Cable sizes for new shop/garage

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Old 10-16-19, 01:11 PM
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Cable sizes for new shop/garage

I have an old farm house that has 200A service. I am building a 22x30 shop. I need to put in a subpanel in that shop from the main panel.

I know I need H, H, N, and G for the subpanel, but what size cables and what size breakers? I don't know enough about code to know the requirements. Here is what the shop will handle:

20A circuit for lights/outlets for various things.
50A 220V circuit for welder
washer
Dryer
Tankless water heater (usually requires 2 40A 220V circuits,OR one 50A)
Fridge/freezer
Deep Freeze

So...this is what needs to go in there. What size breaker from the main should I use and what cable size? Distance is about 50-75 feet from main.

Thanks so much!
 

Last edited by agdodge4x4; 10-16-19 at 01:40 PM.
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Old 10-16-19, 08:10 PM
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Unless you are a welder...... that's only rarely used.
It's the electric tankless that is going to require a large line and if you want to have that running and weld you'll need a staggering sized cable.

Dryer..... gas or electric ?

I'm thinking 150A breaker and 1/0 copper.
Direct burial cable or conduit ?
 
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Old 10-17-19, 05:18 AM
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Dryer is electric. I was thinking 100A and 4 gauge cable, so I'm glad I asked.

The tankless I am looking at to serve a single sink and/or single washing machine will utilize either a single 60A breaker or smaller 220V, if that helps.

I'd prefer to put cable in conduit and was thinking 2", but I can go either way if direct bury is better.
 

Last edited by agdodge4x4; 10-17-19 at 06:17 AM.
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Old 10-17-19, 06:59 AM
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Water heater tanks use around 20A, so if you install one of those instead of the tankless, your requirements become more reasonable.
 
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Old 10-17-19, 04:10 PM
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This heater would get used twice a week for about an hour each. Standard Tank makes very little sense. I thought there were exceptions to loads like this so I guess I thought 100A service and 4 ga copper would be overkill as it was.
 
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Old 10-17-19, 05:23 PM
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100A isn't overkill, it's bare minimum. I'm assuming you aren't going to be heating water and welding at the same time, but you could be washing and drying while heating water, right? So basically everything could be used at the same time except the welder.

BTW the minimum wire size for a 100A feeder is 3awg copper, not 4.
 
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Old 10-18-19, 05:46 AM
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OK...so I can go with 100A and 3AWG Copper with a 100A feed if I drop to a tank heater.

If I must go with Tankless, then I should head over to 150A and 1/0 As PJ suggested, yes?

I went ahead and got UNlazy and tried to read the NEC Code about this. Here is what I came up with.

1.98 KVA = 660 square feet shop general lighting
1.50 KVA = Dryer
3.0 KVA = Shop General Appliances
2.4 KVA = Workbench Outlets
11.00KVA = Welder (50A, assumed, couldn't find nameplate data)

17.50KVA = Water Heater (Fixed appliance)


First 10 KVA @ 100% = 10.00 KVA
Remaining @ 40% = 13.46 KVA
TOTAL = 23.46 KVA -> 97.77 A @ 240V


So...as you said 100A is MINIMUM but makes conservative assumptions and a circuit that is probably not used often or at all.
 

Last edited by agdodge4x4; 10-18-19 at 06:33 AM.
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Old 12-30-19, 10:59 AM
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I need some help with wire sizing on my garage/shop project again.

The person running the project called the master electrician and suggested 2/0 wire and 100A sub. However, the wire sizes he suggested were not all the same. The neutral and grounds were different and I don't understand why.

Here is what I decided we need in the garage/shop and the run from the main is 80'.
We ditched the tankless heater idea, and the welder would be a RARE use occasion.

20A circuit for lights/outlets for various things.
20A circuit for outlets alone
Garage door opener
50A 220V circuit for welder
washer
Dryer
Standard water heater, big enough to serve washing machine and sink. That's it.
Fridge/freezer
Deep Freeze
 
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Old 12-30-19, 11:18 AM
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Can we assume aluminum wiring ? 2/0 is a little large.

