Wire choice for 100 amp sub panel in attached garage

[ktorak]

Hello all!

I am currently reviewing my plans to install a 100 amp sub panel off of my 200 amp main panel in my attached garage. From the sub panel, I plan to install circuits for lighting, convenience outlets, a welder, and an air compressor - in lieu of running separate feeds for all of these pieces of equipment from my main 200 amp panel.

My biggest issue is wire choice... From what I can tell, I need 1 AWG copper for 100 amps @ ~50 feet. 30 feet of my run is above a finished basement ceiling from the garage to the panel (think dry wall with no insulation above it). The other 20 feet is inside of the garage (not finished). I know in the garage I have to protect any wire ran in some sort of conduit. I originally planned on THHN (2 hot, 1 neutral, 1 ground) and using PVC conduit but I have found that THHN requires conduit for the entire length it is used. I am considering liquid tight now for ease of installation - though more money, it would be less fittings and work to pull the wire through.

Any thoughts or insight would be helpful - there's likely other options I haven't thought of yet or considered to make this easier.

 

[Bert_]

I'd be looking at SER cable, no conduit required. Copper could be #3 but I rather aluminum for something like this. #1 aluminum is good for 100a.

Garage part could be slid in some pvc if it's short. Or just run a board in front of it if it needs protection. My opinion is it only needs protection if it is ran exposed low on/in the walls

 

[pattenp]

I believe 100A maybe overkill for your needs. I would use #2 Al SER and go with a 60A feeding breaker and see how it goes on the power needs. If 60A ends up being too lite, then up the breaker to 90A max. I believe you'll find 60A to be enough. With that being said, have you added up the actual max amp loads that you may have going at one time on the subpanel?

 

[wyliesdiesels]

Doubt you will need 100a. Go smaller and save some money

 

[ktorak]

I know 100A sounds like overkill but this is my intent:
50A Welder
30A Compressor (estimated)
20A Lighting/Convenience
20A Outdoor GFCI (since I don't have any outdoor outlets as it)
40A (20A x 2) FUTURE detached garage circuits - who knows if this will happen because it will be a lot of work for something I rarely use...and it's only 25' from the attached garage so an extension cord usually does the trick.

I figure on at least the welder and compressor circuits being on simultaneously (think plasma cutter) and at least some draw from the other circuit.

Instead of running all of these separate, the intent was to feed one large sub panel and then install what I may need or want down the road since my meter/main panel is about as far from the attached garage and my welder/compressor as could be possible. For what its worth, I do work as an engineer and all too often everyone tries to save a few dollars to end up redoing something later because it couldn't be expanded or upgraded easily.

In terms of aluminum, what are the issues with connecting it to breakers other than making sure the anti corrosion paste is used? Can SER be run in the void space above the basement without any code issues? In the garage, I'm not above building a wooden box out to conceal it since the run would be too long for conduit, unless SER can be run in conduit as well. My initial thought was THHN copper, but I'd have to run conduit the whole length which will be a pain.

 

[pattenp]

The SER is subject to the same install rules as NM(Romex). It can be placed in conduit sleeves (usually not over 10' lengths) for protection without having to meet conduit fill restrictions. If placed in a completed conduit system(closed ended) then the conduit fill requirements kick-in.

 

[theoldwizard1]

I am currently reviewing my plans to install a 100 amp sub panel off of my 200 amp main panel in my attached garage. From the sub panel, I plan to install circuits for lighting, convenience outlets, a welder, and an air compressor - in lieu of running separate feeds for all of these pieces of equipment from my main 200 amp panel.

100A is overkill for most residential garages, unless you plan on having a welding party with several folks bringing their welders !

If you are not going to take the time and effort to add up your loads, most residential garages get by fine on 60A service.

There is no code/"requirement" that wiring in a residential garage be inside conduit. NM-B is fine, without conduit, if properly installed.

 

[theoldwizard1]

I know 100A sounds like overkill but this is my intent:
50A Welder
30A Compressor (estimated)

Even a 250A welder would typically only require a 30A circuit. Much of this is due to "duty cycle". (Yes, I know welders have 50A plugs.)

A 30A circuit for a compressor would be a LARGE (>5 HP) compressor.

Even a plasma cutter that requires about the same amount of current as a typical welder and requires air from you compressor can live on 60A assuming no other large loads.

There are some funny rules about running a sub panel off of a main. Typically, you are limited to 90A. Remember, the size of the main breaker in the sub-panel has NOTHING TO DO WITH THE SIZE OF WIRE FEEDING THE SUB OR THE SIZE OF THE BREAKER FEEDING IT FROM THE MAIN.

 

[mike93lx]

the welder won't use 50a. the compressor won't use 30 amps (running). lighting will probably use 4 amps (if LED).

you only use anti-oxidant if the wire manufacturer requires it.

