Garage sub panel for 240 outlets

[Prcd6x]

I need a little help/guidance.

I need to add a few 240 outlets in my garage and my current panel is full. So I plan on adding a sub panel and need a little guidance.

Here is my main panel that has a 90 amp breaker feeding it, of course full. So I plan on consolidating four circuits into two with tandem breakers opening up space for a 50-60(?) amp breaker for the sub panel.

I want to move the sub panel down the wall closer to my bench. Mainly to save on wire cost because I want to add three 240 volt and one dedicated 120 volt outlets. All of which will be located within 5-10 feet of the proposed sub panel location.

I will add a 50 amp breaker for one outlet. For a stick welder and hopefully a cnc plasma table in the future.

I need another outlet for a plasma cutter, I think a 30 amp should cover it but I'm not sure.

I also need another outlet for an air compressor, again I think 30 amps should be good.

Then I will do a dedicated 20 amp 120v for my Lincoln 140 mig.

So my questions are:

Am I good with a 50 amp breaker to the sub panel or do I need to go bigger? The only thing that would be running simultaneously is the air compressor/plasma cutter.

The run of wire to the sub panel will be 30-35 feet. So is 6/3 appropriate for these needs and to have 240/120?

Are my estimates correct in needing 30 amp breakers for the plasma and compressor motor?

Thanks for the assistance! Hopefully I provided enough info, if not let me know what else you need.


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[matt_i]

Im confused why the Ieffective table on the plasma cutter has two numbers for 220vac, 27.5A and 18A... I don't understand that part.

In either case, a 30A breaker should cover it.

2hp motor on the compressor could easily go with a 20A breaker. But, 30A would not hurt anything, and be ready in case you ever wanted to upgrade to a larger compressor.

#6-3 is good as long as there is a ground to go with it. So there will actually be 4 wires in the jacket.

 

[nadogail]

Maybe I am missing something, but I see no half slot breakers in the pictured panel. The addition of half slot, or twin, breakers could give you room to add more circuits to the pictured panel.

 

[Prcd6x]

Thanks, yeah I don't know why there are two different numbers. That got me too. I was thinking one value maybe for 120.


There is one half/twin/tandem (whatever they want to be called) breaker. The biggest reason I want to do a sub panel is because I don't want to have to double up 12 breakers to meet my objective.


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[tfi racing]

I would be concerned with the arc fault labelled "bedroom#1/ smoke detectors"...

 

[Norcal]

I would be concerned with the arc fault labelled "bedroom#1/ smoke detectors"...

The snake oil is required for smokes, bedrooms, no choice unless a State has oped out of AFCI requirements, think Indiana is one.

 

[Todd.Brock]

So your main service is only 90 amps? If I counted correctly you had 120 or 130 A proposed for your subpanel. You mentioned a 50 amp breaker? What is the possibility of it multiple devices could be running the same time exceeding the 50 amp circuit? I.e. Using your stick welder while compressor cycles?
Another thing to think about was do you have enough headroom for running the dryer, the stick welder, etc. that might make the lights go dim when you strike and arc. Not saying you will/won't have an issue, but it seems like you could over run a 90 amp panel if the right sequence of events occurs ?

 

[Prcd6x]

I would be concerned with the arc fault labelled "bedroom#1/ smoke detectors"...

Just like NorCal said. The inspector said something to the affect of "that way you will always know if you fire alarm breaker trips"


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[Prcd6x]

So your main service is only 90 amps? If I counted correctly you had 120 or 130 A proposed for your subpanel. You mentioned a 50 amp breaker? What is the possibility of it multiple devices could be running the same time exceeding the 50 amp circuit? I.e. Using your stick welder while compressor cycles?
Another thing to think about was do you have enough headroom for running the dryer, the stick welder, etc. that might make the lights go dim when you strike and arc. Not saying you will/won't have an issue, but it seems like you could over run a 90 amp panel if the right sequence of events occurs ?

Yes and no. I guess my main panel is 200 amp and it has the furnace, AC, range, and this sub panel ( which I called main) coming out of it.


The total amount of the the new breakers would be 130 amps, I know that's not how the loads work though. The most I will be drawing out of the new sub panel at the same time is the compressor and the plasma cutter. I rarely every use the stick welder, so that's easy to manage.

As far as other stuff in the house, it might be possible that I will over load the 90 amp. Worst case scenario would be the dryer, water heater, microwave, plasma/compressor all going at the same time. But I hope that is a slim chance?


