Sub Panel wire Feeder size

[PWilks]

I'm planning to put in a 60 amp subpanel in my 24x32 garage that I will be building.

Won't power much more than the lights/door opener/boat charger and a few outlets here and there.

From the main panel, the run to the subpanel will be roughly ~100 feet. I'm aware that it has to be buried 24'' deep, and I'll probably just use conduit anyway because it's cheap, so, like ~$30, so why not.

What size wire do I need, and what type? I believe it's either #4 or #6 gauge, but I'm unsure of the type, or where to even purchase it. Links to products at HD or menards would be helpful.

Thanks

 

[pattenp]

Conduit needs 18" of cover. For 60A I'd use three #4's and one #8 for the ground in aluminum XHHW-2 individual wires. The ground will need to be green since it's smaller than #4. You will most likely need to go to a electrical supply house. If using copper use THHN/THWN in sizes 6-6-6-10.

The aluminum wire will be about 1/3 or less the cost of copper.

 

[wyliesdiesels]

Dont forget to isolate the neutral bar and get ground bar kits if theyre not included in the subpanel.

Also need 2 ground rods spaced 6’ apart

 

[spudley]

Lots of detached builds use quadplex AL 2-2-2-4 MHF. Menards has it for $1.30 per foot. This can be direct buried at 24", or in conduit at 18".

Single #6 THHN/THWN is $0.83 per ft (at Menards) for each strand so about $3.00 per ft. for four wires. Must be in conduit.

You don't need #2 wire for 60 amp service but using it allows for a future upgrade to 90 amp service without changing wire.

 

[pattenp]

Be aware that all Quadruplex wire is not the same. If you go with the 2-2-2-4 AL use the Mobile Home Feeder (MHF). URD comes as Quadruplex but is not allowed by the NEC to be installed inside the structure.

 

[csp]

What is it about URD that disallows it from being inside the structure? Fire rating?

 

[wyliesdiesels]

insulation

 

[pattenp]

What is it about URD that disallows it from being inside the structure? Fire rating?

Typical URD only has an insulation rating of USE-2 which is not fire resistant. The URD Quadruplex is a mixed bag because it can be rated RHH/RHW-2/USE-2 which is the same rating that MHF carries. MHF comes colored as black/black/black-with white stripe/green whereas Quadruplex URD is black/black/black/black-with yellow stripe.

 

[engineer2]

I recently did this calculation for a 60 amp breaker and 100 ft. I found it needed #4 THHN.

 

[pattenp]

I recently did this calculation for a 60 amp breaker and 100 ft. I found it needed #4 THHN.

If that was copper THHN you found wrong. #6 Cu THHN is plenty for 60A at 100ft.

 

[engineer2]

If that was copper THHN you found wrong. #6 Cu THHN is plenty for 60A at 100ft.

Stranded copper THHN. It was at the ragged edge according to online calculators (can't believe everything on the Internet).. Show me the calculator or table you used and I can upgrade to what I originally wanted!

 

[pattenp]

First, there is no voltage drop issue at 100ft. Second, NEC table for #6 THHN is 65A. NEC table 310.15(B)(16) 75 deg.C column.

 

[engineer2]

Woohoo! I can use my 60A breaker and set up for two 20's and lighting circuit. Apparently some of the online calculators are too conservative.

 

[pattenp]

The catch is some online calculators limit to using 60 deg.C which would push it to #4, but THHN is 75C wire.

 

[mike93lx]

Woohoo! I can use my 60A breaker and set up for two 20's and lighting circuit. Apparently some of the online calculators are too conservative.

You can put a hell of a lot more than 2 20's and lighting on a 60a feeder. The breakers can add up to way more than the feeder size

 

[wyliesdiesels]

Woohoo! I can use my 60A breaker and set up for two 20's and lighting circuit. Apparently some of the online calculators are too conservative.

I dont ever trust the online calculators. we have found mistakes on some of them.

Do the calcs yourself with the formulas i posted on the electrical FAQs sticky

 

[PWilks]

Lots of detached builds use quadplex AL 2-2-2-4 MHF. Menards has it for $1.30 per foot. This can be direct buried at 24", or in conduit at 18".