The feeder breaker doesn't dictate the size of the subpanel. Go grab a 200a main breaker panel if you want a bunch of space.

I would also run 2 Al SER. No way I'd throw down the money for copper...it's just a waste.

 

[Crazyjake8493]

2/2/2/4 SER in aluminum would be the way to go. Should be easy to get locally and good for 90 amps. You should be able to get a 60 amp breaker with no trouble, if you wanted 70 or 90 amps you might have to order those. I highly doubt you’d need the full 100 in a garage. I would still install a 100 amp 20 space panel in the garage just for the extra space and future flexibility.

 

[ktorak]

2/2/2/4 SER in aluminum would be the way to go. Should be easy to get locally and good for 90 amps. You should be able to get a 60 amp breaker with no trouble, if you wanted 70 or 90 amps you might have to order those. I highly doubt you’d need the full 100 in a garage. I would still install a 100 amp 20 space panel in the garage just for the extra space and future flexibility.

The more I look into it, the better this option sounds. 100 amp(ish) panel with 2/2/2/4 Al wire and a 60 amp breaker at my main panel. Seems to be the most cost effective approach.

I'm still trying to understand the code on SER Al wire though. I'd need about 10 feet of protection to get from my panel to my void space above the basement. Then from that space through the garage (to where i'd like the panel on the back wall, centers, i'd need around 20 feet of protection. I'm not sure if 2" PVC would pass the test, or if it would be a code issue for the longer run.

 

[Bert_]

It only needs protection if it can be damaged. The part above the panel in the basement probably doesn't need anything extra. The part in the garage may or may not need protection, depends on how you run it.

 

[Sticky Grips]

I did 1/0 SER cable from the main panel to the sub.

I did 100A because i left the option of running power to a detached garage.

I have a 50A welder outlet along with a 40A compressor circuit.

 

[mike93lx]

I did 1/0 SER cable from the main panel to the sub.

I did 100A because i left the option of running power to a detached garage.

I have a 50A welder outlet along with a 40A compressor circuit.

Wire gauge is not really meaningful without sharing distance.

And what compressor are you running that requires a 40a breaker?

 

[Sticky Grips]

Wire gauge is not really meaningful without sharing distance.

And what compressor are you running that requires a 40a breaker?

I can't recall the distance exactly, but it went completely across my basement, up 1 floor, into the garage attic, and down the wall. maybe 100ft?

The compressor is a 2 stage 60 gallon HF that required a 40A breaker.

 

[FJ 432]

I'd be looking at SER cable, no conduit required. Copper could be #3 but I rather aluminum for something like this. #1 aluminum is good for 100a.

Garage part could be slid in some pvc if it's short. Or just run a board in front of it if it needs protection. My opinion is it only needs protection if it is ran exposed low on/in the walls

This is good advice and what I did in 2009. And run what you want, I ran 100 amps as well.

 

[ktorak]

This is good advice and what I did in 2009. And run what you want, I ran 100 amps as well.

For what it's worth, I can always use the biggest wire I need for 100A (1/0 AWG Al) and upsize a breaker later if I ever want to expand...however the jump from 2/2/2/4 AL ($1.32/FT) is huge since I can only find 4/0-4/0-4/0-2/0 AL in the big box ($3.98/FT). Otherwise I think I have to go to THHN copper and use conduit.

I'm thinking for ease, I will just build wooden box outs to protect the wire where needed.

 

[pattenp]

For what it's worth, I can always use the biggest wire I need for 100A (1/0 AWG Al) and upsize a breaker later if I ever want to expand...however the jump from 2/2/2/4 AL ($1.32/FT) is huge since I can only find 4/0-4/0-4/0-2/0 AL in the big box ($3.98/FT). Otherwise I think I have to go to THHN copper and use conduit.

I'm thinking for ease, I will just build wooden box outs to protect the wire where needed.

#1/0 Al is not needed for 100A, #1 is 100A, #1/0 is 120A. To find what you need go to an electrical supply house, not the big box store. Get 1-1-1-3 Al SER.
https://www.wireandcableyourway.com/1-3-3-ground-ser-aluminum-building-wire.html


*

 

[brewchief]

If you're planning on feeding it with a 60 amp breaker see what size wire it can handle, a 60 might not fit wire much larger then #2.

 

[theoldwizard1]

If you're planning on feeding it with a 60 amp breaker see what size wire it can handle, a 60 might not fit wire much larger then #2.

Very True !

If you are going to put a 60A breaker in the main, just buy Romex (NM-B). No conduit required. The proper size depends on the total length of the run.

 

[terabitdan]

I don’t understand why anyone would recommend using a 60 amp breaker for 90+ amp wiring. If the OP had one laying around, sure, why not. A 90 amp breaker is $20 more than a 60 and can be had in 2 days, maybe a week at most.

