Electrical advise - Running power to shop

Not sure if we have any electricians on board but I'll ask.

I'm in the process of rebuilding my little 10x10 shed into a nicer 12x24 Shop. I would like to run power out to it in which to run lighting, maybe a small air conditioner and power equipment. I know, for insurance and safety reason, I will need to hire an electrician. However I would like to do some prep work in the mean time.

I have no available panels in my breaker box to run a dedicated line to the shop, so short of spending big bucks to add a new main breaker box that can support more circuits I thought of the following possibilities.

One thought I had, if code allow, or would it be proper to have the 220 breaker box that feeds my Air Conditioner replaced with a newer box that will let me add an additional breaker to it so I can feed 110 out to the shop? In relation to that, the wiring that comes from the main breaker box to that A/C breaker box is an aluminum alloy wiring. Would it be in my best interest to upgrade that line as well?

The other thought I had was to isolate an existing circuit that has a low draw on it, run a heavier gauge wire from the main breaker to a junction in the attic, tie the original circuit into that junction and run the same gauge wiring from the junction to the building.

My dad's an electrical contractor. Not sure of the code but I strongly recommend ditching the Aluminum and replacing it with Copper.

How big is the service to your house? Depending on available amperage you may or may not need to "heavy up" to a larger main. Generally when I've done shops and seperate garages I'd install a sub panel in the garage with a few circuits in it. So that I could have main power, lights, ac, and welder all on their own.

You could use what we call "piggy back" breakers, in the main panel, to create two available spaces to hook the shop line to. I would not advise to use the A/C disc as it probably does not have an insulated neutral. Ran properly you would need a four wire system to subfeed another panel. Seek the advise of a professional on this one.

Spent Brass said:

How big is the service to your house? Depending on available amperage you may or may not need to "heavy up" to a larger main. Generally when I've done shops and seperate garages I'd install a sub panel in the garage with a few circuits in it. So that I could have main power, lights, ac, and welder all on their own.

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This...^^^

How old is the panel ( original ) and maybe post a pic of main panel with cover off.

CrkdLtr said:

...rebuilding my little 10x10 shed into a nicer 12x24 Shop... lighting, maybe a small air conditioner and power equipment... need to hire an electrician... no available panels in my breaker box to run a dedicated line to the shop... have the 220 breaker box that feeds my Air Conditioner replaced with a newer box that will let me add an additional breaker to it so I can feed 110 out to the shop?... wiring that comes from the main breaker box to that A/C breaker box is an aluminum alloy wiring...

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I'm not an electrician, but have done similar projects in the past. First thing I would do is figure up how much amperage you would expect to need in the shop, then double (at least) that number to calculate breaker and wire sizes. IMO your best option would be your thought about installing a larger breaker box for the AC (which may also require installing heavier cable from the main panel to that box), but I would suggest you consider running 220 to the shop and installing another box there to split it down to 120/220 circuits. And ditch the aluminum wiring(!)

And before you actually do anything, consult a licensed electrician.

Yrdawg said:

This...^^^

How old is the panel ( original ) and maybe post a pic of main panel with cover off.

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Was working outside on the shop all day and didn't check back on this until this morning.

House was built between '75 or '78, don't recall which. I want to say the main breaker is 200 amps. I would figure that a small window A/C unit wouldn't draw but 6 or 7 amps, maybe 10 during start up? Air compressor that draws about 5 amps. And those are my largest tools. So I wouldn't think more than (2) 15 amp circuits would be needed in the shop.

I have a 24X 66 shop in the back of my house. After searching and talking while planning to add power to it, It was cheaper for me to get the power company to drop another seperate meter in the shop and leave the house alone. I had to purchase another 200 amp inside breaker set up but that cost was not bad considering the upgrades and retrofits needed to run it from the house. Power company covered all items and meter pan to the building, all i had to do was inside. I needed a permit and electrical inspection so I only ran a light and a few plug ins for the inspection since it was an open framed building everything had to be in conduit with no visible wiring anywhere. Once I was hooked up, I added what I needed and have tons of room to add anything electrical in the future. I believe the cost of the meter is 5 or 7 bucks a month added to the bill but that doesn't bother me. Our house bill runs about $130.00 a month and the bill marked shed runs a whopping $9.00. It saved me alot of headache.

jm2c.... good luck and sorry I dont have any answers for you.

southlaems said:

I have a 24X 66 shop in the back of my house. After searching and talking while planning to add power to it, It was cheaper for me to get the power company to drop another seperate meter in the shop and leave the house alone. I had to purchase another 200 amp inside breaker set up but that cost was not bad considering the upgrades and retrofits needed to run it from the house. Power company covered all items and meter pan to the building, all i had to do was inside. I needed a permit and electrical inspection so I only ran a light and a few plug ins for the inspection since it was an open framed building everything had to be in conduit with no visible wiring anywhere. Once I was hooked up, I added what I needed and have tons of room to add anything electrical in the future. I believe the cost of the meter is 5 or 7 bucks a month added to the bill but that doesn't bother me. Our house bill runs about $130.00 a month and the bill marked shed runs a whopping $9.00. It saved me alot of headache.

jm2c.... good luck and sorry I dont have any answers for you.