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[vartz04]

I think you're pushing your luck. Do you have gas or propane available? If you could switch your dryer and water heater and maybe your range to gas it would free you up quite a bit. Let's say your compressor and plasma are running in the garage and your wife is doing laundry, kid is taking a shower, and someone decides to make a frozen pizza - pop - darkness.

I really feel at some point in time you'll either need to convert some stuff to gas or upgrade to a 200 amp service.


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[tfi racing]

The snake oil is required for smokes, bedrooms, no choice unless a State has oped out of AFCI requirements, think Indiana is one.

Interesting,the 2012 Canadian code specifically prohibits smoke alarms/CO detectors to be on a circuit that is protected by a GFCI or AFCI,haven't checked the new code with its expanded AFCI requirements that closely follows the NEC.

 

[wyliesdiesels]

OP- wire and circuit sizes for compressors are based off of HP. Your small compressor could easily go on a 20a circuit...

I think you're pushing your luck. Do you have gas or propane available? If you could switch your dryer and water heater and maybe your range to gas it would free you up quite a bit. Let's say your compressor and plasma are running in the garage and your wife is doing laundry, kid is taking a shower, and someone decides to make a frozen pizza - pop - darkness.

I really feel at some point in time you'll either need to convert some stuff to gas or upgrade to a 200 amp service.


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he has 200a service. See his post above yours...The 90a was for the subpanel....

 

[myredracer]

Just install a 2-pole breaker in the panel with the 200 amp main breaker in it. I would install a panel just for the garage and run a sub-feeder back to this panel. The 30 circuit panel is be fed off the small (in circuits) main panel with a 90A breaker. Kind of an odd way of doing it I think. Could have been done with a single 40 circ. panel.

Personally, I'd want to start by doing a full load calculation on everything existing in the house as per NEC to see where you stand on available spare capacity. There are no hard and fast rules for sizing a panel for a workshop in house in the NEC from what I understand.

One way of looking at this is to take the required breaker size for the largest motor, compressor in this case at say 20 amps, then add up all of the other loads that can be running at the same time and add 25% to that. (Or maybe the sitck welder has the larger required breaker size?) You will have diversity (demand factor) in your favor though as not everything can/will be running at the same time.

You could potentially end up one day going to a larger compressor. That is a 2HP "SPL" motor and the true output will be less. I would suggest allowing for a 5HP (240V) compressor with a 30 or 40 amp breaker.

This is probably more of a consensus of opinion sizing based on experience rather than by load calc. I would say a min. 60 amps, 120/240 volts. but would suggest the next size up. It can't hurt to oversize in this case and the feeder run is relatively short so not expensive.

By way of comparison, our house has an attached garage of 2K sq. ft with a suite above of 1K sq. ft. There is a panel in the garage area with a 100 amp feed off our 200 amp main panel. The suite in turn is sub-fed off the panel in the garage with a 60 amp feed, leaving essentially 40 amps for the garage by load calc. The suite was calculated to the absolute bare min. at 60 amps by code. I have a 5HP compressor (with a 40 amp breaker), 30 amp plasma cutter, table saw, 240V spot welder, MIG and some other misc. smaller items of equip. and lighting. Never a problem. Diversity is what makes it all work.

 

[Prcd6x]

OP- wire and circuit sizes for compressors are based off of HP. Your small compressor could easily go on a 20a circuit...







he has 200a service. See his post above yours...The 90a was for the subpanel....

Thanks!


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[Todd.Brock]

So could you run your subpanel off of 200 amp panel? It seems like the 90 amp breaker would be the bottleneck? Could you possibly upgrade the 90 amp breaker and then run your sub panel off of that subpanel?

 

[Prcd6x]

So could you run your subpanel off of 200 amp panel? It seems like the 90 amp breaker would be the bottleneck? Could you possibly upgrade the 90 amp breaker and then run your sub panel off of that subpanel?

Of course it is a possibility, but the main panel has no more open spaces and is on the opposite side of a two story house without a crawl space. So it just seems like a lot more work than I was looking to do at this time.

From the pics on my phone it looks like the sub panel is wired with #1 AWG AL. Would I be able to put a 100 amp breaker in there giving me more room to play with?


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[wyliesdiesels]

How long is the run?

If its #1 al and 75* c rated(verify first should be on the insulation) then yes u could switch to 100a as long as the wire length isnt too long(causing excessive voltage drop).