The two hot wires carry the bulk of the power.
The neutral carries the imbalance or the current from one leg to neutral. That could be #2 al.
The ground only needs to be #4 al. for a 100A sub panel with upgraded wiring size.
 
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Old 12-30-19, 12:31 PM
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OK. I just confirmed copper 2-2-4-6 for the wiring. 4 for neutral 6 for ground. I didn't know you could do this. Thats why I'm asking if this is OK for 100A. I have 2" conduit I'm going to put it all in.
 
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Old 12-30-19, 02:22 PM
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You mentioned cable earlier and now are saying 2-2-4-6 cu. What type of cable are you thinking to use? If it happens to be SER, it's not allowed in conduit when underground.
 
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Old 12-30-19, 02:34 PM
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I'm just going by what the electrician said. My plan was 2-2-4-6 copper wire individual wires...just like I was going to a subpanel. Maybe my nomenclature is wrong. I don't know. I'm trying to figure out what I need. For whatever reason, I can't manage to get 3 master electricians to agree, so I'm hoping to get a straighter answer here.

I was told COPPER 2 gauge for L1 and L2, 4 Ga for Neutral 6 gauge for ground is what was suggested inside conduit. THHN, the individual wires. Is this big enough??? Electrician said there is ZERO reason to spend the money on 2 AWG for all. I don't understand this or why. I don't understand why its OK for the neutral to be reduced and teh ground to be reduced yet again.
 
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Old 12-30-19, 02:47 PM
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The 2-2-4-6 Cu is fine for 100A. You can use either THHN/THWN or XHHW-2. Just remember the #6 needs to be bare copper or have green insulation, and actually the ground for 100A can be #8Cu.. Conductors #4 and larger may be reidentified.

You could save some $$ by using Al XHHW-2 in the sizes of 1-1-3-6 for 100A.

Also by the NEC, #3Cu is good for 100A.

Personally, if I was doing it for myself. I'd do AL XHHW-2 using 1-1-1-6 for 100A. I just don't like reducing the neutral.
 
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Old 12-30-19, 03:04 PM
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IDonít like reducing it either. Thatís why I was wondering why we didnít just use THHN 2 gauge all the way across and drop it down to six gauge for the ground and call it a day, other than cost, of course.
 
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Old 12-30-19, 03:15 PM
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If you want 2-2-2-6 Cu, go for it. Nothing wrong with it. That's actually good to 115A.
 
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Old 12-30-19, 05:37 PM
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Can I just use all black wire as long as I put colored tape on the 2 awg?
 
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Old 12-30-19, 06:01 PM
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The #6 can't be black and be marked with green tape on the ends. It needs to be green insulated or bare copper. One of the 2's can be taped white on the ends to mark it as the neutral. Only #4 or larger wires can be marked a different color.
 
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Old 12-30-19, 07:13 PM
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Interesting. Yeah, the ground I can find in green no problem.
 
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Old 12-30-19, 11:01 PM
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Alright, so I'm going to run 2/2/2/6 wire from the main to the 100A subpanel in the new shop, I'm going to UNBOND the Neutral/Ground at the shop subpanel and we will then have power to the shop.

Now....are there any tricks and rules I need to follow when wiring the shop itself? Since this building is ALL METAL....does this mean I am required to run all of my romex in EMT or MC conduit? For some reason, I don't feel like I can just string out romex like I would a wood framed structure.
 
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Old 12-31-19, 08:18 AM
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Technically the NM can be run exposed, but if it is possibly exposed to being damage it should be installed along running boards or placed in protective sleeves where needed. EMT or PVC can be used. Place plastic bushings on the ends of EMT to protect the NM from rubbing on cut ends. Also, all the 120V outlets will need to be GFCI protected.

