ECN Forum Forums General Topics of the Trade General Discussion Area Threading 2 1/2" Gal pipe.

Ed,
My entire life we used stright thread, even in field bends, your are right taper for plumbing straight for electrical, what they did, in the NEC is allow field threads to use tapered plumbers thread, a bunch of penny pinching contractores must of cried, about having to buy a stright die set, so they allowed the tapered thread to be used in the field. Many years of major conduit projects, and all were stright threads, even in the field.

I guess they figured by using the tapered thread, they slow down the leaking electrons.

Here we place our meters at the bottom of the mast That is, the PoCo rules not just to the meter, but up to the first overcurrent device. Everything upstream of that point is sealed by the PoCo. Therefore, I infer that PoCo rules apply.
(As a side note, have you ever noticed that most meter pans do NOT have any UL label on them?)

Does the NEC have a section on services? Sure, it does. This section, however, is largely irrelevant when there's a PoCo involved.

In practical terms, there might be an issue in areas of great smowfall. Since we usually use the "all in one" style of combined meter / disconnect / panel, it's not impossible for the PoCo to want the meter placed so high that some of the breakers are higher than the NEC permits.

As for the thread specification ... many factory-made electrical parts have straight threads, rather than tapered. That's not the issue. The NEC specifies tapered threads for "field made" threads ... which I consider applies to any threads you make, or have made.

Now why would they want a tapered plumbimg thread if you have a all the proper die sets, to make stright threads, did anyone ever notice how bushings and locknuts, used on tapered ends are loose, and tapered threads in manufactured products are sloppy, all i can see it they allow it for all the cheap penny pinching EC's that will not buy the proper tools, or tool manufactures must of decided they could save money and increase profits, by only making one set of tapered tools, so they lobbied for the change.

The tapered thread makes a much better grounding connection then does a straight thread. As far as I know factory conduit threads have always be NPT. Not sure when the rule for field cut tapered threads went into the code, but I would bet that it was put in to require the field cut threads to match the factory cut ones.
I do know that about 20 years ago that the Canadian code required tapered thread in the conduit couplings as well as on the conduit threads. When the conduit manufactures got the code changed so that they could supply the cheaper straight thread couplings, the electricians wanted to know why their conduit "leaked" in wet locations more than it did before.

Reno,
Where is the service point? Everything on the load side of the service point is covered by the NEC. As I said in my earlier post there is some dual coverage for things like the mast. In our area the service point is the line end of the service entrance conductors that hang out of the weather head, but the utility has rules that apply to the size and installation of the mast because it supports their service drop. The fact that the utility has rules, does not mean that the NEC does not apply.

In the 1968 NEC, Article 346 there's a note at the top of the page:



I don't have any copies of the NEC 1957-1965, but it didn't appear in the 1953 NEC.


From Allied Tube & Conduit's website:




The SCE Overhead Service Requirements state that GRC or IMC conduit be used for a mast, so there's no water pipe allowed, at least down here in So Ca. (Sierra Pacific's Requirements say that "Periscope service entrance per NEC, Article #230 and must be approved by SPPC prior to installation") I don't imagine that it would be the same anywhere else.

That's the 'fine print" I was referring to, Scott... it may say 'conduit,' but it doesn't say 'listed.' The only reason I brought this up was the possibility raised by the OP - that having a coupling might result in a much weaker mast.

ANSI specs for electrical pipe (RMC) and water pipe are identical, with the sole exception that electrical pipe is to have a 'smooth' finish inside. "Smooth" is not further defined; the clean weld seam you often see certainly looks smooth (not likely to snag or catch wires) to my eyes.

Our PoCo service specs are completely without reference to the NEC. Indeed, they are considerably more detailed and specific. Yet, there are no referenced to 'listed' or 'approved.' The install simply has to be acceptable to them - and they have no interest in what anyone else may think.

As for the use of straight threads on some electrical parts .... apart from 'running thread,' I have no idea how that situation came about. I don't think it was about saving money ... perhaps manufacturing processes came into play. Or, perhaps someone tried to over-engineer things. I simply don't know.

Keep in mind that the original 'conduit' was nothing but ordinary gas piping, with ordinary tapered threads. I suspect that the straight threads, and the conduit specs, came late to the party.

I believe we use running thread on things like box connectors so you know the lock nut is tight against the enclosure and not just tight on the threads. On the other hand when you screw RNC into a hub or connector you want a tight thread to thread connection.

Reno,



How can you say that? The quotation I gave was taken directly from your utility's service requirements.

("Periscope service entrance per NEC, Article #230 and must be approved by SPPC prior to installation")

To tell the OP to just use threaded water pipe is not at all acceptable in this case, where it might be turned down by the AHJ or the serving utility.

Even the standard tapered NPT leaks. The way the thread was designed in the 1800's, there is a small gap at the top of the threads, which always results in a helical leak path. That is why pipe dope or Teflon tape is always required with NPT plumbing joints. (I note that there exist other threads that seal without the need for a sealant.)