Garage Sub-panel Wiring Confusion - Please Help (?)

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salshoes
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Garage Sub-panel Wiring Confusion - Please Help (?)

Post by salshoes » Sun Mar 17, 2019 6:29 am

Hello all – I’m looking for some clarification on wiring my newly-built detached garage.

At the outset, I’ll say I am not a complete novice with electrical, as I wired half of my house myself and installed an automatic standby generator myself as well. I’ve done a lot of minor electric work, though never major stuff like service entrance work with large aluminum wire. My setup is as follows:

I have 200 amp service in my house (2 main panels), with plenty of empty spots for circuits and breakers. I would need a little over 100’ of wire to connect the main service panel in the house to the subpanel in the garage. I already have 1 ¼” grey pvc conduit buried between the house and the garage site. I do wish now I have gone for something bigger, depending on what size wire I end up having to pull. AND, for what it’s worth, it is considered a farm building by my county, so it will not get inspected (which does NOT mean I want it to be unsafe, however!)

The garage is going to have two garage door openers, some general use receptacles, some lights, and a workshop. The biggest load I’d have in the workshop would be a compressor (just larger than a pancake one, but NOT one of the big stand-up ones) and a table saw (not a real industrial one, basic Lowes model). Only one or two tools would be used at the same time – no welders or anything like that.

My plan was to install a 60-amp breaker in my home’s main service panel, a 100-amp subpanel in the garage, and to connect to the two with 6-3 copper wire (NM-B/Romex). In reading about the question of a ground wire, it seems that my sub-panel in the garage should be the SE-R type and have a separate ground and ground rod, right?

My questions are about 1) the breaker in the house main panel, 2) the sub-panel in the garage, and 3) the most confusing part of it all seems to be the wire. I’ll start there.

1) Will 6/3 copper wire suffice for this project? AND, how much of a bear will it be to pull 100’ of that through the 1 ¼” conduit?
2) I am very confused about THHN wire – are they copper or aluminum or either? Why would I choose THHN over either NM-B/Romex or aluminum?
3) If I needed something more than 6/3, should I consider aluminum? If I went with aluminum would I need #2, #4, or #6? If it’s being fed from a 60amp breaker in my main panel, it seems like I could use #4 wire (smaller and easier to pull I imagine)
4) If I really needed to, I could dig and use Direct Burial Romex if that makes the process easier (although it seems they also make direct burial aluminum).

It’s really the wire that there seems to be a lot of debate about. Perhaps 6/3 is too small?

Any help greatly appreciated!

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Aaron
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by Aaron » Sun Mar 17, 2019 7:29 am

Hello. So you already have 1 1/4" PVC between the two buildings, my suggestion would be to use that.

The only wire you can use in conduit is THHN/THWN conductors. All of today's conductors are 90°C rated so it should supply up to 60A. I'd go with #6 awg, that should be plenty to supply 60A out there. You'll need white, black, red, and green. I think you could use smaller #8 for the green.

For fishing the wire, you need supplies: string, rope, and a Shopvac. The string and rope need to be as long as the pipe plus, say, 4 extra feet to work with. Tie one end of the string to a ball of wadded up paper that just barely fits through the end of the conduit. Use a Shopvac on the other end of the conduit to suck the paper and pull the string through to the other end. Once the string is fished through, use the string to tie rope to it, and pull the rope through. Now you have strong rope fished to pull the cable through.

Make a knotted loop at the end of the rope and use pliers to shape hooks on all the conductors. Hook the conductors onto the rope and wrap it all with electrical tape so nothing can get snagged. Use lube for insurance! There is dedicated wire pulling lube but I've heard hand sanitizer works well and it's nice because it evaporates.

Yeah you'll need a couple ground rods on the garage end, every building needs its own ground reference. Use the 5/8" diameter rods at least 8 feet long and space them at least 6 feet apart into a trench 18" deep. They should be pounded completely into the earth and should be at least 18" below grade. Use acorn clamps and #6 bare conductor to make the connections of conductor to rod. So your garage subpanel will have two ground connections, one from the house and another from the rods.

The backfed disconnect breakers in the subpanel need to be fastened to the panel with a hold-down strap or bracket. This strap is a separate accessory for the panel typically.

Make sure your grounds and neutrals are segregated. You'll probably need to buy a separate terminal strip for the grounds, which you will bond to the panel enclosure.

The strip for the neutral connections are NOT bonded to the box.

Make sure you have PVC bushings screwed on the threaded ends of the 1 1/4" box connectors on both ends. Some people forget that.

Running branch circuits, always knock out holes starting from the rear and work your way toward the front. You can insert one or two 14/2 or 12/2 NM cables per clamp.

Let's see that's all I can think of at the moment.

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Shannon
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by Shannon » Sun Mar 17, 2019 8:54 am

I hope you do not have too sharp of bends cause 1-1/4" seems pretty small.
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salshoes
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by salshoes » Sun Mar 17, 2019 9:06 am

There is one 90 degree sweep in there somewhere. I guess I'm going to have to lubricate the crap out of it, huh?

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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by salshoes » Sun Mar 17, 2019 9:39 am

Aaron wrote:
Sun Mar 17, 2019 7:29 am
The only wire you can use in conduit is THHN/THWN conductors. All of today's conductors are 90°C rated so it should supply up to 60A. I'd go with #6 awg, that should be plenty to supply 60A out there. You'll need white, black, red, and green. I think you could use smaller #8 for the green.
Aaron - thanks for the response, and just to clarify, when you #6 awg THHN, we're talking about copper here, right? Thanks!

