I'm preparing to do a service that requires a 16 - 17' mast(The property slopes away from the street and the POCO's lines are on the opposite side. The meter pan's location will be on the back side of the garage peak, so I'll need to project far enough above that so I'll be able to have a 18" drip loop.). I have a 7' piece of 2 1/2" gal and need to get that threaded to be used as the bottom piece. I spoke to a master plumber and he said that most plumbers only go as far as 2" pipe. The orange box store said the same. Any suggestions? pete

You need to get up close and personal with someone at a company that regularly works with larger size pipe and has the equipment to thread that pipe.

This is a good contact to develop anyway for all sorts of reasons (like this) and the occasional smaller job a regular customer of theirs needs but they don't want to mobilize for.
May be right up your alley.

Humbug!

I recently needed some 4" threaded pipe .... the plumbing supply house had no problem providing me with the pipe I asked for, cut to length, and threaded. Since pipe commonly comes in 20ft lengths, they ought to be able to make a piece for your mast - if you can transport it.

BTW, it may be a fine point, but I don't think a service mast need be made of 'listed' material. Conduit, yes ... but the code is silent as to the mast.

Failing a friendly supply house, any machine shop with an "engine lathe" ought to be able to cut the threads into anything up to 4" OD.

why not just put the bald end on the top?
or are you concerned about the coupling up there ?

Pipe comes in 21 ft lengths

There's always threadless couplings and connectors too. Yes they are a little more expensive, but may be worth the cost in this case.

Thanks for the correction

Rigid makes an attachment gear for threading 2-1/2 thru 4" galvanized rigid. Trade slang is I think hog leg. I just now walked into my shop to look at the model number. 4P-J . You use it in conjunction with a Rigid 300 and a porta pony threader. A new one would be way too pricey if you only are using it this one time. Some hardware stores have a stand up threader that threads up to 4" for threading pipe they sell. Call around.

My first reaction was to put the "bald" end up top, but the AHJ wants the smaller length closer to the meter pan. I believe that his reasoning is that you'll have more meat attached to the house before it goes through the roof. Two clamps and then through the roof (in the 7' of pipe) vs. 1 clamp on the 3' (leaving the 3' beyond the roof out of these calc). Also, I guess since the coupling is further down you'd have less strain on it. It's an 84' drop from the pole to the house. Thanks for all the suggestions.

Call around, threading dies up to 4" are pretty common on threading machines. I know that both plumbing suppliers I regularly deal with have them. I'm sure someone in your area does too.

Locally a metals supplier/fab shop was threading pipe for $10.00 a thread it's been a while so may be more now.

Any big commercial/industrial electrical contractor should be able to thread pipe. I remember at my old job we used to thread pipe for smaller companies/individuals sometimes.

I guess a machine shop should be able to thread pipe but electrical-type threads aren't the same as machine threads are they?

Judsin, a machine shop can make any kind of threads you want. It's their business to cut, drill, and shave metal into unusual - yet precise - shapes.

In our case, the NEC says to use NPT taper threads. That's all you need to tell the shop.

reno,
How is the mast not conduit?.

The mast is subject to PoCo rules, not NEC rules .... and PoCo specs, at least in my experience, lack such terms as 'listed.'

The mast should be installed IAW PoCo standards. The rule of thumb is the PoCo is responsible up to the meter until something goes wrong with it then it is the customers that suddenly becomes responsible.

Threading ridged conduit, the threads are the same as a water pipe. NPT is the standard. Take any plumping fitting and you can easily thread it onto a peice of stock ridged pipe.

I thought conduit threads were straight where plumbing threads are tapered. I know that I have tried to use a plumbing nipple before as a conduit nipple and the locknut won't thread all the way down, while at the end, the locknut is very loose-fitting.

The mast is typically on the load side of the service point and is covered by the NEC. In addition to being covered by the NEC, there may be size and support rules from the utility if the service drop is being supported by the mast.

