I'm building a garage and I'm running power to a 100amp panel in the garage. My garage is being feed from a 200 amp panel from my house. I'll be running copper wire in conduit under ground 150 feet. What size copper wire should be used according to NEC. Considering voltage drop and conduit under ground. Thanks in advance.
100 amp service
- Thread starter Breezy
- Start date
VHF
Well-known member
#3 CU (copper) wire is the minimum size for 100A, but you might need to go down to #2 to limit voltage drop given the distance. You'll need 3 conductors (hot, hot, neutral) that size, but ground can be smaller (#6 or maybe even as small as #8).
If you read through the electrical forum you'll find lots of discussion on 100A feeds to a detached garage. Although copper has come down a little since it peaked, it will still be several hundred dollars worth of wire. Many guys use aluminum (AL) which can be purchased economicaly as "mobile home feeder" wire, which is good for 90A.
If you read through the electrical forum you'll find lots of discussion on 100A feeds to a detached garage. Although copper has come down a little since it peaked, it will still be several hundred dollars worth of wire. Many guys use aluminum (AL) which can be purchased economicaly as "mobile home feeder" wire, which is good for 90A.
wyliesdiesels
Well-known member
At that distance u could get by with #1 al or #3 cu....AL will be a whole lot cheaper...
theoldwizard1
Well-known member
Remember, just because the box you install in your garage has a 100A breaker, it does not need to have a 100A wire and matching breaker in your house. 60A is typically more than enough for a 1 man garage operation, even with A/C !
pattenp
Well-known member
Falcon67
Well-known member
Ehhh.... I was with you on this until you threw the A/C on the end.
Eh, I have two AC units, and run the whole shop on a 70A breaker.
pattenp
Well-known member
Are those window units? I was thinking more on the line of a central A/C unit. I have a single window unit in my shop and the shop is on a 60A breaker. If I crank up the plasma cutter along with my compressor I turn off the A/C because I have had the A/C startup at the same time and popped the feeder breaker. Also the lights and a TV was running at the same time. That extra 10A you have may have solved my popping the feeder breaker. I have thought of upping the breaker to 80A or 90A but I'm too cheap to spend the $$ because it's rare that I use the plasma cutter.
theoldwizard1
Well-known member
Ehhh.... I was with you on this until you threw the A/C on the end.
Worse case scenario, turn off the A/C when welding or using a plasma cutter. 5 - 15 max.
Thanks for the reply. I do plan on using copper, I didn't think I had to pull a ground wire with the current carrying conductors as long as I ground my service at the garage end. Which I plan on doing. I did read those other posts about 100 amp garages, but there is a lot of contridicting going on there. They seem to get off track a lot. I will buy copper but wasn't sure how much bigger of wire to go with for the voltage drop. Because of the 150 distance. Perhaps I will look harder in the code book for formulas on voltage drop. I was always taught after 100 feet there will be a voltage drop.
aandpdan
Well-known member
You do. 4 wires are required, hot-hot-neutral-ground and you also need ground rods at the detached structure (garage).
wyliesdiesels
Well-known member
Read comment #3....I already did the calcs for u.
And yes u do need 4-wires- grounding electrodes serve a different purpose from what an EGC is for.
Also, make sure the neutral bar in your panel is isolated from the enclosure and the ground bar....
wyliesdiesels
Well-known member
If u use individual wires and cu then u can go with 3-3-3-8. Al would be 1-1-1-6.....
Falcon67
Well-known member
Window units. But we've got 3.5 tons on the house and I think the compressor doesn't draw that much. Have to look it up. I can run both shop units (10.5k and 8 k) using our 3500 Champion genset.
mikeyc.
Active member
Hey guys, I have the same project going on. Dumb question. What is the benefit of Cu. over Al. wire besides cost? I would like to save the money, but not if Al. is cutting corners on safety and quality. Any insight is appreciated. Thanks.
^ ^ ^ Your power feed from PoCo (ie aerial drop to house) is aluminum . . . .
. . . . . that been working out alright for you ??
. . . seriously, nothing wrong with Aluminum. It's reliable and proven solution.
Only drawback would be possibly at very limit of conduit size, then larger aluminum wire would be limiting factor and may force you to use smaller copper wire that could carry same amps, but with smaller wire.
. . . . . that been working out alright for you ??
. . . seriously, nothing wrong with Aluminum. It's reliable and proven solution.
Only drawback would be possibly at very limit of conduit size, then larger aluminum wire would be limiting factor and may force you to use smaller copper wire that could carry same amps, but with smaller wire.
VHF
Well-known member
Don't forget the increased difficulty of getting the larger AL wire into the main panel and landed on a breaker. I would much rather wrestle with #3 CU than #1 AL!