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Discussion Starter #1
1) Which table applies for the wire size I need for my wire going from my main panel, underground through 2" rigid metal conduit, to my garage where I intend to instal a 100 A subanel?

2) Which table applies for the wire from my meter to the service mast where I am putting in my wires in preparation to upgrade to 200A service and change the loction of the service entrance?

3) I have 4/0 aluminum SEU to go from the meter to the panel, please tell me I'm okay on tht one, at least in that case though it's only a few feet so not to big of a deal ifI have to get copper.

4) My understanding is that I can use the rigid metal conduit (buried) as my ground conductor, is this correct? I assume I'm still also putting my ground rods at the garage and my new service entrance, so do I bond both the conduit and ground rod at the respective main and sub panel ground bus or can they be wired together outside?

I'm just getting confusd because I start talking to these guys at Home Depot and the seem to think all I need for the 100A to the garage is 2 AWG and I know they're probably informed basedon table 310.15 but I've heard it over and over here that 2 gage aluminum is good to 90A except for service entrance, and I've heard the same from my inspector.

I'm going to an electric supply store to get this, but I want to be sure I go in knowing EXACTLY what I need and what code references are because electric supply stores are only open during the day, so it's time off work to get there and I can't easily make multiple trips in evenings like I can with Hme Depot. That and the fact that when I spoke with one electric supply store, the guy seeed to also think 2 ga. aluminum was good to 100 amps.
 

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Scared Electrician
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1. table 310.15(B)(6)

2. same

3. 4/0 al FEEDERS can be up to 200a

4. yes metal conduit can be used as a GEC, ARE YOU using RGC not EMT?? the RCG is too hard to install for a DIY. PVC pipe is far cheaper to install and easier, then install a ground, remember that the ground can be undersized. fro 200a=#6cu #4al - table 250.122 SOMEBODY CHECK THAT PLEASE. i think i got the right table :)



don't take advise from HD. I shouldn't have to tell you this. Go ask the guys at the electrical supply shop if you don't trust us:laughing:
 

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Discussion Starter #3
Well, okay I have to ask on question #1 because that would tell me that 2 gage aluminum should be good to 100 amps for my subpanel, and while HD guy thinks 2 gage is good to 100 amps, I've been told here and by my inspector that 2 gage aluminum for a subpanel is only good to 90 amps and that suggests that for the subpanel I need to go by the 75 degree C column in 310.16.

And as I said in another thread, I definitely have the $50 RGC pipes not the $16 EMT pipes. I don't anticipate any issues using it, the distance between the garage and house is 31 feet, so 3 lengths of 10' pipe with long radius elbos should fit perfectly in between, I'll just have to angle the trench to make it fit, then I'll rent the tools to cut and thread the pipe for the risers. Other than filing the edges smooth, anything else I'm missing?
 

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Scared Electrician
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1. Remind the inspector that the wires going from your main panel to your sub panel are feeders, as such they can use the mentioned table. Not saying that you will be able to persuade him but you can try. Or you can use this argument: It is only 90a wire and I am allowed to use the next size breaker(100a).


Sounds like you are going in to the RGC with open eyes:thumbup:
 

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90 amps is a standard breaker size so the next size up exception would not be allowed.

Unless the cable carries the entire load of the dwelling you need to use table 310.16. #2 AL =90, unless in a cable like SER where it would be 75 amps.
 

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Discussion Starter #6
Sounds like you are going in to the RGC with open eyes:thumbup:
So I did some dry fitting on the RGC last night to see how well it would fit between the house and garage, and it lines up best to go into the garage at the corner on the side rather than the wall that faces the house.

So I know the idea is to keep the conduit run water tight. I'm thinking maybe I should use rectorseal or something similar on the joints, anything wrong with that?
 

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So I know the idea is to keep the conduit run water tight. I'm thinking maybe I should use rectorseal or something similar on the joints, anything wrong with that?
This is not at all true or necessary. This is not plumbing work.

The inside of an underground conduit run is considered a wet location in the eyes of the code, and a conduit with water in it is petty typical.
 

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Get some #1 Aluminum conductors if you want a full 100 Amps capacity out there.

If installed in a raceway system, type XHHW or THWN insulation would be appropriate.
 

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Discussion Starter #9
This is not at all true or necessary. This is not plumbing work.

The inside of an underground conduit run is considered a wet location in the eyes of the code, and a conduit with water in it is petty typical.
K thanks for clearing that up.

I just bought 1/0 aluminum conductors for the 100 amp subpanel feed, I just wanted to be sure that I would absolutely not be undersized. I had actually bought a 125 amp subpanel so I could go up to a 120A breaker on the main panel if I was able to find such a thing... Homeline panel on both ends, I'm only seeing 110 amp and 125 amp breakers on their web page though. I'm perfectly happy with 100 amp anyway for now.

I did go to a pretty solid electrical supply store, but they tried to tell me #2 aluminum was okay for subpanel feeder.

