rick1991
join:2003-01-22
East Fultonham, OH
|  Wire sizing question
I need a few opinions on the best size wire for the following job. I'm wiring a detached garage for 240v 60amp service. It is roughly 100'-125' between the main panel and the sub panel in the garage. It will be an underground run, through 2" PVC and yes, the garage does have a separate ground rod installed.
The biggest pieces of equipment that I'm planning on using right away are, a gas fired Reznor heater, possibly a small window AC, and a small 120v air compressor, other than that it will be mainly lighting and small power tools. It is possible, in the future, that I will be upgrading to a 240v upright air compressor. 
Now, with all of that stated, and keeping in mind that wire cost is a BIG factor in all of this, the following are the wire combinations that I have been kicking around. All combos are THHN/THWN stranded.
1. 4-4-4-4
2. 4-4-4-6
3. 4-4-6-6
4. 4-4-6-8
5. None of the above/add your own combo
I like combos 3 and 4, from a cost perspective, but, it seems like combo 2 makes the most sense. I want the best bang for the buck, but, at the same time, I don't want to be caught with my pants down. Thanks in advance to all who answer! I trust you guys and I value your input.  |
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Waterbug
join:2008-03-30 | Personally, I'd go with #1. Here is some info:
»www.thathomesite.com/faq/lists/w···600.html |
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
 ·Earthlink Cable Mo..
1 edit | reply to rick1991
6 gauge THWN will support 65 amps. Provided you have done a voltage drop calculation and have less that 2.5% voltage drop, you don't need to upsize the gauge. (I'm not doing the calculations for you, but suspect for that length you will be fine.) Remember, this is not a service, but a feeder. So you can use feeder sizing for the conductors. The neutral MUST be the same size as the hot leg conductors. Assuming there are no special local code requirements, these are the size conductors I would use:
6 - 6 - 6 - 10 |
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs: |
Will he also need to bond the two separate ground rods? |
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rick1991
join:2003-01-22
East Fultonham, OH
| reply to rick1991
Thanks for the replies so far guys. I found a voltage drop calculator and plugged in the figures and came up with a 1.4% drop, assuming 120'. As soon as I get an exact measurement I'll figure it again and see what I come up with. Now if the voltage drop ends up being more than 2.5% then should I use 4-4-4-10 or 4-4-4-8?
One more thing. The link that Waterbug posted was very informative. I thank you much and I will be bookmarking that link. I do have one question though. According to them I can protect #6 75 degree wire at 70 amps, is that something anyone else would recommend, or should I just stick with the 60 amp breaker? |
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs: |
I would do exactly what whizkid3  says, and you'll be fine. |
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
·Earthlink Cable Mo..
| reply to rick1991
You're fine on voltage drop, unless you are off by about 100 feet.
As far as 'bonding the two ground rods', I personally would not install a ground rod at the sub-panel. I don't believe there is a need to, unless its is in the local codes, or 2008 edition of the NEC (and that is the version your town is using).
If you do place a ground rod at the sub-panel, note then that you will need to run #6 gauge for the ground. (Bonding ground rods requires a minimum of 6 gauge.) |
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Speedy Petey
join:2008-01-19
| reply to rick1991
This is a detached garage. At least one grounding electrode is required since a feeder is being run.
Also, allowing for voltage drop is a suggestion, NOT a code requirement. Besides, you'd need to know the calculated load to accurately calculate VD.
The VD suggestion is 3% for circuits and 5% to the farthest outlet for a combination of feeders and branch circuits. |
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rick1991
join:2003-01-22
East Fultonham, OH
| reply to rick1991
Well I measured it out and it looks to be more like 80'-90', so I'm off to get the materials to finish up the job. Thanks to all who replied. I knew I could count you guys to answer my questions. |
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nunya
SEE ROCK CITY 475 MILES
Premium,MVM
join:2000-12-23
O Fallon, MO
clubs:
 ·AT&T CallVantage
| reply to rick1991
If you haven't purchased yet, you can use 4-4-4-6 AL xhhw and save some cash. You don't have to buy quad-plex cable. You can use four individuals. I do it all the time. The supply house can spin them onto a master reel for pulling.
As mentioned, a ground rod is required for your detached setup. Since you have one already, you are o.k.
--
Looks like Reverend Wright got his wish - God Damn America. |
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