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-   -   Service mast bracing (http://www.diychatroom.com/f18/service-mast-bracing-105654/)

WillK 05-26-2011 12:30 PM

Service mast bracing
 
One of my corrections my inspector required was bracing the service mast because he goes by the height of the weatherhead. So I intend to brace it using 3/4" EMT conduit with the ends flattenned and drilled so it can be bolted at the insulator clamp at the top and bolted to the roof at the bottom.

My question is if there would be any issue doing the bottom attachment using lag screws into rafters, or if I should use carriage bolts with plates on both sides?

My plan for bracing is based on this:
http://www.electriciantalk.com/f9/he...er-mast-10341/

hpp58 05-26-2011 03:26 PM

Use a guy wire system. Available at the electrical supply house.

WillK 05-26-2011 03:31 PM

Yeah... inspector didn't like the guy wire idea.

I wish I had a chance to take a picture of another service entrance in the neighborhood. It's SEU cable. It goes up and forms the drip loop. It's suspended in the air and at the top it's about a foot from the house. It's not secured AT ALL to the wall. It's a corner house on the next street over from me.

Saturday Cowboy 05-26-2011 06:38 PM

why won't he let you use a guy wire??? It is better and does less damage to the roof.

WillK 05-26-2011 06:48 PM

He doesn't like the idea of it breaking and whipping around and hitting the hot conductors, plus he says he'd require one that has a UL listing for the application which he doesn't think there is such a thing.

Personally I'm all for 3/4" tube. I'd be able to do the strength calculations myself if I had to.

I really haven't been able to find any sort of guy wire system in my online searching, aside from some Thomas and Betts stuff that was only available in Canada. I saw some things for antenna applications, and some of the discussions I came across elsewhere made it sound like there's a move away from guy wire support for service masts.

Saturday Cowboy 05-26-2011 07:11 PM

ok....

hpp58 05-27-2011 10:22 PM

Quote:

Originally Posted by WillK (Post 655655)
He doesn't like the idea of it breaking and whipping around and hitting the hot conductors, plus he says he'd require one that has a UL listing for the application which he doesn't think there is such a thing.

Personally I'm all for 3/4" tube. I'd be able to do the strength calculations myself if I had to.

I really haven't been able to find any sort of guy wire system in my online searching, aside from some Thomas and Betts stuff that was only available in Canada. I saw some things for antenna applications, and some of the discussions I came across elsewhere made it sound like there's a move away from guy wire support for service masts.

What does your utility co. require?
I don't think that 3/4 EMT is listed for that use.

WillK 05-27-2011 11:36 PM

POCO requires no support if the attachment point is 30" or less above the roof for 2" rigid conduit. They don't require bracing at all. It's just my inspector that is requiring the bracing because he goes by the weatherhead. Which irritates the heck out of me because as a mechanical engineer, I know that the physics of the pole beyond where the load is applied is irrelevant.

If I had to guess, which is my only option until Weds., his reasoning may be that if I have another 12" of pole available (which I do) then somebody at some future date could move the service attachment up, resulting in the attachment point being above 30".

That being the case, the fact that bracing is unnecessary makes the strength a consideration of secondary importance. The real primary function of installing bracing is that, by attaching it at the service attachment, it keeps the attachment from being moved on the pole.

I guess if I think about it that way, I can also see why guy wire wouldn't serve that purpose since it should be installed with a turnbuckle and hence it could be readjusted in the event somebody wanted to move the attachment point.

I'm probably also overthinking this, but that's in my nature as an engineer.

On the question of EMT being approved for use, I did a search and this was discussed on Mike Holt's forum and their consensus seems to be that EMT without wiring is not covered in NEC. If there is no electrical involved it's just metal tube.

0.042" wall 3/4" tube I believe, which should be able to handle 1500 N of force or 337 pounds. (not sure what grade of steel is used for EMT, so I used the lowest available grade for my calcs) POCO says a 2" riser supports a maximum of 750 pounds of loading. I'd be using 2 pipes in a V for support bracing, so I'd practically be able to support the load with the braces. The braces would never see that load unless the anchors pulled out of the wall, and those are rated for more load each... Geometry plays into it, the bottom line is I could justify not needing the braces to carry load at all.

bobelectric 05-28-2011 05:14 AM

This needs a picture.

Jim Port 05-28-2011 06:41 AM

I think Will needs an inspector with common sense and a code book.


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