Conduit threading

[wireman3736]

I have always understood that electrical and plumbing threads were different, I have read alot of conflicting imfo on this and even mentioned this at my code update course and was told they were straight even though I referenced 344.28, all the guys in the class agreed with him and said you could not use plumbing dies. I always new the couplings were straight but felt there was a taper in the pipes we threaded, I don't do much threading and just went with the flow since I wasn't buying them and only used them. Now that I work for myself I have been thinking about buying a ratcheting hand threader and a couple of dies for explosion proof I do once in awhile and service masts that I do quite a bit. Today I got my code question of the day that I get and more confusion. this is what it said.

Answer to Previous Code Question of the Day for Friday, June 23, 2006
Question:
Greetings:

I teach the first and secnd year curricula at the Denver Joint
Electrical Apprenticeship Training Program, and some of my students
have followed my suggestion to become subscribers to your Code Question
of the Day.

We would like to know definitively whether or not differences exist
between the appropriate thread pitches for threaded conduit and
threaded plumbing pipes. For instance, we know that the National
Electrical Code requires 3/4-inch taper per foot for rigid conduit.

We are told that threaded plumbing pipe also requires a 3/4-inch
taper per foot. That would certainly indicate that the same dies could
be used for all same-size piping needs on any given job, unless there
are differences in the pitch. Is it appropriate and correct to thread
both with the same set of dies??

THANKS!!
ED Knox
Aurora, CO 80013



Answer:
Hi Ed, thanks for putting your guys onto CQD. NECA 101-2001,
Standard for Installing Steel Conduits, Section 4.1.1 says "Although
coupling threads are straight-tapped, conduit threads are tapered. Use
a standard 3/4-inch per foot taper National Pipe Thread (NPT) die."

This is, indeed, the same die that plumbers use.


Section:
NECA-NEIS 101-2001


Source:
Charlie Trout

Can anyone convince me to what is right.
Thanks Stan

 

[LarryFine]

The threads are the same; the couplings are different. A rigid-conduit system should not be expected to perform as if it were 100% waterproof, whereas a plumbing system should.

 

[wireman3736]

Thats the info that i'm looking for, why are there so many that disagree. when I called a plumbing supplier and asked about dies he told me that he doesn't stock electrician dies because there straight dies but he could order them for me.

 

[infinity]

In the past when we've purchased threading equipment our supplier invariably asks if we want electrical dies or plumbing dies? Seems that the guy thinks that the two are different. NPSM dies are straight and are not for electrical conduit. For what it's worth in the past we've mistakenly used both types depending on what the supplier delivered to the job. In hindsight it seems that the straight ones allow for easier installation of the locknuts. Since all of this conduit was embedded in concrete we didn't lose much sleep over it.

 

[don_resqcapt19]

At a trade show a few years ago there were two conduit threading machines on display from two different manufacturers that only cut straight threads. When I told them that the code requires tapered threads, they said that they their customers wanted straight threads. They didn't care that they were aiding and abetting in the creation of code violations.
Don

 

[hillbilly]

344.28 requires tapered threads for pipe threaded "in the field" (2005). What about "factory" threads, what type are they? 344.42 says that "Running Threads" shall not be used on conduit for connection at coupling.
Looking for insight.
steve

 

[don_resqcapt19]

Steve,
Factory threads are the same as requied for field threads. Running thread is straight thread and can be used where not installed in a coupling. A common use is between ajacent panels.
Don

 

[hillbilly]

Steve,
Factory threads are the same as requied for field threads. Running thread is straight thread and can be used where not installed in a coupling. A common use is between ajacent panels.
Don

gotcha.
thanks

 

[sc57ford]

Standard Threads

Standard Threads

The NEC requires "standard threads" in Art. 555.13(B)(5). I assume that is the same as the running thread Don is speaking of above, ie, not a 3/4" tapered thread. In this case, Marinas and Boatyards, one would want water tight connections as a plumbers pipe thread would give you.

 

[dlhoule]

Steve,
Factory threads are the same as requied for field threads. Running thread is straight thread and can be used where not installed in a coupling. A common use is between ajacent panels.
Don

As usual Don is correct.

You can use standard pipe die to get your running thread. The portion of conduit extending beyond the die will be a straight thread. There are a few other places to use running thread but between panels is by far the most common.

 

[don_resqcapt19]

SC,

The NEC requires "standard threads" in Art. 555.13(B)(5). I assume that is the same as the running thread Don is speaking of above, ie, not a 3/4" tapered thread. In this case, Marinas and Boatyards, one would want water tight connections as a plumbers pipe thread would give you.

I would assume that "standard thead" is the tapered thread that is required for conduit. This thread is plumbers thread, but you can't have a water tight conduit system because our couplings are straight thread. With plumbers pipe, both the male pipe thread and the female coupling thread are tapered. This ensures solid metal to metal contact that produces the water tight connection.
Don

 

[paul]

While electrical threaded couplings are straight threads, the hubs and unions are not.

Since EMT compression fittings had to be made watertite, most likely due to some lobbying by the parts people, shouldn't threaded rigid also fall into that same category??? Why the discrepancy? I want to see some O-rings and/or gaskets to make sure there are no leaks.

 

[steve66]

I want to see some O-rings and/or gaskets to make sure there are no leaks.

I don't see anything in the electrical code that prevents you from putting pipe dope on your conduit couplings. Of course, you may get some funny looks from the other trades

 

[paul]

I don't see anything in the electrical code that prevents you from putting pipe dope on your conduit couplings. Of course, you may get some funny looks from the other trades

And from the forman, the boss and everyone else. I'd be heckled right out of the break shack for that one. Although I have been known to smear some copper coat on the threads where exposed to the weather. I do that more for corrosion protection on fresh cut threads, rather than worrying about water seeping in, especially when I'm installing it around the salt water.

 

[don_resqcapt19]

Steve,

I don't see anything in the electrical code that prevents you from putting pipe dope on your conduit couplings.

That would not make the conduit system watertight. The main purpose of pipe dope is to lubricate the threads so that they can be tightened enough to cause the direct metal to metal conduit that creates the seal.
Don

 

[don_resqcapt19]

Paul,

lthough I have been known to smear some copper coat on the threads where exposed to the weather. I do that more for corrosion protection on fresh cut threads, ...

That is required by 300.6(A).
Don

 

[tom baker]

Electrical conduit is not water tight. The couplings and hubs are not tapered. Use of Kopper Shield is an excellent practice, yes its messy and "it gets home before you do" but it limits corrosion and allows taking apart years later, as I have found out.
Burndy Penatrox e is the same as T&B Kopper Shield but is a squeeze bottle and easier to work with. Both look like the head gasket compound for cars.

 

[izak]

i have argued the tapered/straight thread issue before with someone and his position was, plumbers thread is tapered, electrical threads are straight, and we know this because when WE (electricians use the hogs-head threading die, we set it this way, and when the plumbers use it, they set it this way...


the hogs head threading unit on one side has a straight channel for the die to ride through, and if you TAKE IT ALL APART, you can turn it around to ride through a somewhat curved channell....

does anyone know what im talking about with the hogs head thing?

 

[Smart $]

FWIW...

A GRC/RMC Coupling = Galvanized Steel Pipe Thread Protector

 

[allenwayne]

Plumbers install pipe to keep water from coming out of it and if they fail it is know right away.We install pipe to keep water from coming in but if we fail we don`t know it till it is too late.