Single #6 THHN/THWN is $0.83 per ft (at Menards) for each strand so about $3.00 per ft. for four wires. Must be in conduit.

You don't need #2 wire for 60 amp service but using it allows for a future upgrade to 90 amp service without changing wire.

I think the single #6 is THHN from menards is the route I will be taking. Do I need to purchase different colors, or can I use all black and tape each end respectively? The inspector might have a problem with this due to the potential of crossing wires inside conduit. Other than my word of "I ran them one at a time", there's really no other solution other than different colors.

 

[Aceman]

I think the single #6 is THHN from menards is the route I will be taking. Do I need to purchase different colors, or can I use all black and tape each end respectively? The inspector might have a problem with this due to the potential of crossing wires inside conduit. Other than my word of "I ran them one at a time", there's really no other solution other than different colors.

At a minimum, you need:

Two #6 black (we typically tape one red or use red wire, but you don't have too)
One #6 white (buy white wire, tape doesn't meet code for #6 and smaller)
One #10 green

 

[pattenp]

NEC doesn't allow color re-identification of individual neutral and ground conductors #6 and smaller.
Oops.. didn't mean to parrot Aceman.

 

[PWilks]

At a minimum, you need:

Two #6 black (we typically tape one red or use red wire, but you don't have too)
One #6 white (buy white wire, tape doesn't meet code for #6 and smaller)
One #10 green

NEC doesn't allow color re-identification of individual neutral and ground conductors #6 and smaller.
Oops.. didn't mean to parrot Aceman.

Well, menards doesn't stock multi-color THHN by the foot, which kinda *****.

It appears that HD doesn't stock #6 THHN by the foot either, meaning my only option would be using #4 by the foot from HD in the four colors you listed, or buy #6 elsewhere.

If I'm going to run #4 instead of #6, for both hots, the neutral, and the ground, I may as well upgrade from 50 AMP (I'll put in a 100 or 125 subpanel anyway, just for the amount of space inside of it). The question is what size is permissible for #4 THHN?


https://www.homedepot.com/p/Southwi...anded-CU-SIMpull-THHN-Wire-20498299/204724897

 

[PWilks]

At a minimum, you need:

Two #6 black (we typically tape one red or use red wire, but you don't have too)
One #6 white (buy white wire, tape doesn't meet code for #6 and smaller)
One #10 green

I misread what you said in my post above. If I ran #4 stranded THHN in black, red, white, what size ground would I need? I assume it gets larger (the gauge number decreases) if I have a larger breaker?

https://www.homedepot.com/p/Southwire-500-ft-10-Green-Stranded-CU-THHN-Wire-22977357/202316481

Would that be sufficient if I ran #6 hots/neutral

 

[mike93lx]

Why not buy AL XHHW online? Wireandcableyourway.com has good prices

 

[wyliesdiesels]

I misread what you said in my post above. If I ran #4 stranded THHN in black, red, white, what size ground would I need? I assume it gets larger (the gauge number decreases) if I have a larger breaker?

https://www.homedepot.com/p/Southwire-500-ft-10-Green-Stranded-CU-THHN-Wire-22977357/202316481

Would that be sufficient if I ran #6 hots/neutral

depends on the size of the breaker feeding it and whether the wire is upsized beyond its ampacity due to voltage drop etc

see table 250.122(b)

so what size breaker will you be using?

 

[PWilks]

depends on the size of the breaker feeding it and whether the wire is upsized beyond its ampacity due to voltage drop etc

see table 250.122(b)

so what size breaker will you be using?

I originally planned on 60 amp, when I expected to use #6 stranded copper, but seeing as I can't get it locally (at least not at the big box stores), #4 seems more likely, and therefore I don't see a reason why I shouldn't just put a larger breaker more suitable for the wire size in it's place.

It's merely $.30 a foot, which yeah, I guess is ~$100 more, but if it saves me from having to re-do everything at a later date to upgrade, I may as well do it that way to begin with.

Am I right in thinking that I could put an 80 Amp breaker on

two #4 hots (red/black)
one #4 neutral (white)
one #8 ground (green)

Could these all be ran in the same conduit between the house and garage, and what size conduit would you suggest? 3/4'' and 1'' PVC conduit at menards are the same price for schedule 40, but a price difference of almost $2 for schedule 80.

