ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
NEC- 314.23 (H) (1)
by GWEnergy - 08/07/22 10:40 AM
Wiring method choice
by gfretwell - 08/07/22 01:29 AM
Back From Retirement
by Bill Addiss - 08/05/22 07:39 PM
Load Calcs for EVs and RVs
by renosteinke - 08/04/22 07:34 PM
The "N" in the THHN/THWN
by HotLine1 - 08/03/22 04:06 PM
New in the Gallery:
240/208 to a house
240/208 to a house
by wa2ise, October 9
Now you know.
Now you know.
by Tom_Horne, September 7
Who's Online Now
0 members (), 25 guests, and 13 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 4 of 6 1 2 3 4 5 6
Joined: Nov 2000
Posts: 2,148
R
Member
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.


Don(resqcapt19)
Joined: Dec 2003
Posts: 751
E
Member
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.


Earl
Joined: Jan 2005
Posts: 5,323
Cat Servant
Member
All right, I admit it, I was wrong ... there IS a reference to the NEC frown. BTW, who's SCE? laugh

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:

[Linked Image]

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.

[Linked Image]


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.

Joined: May 2003
Posts: 1,157
Member

Joined: Jul 2004
Posts: 9,707
Likes: 11
G
Member
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?


Greg Fretwell
Joined: Jul 2002
Posts: 717
M
Member
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.

Joined: Jul 2004
Posts: 9,707
Likes: 11
G
Member
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.


Greg Fretwell
Joined: Jul 2004
Posts: 625
S
Member
Originally Posted by gfretwell
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."

Last edited by SolarPowered; 05/30/08 09:50 AM.
Joined: Nov 2000
Posts: 2,148
R
Member
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(resqcapt19)
Joined: Jan 2005
Posts: 5,323
Cat Servant
Member
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.

Page 4 of 6 1 2 3 4 5 6

Link Copied to Clipboard
Featured:

Tools for Electricians
Tools for Electricians
 

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
RonKipperDatacom
RonKipperDatacom
Kansas City, KS
Posts: 30
Joined: January 2013
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
294,638 Are you busy
226,406 Re: Forum
211,643 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5