Detached Garage Feeder (types, ampacity)

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xguard

Senior Member
Location
Baton Rouge, LA
I'm looking for wire/cable suggestions for a 100 amp feeder to a detached garage. It's only a forty foot run. Normally I use individual conductors in raceway but wanted to look at some other options, this is my first residential job. Looks like USE and UF may be alternatives as well as Tray Cable. Which leads me to my next question.

The panel label states "Line Terminals A,B, and N Suitable for 60/75 C Conductors". The breakers state "CU-AL 60/75 C Wire". One code class I went to the instructor said the 60/75 meant you could use the 75 deg ampacity for motors (100 amps or less). I've also read on here a circuit breaker 60/75 C rating means if the breaker is installed alone in an enclosure you can use the 75 deg C ampacity but if it's in a load center with other breakers you have to use the 60 deg C.

So my question is even if the incoming line terminals are 60/75 the branch breakers in the panel would only be good for 60C, because they are next to each other, so the wire supplying the panel would have to be rated 60 deg C?

I see that the type UF (TC) may be limited to 60 deg C anyway. (NEC 2020 - 340.80) Is that right?

Additional information:

The supply side of this feeder will splice to an existing 4/0-4/0-4/0 & 2/0G, AL, SE style R that runs through the attic, down the inside of a wall and ends in a box on an exterior wall.

The homeowner has also stated they prefer the wire or cable be installed in conduit.

Thanks for any input.
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Chances are that a PVC conduit with THHN wires in it will be as cost effective as any of the cable options available to you.

If the customer wants it in conduit, PVC is the way to go. Why is there even any real question when the customer has expressed a preference and it is an appropriate and cost effective solution?
 
V

VirutalElectrician

Senior Member
Location
Mpls, MN
Occupation
Sparky - Trying to be retired
Normally an external structure needing a sub panel would be connected with 2-2-2-4 MHF which can handle 90A. Direct burial or conduit as desired.

What was the existing 4/0 SER used for? That would typically have a 150A or larger breaker for termination. You won't be able to splice the 2-2-2-4 into that and terminate into a 90A breaker at the supply side as a 90A breaker would not accept 4/0.

You could add a sub panel on the end of that 4/0 and then connect the 2-2-2-4 to a 90A breaker in that panel.

How/where does this existing 4/0 terminate on the other side?
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
xguard said:
I'm looking for wire/cable suggestions for a 100 amp feeder to a detached garage. It's only a forty foot run. Normally I use individual conductors in raceway but wanted to look at some other options, this is my first residential job. Looks like USE and UF may be alternatives as well as Tray Cable. Which leads me to my next question.

The panel label states "Line Terminals A,B, and N Suitable for 60/75 C Conductors". The breakers state "CU-AL 60/75 C Wire". One code class I went to the instructor said the 60/75 meant you could use the 75 deg ampacity for motors (100 amps or less). I've also read on here a circuit breaker 60/75 C rating means if the breaker is installed alone in an enclosure you can use the 75 deg C ampacity but if it's in a load center with other breakers you have to use the 60 deg C.

So my question is even if the incoming line terminals are 60/75 the branch breakers in the panel would only be good for 60C, because they are next to each other, so the wire supplying the panel would have to be rated 60 deg C?

I see that the type UF (TC) may be limited to 60 deg C anyway. (NEC 2020 - 340.80) Is that right?

Additional information:

The supply side of this feeder will splice to an existing 4/0-4/0-4/0 & 2/0G, AL, SE style R that runs through the attic, down the inside of a wall and ends in a box on an exterior wall.

The homeowner has also stated they prefer the wire or cable be installed in conduit.

Thanks for any input.
Click to expand...
If it is marked 60/75, you can use either 60°C or 75°C ampacity conductors.
 
Sberry

Sberry

Senior Member
Location
Brethren, MI
Occupation
farmer electrician
I use 2 2 2 4 mhf and breaker from 60 to 90 and out of the couple dozen I have done and some I use, a couple busy ones NEVER tripped up a 60
 
X

xguard

Senior Member
Location
Baton Rouge, LA
petersonra said:
Chances are that a PVC conduit with THHN wires in it will be as cost effective as any of the cable options available to you.

If the customer wants it in conduit, PVC is the way to go. Why is there even any real question when the customer has expressed a preference and it is an appropriate and cost effective solution?
Click to expand...
he's not married to it. I'm not trying to push the cable options on him, someone else suggested it to him. Just checking.

Sent from my Pixel 6 using Tapatalk
 
X

xguard

Senior Member
Location
Baton Rouge, LA
VirutalElectrician said:
Normally an external structure needing a sub panel would be connected with 2-2-2-4 MHF which can handle 90A. Direct burial or conduit as desired.

What was the existing 4/0 SER used for? That would typically have a 150A or larger breaker for termination. You won't be able to splice the 2-2-2-4 into that and terminate into a 90A breaker at the supply side as a 90A breaker would not accept 4/0.

You could add a sub panel on the end of that 4/0 and then connect the 2-2-2-4 to a 90A breaker in that panel.

How/where does this existing 4/0 terminate on the other side?
Click to expand...
Good point. The 4/0 currently terminates in a load center in a 200 amp circuit breaker.
 
B

BarryO

Senior Member
Location
Bend, OR
Occupation
Electrical engineer (retired)
petersonra said:
Chances are that a PVC conduit with THHN wires in it will be as cost effective as any of the cable options available to you.
Click to expand...
You mean THWN or THWN-2 😉

Around here, given that in many residential locations the soil layer can be very thin, it can be more cost effective to use IMC, to avoid jackhammering through an extra 12 inches of volcanic rock.
 
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