Is schedule 40 sufficient, and what diameter if so?

 

[pattenp]

Buy it from here....
https://www.wireandcableyourway.com...KDLcV8SVvvvt3MBT1Wiwwkzm1zRuVPvxoCNxoQAvD_BwE

#6 use 3/4" conduit
#4 use 1" conduit
#4 Cu good for 85A
Sch 40 PVC is fine as long as not subject to damage.

 

[wyliesdiesels]

#8 cu grnd good to 100a breaker

 

[theoldwizard1]

Wireandcableyourway.com has good prices

They also sell THHN in colors cut to length.

 

[Aceman]

Buy it from here....
https://www.wireandcableyourway.com...KDLcV8SVvvvt3MBT1Wiwwkzm1zRuVPvxoCNxoQAvD_BwE

#6 use 3/4" conduit
#4 use 1" conduit
#4 Cu good for 85A
Sch 40 PVC is fine as long as not subject to damage.

Standard for us is:

#6 in 1"
#4 in 1.25"

It is considerably easier to pull, he will definitely notice a difference at 100'.

 

[sberry]

I tend to agree with Ace about the size especially with 4 wires and some distance especially with some turns.

 

[pattenp]

Standard for us is:

#6 in 1"
#4 in 1.25"

It is considerably easier to pull, he will definitely notice a difference at 100'.

I should have said use 3/4" and 1" sizes at a minimum. Bigger than minimum is better if you are able to manage it.

 

[engineer2]

To bond my subpanel I drove in two 8 ft ground rods. A good air hammer made it easy. We are an EMT locale. Having trouble finding consistent info on what type of bonding wires are OK for a #6 four wire THHN RMC 60A circuit at the subpanel.
bare or insulated
#6 or #8
solid or stranded
series or parallel for the rods
in conduit or no conduit or bonded conduit

 

[wyliesdiesels]

To bond my subpanel I drove in two 8 ft ground rods. A good air hammer made it easy. We are an EMT locale. Having trouble finding consistent info on what type of bonding wires are OK for a #6 four wire THHN RMC 60A circuit at the subpanel.
bare or insulated
#6 or #8
solid or stranded
series or parallel for the rods
in conduit or no conduit or bonded conduit

Are you referring to the wire for the ground rods? Its called a GEC- grounding electrode conductor.

This can be #8 but must be in conduit or solid bare #6 can be used without conduit as long its not subject to damage. Just follow the building contour

 

[engineer2]

Yes GEC. The Square D QO panel will be surface mounted. I'd like to protect the GEC wires with 1/2 EMT from the panel to just below the floor. Under the floor is not subject to damage.
Is this OK to do?

Info seems to indicate solid wire is the way to go. I have shitloads of stranded THHN #6 and #8, but can buy bare solid if required.

Can I run one conductor to both rods or separate conductors to each rod?

Cost is not an object, just trying to meet code.

 

[wyliesdiesels]

Yes GEC. The Square D QO panel will be surface mounted. I'd like to protect the GEC wires with 1/2 EMT from the panel to just below the floor. Under the floor is not subject to damage.
Is this OK to do?

Info seems to indicate solid wire is the way to go. I have shitloads of stranded THHN #6 and #8, but can buy bare solid if required.

Can I run one conductor to both rods or separate conductors to each rod?

Cost is not an object, just trying to meet code.

If you go with metal conduit, it makes it more complicated as you will need to bond the conduit at both ends. Otherwise you create a "choke". Is the wire subject to damage in the shop?

And yes use solid bare cu.

you want to use on piece of wire and go from panel to rod ro rod.

 

[engineer2]

Good info Wylie as always. I owe you a beer (or wine since you are in Modesto). There is so much BS on the internet, but codes vary all over. We are more like Chicago and EMT.
Yes, the subpanel is surface mounted and I'd like to protect the GEC wire. I too read about bonding both ends of the conduit. What fitting is acceptable under the floor?

 

[nadogail]

All of the responses remind me that I am still learning about the limits of my knowledge.