Ed,
Conduit and plumbing pipe both should have the same threads... 3/4" to the foot taper.
NPT - National Pipe Thread Taper ANSI/ASME B1.20.1

This is the thread that is specified in 344.28 and its FPN.

The real difference is that conduit couplings are straight thread and plumbing couplings are tapered.

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.)

Solar,
While NPT may leak, it has a much tighter seal than when conduit is used with straight thread couplings. You can get a good interference fit when both the male and female parts are threaded.

230.43 covers allowable wiring methods for service-entrance conductors. We cannot use plumbing pipe. Must be listed conduit: either RMC or IMC for masts.

All right, I admit it, I was wrong ... there IS a reference to the NEC . BTW, who's SCE?

Now, let's look at exactly what both the local (SPPCo) specs, and the NEC have to say about the periscope mast.

The PoCo spec says "minimum 2" rigid steel." That's it. There is also considerable detail as to bracing, etc., not included in the NEC. I've attached a copy.

The NEC, regarding "Service Masts as Supports," simply says "it shall be of adequate strength." Further on, it continues "Where raceway-type service masts are used, all raceway fittings shall be identified for use with service masts."

Now, the wording of all those citations seems to suggest that there is no requirement to use ant particular material - that the mast can be made in nearly any manner, including by using conduit. There is a notable failure to use words such as "listed," or even specific trade terms, such as 'rigid metallic conduit.'

Lest we forget from whence we came, this pic shows a house here that has already had one service upgrade:



Please note that the original mast was all wood; the steel mast is 1 1/4 RMC (I assume), and was replaced (by me) with the current 2" RMC.

I apologize for the size of the next file, but I wanted everyone to be able to print off a good copy. This is one page -of about five- of the local PoCo specs regarding overhead residential service drops.




As outrageous as it may seem to use water pipe, the amount of weakening that may be caused by coupling two pieces together, rather than using a single piece of pipe, is not to be casually ignored. 100 ft. cable drop, 80mph winds, inclines and other reasons requiring a substantial projection above the roof .... all can require the 'standard' methods be reviewed.
For example ... that 40" maximum projection above the roof shown in the PoCo specs ... I was REQUIRED to exceed that by clearance requirements over an intervening building. Naturally, that mast required some substantial bracing.

Again, let's return to the very basics of the NEC (as outlined in Article 90). 90.4 make clear that it is the responsibility of the AHJ to interpret the rules, approve materials and methods, etc. "One size fits all" works in codebooks just about as well as it does in clothing .... that is, it doesn't - and this discussion underscores that point.

This pdf makes me think its not water pipe.

http://www.nevadapower.com/services/business/construction/distribution_standards/rr/RR-2.pdf

I guess the real question is whether there is any difference in the pipe? Does this all come off the same assembly line in China and some gets marked as conduit, the rest gets marked as plumbing pipe?

I was taught a very long time ago that the reason for tapering the threads is that it allows explosive gases to cool as they are forced out thru the threads if there is an internal explosion in a rigid conduit in a hazardous enviroment. This info may not or may be true, I have no idea. Never researched it at all.

I have always heard that the tapered thread pipe actually seals metal to metal. The "dope" or "teflon" is only there to act as a lubricant.

Unfortunately, that's not the case. See for example, http://en.wikipedia.org/wiki/National_pipe_thread , which explains, "... a clearance remains between the crests and roots of the threads, resulting in a leakage around this spiral. This means that NPT fittings must be made leak free with the aid of thread seal tape or a thread sealant compound."

Jon,
If you put wire in it is conduit. The fact that it is also used as a mast does not change the fact that it is a raceway and is covered by the NEC as it is installed on the load side of the service point. The NEC requires all raceways to be listed.

Don, that's where the NEC has me puzzled. It starts off by saying IF raceway materials are used as the mast ....

As shown in my first pic, there are plenty of way to have a mast- without using a raceway at all.

