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-   -   Section 310.15(B)(6) vs. 210.4. Don't assume, call your friendly AHJs! (http://www.diychatroom.com/f18/section-310-15-b-6-vs-210-4-dont-assume-call-your-friendly-ahjs-139932/)

Daneel 04-11-2012 12:21 AM

Section 310.15(B)(6) vs. 210.4. Don't assume, call your friendly AHJs!
 
PROJECT HISTORY
 
An elderly Aunt of mine used to have 60-plus-year-old electrical service with some remarkable, non-standard features:
 
[1] The POA for cables from the power pole (about 11 feet above grade) was pulling out of the wall.
[2] The insulation on the 3x #10 entrance service between the bi-metal connectors and the weatherhead had pretty much cracked or peeled off.
[3] There was no ground reference.
[4] The entrance service conduit was 3/4" RMC.
[5] Entrance service was first connected to a triple-knife disconnect switch with 30A plug fuses.
[6] The Neutral was plug-fused just like the hots.
[7] LOAD terminals from the disconnect switch were connected to LINE terminals on the meter.
[8] LOAD terminals on the meter were connected to the sub-panel.
[9] The meter was mounted on an inside wall facing a window (for the meter-reader).
[10] The two pair of meter wires were exposed outside the wall (about 5 inches in length) and were protected with extra insulation sleeves.
[11] The sub-panel had no main lugs. The hots from the meter were straight-through #10 conductors with bared portions clamped in the sub-panel by metal strips that fed plug-fuse sockets.
[12] Each circuit in the sub-panel had both hot and neutral conductors fused.
 
I would include before and after photos, but I have not mastered this yet and did not find an "admin" link to ask. Is there a tutorial or description of this procedure, aside from the "album" route?
 
I was surprised by what I saw, but the wiring job seemed careful, with black pipe for conduit. Auntie's electrical system has been an uneventful part of her life. She has never blown out a 30A main fuse. She has gas heat, a gas stove, a gas water heater and a gas dryer. Auntie lives alone. She did not need an upgrade from an operating perspective. I just wanted her electrical system to be more safe. So I called the local power company.
 
The POCO moved the power pole lines to a temporary POA. An inspector came out and requested that we do three things:
 
(A) Replace service entrance conductors;
(B) Repair or replace the defective electric panel;
(C) Reattach the electric service bracket that holds the electric wires to the wall of the house.
 
We ended up doing the following:
 
{1} We demo'd the main fused disconnect panel. It had a curious arrangement of cutouts for conduit inside the wall and meter leads outside of the wall. The copper knife blades, contacts and terminals were dirty from 60 years of airborne deposits. I think the time to rehab this relic would not have been time not well spent.
{2} In 3/4" RMC, one can run up to 3x #8 or (maybe?) #6 THHN. I was unable to find #10, #8 or #6 cable with "sunlight-resistant" specs. It was not at all clear how to replace this knife disconnect panel, connect the entrance service first to the meter, and then to a new panel. And the wall had to be opened (behind the meter) if incoming conduit large enough to accommodate the smallest sunlight-resistant cables locally available were to be installed. So we removed the meter.
{3} We put in 3x #4 entrance service in 1-1/2" RMC service to a new panel ($59 -- I will call this Panel #B) that combines a meter base (not compatible with the old meter) with a 100A main disconnect breaker and room for at least ten circuits.
{4} We installed a #6 Armored ground -- water pipe to rod to Panel #B neutral/ground bus.
{5} We pulled out the guts of the sub-panel and turned it into a large J-box.
{6} We ran eight circuits over to the J-box through three conduits from the adjacent main panel.
 
What we did seemed to address the POCO's concerns and create a safer and much more Code-compliant electrical system than was there before. Well yes, but...
 
PROJECT GOING FORWARD
 
I spoke again with the same inspector. He could not approve the work because the meter was changed and unfused conduit entered the residence. I spoke with the City inspector. He was not concerned about placement of the meter but would not pass the entry of unfused conduit.
 
So the project is not over. We have to locate the meter and a disconnect panel (I will call this panel #A) on an outside wall. The POCO did the meter-spotting and was accommodating in where they will allow us to mount the meter base.
 
My current understanding is that if we had stuck with an easy re-pull of 3x #10 in the existing conduit, added a real ground, drilled extra holes in a new, two-pole 30A breaker panel to accommodate cable entry outside the wall for the existing meter, and kept the original non-standard meter wiring, with insulation sleeves and the original meter --- if we had only done that much, then the POCO would have said "fine, thank you very much" and the city need not have been involved. There appears to be no room for what seems to me to be a better (more safe, more Code-compliant, more forward looking) install. Unless it is strictly repair of an existing, already approved electrical system, if you change anything in the slightest way, then it must be 100% Code-compliant with current Code. And there is no "better but less than 100% compliant" place in the middle.
 