I know for certain my inspector would've rejected it because I had run my 200 amp panel as a subpanel using #2 with a 60 amp breaker in the main panel, and I asked if it would've been allowed to use a 100 amp breaker or if the highest I could go is 90, and he said 90.
 

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Discussion Starter #10
This is not at all true or necessary. This is not plumbing work.

The inside of an underground conduit run is considered a wet location in the eyes of the code, and a conduit with water in it is petty typical.
Actually, let me ask this then... I have a 125 amp panel, 1/0 aluminum would be rated for 120 amps. Homeline breakers available are 110 amps and the next size available is 125 amps.

Would this exception allow me to use the 125 amp breaker for feeding this subpanel, and if so what is the code reference if I needed it?

I'm considering perhaps putting in electric baseboard heat and not bothering with the gas furnace. Maybe that would make more sense for the workshop usage on weekends in cold weather where I probably just don't need to heat it full time.
 

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Scared Electrician
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check out section 240.6A standard sizes and 240.4B ~"next higher standard overcurrent device rating" above the ampacity which we find from table 310.16 or other such tables.
 

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Discussion Starter #12
So it states:

(B) Devices Rated 800 Amperes or Less. The next higher
standard overcurrent device rating (above the ampacity of
the conductors being protected) shall be permitted to be
used, provided all of the following conditions are met:​
(1)​
The conductors being protected are not part of a multioutlet
branch circuit supplying receptacles for cordand-
plug-connected portable
lo~ds.

(2)
Th~ ampacity of the conductors does not correspond
with the standard ampere rating of a fuse or a circuit
breaker without overload trip adjustments above its rating
(but that shall be permitted to have other trip or
rating adjustments).
(3) The next higher standard rating selected does not exceed

800 amperes.

So I meet condition 2 and 3, but condition 1 depends on if the feeder wires for the subpanel are considered part of the branch for the receptacles?
 

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Discussion Starter #13
I'm just going to stick with a 100 amp breaker, I asked the inspector about it and he started saying things like he'd need to see load calculations for a 125A sub off a 200A main, and he wouldn't need it for a 100A sub. So I'll just keep it simple. And bear in mind that if I actually need to change anything at a future date (probably won't) then I can think about it then.
 

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Scared Electrician
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you meet all there conditions. His requirement for a load calc, while always a good idea, sounds like a scare tactic. There is no rule that you can't over size something. Be that what it may-you still have to please the inspector as they can make life miserable.
 

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The eason some inspectors require a load calc, is that they want to make sure the total combined load does not exceed the service main breaker.
 

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Discussion Starter #16
I don't really blame him, if I didn't think there was a chance I'd run into an issue I wouldn't have minded doing the calculation - and I am certain I wouldn't have any problems with my configuration as it stands today (I have no central air and possess no window AC). I am less certain that I'd have available capacity for electric baseboard in the garage with my eventual plans for increasing livable floor space and getting central air installed. Then again, when am I going to use central air and garage baseboard heat at the same time? Or for that matter, how likely am I to be welding in the garage and needing more than 100 amps during the heating season. (Maybe some light welding indoors in the winter, but if I'm ever doing heavy welds I'm going to want the garage door open.

It may have been more that I did state that I was using 1/0 feeder and that I recognized that table 310.16 rates it at 120 amps but since the next standard size up is 125, I wanted to know if he'd allow it and that I was considering electric baseboard heat in the garage - somewhat implying I expected to be at capacity in the garage without the extra 125 amps.
 

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BAseboard heat will be the most expensive way to heat the garage....and it will make your electrical load much greater. I'd stick with gas if possible....perhaps a heater hung from the rafters.
 

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Discussion Starter #18 (Edited)
Well... the idea is that I could install electric baseboard heat myself at considerably less expense, and for the amount of time I'd heat the workshop (weekends only, probably never a full weekend) it would take many years before the extra cost added up to as much as I'd spend on a heater, ducting, venting and professional labor.

Also the electric heater would be less prone to introducing humidity than petroleum based portable heating methods.

And it's all a long way off. The garage... has insulation in the workshop, panelling in the workshop, then an open doorway to the garage bay where there is insulation in the walls with no drywall or panelling, and then the rafters are wide open exposed. So none of the insulation is worth anything and needs to be replaced.

Plus I know there are squirrels that have lived in the attic and/or walls. And I have no interest in openning walls or ceilings until I'm ready to do the full job that will come with it.

And the roof will need to be ventilated, the trusses redesigned, joists sistered and upsized so I can get storage above.

So in short, I'm just trying to do what I need to do, but do it in a way that gives me options for what I expect to do later. :)
 

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BB heat is most expensive when it comes to operating costs. But cheap on the installation costs.

I'd be willing to bet that after a month or 2 of using that out there -- once you get the electric bill -- you'll think twice ( or more) before using that stuff again!
 
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