Otherwise, the language seems to suggest that there just might be other ways to make a mast, apart from using electrical conduit. Are they suggesting this? Or, are they referring to perhaps using, say, EMT for the wire - and something else to take the loading? I simply don't know. It seems that if the code panel wanted to require you to make the mast in a particular manner, with particular materials, they certainly could have said so.

IMO
The service mast can be a raceway type or another type such as wood.
That would include other methods such as cable or the other approved methods.

230.28 Service Masts as Supports.
Where a service mast is used for the support of service-drop conductors, it shall be of adequate strength or be supported by braces or guys to withstand safely the strain imposed by the service drop.
Where raceway-type service masts are used, all raceway
fittings shall be identified for use with service masts. Only power service-drop conductors shall be permitted to be attached to a service mast.

As a guy who uses both pipe and conduit I'd say they aren't the same. Maybe its just who manufactures it but the galv coating on pipe doesn't look the same as the coating on conduit. On the other hand I see no difference on the inside, in other words I doubt its a safety hazard to use pipe for a mast?

Walrus, that's kind of the dangerous ground I'm walking on, in suggesting the use - in certain circumstances - of plumbing pipe.

First of all - as a reminder - the AHJ has the authority to approve alternate materials. Article 90 and all that.

Secondly, in the case of pipe .... "listed" seems to be, in this case, a distinction without a difference. (I can hear the howls already!) That is, pipe is a pretty straightforward product, and the ASTM specs for the two products ensure that the similarities are more than skin-deep.

After all, what's there for UL to inspect? Look inside, and say 'yup, it's smooth?'

I've been down this road - the use of plumbing pipe - a few times before. While this was (in the past) on account of the materials needed for chemical resistance, and was run past the AHJ for approval, the principles apply here.

Indeed, I've also had a job where rectangular, structural steel tubing was used as a raceway ... with AHJ approval. It was simply a solution to a wire protection problem. The point, again, is that there IS room for innovation.

Not that any of this is to taken as a wholesale disregard for the usual practices. I've yet to make a mast, myself, from anything but listed RMC. I have no plans to do so, either. If I had a mast that needed to project above a roof more than 7 ft., and my run to the meter below the eave was more than 5 ft., I'd surely consider it, though - along with substantial additional bracing!

Reno, you can cite 90.4 all you want until you're blue in the face.

The fact of the matter is that barring the AHJ's intervention in the process......plumbing pipe is not in accord with the NEC.

I suppose the question to be asked of the AHJ is, "May I have permission to use this unspliced section of plumbing pipe to make this service mast?

Who ever denied involving the AHJ?

My bet is if you installed it in a secure manner, following all the other NEC rules the AHJ would sign the card and drive away without ever suspecting that was plumbing pipe or really caring.

Dang! You mean that "Union-made, UL-Listed" label was on the part I cut off before I threaded it? I took that down to the recycling yard last week.

Whew, Been away from the forumns for a little while, but it did stir up some discussions. Went to the local Blackman Plumbing supply. I was told that they will thread pipe up to 4" in diameter. Good, I thought, I'm good to go. Got to the counter and they said, "We don't thread any one else's pipe. You'll have to buy a length here and we'll thread it for you." Okay I figured, let's price it out. "Hmmm, a length of 2 1/2 gal pipe, and I'll give you a full trade discount, ummmm $182.00." (Seemed a bit excessive to me. Some discount!) Plus I'd have to pay an additional $20.00 to have it cut and threaded. I'll ask the local AHJ if I can use a 2 1/2" compression connector ($50.00). Why didn't I think of that before? D'oh....

The Pipe that Blackman would thread for you, are the threads electrical pipe threads? I think there is a diffrence with the taper. Sounds like the 2 1/2" Comp. connector would be OK.

There is no difference between plumbing pipe and conduit threads. They have the same tape...3/4" per foot.