Sub panel to detached garage

[jroes86]

I’m in the process of buying supplies to add a subpanel to my detached 2.5 car garage and I have a few questions. I have a 200A service to my main panel inside my house, the cable run will be 50ft underground to my garage.

I plan on running a MIG, 120v compressor, various saws/grinders, lighting, etc. With a possibility of a knee mill and a furnace in the distant future.

So my plan is to run 3,3,3,5 copper stranded THWN through 1.5” schedule 80 PVC conduit (buried 18") out to a 100A subpanel. The neutral bonding strap will be removed, the grounding bus will be bonded to the case and ill run #5 stranded copper to two grounding rods 6.5’ apart on the outside of the garage. Inside I will have a 60A or 70A breaker in the main feeding the subpanel in the garage as I would like the capability of 100A in the future but don’t think ill need quite that much in the present. I’ll also be running a second 1.5” PVC conduit for comm wires.

My main reason for posting is that I live in the NW Chicago suburbs and I know electrical practices are more stringent out here. My suburb has adopted NEC 2011, with the two main exceptions that no aluminum wire is allowed (no romex either) and everything must be in conduit. My concern right now is how to get the wire into my main panel. I have a short run (<5’) inside to the panel that must pass through an outside brick wall. Im not certain on what fitting(s) to use to get the wire through the brick wall and once inside the basement, can I continue with PVC conduit or do I need to convert to EMT?

 

[gtae07]

I can't speak to your oddball codes, but just go ahead and put in the largest sized breaker you can support. No sense putting in a small one now just to change it out later; you won't be wasting the electrons. I am rather surprised that you can't use any aluminum wire for feeders... and am I understanding that you aren't allowed to use romex anywhere?

 

[wyliesdiesels]

For the feeder wires u would need 3 runs of #3 cu THWN and 1 #8 THWN cu green jacketed for the EGC for 100a breaker. u wont find #5 cu and it would be oversized.

For the GEC for the rods max size u need is #6 bare solid cu. as long as its not subject to damage. again u wont find a #5 bare or stranded cu.

For entering the brick u could use an el B and continue with pvc inside. Make sure to use sch 80 pvc where subject to damage.

 

[pattenp]

When you stated 3-3-3-5, that rang a bell with me because that combination is a size that copper SER comes in. If by chance you are looking at SER it can't be used under ground, even in conduit. You need to use individual THHN/THWN wires. Just wanted to say this to be sure of what wire you planned to use.

 

[jroes86]

am I understanding that you aren't allowed to use romex anywhere?

That is correct. Romex is not allowed.

For the feeder wires u would need 3 runs of #3 cu THWN and 1 #8 THWN cu green jacketed for the EGC for 100a breaker.

That's great if i can get away with #8 for ground. Whats the reasoning behind #8 for the panel feed and #6 for the ground rod connection? Do you think 1.5" conduit will be big enough to make pulling the wires through easy enough?

For the GEC for the rods max size u need is #6 bare solid cu. as long as its not subject to damage. again u wont find a #5 bare or stranded cu.

Do the ground rods need bare wire? I would rather use insulated all the way out, I plan on running it in conduit down the outside of the garage. Can I bury the clamps for the grounding rods for a cleaner looking install? If thats the case I may run the conduit into the ground and seal up the end where the wire exits to connect to the rod.

 

[bob_mp]

Are you planning on running a rotary phase converter for your knee mill? If so, you may want to consider up-sizing the conductors.

The inrush current of some rotary phase converters can be stupidly high. I have a GWM 286 converter, which is based on a 30 HP motor. It won't start reliably behind anything less than a 100 amp breaker.

 

[matt151617]

The ground rods are for lightning protection, while the ground running back to the main panel provides the actual grounding. 1.5" conduit should be plenty big. A common recommendation on there is to run 2 separate conduits side by side, with the second one for additional low-voltage applications such as cable or telephone lines.

You can use insulated, but don't forget you have to install 2 ground rods at least 6 feet apart. That means either removing the last 6+ feet of insulation, or somehow removing insulation in the middle part of the wire where it contacts the first ground rod. I prefer the bare wire, which fades to a dull green color, instead of the bright neon green jacketing.

The ground rod clamps should be buried 6" or so under the surface of the dirt, but left exposed for the inspector. After it's signed off on they can be covered. The ground wire to the rods doesn't have to be in conduit.

 

[marklc]

Why do you need ground rods for a subpanel that seems odd? Especially since they are not to be bonded in a subpanel. Unless I missed something.

 

[jroes86]

Are you planning on running a rotary phase converter for your knee mill? If so, you may want to consider up-sizing the conductors.

If I get a knee mill it will be run with a VFD.

Why do you need ground rods for a subpanel that seems odd? Especially since they are not to be bonded in a subpanel. Unless I missed something.

See...

The ground rods are for lightning protection, while the ground running back to the main panel provides the actual grounding.

 

[marklc]

AHH thx