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I'll have to call Entergy and see if that's an option. That sounds like a better route.

You will definitely need more than 2 - 15 amp breakers . As time goes on , you will add tools and lighting .

I window AC unit is usually going to need its own 15 amp breaker. I like to put them on a dedicated 20, the same thing with microwaves and bathroom outlets (hairdryers). Your compressor should be on its own 15. It may only draw 5 when running but it will have a 10 amp startup surge every time it kicks on. Anything else on that circuit and you'll trip it. You can do a small sub panel with a 50amp service and you should be fine. Set up 2 circuits for power, 1 for lighting, 1 for AC/heat, and 1 for the compressor. I say heat because you can add a baseboard oil heater relatively cheap to keep it kozy in the winter and put it on the same circuit. You'll need to have available amperage in your main panel and run a service cable to your shed. From the house to the shed it will need to be either UF cable buried deep, or the cable will need to be in PVC underground.

As a less user friendly alternative you could run 3 12-2w/ground and 1 10-2w/ground from your main in the house to the shed and have the breakers for the shed at the main panel. Problem with this is that if you do trip a breaker you have to go all the way to the house to reset it.

If you go with the entergy option and get a new meter on the shed, you can go buck wild with your options inside. Literally limitless. Pick a dream amount of power (say 100a) and have them make the drop for that. That way you can use the same panel to power out door lighting, pools, fountains, or anything else you dream up.

southlaems said:

I...cheaper for me to get the power company to drop another seperate meter in the shop and leave the house alone...

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I did the same thing. My shop is 24x32, maybe 100 feet behind the house, and putting a 200A panel in gave me all the capacity I might ever need for inside power demand, plus outside lighting, power to a seperate storage shed, patio and pool, etc. Shop is climate-controlled, costs me about $12/mth; definitely (for me) the best long-term option.

Spent Brass said:

I window AC unit is usually going to need its own 15 amp breaker. I like to put them on a dedicated 20, the same thing with microwaves and bathroom outlets (hairdryers). Your compressor should be on its own 15. It may only draw 5 when running but it will have a 10 amp startup surge every time it kicks on. Anything else on that circuit and you'll trip it. You can do a small sub panel with a 50amp service and you should be fine. Set up 2 circuits for power, 1 for lighting, 1 for AC/heat, and 1 for the compressor. I say heat because you can add a baseboard oil heater relatively cheap to keep it kozy in the winter and put it on the same circuit. You'll need to have available amperage in your main panel and run a service cable to your shed. From the house to the shed it will need to be either UF cable buried deep, or the cable will need to be in PVC underground.

As a less user friendly alternative you could run 3 12-2w/ground and 1 10-2w/ground from your main in the house to the shed and have the breakers for the shed at the main panel. Problem with this is that if you do trip a breaker you have to go all the way to the house to reset it.

If you go with the entergy option and get a new meter on the shed, you can go buck wild with your options inside. Literally limitless. Pick a dream amount of power (say 100a) and have them make the drop for that. That way you can use the same panel to power out door lighting, pools, fountains, or anything else you dream up.

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Goin with this guy again...good plan.

Ditch Aluminium...even if it's free

Additional meter is nice...I couldn't afford that ..if you have 200 on the house there's plenty to add a 50a sub. Unless you have a really loaded up house with other subs.

Hand dig a trench, drop in some PVC ...no problem. If you start the licensed electrician thing you may end up with permits and inspections...usually not a problem.

Unless UF has dropped in price I'd rather pipe...for the safety factor...however anyone who has stripped UF can testify it ain't easy to cut. Afterbirth here...adding another meter would complicate any wholehouse standby generator plans for the future...

*advice

Crkdltr If your not in too much of a hurry I can come over and take a look at it for you. I was an electrician for several years before going back to college. Any day after May 17 and I can give you a hand.

Resurrecting this thread as I'm getting closer to finishing my shop and have more information toward running power.


Seems like the more I probe the more complex this becomes. I found that I have a 20 pole breaker box that is Class "CTL". Basically meaning it's only intended to supply the number of circuits that the poles allow. Not supposed to use tandem (cheater) circuit breakers to give you more room. I found a formula that tells me how many circuits are allowed on my breaker box. ( reference: http://www.ashireporter.org/articles/articles.aspx?id=2047 ) Using a formula of 125amp main breaker, 2 poles divide by 10 I am able to utilize 25 circuits.

I was able to find a tandem circuit breaker that would fit my box but it has the safety label "For Replacement only, Not for CTL Assemblies". If I were to proceed I would be looking at consolidating 4 15 amp breakers into 2 15/15amp tandem breakers and installing a 30 amp two-pole breaker (240) and connect it to a run of 10 awg UF wiring (10 gauge max amp is 30 and UF wiring is "Underground Feeder") from the main panel to a sub box to the shop. I will have a grounding rod at the shop and connect that grounding rod to a ground bus at the sub panel which will not be tethered to the neutral bus on the sub box.

