Wiring for My Detached Garage

[starting]

I know that this question gets posted a million times but I am just looking for final input before I pull the trigger.

Background:
200 Amp service to the house
Oil Heat and Water Heater
Electric Stove
No Central AC
About 100' run to the garage
The garage is 24x24 with an upstairs and is divided into 3 spaces. The lights would only be on in one section at a time and would use about 8 amps if that much.

The wiring in the garage is an absolute mess. Old style fuses and it appears everything is being run on one fuse. The person before sorta added a ground. Overall it scares the **** out of me. Everything that is out there will be pulled out and run new.

What I want to run in the garage:
I will be working by myself in the garage and only running 1 machine at a time. I will of course have the lights on and also a radio. I plan to add a tig welder, mig welder and a fairly decent compressor at least 60 gallon down the road

From my research it seems that the following will work:
60 Amp breaker in the main
#6 copper wire with a #10 ground
THWN or THW wire in pvc conduit buried at at least 18" deep
2 Grounding Rods outside the garage 6 feet apart
Wire run to a 100 amp box 20 space box using a 60 amp main disconnect
Neutral and Ground in the box to be kept separate.
4 220v outlets to be placed in the garage for the future machines on 2 30 amp breakers
4 120v outlets on 1 20 amp breaker using 12 gauge romex
4 120v outlets on 1 20 amp breaker using 12 gauge romex
8 120v outlets on 1 20 amp breaker using 12 gauge romex
Lights to be run on 2 15 amp breakers using 14 gauge romex
Outdoor lights on 1 15 amp breaker using 14 gauge outdoor romex

Anything I should change? Anything not look right? I think i did my research but I just want to confirm everything before I go out and buy the materials.
Thanks for reading the long post.

 

[Aceman]

Everything sounds great other than the 60 amps feeding it. There is the possibility your compressor may kick on while you're tig welding, which may be pushing a 60 amp circuit depending on how large your welder and compressor are.

I'd probably suggest something like #2 AL on a 90 amp breaker just to give you some more cushion and help a little bit more with voltage drop.

 

[trbomax]

What he says. My tig is on a 60,my compressor a 40,migs on 40's.Niether the compressor or the tig would tolerate a low voltage situation for very long.Around here they would still want a 4th wire to tie the gnd to the main service disconnect,and a gnd bar in the subpanel for the gnd wires in the shop.

 

[starting]

So if I went with 90 as the breaker I would be looking at #3 copper and #6 for the ground? Its late and i have to think tomorrow but I appreciate the input and will have to rethink the wire.

 

[p_mori7]

Correct. I just ran 80' to a sub panel for my future detached garage. The panel is temporarily mounted in a weatherproof enclosure on a post in the yard and is powering all the stuff for my new inground pool.

100A breaker in the main box. 3/3 copper out to the subpanel, did not use the ground wire, used a ground electrode next to the subpanel and tied the mechanical & appliance grounds together in the subpanel.

Checked the circuits with my multimeter, 0 voltage drop (maybe .5 volt on the 240 because the meter was flipping between 239 - 240).

Everything for the pool is running great.

 

[Charles (in GA)]

did not use the ground wire, used a ground electrode next to the subpanel and tied the mechanical & appliance grounds together in the subpanel.

Don't know about Canada, but in the US, that would not pass inspection. NEC requires that the ground and the neutral be carried to the subpanel. Ground rods do not make a totally safe ground by themselves.

Charles

 

[starting]

Ok so it seems like it would be a lot better for me to do a 90 amp breaker in the main box. Run #3 copper and a #6 ground to a 100 amp subpanel with a 90 amp main breaker. Also run 2 grounding rods at the garage 6 feet apart.

 

[SM Racing]

Why not just run a dedicated 200amp panel? Just convert the house to 400Amp service, as a 40 slot 200Amp breaker box to the shop. Never worry about the wiring. Service entrance cable isn't that expensive.

 

[starting]

From doing a little further research it looks like i can use #4 THHN instead of 3 and save a little money.

 

[cj7jeep81]

might also look at running aluminum. not sure on the price of copper, but #2 aluminum at home depot isn't bad priced at all, and good for 90 amps.

 

[VHF]

...a 100 amp subpanel with a 90 amp main breaker.

It is code-compliant to use a 100A subpanel with a 100A main breaker in the garage even though you have a 90A breaker feeding it from the house. Probably much less expensive than trying to get a 90A main.

It is the 90A breaker in the house that would be providing overlaod protection for the wire between the house and the garage. The 100A main in the garage would serve as the required disconnect for the garage, but it would be the house breaker that would trip first in an overload situation.

 

[dipper]

I doubt you'll find a 90a breaker.
I have a 200amp main panel in my house, 100A breaker feeding the garage on 4 pieces of #4 THHN copper underground thru conduit 75' to detached garage. Garage has a 40slot 100A main breaker sub panel. Also have a ground rod coming into the subpanel, and have the ground and neutral bars separate.
Check local codes on the grounding electrode system and ground rods/bars, there are a lot of ways you will hear about how to hook it up and what you should use, best to just do it exactly how your inspector wants to see it and not have to worry about it.

The 100amp feed may end up being cheaper for you since the 100amp boxes are more readily available. Regardless of what size breaker and boxes you put in, i would wire it for 100amps so you don't have to do it over later on when you need more power. 100amps in you shop should be sufficient but 60 will be pushing it.

Just my .02

 

[Norcal]

I doubt you'll find a 90a breaker.
I have a 200amp main panel in my house, 100A breaker feeding the garage on 4 pieces of #4 THHN copper underground thru conduit 75' to detached garage. Garage has a 40slot 100A main breaker sub panel. Also have a ground rod coming into the subpanel, and have the ground and neutral bars separate.
Check local codes on the grounding electrode system and ground rods/bars, there are a lot of ways you will hear about how to hook it up and what you should use, best to just do it exactly how your inspector wants to see it and not have to worry about it.

The 100amp feed may end up being cheaper for you since the 100amp boxes are more readily available. Regardless of what size breaker and boxes you put in, i would wire it for 100amps so you don't have to do it over later on when you need more power. 100amps in you shop should be sufficient but 60 will be pushing it.

Just my .02

90 A circuit breakers are quite common just not at idiot boxes like Blowes or HD, and #4 THHN is is undersized for your application + THHN is not permitted underground or in any wet locations, one can only hope that the cable is dual rated THHN / THWN which is permitted in wet locations, see NEC table 310.16 for proper sizing of your cable.

 

[dipper]

well i guess i'll go out and by those 90 amp breakers. FWIW, all the electrodes at work said #4 is okay for 100a, and 310.16 says it is okay for a 3 wire...but whatever.
And it is thhn/thwn so that is okay.

 

[Norcal]

Here it is:


(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of onefamily,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unitand are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit. The feeder conductors
to a dwelling unit shall not be required to have an allowable
ampacity rating greater than their service-entrance conductors.
The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.

A detached structure does not meet the criteria in that code section that allows one to undersize those conductors.

 

[starting]

Thanks for all the help. I ordered the 90 amp breaker the other day and will be getting #4 THWN soon.