Service masts support

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kevinware

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Louisville, KY
Good after noon everyone,
I need some opinions on NEC section 230.28. My situation is this: I am upgrading the service on a 80 year old house, don't worry the house itself is structurally sound it just has a 60 amp service panel right now and I am looking to upgrade it to the minimum 100 amp. My question deals with the overhead service mast support. Table 310.15(B)(6) tells me the minimum conductor size I should use is #4 AWG (copper). Using three conductors annex "C" table "C8" under THHN/THWN tells me I can use 1" RMC. (so far so good? or should I use THW?) As the service exist now on the house it looks like it will not meet compliance with 230.24(B)(2) so I was going to install a service mast using 1" RMC. The mast will be a through-the-roof installation close to a corner so I was going to try to apply 230.24(A) exception No. 3. What all this rambling on boils down to is this I guess. Section 230.28 makes this statement "Mast shall be of adequate strength or be supported by brace or guys to withstand safely the strain imposed by the service drop". How do I know what adequate strength is? If I can apply 230.24(A) exception No. 3 and get my 18" clearance and still have 12 feet over the driveway I understand I don't need a brace to support the mast, but if I have to go 3 feet above the roof with 1" RMC do I need to start thinking about guys and braces or will 1" RMC be strong enough to handle the strain? Please give me your opinion on this ideal and my application of the NEC.

Thanks for all your help,

Kevin
 
Re: Service masts support

I would suggest that you contact the power supplier first & see what they require. In the areas I work in the power suppliers require that the min. size of the service mast has to be 2" GRC if it is going to support the over head service conductors. Keep in mind that the conductors that are exsposed out side the weather head has to be sun light resistant as required by Art.310.8(D).
 
Re: Service masts support

I agree with John. The PoCo will have to tell you what they will connect to.

You can put together a NEC compliant installation that easily flies in the face of what the PoCo needs. As a general rule, the PoCo will have a published document that specifies what they will connect to, and what their meters require.

There may also be a Local Ordinance spin on service configuration. . .I'm thinking of some areas that run the service mast inside the wall with limits on degrees of bend.

In my area, though hardly publicized, the PoCo says I have to contact them even on a service panel change out where the point-of-attachment and service conductors are not altered, to see if "reconnection" of the "new" service will meet their requirements in effect today. In extreme cases, changes of land use and building configuration (especially other buildings), can dictate relocating the point-of-attachment.
 
Re: Service masts support

The POCO I deal with specifies a 2" RMC although I did manage to get a connection to a 1?" when the drop was only about 75ft. to a 150A service.
 
Re: Service masts support

My POCO only required a 3" RMC mast for my 400A service. However, the inspector required a leg or guy kit because the service drop was over 100' long (it was 110'). This seemed excessive to me, but what is required seems to be an inspector's call. At least all of the inspectors in the state seem to use the 100 foot rule.
 
Re: Service masts support

Our inspectors don`t make the call of attachment.That is soley on the poco side of the fence NEC compliant he passes it.They don`t accept the install,It`s game on ;) County releases the install,Poco turns it down and a new permit is required to comply with poco ;)
 
Re: Service masts support

Times have changed, back in the day,We did 100a services with #2cu. and 1-1/4 inch pipe. I didn't think that would ever change!!!

frank
 
Re: Service masts support

Here in NJ the POCO requires 2" RMC also. The one big stipulation it that there isn't a coupling above the roof line. Many contractors start out with a 10' length of conduit out of the meter pan, then realize they don't have the clearance above the roof so they add on a 3' or 4' nipple which puts a very weak point in the RMC.
 
Re: Service masts support

We are required a minimum of 2" RMC by the POCO in our area. We only install 200 amp meter pans, service stem and wires sizes, no matter what comes out of the load side of the meter pan.
Be it 100, 125, 150 or 200.
We tend to keep our customers for a long time and the extra cost is not that much.
If the customer wants to upgrade to a 200 panel in the future because of added load- swimming pool, spa, welding machine, ect. The service from the meter pan UP is there.

Just a thought. It works out quite well.
 
Re: Service masts support

Thanks everyone I did check with the power company in my area and there was a handbook that covered the specs for a service mast. The handbook requires a minimum of 2" RMC. Thanks for everyone's help. The handbook is really going to be helpful in the future. Thanks again everyone........man I love doing what I do.

Kevin
 
Re: Service masts support

man I love doing what I do
Click to expand...
You have to love it Kevin. Why else would any sane person drag a roll of romex, hammer and a box of staples through a dusty attic in July for what we make. ;)
 
Re: Service masts support

Check the manufacturer's data for the weatherhead and any LBs that you are using. In some cases you must use 1 conduit size larger than what the Chapter 9 tables requires - the weatherhead or LB must also have enough wire bending space. Same also for Fine Print Note #2 for jamming in bends.

First Energy requires a minimum of 2.5 inch galvanized rigid conduit for service masts. At this size, you might as well go for 200 amps. Also, your inspector may require a guy line unless the conduit is well braced with 2x4 or 2x6 blocks that are nailed into the rafters. Today, you need to do quite a bit of carpentry work to get a service mast to work. Last service mast was 400 amps and I used quite a bit of ordinary 2x4s as well as redwood 2x6s to create a mounting surface that was independent of the siding. The siding in this case was also redwood.

A lot of utilities prohibit recessing a service and socket so many times you have to build a wood surface for mounting a service such that the siding people will not recess the service. Around the corner last summer an electrician forgot to ask of foam insulation would be going in because foam insulation was NOT on the print.

That said, at about the same time I said to our general contractor, "Since when do we get correct prints?" he said, "Never!"
 
Re: Service masts support

It is interesting that we all sell the same product and our rules are all so different. I must echo everyone else's opinion to check with the serving electric utility. :D
 
Re: Service masts support

You would still need to install some 2x6s where the mast passes through the rafters or joists so that the conduit is firmly braced by the structure as close to the weatherhead as possible.

The minimum size mast for First Energy is 2.5 inches unless the span is very short say 30 feet or less.

Also, running galvanized rigid conduit ( or metal clad cable ) from the meter socket to the service switch does two bad things:

1. It creates a parallel path for neutral current unless the neutral is attached to an isolated neutral bar in the meter. Milbank makes an insulated neutral bar for this purpose.

2. Any kind of steel conduit or cable armor disables any kind of surge or lightning protection in an electronic meter. The steel acts as an inductance core that keeps lightning current from following the neutral. This can explode or blobify the meter. You would need a grounding electrode conductor from the meter to the nearest grounding electrode in as straight a line as possible with this GEC outside of metal enclusures. A 10 foot ground rod that is driven beneath a basement floor will be superior to one driven fron the surface unless the surface driven rod is say 18 feet long using rod couplings. Essentially, GRC or EMT requires an external bonding jumper to provide a lightning path.

On a further note, about 97% of lightning damage in a telephone cable plant is from silent or invisible lightning. When a big one does stike, you have about 100 side strikes over a 100 yard radius.

Also, NEC 300.6(A) requires that you use Noalox(R) or Penetrox(R) A or A13 on the GRC threads.
 
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