The shop will have (2) 15 amps circuits. 1 - 15 amp circuit would feed my lights (probably will end up using with 6 florescent light fixtures, about 700 to 800 watts, and <8 amps and maybe an outside security light with a pair of 100 watt flood lamps (200 watts about <2 amps). All lights will be on individual switches to minimize the use of power.

The second 15 amp circuit will feed half a dozen electrical outlets which will be used by table saw, compound miter saw, 5 hp air compress and so forth (not all simultaneously). The two largest appliances I'm considering running will be a 5000 BTU A/C unit and the 5 hp Air Compressor. I would assume as long as I am not running both simultaneously I will not overload my circuit.


I know there are issues and concerns about insurance claims and such should something bad happen, but I figure I've got a lot of my ducks in a row. Any thoughts or input on these findings?

Well CTL is fine since most all panels are. The only place you'll find non CTL is in real old installations. You should be able to use a standard tandem breaker and just make sure it's in a proper tandem slot and be ok. The "not for CTL" should work as well, but you're defeating a safety feature of your homes panel by installing it in a non tandem location. Since you'll be drawing the same total amperage you should be fine there as well. The 10 gauge is fine, but you'll never be able to up the service with that as 30amp is max for that gauge wire. Also make sure you get 10-2w/ground so that you can tie the two grounding systems together to improve ground protection for both structures. I still think you'd be better running a 60amp line on a number 6 to the shed with a sub panel out there. But your current plan is going to be more economical, just remember if you do trip anything you'll be walking to the house to reset it. Also all the outlets in the shed should be on GFCI.

Spent Brass said:

Well CTL is fine since most all panels are. The only place you'll find non CTL is in real old installations. You should be able to use a standard tandem breaker and just make sure it's in a proper tandem slot and be ok. The "not for CTL" should work as well, but you're defeating a safety feature of your homes panel by installing it in a non tandem location. Since you'll be drawing the same total amperage you should be fine there as well. The 10 gauge is fine, but you'll never be able to up the service with that as 30amp is max for that gauge wire. Also make sure you get 10-2w/ground so that you can tie the two grounding systems together to improve ground protection for both structures. I still think you'd be better running a 60amp line on a number 6 to the shed with a sub panel out there. But your current plan is going to be more economical, just remember if you do trip anything you'll be walking to the house to reset it. Also all the outlets in the shed should be on GFCI.

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Thanks for the info. 10-2 UF-B (white/black and uninsolated wire) is what I am using and I am going to on a 30 amp breaker. I know I'm cheating the panel with the tandems, but I figured since I will not be using the power in my shop no more than a couple hours everyday I shouldn't over tax the panel.


I'd love to run #6 wire to the shed but I would think I'd have to run a sub panel to redistribute some of that load and at the current cost of copper (or even aluminum feeder) I'd go broke. I have an 80 foot run from the house to the shed.

be carefull with that 125 amp box. when i bought my house it had a 125amp lug panel (no main) on the outside. the entire thing is wrong. i actually have 2 200amp feeds coming from the meter which is not allowed but they allowed it because the house has been like that since it was built. i have 1 set of feed wires going to the outside panel and another set feeding the inside panel instead of one feeding the outside panel and then that panel feeding the inside panel. the problem was that the outside 125 amp panel had all of my 220 appliances on it. plus it had several lighting/receptacle circuits on it. the panel was overloaded but i knew nothing about it so never worried. i dropped to half voltage on one of my 110 circuits one day and when i went to check the breaker box i saw something that scared me. the main feed wire going into the box had damn near burned all the way through at the lug where it connected. an electrician wanted $900 dollars to change the panel. i decided to do it myself. it wasn't all that hard i had the electric company drop the service at the transformer and i put in new feed wire and a new 200 amp main breaker panel. i then changed all the breakers and re-connected everything. this gave me plenty of power with no worrying about overloading the panel. if you have several 220 appliances on that panel you may seriously want to consider changing it out now and then doing the 50amp sup to the shed.

all that said i did run my old little shed on 1 20 amp breaker for 6 years. i had 1 circuit ran through the entire shed with several receptacles and 2 flouresent lights. i had a small fridge for beverages and plenty of times ran power tools in there nothing large but did run them. i tripped the breaker once in that shed and i was welding with my little lincoln 110 wire welder and had the lights on with the radio going and the compressor for the fridge kicked on. i built a new shed 16x24 and have a 50amp sub panel ran to it with 1x15amp lighting circuit and 3 circuits for receptacles. i have tripped the main on this once. i was running a portable heater and welding at the same time. i never realized how much power those little heaters use. if you are conciensous of what you are using you should be fine. but it would be nice to go the option that gives you the most available power.