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Old 09-06-2008, 12:30 PM   #1
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Wire Gage for the Sub-Pannel


The sub panel will be feed by a 100A breaker in the main. It will be a short run, a total of 5 to 6 feet of wire.

I have looked at a number of charts, and I get answers anywhere from needing 1 gage for this feed up to 4 gage being fine.

I assume I use the same gage wire for the neutral as well?

All the feeder wires should be stranded Copper correct?

I have done a lot of this working with my dad in the past, but have not done a full sub panel on my own before, thats why I am just verifying things. I will have my dad look at the finished setup to verify my connections and such.

One last question, and I will physically look at the panel again and see if I can make this determination, I was going to start with using the 30A breaker I have right now to feed the sub panel. Will the wires that support 100A be likely to fit onto the 30A breaker? This is the pushmatic box, and I can't find the breakers locally - so there is no easy way for me to look up close at a 100A vs a 30A, I have to wait for them to come mail order.

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Jamie

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Old 09-06-2008, 01:12 PM   #2
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Wire Gage for the Sub-Pannel


Depends on the type of wire used and the temp rating of the wire. If you are using THHN/THHW 75c & 90c the correct size is #3. If you are using cable or wire with a temp rating less then 75c (60 degree column) you need #1. The neutral will be the same size. The ground will be an insulated green #8.

Slim chance a 30 amp breaker will accept a # 3 wire. Use the correct breaker.

Don't forget to pull 4 wires. 2 hots, 1 neutral, and 1 ground (EGC).

You did not say if the sub panel is going into an attached structure or an unattached structure? This question must be answered.

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Old 09-06-2008, 01:30 PM   #3
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Wire Gage for the Sub-Pannel


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Depends on the type of wire used and the temp rating of the wire. If you are using THHN/THHW 75c & 90c the correct size is #3. If you are using cable or wire with a temp rating less then 75c (60 degree column) you need #1. The neutral will be the same size. The ground will be an insulated green #8.

Slim chance a 30 amp breaker will accept a # 3 wire. Use the correct breaker.

Don't forget to pull 4 wires. 2 hots, 1 neutral, and 1 ground (EGC).

You did not say if the sub panel is going into an attached structure or an unattached structure? This question must be answered.
Same building, same wall, just a few feet away. In a heated basement.

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Old 09-06-2008, 01:54 PM   #4
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Wire Gage for the Sub-Pannel


Do you actually need the 100 amps? Could be a waste of money if you really only need less than 100.

To answer you question, #3 Cu, or #1 Al. will work.
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Old 09-06-2008, 01:58 PM   #5
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Wire Gage for the Sub-Pannel


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Do you actually need the 100 amps? Could be a waste of money if you really only need less than 100.

It's a hard call, Planing to put a Hot Tub on the new box (50A breaker) a espresso machine (30A breaker), and several other lighting and small appliance circuits, and it would be very likely the espresso and the hot tub would be on at the same time. I don't know what the espresso or the hot tub would really draw, just what breakers they require.

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Old 09-06-2008, 02:36 PM   #6
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Wire Gage for the Sub-Pannel


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It's a hard call, Planing to put a Hot Tub on the new box (50A breaker) a espresso machine (30A breaker), and several other lighting and small appliance circuits, and it would be very likely the espresso and the hot tub would be on at the same time. I don't know what the espresso or the hot tub would really draw, just what breakers they require.

Thanks
Jamie

IMO, if you hired me to do this install, you would get an offset nipple off your existing panel to the new subpanel, and I would feed it with #2 AL wire backed with a 90 amp breaker.
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Old 09-07-2008, 11:44 PM   #7
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Wire Gage for the Sub-Pannel


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IMO, if you hired me to do this install, you would get an offset nipple off your existing panel to the new subpanel, and I would feed it with #2 AL wire backed with a 90 amp breaker.


Now, I am thinking that I am going to put in a Square D QO 42 position load center as my main panel, even if I don't move up to 200A service right now. Since I would drop $150+ just on the pushmatic 100A breaker, in addition to the money for a sub panel and breakers. I think I am much better off just putting my money into one modern main panel that has room for some more circuits.

Now that I am realizing the cost of a Pushmatic breaker & a decent sub panel vs a new main panel with 40 or 42 positions, it seems far better to just get a new main panel.

Thank you.
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Old 09-08-2008, 07:32 PM   #8
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Wire Gage for the Sub-Pannel


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Originally Posted by jamiedolan View Post
Now, I am thinking that I am going to put in a Square D QO 42 position load center as my main panel, even if I don't move up to 200A service right now. Since I would drop $150+ just on the pushmatic 100A breaker, in addition to the money for a sub panel and breakers. I think I am much better off just putting my money into one modern main panel that has room for some more circuits.