Edit: If you are subject to having an inspection you should check with the local inspection department to see what they require as install methods and protection for the wiring
 
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Old 12-31-19, 08:32 AM
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Ok. I just never see Romex (NM) run exposed in metal barns. I assumed it must be inside some sort of conduit because itís a metal building. I didnít know I can just drill holes in the frame and run bare Romex through it with a bushing or something.

also, how do you secure the wire to metal? Iíd rather not drill holes thorough every support member. Lol.
 

Last edited by agdodge4x4; 12-31-19 at 08:48 AM.
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Old 12-31-19, 08:41 AM
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Not knowing the actual construction of your metal building I can't say. I'm inclined to say you most likely should install a complete EMT conduit system and run individual wire. In general being a metal building doesn't mean the NM has to be in conduit.
 
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Old 12-31-19, 07:14 PM
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I'm going to run 2/2/2/6 wire from the main to the 100A subpanel in the new shop, I'm going to UNBOND the Neutral/Ground at the shop subpanel and we will then have power to the shop.

You'll need to add a ground bar kit to the subpanel. Also, you will need at least one 8 foot ground rod at the building connected to the ground bar in the subpanel with #6 copper. I prefer #6 bare stranded copper ground wire. Check with the local building department, they may require two ground rods at least 6 feet apart.
 
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Old 02-14-20, 09:02 AM
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Why do we need a ground rod? We have a metal panel attached to a metal building and ground inside running back to a main panel with ground rods, etc. In fact, the electrician explicitly stated not to do that, which is why the conduit for the electrical supply goes up through the concrete.
 
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Old 02-14-20, 09:25 AM
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For one thing the NEC requires a grounding electrode at detached structures. The ground rod is for diverting lightning strikes and is not for clearing fault current, that is what the EGC back to the main panel is for.
 
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Old 02-16-20, 08:54 AM
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Iím confused now. I have four wires going to my building. Hot hot neutra and ground. All of these go back to the main panel. Ground and neutral are unbonded in the detached building.

where does the ground rod go and what does it connect to?? Do you mean like this:

https://i.stack.imgur.com/8rdL5.png
 

Last edited by agdodge4x4; 02-16-20 at 09:11 AM.
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Old 02-16-20, 10:41 AM
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Do you mean like this:
Yes, the ground rod connects to the ground bar you purchase separately and install in the subpanel. You still should check with the local building department, they may require 2 ground rods at least 6 feet apart.
 
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Old 08-26-20, 07:37 PM
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Good news everyone.

My 2awg wire is run to the new building 80 feet away. The load center I got for that building is a 125A Contractor pack. As such, it has a 125A main breaker. Thatís all they had in stock and the price was right.

The main pane that is going to feed that is where the 2awg wire is and will be a 100A breaker.

is there any world in which leaving that 125A main breaker in the sub panel is ďokĒ or do I have to swap that out for a 100A breaker as well?

just trying to see if I can save money on buying a 100a breaker if not necessary.
 
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Old 08-26-20, 07:56 PM
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As long as the feeding breaker is sized correctly the 125A main breaker in the subpanel is okay because it's just a disconnect.
 
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Old 08-27-20, 06:51 AM
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Why the ground wire (equipment grounding conductor) may sometimes be thinner than the circuit conductors it accompanies:

1. It will still bring to near zero any voltage differences between energized exposed objects such as appliance outer shells and unrelated grounded objects such as wet floors should a small fault current be the cause,
2. It will still trip the breaker if a large fault current should find its way onto or past exposed (metal) grounded objects.This will still happen quickly enough that the (thinner) ground wire does not overheat.

When any given building or structure is provided with one or more panels, which in many cases would be required, then a grounding electrode system, with ground rods as applicable, is needed at the first panel (sub or main).

 
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Old 08-27-20, 09:20 AM
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OK. Awesome. The main panel breaker will be sized properly.
 
 

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