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6% voltage drop for 60 amp sub panel?

12K views 63 replies 11 participants last post by  andrew79 
#1 ·
Hello,

I am planning on installing a 60 amp sub panel in my detached garage. Originally I was going to run (3) #6 THWN feeders with a #8 ground, buried in conduit. The total distance from main panel to sub panel is about 160 feet.

After using a voltage drop calculator at southwire, it is saying my voltage drop is going to be 6%+ using this wire.

1) At what percent of voltage drop should I try to stay under?

2) Southwire calc is recommending #2 THWN or #2/0 Aluminum for my feeder, does this sound about right?

Thanks for the help!
 
#38 ·
Thanks guys for the replies. My power company will allow a second meter here, but they charge commercial rates as Jim pointed out. The commercial rate is not very much more than residential here, with the amount of power I will be using it would not be much of an increase.

My question I am unsure of is, is there anything different regarding the install in a garage that needs to be done vs an install in a residential dwelling?

Around here (and probably everywhere else to) electrical work in commercial spaces is installed a bit different than in residential dwellings. Like no romex, anti short bushings must be used, etc...

Would that apply to garages on a residential property as well?
 
#39 ·
Ok it appears I am back to the sub panel setup instead of a new service. Apparently I have some clearance issues with the service drop because the neighbors garage is only 2' away from drop and I need 5', sigh.....

When running pvc conduit from main panel to sub panel, does the ground need to be insulated or can solid bare copper be used?
 
#42 ·
Thanks Jim...

If I absolutely need to use more than 360 degrees in bends between pull points, can some sort of junction box (that can be buried) be added between points to add another pull point to stay within code?

My current layout is using 450 degrees in bends and I'm not sure how I can get this down because of lot size/boundary lines.
 
#44 ·
The 450 degrees in bends I currently have are between both LB's.

I don't have drawing of lot size handy that includes all the boundary lines and easement, but my lot is pie shaped with a narrow L shaped walkway (easment) connecting to my detached garage that I have to follow when running the conduit.

Just coming down off the LB's in both spots into 90's underground are half the bends allowed and I still got about 130' to go with only 180 degrees more allowed. They sure don't give you many more bends allowable :(

I just figured if there was some sort of pull point I could add in the middle of run, either completely buried or surface mounted (depending on how it looks), I would be ok.
 
#47 ·
You guys can use plumbing elbows? We have to follow a minimum bend radius as in pic 1
 
#53 ·
Ok... So I got the conduit buried and pull string through..

If I do not wish to continue conduit run through basement into panel, can I splice on NM cable and pull this through floor joists?

If so, should I use 4/3 with ground NM cable, my THWN feeders are (3) #4 CU and (1) #8 copper?
 
#57 ·
Alright.. FINALLY getting moving on this project again....

I have the mason here and he's gonna punch a hole through the brick to install the LB in the garage wall, but I forgot to ask...

1) The ground wire from the (2) rods going into the sub panel, does this run outside the conduit from rods and come in through bottom of sub panel -or- does it run inside conduit from sub panel to LB and I drill a hole through LB at bottom to come out of here into ground rods?

2) What size solid bare ground (from rods to sub panel) should I run? I was told something about if it's #4 it doesn't need to be protected by a raceway, so that's were I'm getting confused.

Many thanks for the help!
 
#58 ·
Number 6 ground is sufficient. It need to be run seperate to the ground rods. Personally i would run it in its own PVC pipe for protection. There is an article on the sizing and protection but by the time I actually find it an American sparky will probably already have posted it lol.
 
#59 ·
Thanks andrew, hopefully someone comes along and can verify if #6 ground is required to be protected. If it is, can I use #4 without protection? About 18" would be exposed above ground.


I really did not want to run another piece of conduit and LB for the ground, the feeders LB already sticks out enough against my brick garage...lol
 
#60 ·
250.64

(B) Securing and Protection Against Physical Damage.
Where exposed, a grounding electrode conductor or its en-
closure shall be securely fastened to the surface on which it
is carried. Grounding electrode conductors shall be permit-
ted to be installed on or through framing members. A 4
AWG or larger copper or aluminum grounding electrode
conductor shall be protected if exposed to physical damage.
A 6 AWG grounding electrode conductor that is free from
exposure to physical damage shall be permitted to be run
along the surface of the building construction without metal
covering or protection if it is securely fastened to the con-
struction; otherwise, it shall be protected in rigid metal
conduit (RMC), intermediate metal conduit (IMC), rigid
polyvinyl chloride conduit (PVC), reinforced thermosetting
resin conduit (RTRC), electrical metallic tubing (EMT), or
cable armor. Grounding electrode conductors smaller than 6
AWG shall be protected in RMC, IMC, PVC, RTRC, EMT,
or cable armor.
 
#62 ·
you've got to clip it nice and neat or else it won't pass inspection. Best to call your inspector and have them tell you what they want to see. The do make clips to fasten the wire. any electric supply should carry them.
 
#63 ·
Thanks again... Last question for now..

I'm thinking of having a switch inside house to turn outside garage lights on/off. I was going to run (3) #12 THWN for the switched hot and ground in the main conduit with feeders. Do I need to bring in a neutral as well for the switch?
 
#64 ·
You need a neutral at the switch location. As for running the branch with feeders that's a whole other arguement.
 
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