Now that I am realizing the cost of a Pushmatic breaker & a decent sub panel vs a new main panel with 40 or 42 positions, it seems far better to just get a new main panel.

Thank you.
Jamie
I think you would be wise in the long run with a new panel that has 30 or 40 spaces. Sounds like you wouldn't need the sub then?? For the price of the Pushomatic 100A alone, you can get a new panel, albeit not many breakers will come with it. But the cost of the sub and wiring will help offset the cost of some of the breakers for the new panel. If you want a new panel now, but don't want to change the service conductors, meter box, etc. until later (to increase it to 200A), you'll need a panel rated for 200A, which should come with a 200A main brkr. You'll have to get a 100A brkr, and swap it out with the 200A for now, to stay within the limits of your service entrance conductors, meter, etc.

I installed a Pushomatic 2P 20A in a panel this weekend. This same panel I installed a 2P 30A last year. No way is a #3 AWG going into its lug without cutting some of the strands away. If I remember correctly, you asked in another post about 100A brkr being a main only or not. I recall you said you have a 100A main now. The size of the lugs of a new 100A you order will be the same as the 100A you have now. You can visually check your current 100's lugs against your 30's lugs and see the difference.

Last edited by SD515; 09-08-2008 at 07:42 PM.
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Old 09-09-2008, 10:11 AM   #9
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Wire Gage for the Sub-Pannel


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Now, I am thinking that I am going to put in a Square D QO 42 position load center as my main panel, even if I don't move up to 200A service right now. Since I would drop $150+ just on the pushmatic 100A breaker, in addition to the money for a sub panel and breakers. I think I am much better off just putting my money into one modern main panel that has room for some more circuits.

Now that I am realizing the cost of a Pushmatic breaker & a decent sub panel vs a new main panel with 40 or 42 positions, it seems far better to just get a new main panel.

Thank you.
Jamie
Very good idea. Why not move up to 200? You have to install the panel. Why not install the meter/load center and run your SE to the new panel and be done with it?

If you are not going to do it all at once, get a 100 amp breaker and install it as you would any other breaker. This will be your main until you complete the job.

PS....If you use a combo meter unit, meter base with load center, you can use a lug panel inside. It will give you four spare slots outside at the meter too.

Last edited by J. V.; 09-09-2008 at 10:14 AM.
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Old 09-09-2008, 10:52 AM   #10
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Wire Gage for the Sub-Pannel


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Very good idea. Why not move up to 200? You have to install the panel. Why not install the meter/load center and run your SE to the new panel and be done with it?

If you are not going to do it all at once, get a 100 amp breaker and install it as you would any other breaker. This will be your main until you complete the job.

PS....If you use a combo meter unit, meter base with load center, you can use a lug panel inside. It will give you four spare slots outside at the meter too.
Your right this is what I should do. Honestly my biggest concern is that I think they are going to butcher my Maple tree when they install the new line. I am now wonderiong if I could get them to move the line drop to a different part of the house and I could just make a longer run to the service panel. Can I make a 50 foot run to the service panel from the drop?

I am going to go out and take some photos in my yard and will post them here in a new message.

What brand of combo meter bases do you use? That sounds like a good idea.

Thanks
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Old 09-09-2008, 11:19 AM   #11
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Wire Gage for the Sub-Pannel


Quote:
If you are not going to do it all at once, get a 100 amp breaker and install it as you would any other breaker. This will be your main until you complete the job.
This would require the panel label listing that a backfed main is acceptable and hold down kit capable.

Jamiedolan:

Square d QOM breakers generally are interchangable from 100 amps up but why buy a 200 amp main breaker panel if not upgrading completly to 200 amps. You could get a convertible mains 42 circuit panel that would let you install a 100 amp main breaker without the cost of the 200. But total cost isn't going to incure all that much savings either way.... but I think the important point being made by SD515 is that you cannot have a 200 amp main protecting a 100 amp service entrance. My opinion is that if you are not going to upgrade the service entrance to 200 amps then just install the sub-panel or install a 100 amp panel with 30 or 40 spaces and not the sub.
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Old 09-09-2008, 11:33 AM   #12
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Wire Gage for the Sub-Pannel


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the important point being made by SD515 is that you cannot have a 200 amp main protecting a 100 amp service entrance. My opinion is that if you are not going to upgrade the service entrance to 200 amps then just install the sub-panel or install a 100 amp panel with 30 or 40 spaces and not the sub.
I was thinking of the QO panel and putting in a 100A to back feed it. I did look at the interchangable main 42 position QO boxes as well. I have to look at the prices more.

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