RMC couplings and get them by the box. Should be a standard item for a decent supply house.
 
These are a regular everyday item.

I'd suggest putting your time into locating the correct UL listed rigid coupling rather than spending your time researching galvanized water pipe fittings.

Heck, I just looked on Amazon for about 5 seconds, and found .5-1.25" couplings in box quantities with prime shipping in stock.
 
infinity said:
They're standard, listed RMC couplings which makes them straight thread.
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I took the OP to be a request for tapered couplings, and asking whether the only tapered ones available (for plumbing) would be acceptable.

The wires don't contact the coupling, so I don't see why it would be an issue other than the obvious lack of listing.
 
Not sure why you would tapered thread couplings when standard listed RMC couplings are straight thread.
 
infinity said:
Not sure why you would tapered thread couplings when standard listed RMC couplings are straight thread.
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This is what the OP posted:
Wire-Smith said:
I cannot find NPT conduit couplings(normal ones are NPSM (straight thread)

And for the ones asking, i am using these for improved electrical connection at the joints and for water tight conduit, don't worry about telling me its a waste of time, you would be wasting your typing.
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The steel coupling that comes on a piece of galvanized steel water pipe is known as a “merchant” coupling. It is straight threaded just the same as a coupling on RMC. it has no taper to the threads. Just the threads on the pipe itself have a taper. UNLESS, You buy the cast couplings. Then each end is threaded separately with a taper matching the male tapered threads on the pipe.
 
If you want to improve water tightness use a thread sealing compound. Even with water pipe you need to do this or they usually will leak some. For those concerned about continuity, the threads still jam against one another and you still have continuity, the compound just fills any voids.
 
FWIW, in many parts of the world, straight threads are used for watertight joints, with appropriate joint compound. I worked, primarily as an electrician, for a couple years in Papua New Guinea, and managed to do more than my share of plumbing while I was there. All the threaded joints were BSPP, British Standard Pipe Parallel. And these were for pressurized domestic supply.
 
Dzboyce said:
The steel coupling that comes on a piece of galvanized steel water pipe is known as a “merchant” coupling. It is straight threaded just the same as a coupling on RMC. it has no taper to the threads. Just the threads on the pipe itself have a taper. UNLESS, You buy the cast couplings. Then each end is threaded separately with a taper matching the male tapered threads on the pipe.
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Are you saying you have found tapered conduit couplings? If so can you point me in direction to them?
 
I use kopr-shield joint compound. The joints are water tight, I point people to plumbing(gas and liquid) pipes that don't leak when they say stuff like that, your keeping water out but it is same joint. I know npsm can be assembled to watertight but npt also makes better electrical connection.
 
Wire-Smith said:
Are you saying you have found tapered conduit couplings? If so can you point me in direction to them?
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i am licensed as both a specialty electrician and a specialty plumber, for pump and Irrigstion work. We will install deep set submersible pumps on galvanized pipe, with the non-tapered merchant couplings. Do not have any leakage problems, even at 300-400 psi.

In my industry we have mostly gone to sch 80 or 120 PVC pipe for drop pipe for applications under 2 inch diameter and less than 400 ft depth. We cut and thread this pvc pipe, just like galvanized steel pipe. We use stainless steel couplers that are tapered. Though I have installed 1,000’s of feet of PVC pipe on black or galvanized steel merchant couplings. The reason I stop using pvc at 400 ft is that is as deep as the manufacturer will warranty it. I do know installers that think nothing of using it for a 700 ft setting. So any way, if the pump gets set deeper than 400 ft, I use galvanized steel pipe. Or if it’s larger than 2” diameter, it’s steel pipe only.

if you use a thread compound, you shouldn’t have a problem with straight threaded galvanized steel couplings. On non-potable applications I use Jet-lube Kopr Kote. On potable applications, I use Jet-lube Eco-safe, or one of the other quality thread compounds.

if you really want couplers with tapered threaded fittings, you have to go to the cast iron plumbing couplers. Available at Orange and blue big box stores or any plumbing supply. Any inspector will notice that you are using plumbing cast couplers though.

i did work for one drilling and pump contractor years ago, that had an application for left hand threaded pvc pipe. We had a Ridgid hand die set up to cut the left hand threads on the pvc pipe. We bought DOM steel tubing and made the left hand threaded couplers on a lathe in the shop. Of course the saying at that contractor was “Why buy it for $5000 if we can build it ourselves for $10,000”.

So use the standard conduit coupler with a thread compound. Or use a cast coupler with tapered threads, with a thread compound, and run the risk of the inspector rejecting it. Or machine your own couplers with a tapered thread. I would pick option 1.
 
Were our (USA) conduit couplings ever tapered thread?

I know that up until the early 80s, the ones used in Canada had tapered threads. The manufacturer's lobbied for a change in the Canadian standard because straight thread couplings are much cheater to manufacturer.
 
don_resqcapt19 said:
Were our (USA) conduit couplings ever tapered thread?

I know that up until the early 80s, the ones used in Canada had tapered threads. The manufacturer's lobbied for a change in the Canadian standard because straight thread couplings are much cheater to manufacturer.
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I have seen very old installations with tapered, they started with actual plumbing pipe/reusing gas pipe that had tapered coupling.

Thanks for the Canadian thought, I will look for them from that angle, perhaps someone up there still makes them.
 
Not to derail the thread much. But my pipe threading knowledge is basically nonexistent.. any good sources to learn more as I don't get it in the field?

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