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emtnut
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by emtnut » Sun Mar 17, 2019 11:43 am

salshoes wrote:
Sun Mar 17, 2019 9:39 am
Aaron wrote:
Sun Mar 17, 2019 7:29 am
The only wire you can use in conduit is THHN/THWN conductors. All of today's conductors are 90°C rated so it should supply up to 60A. I'd go with #6 awg, that should be plenty to supply 60A out there. You'll need white, black, red, and green. I think you could use smaller #8 for the green.
Aaron - thanks for the response, and just to clarify, when you #6 awg THHN, we're talking about copper here, right? Thanks!
Yes, he was.

At 100', it might be good to run #4 XHHN Aluminum. Rated for 55A, but you can go the next size up breaker at 60A.
It'll save quite a few bucks !
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emtnut
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by emtnut » Sun Mar 17, 2019 11:44 am

salshoes wrote:
Sun Mar 17, 2019 9:06 am
There is one 90 degree sweep in there somewhere. I guess I'm going to have to lubricate the crap out of it, huh?
Shouldn't be that tough. A little 'yellow 77' (from Ideal) never hurts thou :mrgreen:
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by salshoes » Tue Mar 19, 2019 10:00 am

Thanks for all the responses, everyone. Based on the size of my conduit, it looks like i will have to go with #6 awg copper. I looked at the aluminum wire I'd need and that would be insane trying to pull that through. Copper is more expensive, i know, but I guess that's the price of my poor planning!


so XHHW-2 stranded copper it is - 3 conductors at 6 gauge for the hots and the neutral, one 8 gauge conductor for the ground -


BUT, about the ground, everyone is telling me that I'll do a separate ground rod at the garage (2 rods actually), so why do i need the ground running from the house to the garage subpanel?


As for the subpanel, I've read that I need to "isolate the neutral from the ground," but I do not know exactly what that means. I'm looking at a sub-panel that is "plug-on neutral ready." Is that the kind I'm looking for?


Thanks again!

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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by emtnut » Tue Mar 19, 2019 1:55 pm

salshoes wrote:
Tue Mar 19, 2019 10:00 am
Thanks for all the responses, everyone. Based on the size of my conduit, it looks like i will have to go with #6 awg copper. I looked at the aluminum wire I'd need and that would be insane trying to pull that through.
Technically, you can run #2 conductors and still not be over filled (40% rule)
Aluminum is lighter, so running #4 Al may actually be easier. But the choice is yours.
salshoes wrote:
Tue Mar 19, 2019 10:00 am
so XHHW-2 stranded copper it is - 3 conductors at 6 gauge for the hots and the neutral, one 8 gauge conductor for the ground -
Ground needs to be #6
salshoes wrote:
Tue Mar 19, 2019 10:00 am
BUT, about the ground, everyone is telling me that I'll do a separate ground rod at the garage (2 rods actually), so why do i need the ground running from the house to the garage subpanel?
You need the ground back to the house to clear a fault.
The ground rods are just for lightning and equipotential reasons
salshoes wrote:
Tue Mar 19, 2019 10:00 am
As for the subpanel, I've read that I need to "isolate the neutral from the ground," but I do not know exactly what that means. I'm looking at a sub-panel that is "plug-on neutral ready." Is that the kind I'm looking for?
Your talking 2 different things.
If you want a plug on neutral panel, they can look a bit cleaner for the wiring ... no other functionality.

There will be instructions that come with the panel for ground/neutral isolation.
Generally there is a bond screw that you must remove.
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Aaron
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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by Aaron » Tue Mar 19, 2019 3:04 pm

salshoes wrote:
Tue Mar 19, 2019 10:00 am
As for the subpanel, I've read that I need to "isolate the neutral from the ground," but I do not know exactly what that means. I'm looking at a sub-panel that is "plug-on neutral ready." Is that the kind I'm looking for?
I'm guessing "plug-on neutral ready" is a feature of the panel that means that breakers made for that panel that require a neutral to function, such as GFCI, AFCI, and combo AFCI+GCFI breakers, have a neutral lug that the breaker can get seated into, in addition to the hot lug. This would replace the white neutral pigtail wire that these breakers had before, in order to work in legacy panels.

That's not the same thing as segregating neutral from ground. Neutral and ground only bond at the main service panel, the one with utility/hydro service entrance. Ground and neutral remain segregated beyond the service, including sub-panels.

Usually new panels out of the packaging already have the neutral terminal strip NOT bonded to the box, and you would have to screw in a bonding screw and/or strap in order to bond the box to the neutral terminal strip. So you want to leave that neutral strip alone, unbounded. It will have some sort of insulation (plastic) separating it from contact with the panel enclosure.

But you need to ensure you have a SEPARATE terminal strip to terminate all your grounds and just your grounds. This terminal strip DOES bond with the panel enclosure.

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Re: Garage Sub-panel Wiring Confusion - Please Help (?)

Post by emtnut » Tue Mar 19, 2019 4:00 pm

Aaron wrote:
Tue Mar 19, 2019 3:04 pm
I'm guessing "plug-on neutral ready" is a feature of the panel that means that breakers made for that panel that require a neutral to function, such as GFCI, AFCI, and combo AFCI+GCFI breakers, have a neutral lug that the breaker can get seated into, in addition to the hot lug. This would replace the white neutral pigtail wire that these breakers had before, in order to work in legacy panels.
The plug on neutral just connects the system neutral for you.
So, for a regular breaker, you just plug it in and connect the hot wire.
For AFCI/GFCIs , it eliminates the pig tail (still need the line neutral obviously)

This requires you to use 'plug on ready' breakers.

They accept regular breakers / regular AFCI/GFCI as well , but you need to wire up the neutral to the neutral bar.
~~ Ford Ford Ford Ford Ford Ford :mrgreen: ~~

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