[mtstewart1]

I have a 200 amp main panel, not using all the spaces provided. I would like to run a feedr line to a detached garage to use as a wood and metal working shop, with 220v compressor, welder and Nissan Leaf charging location. Other tools are 110v with varying loads. I will likely be using one or two tools at a time or in succession. I would like more breaker spaces than a 60 amp sub provides.

Can I feed a sub panel with a smaller breaker than the subpanel main breaker?

What size cable would be necessary for the feeder line? I intend to bury in 2" PVC at 18". The garage is seventy five or so feet away.

Thanks
Mts

[donf]

Your cable requirement is the simplest part of your question.

Yes you can feed your secondary panel from your main panel. The size of the breaker is dependent on the load (amperage) you will need in your shop.

In your case, 75' will not cause any appreciable voltage drop so you do not need to calculate that.

What you do need to tell us is the type cable (must be listed for use in wet environment, even though you are placing the cable in conduit. Also, you must use a four wire cable. Two hot conductors, one Neutral and one Ground.

Also, at the secondary panel, Neutral and ground must be isolated from each other. You need to put in a grounding system (usually one or two ground rods) or a "Ufer", which is a concrete encased grounding electrode.

One other thing, if you install an electrical system in this shed, you must (by code) install a light near the entrance of the shed.

[mtstewart1]

THHN THWN Electrical Wire 3 AWG

3 conductors Red, Black, White from what I have seen a bare wire ground may not be necessary if a local two ground rod system is installed at the remote location and the bonding screw is removed from the sub panel neutral/ground bus?

If needed I could add a smaller bare wire or shielded green wire to tie the remote sub to the house? Is it necessary?

If there are future solar or wind considerations, should I pull some string or other cable to tie house and garage renewable generation to the transition panel near the main? If so what would you recommend for a 2Kv garage system going into the house?

[hfcarson]

Mt, you always need an equipment grounding conductor regardless of how many ground rods you use...

For 100 ampere, the EGC is a minimum of #8 AWG copper.

[mtstewart1]

mt, you always need an equipment grounding conductor regardless of how many ground rods you use...

For 100 ampere, the EGC is a minimum of #8 AWG copper.

MTS - If the sub panel neutral and equipment ground is broken by removing the screw in the box, where do you attach the ground wire from the main panel in the house to the garage or subpanel?

If a separate grounding system is required due to distance and GFCI operation wouldn't that (remote two rod grounding system) serve as your equipment ground?

[hkstroud]

You install an additional grounding bar in the sub panel.

hfcarson,

Doesn't that ground wire have to be an insulated grounding conductor?

[hfcarson]

Hk:.. the equipment grounding conductor could be metal conduit, so no it doesn't.

Mts - let's be clear about something. Services are required to make connections to earth ground for creation of an equipotential reference. With grounding electrodes the earth and the electrical system ground will be essentially equal.

The equipment ground is connected to the grounding electrode system, to the grounded conductor at the first overcurrent device and to all metallic equipment that is likely to become energized. This is to ensure operation of the overcurrent devices when faults occur.

Don't "assume" anything... do your homework, ask questions and try to do it correctly... for safety sakes.

[hfcarson]

Mts - I'm trying to say that you cannot create the equipment grounding conductor with ground rods. That could be a hazardous mistake...

Follow the electrical code rules. If you are not sure, hire someone who is...

[donf]

Good morning.

To answer your question regarding the ground wire from the main panelboard. This wire is connected to the ground bus on the secondary panelboard.

The reason you do not connect the Neutral and Ground together is that the NEC requires that there be only one location where Neutral and Ground are bonded together and that is the main service panelboard.

Also, you have to install a disconnect method to quickly kill the secondary panelboard. A main disconnect switch, placed on the circuit in front oh the secondary panelboard is my preferred method. Or you can use a panelboard that has a main cutoff breaker (just like your main service panelboard. Another method is to use what is called a "MLO" panelboard. This type of panelboard does not have a main breaker cut off. The panelboard can be shut down by using no more than six switches.

Also, the earlier posting telling you what type of wire to use had a typo. "THHN" wire cannot be used in a wet environment. However "THHN/THWN" can be used.

[mtstewart1]

mt, you always need an equipment grounding conductor regardless of how many ground rods you use...

For 100 ampere, the EGC is a minimum of #8 AWG copper.

So let me get this connection from main to sub-panel correct:

Four conductors: red, black, white, green #3 copper for 100 amp panel 75 +/- feet away installed in 1 1/2 - 2" PVC buried min. 18".

Remove bonding screw from 100 amp panel joining neutral to equipment ground. Run neutral to neutral, black and red to either side of the sub panel bus, green equipment ground to equipment grounsd in 100 amp panel.

Yes/no - ADD REMOTE TWO ROD GROUND SYSTEM TO SUB PANEL EQUIPMENT GROUND (to insure GFCI operation at remote location)

Then wire breakers to circuits in garage as needed.

[mtstewart1]

Any help with my renewable energy questions?
I may be adding a solar array to the house and garage. I will need to tie them together I am guessing near the main panel?
If II use the 2" conduit from house to garage can I pull the neccessary conductors for the solar array back to the house in the same conduit?

I intend to also bury a 1" conduit for communication, LAN set up.