[Q1] Does anyone have an idea when this old style of wiring was in vogue?
 
My next questions have to do with Panel #A (either A1 or A2).
 
Outside we have to mount a meter base and -EITHER- (A1), a Main-Disconnect-Only breaker panel -OR- (A2), a Main-Disconnect-With-Additional-Circuit-Capacity breaker panel in which panel #B becomes a sub-panel.
 
(Alternative-1) If Panel #A is A1, Code Section 310.15(B)(6) entitled "...Dwelling Services and Feeders" seems to apply: "... For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part [of] or associated with the dwelling unit. ..." The cables between Panel #A1 and Panel #B would be the main power feeder with conductor size chosen from Table 310.15(B)(6) -- minimum size is AWG #4.
 
[Q2] If the Main-Disconnect were 100A, can the breaker(s) that feed Panel #B also be 100A or must they be less?
 
(Alternative-2) If Panel #A is A2, Code Section 210.4 entitled "Multiwire Branch Circuits" appears to apply.
For Panel #A, I was thinking of putting in a panel physically identical to Panel #B. This would be more forward looking if the next owner of the property wants to upgrade the electrical system.
 
[Q3] Am I reading the Code accurately?
 
[Q4] With (Alt-2), what is the minimum size circuit and wire I can run to Panel #B? Can I put a sub-feed 30A DP-breaker in Panel #A2 and use #10 in 1/2" EMT (where I have not already run 1-1/2" RMC)? I have enough 1/2" EMT and #10 wire in colors to do this. The POCO inspector gave me official meter bypass jumpers and a cover for Panel #B.
 
[Q5] I would run 3x #4 in 1-1/2" for the entrance service outside. Only the first section of conduit attached to the weatherhead has to be rigid. The rest can be EMT. Even with raintight connections, I wonder if EMT is a less expensive way to avoid dealing with threading RMC in exact lengths.
 
With permit and supplies costs so far, the project is way over budget. So I am looking to minimize additional cost here, but still be Code-compliant. I know I would need rain-tight connection hardware and would have to re-do separate Neutral and Ground buses in Panel #B.
 
Thanks for taking time to view this. Comments are appreciated.
Daneel

rrolleston 04-11-2012 12:35 AM

While my head stops spinning I will ask why not just replace the service and install a meter main panel?

a_lost_shadow 04-11-2012 01:12 AM

Alright, you seem to be jumping around a bit on your ideas. So I would suggest doing the following. First sit down, and come up with what you want to do next. Sketch it out in a very detailed manner. Then before you buy anything or do any more work, meet up with your inspector and go over you're plan. That way they can inform you of gotchas before you do any more work. Now here's my best attempt at your answers, but remember services are complicated and I'm only a DIYer.

[Q1] - Probably before I was born..:jester:

[Q2] - Once you hit your main 100A disconnect, everything past is now protected at 100A. So using a second 100A breaker won't introduce a safety problem. It could make diagnosing a trip difficult, since it'll be a toss up as to which breaker trips first. Now does panel A have feed through lugs? Since everything is protected at 100A, you could use feed through lugs to feed panel B at 100A.

[Comment on Q2] - Be nice to yourself and future owners, use the same brand and model line. That way spare breakers can be used in either panel.

[Q3] - When I was researching doing my service upgrade, I found there was a lot of disagreement about what exactly classified as the "Main Feeder". So I would definitely check with your AHJ for their interpretation. Online, the interpretation I found most common was: "if 100% of the houses electrical goes through the wire, then it's a main feeder".

[Q4a] - I've never heard of a minimum on the size of a breaker that can power a sub panel. If sized to small, the only issue I see with functional breakers is the small breaker tripping due to overloading.

[Q4b] - I suggest you look into conduit fill regarding the 1/2" EMT with 4x #10s. Doing a quick search, yields that 1/2" EMT can hold 5x #10.

[Q4c] - Can you use EMT where you're thinking. Probably, but you've started throwing around enough options that it's getting confusing. Once you form a clear plan, we can get back to this.

[Q5] - You can ask at the Big Box stores if they'll thread the RMC. One of the two in my area was willing to do it. Also, I've read mixed reactions to the use of EMT as service conduit. Finally, what does you're POCO require? Here the POCO demands RMC for the entire length.

rrolleston 04-11-2012 08:24 AM

Pictures of what you are talking about will also be helpful in pointing stuff out and making suggestions.


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