This projects budget or timeline won’t be blown on the right circuit breaker.



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[ktorak]

I don’t understand why anyone would recommend using a 60 amp breaker for 90+ amp wiring. If the OP had one laying around, sure, why not. A 90 amp breaker is $20 more than a 60 and can be had in 2 days, maybe a week at most.

This projects budget or timeline won’t be blown on the right circuit breaker.



Sent from my iPhone using The Garage Journal mobile app

The biggest cost is the wire and just the effort of sourcing it. Everything else I can get locally at a big box, though i'm not sure why Home Depot stocks all Eaton breakers but no Eaton panels unless you special order - but Mendards stocks Eaton panels on the shelf.

 

[mike93lx]

I don’t understand why anyone would recommend using a 60 amp breaker for 90+ amp wiring. If the OP had one laying around, sure, why not. A 90 amp breaker is $20 more than a 60 and can be had in 2 days, maybe a week at most.

This projects budget or timeline won’t be blown on the right circuit breaker.



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You listed two good reasons why. It costs more and will likely take more time to source. Combine that with it being unnecessary and i see three solid reasons to go with a 60.

 

[pattenp]

I don’t understand why anyone would recommend using a 60 amp breaker for 90+ amp wiring. If the OP had one laying around, sure, why not. A 90 amp breaker is $20 more than a 60 and can be had in 2 days, maybe a week at most.

This projects budget or timeline won’t be blown on the right circuit breaker.



Sent from my iPhone using The Garage Journal mobile app

You have a good point, but $20 difference is the low end depending on the panel brand. Some 90A breakers can run $40 - $50 more than a 60A depending on market area. #2 Al is a common size and is 90A max and 60A breakers are common and cheap. If 60A is plenty to meet power needs then the #2 Al and 60A breaker is usually an easy combination to get at a big box store.

 

[Bert_]

Very True !

If you are going to put a 60A breaker in the main, just buy Romex (NM-B). No conduit required. The proper size depends on the total length of the run.

I'd still be looking at SE. Same rules as Romex with the addion of being allowed to run outside.

You could get 100a wire in aluminum SE for less that 60a wire in Romex.

 

[ktorak]

I'd still be looking at SE. Same rules as Romex with the addion of being allowed to run outside.

You could get 100a wire in aluminum SE for less that 60a wire in Romex.

This is what I am looking at for locally supplied AL... ~$3/foot for 1/0-1/0-1/0-2 SER. I might be able to get it for less with the account, but it wont be a huge price change.

AL SER


I can order it for ~$2.34 or less from Home Depot. 1-1-1-3 AL SER is actually more expensive.

Home Depot SER

Menards doesn't seem to stock x-x-x-y AL SER, even online.

 

[ktorak]

I was able to find 1/0-1/0-1/0-2 Al SER at another local electrical house for $1.80/FT. Sounds like that is my best bet.

 

[3rdgendslmech]

Do you have any plans for heat or A/C? That's an extra load on the system.
I'm going with a 5000 watt electric heater at least for now until I can spring for a mini split. Between that heater going full blast, 3.5 hp compressor kicking in while I'm welding with a 210 amp Hobart. Haven't put an amp clamp on anything yet but what I'm getting at is I snapped in a 60 just to get me up and running. If you're gonna put in wire that's good for 90 amp service you should put in a 90 amp breaker.

 

[ktorak]

Do you have any plans for heat or A/C? That's an extra load on the system.
I'm going with a 5000 watt electric heater at least for now until I can spring for a mini split. Between that heater going full blast, 3.5 hp compressor kicking in while I'm welding with a 210 amp Hobart. Haven't put an amp clamp on anything yet but what I'm getting at is I snapped in a 60 just to get me up and running. If you're gonna put in wire that's good for 90 amp service you should put in a 90 amp breaker.

The garage is part of a walk out basement with ducting (heat/AC) from the house - at this time I have no additional HVAC plans since the space stays comfortable year round. I have considered a gas wall mount unit if I ever needed more heat in the winter.

With the 1/0 wire I am going to do a 100 amp feed and be done with it. Then I can run all of my garage loads from the new subpanel.

I just have to build box outs for the SER in the electrical room where my main panel is and from the ceiling down to my new sub panel in the garage. I will spend a little more on wire now, but putting my new subpanel centered on the back wall allows me to run really short future circuits for a welder and compressor.

 

[mike93lx]

That garage should not be connected to the home's HVAC (if forced air). I believe its against code, due to the risk of fumes and CO spreading to the rest of the home

 

[ktorak]

That garage should not be connected to the home's HVAC (if forced air). I believe its against code, due to the risk of fumes and CO spreading to the rest of the home

That’s likely why the vent is sealed off since the ducting runs through there. The new HVAC was permitted and inspected so I’m guessing they sealed it then.