How much power do I need?

[Lariatstang]

I’m in the process of building a pole barn. I’m trying to decide how much electrical power to run out to the shop. What’s everyone’s opinion on 50A vs 100A?

I’m planning to run a few LED interior and exterior lights, about 12 electrical outlets, a couple of built in exhaust fans, a small air compressor and I’d like to be able to add a lift down the road. I think 50A will work fine for now but I’m always a fan of overengineering to prevent any issues In the future. My biggest concern with going to 100A is that the main panel I’m pulling off of from the house is already full, I’m not sure if I’ll have to upgrade anything to get 100A out to the barn, the barn sub panel is going to be a little over 100ft from the main panel.

So what are the pros and cons of going with 50A,70A, or 100A?

 

[bad_idea]

You can combine a couple circuits on your house panel to make room for the breaker for the shop. They make 110 breakers that have two breakers (with their own switch) in the same size case as the breakers in you panel now. https://www.homedepot.com/p/GE-Q-Line-30-Amp-1-in-Double-Pole-Circuit-Breaker-THQP230/100356518

I would run 100 amps out there. I am in process of building a 30x40 building myself and will run 100 amps out there this spring. It's not going to cost significantly more to run 100 amps over 50 amps.

 

[CraigStu]

If it's not too much more expensive I'd go w/ 100A. At some point down the road a 50A may not be enough and it will be a real pain to get more.

 

[pattenp]

The cost difference is mainly in the feeder wire for 100A vs. 50A.

You should ask for this thread to be moved to the electrical forum. There are lots of threads about the same topic.

 

[Handyfarmer]

I would suggest the 100 amp. possibly a bit more.
a transformer welder will need a 50 to 60 amp breaker,

(my old 230 amp welder takes a 60 amp breaker by the book, never tripped a 50 amp breaker tho),

a bit larger wire, (100 amp) will have less voltage drop, in normal use, seldom will one pull over 50 amps, but on 50 amps, your light may be blinking, when the air compressor is running, or when other motors start, on 100 amp, you will have extra reserve to keep the voltage up when there is surge loads or if you really do have something that needs a lot of amps you will have them,

a number of years, I put in some wiring, and only ran a 50 amps line, now changes, and growth has happened and I may be having to re run the power to the building, as I may be soon maxing it out, and there is a desire to put another building, and there is no reserve off that line to add the new building,

 

[theoldwizard1]

The cost difference is mainly in the feeder wire for 100A vs. 50A.

For some reason 60A seems more popular than 50A.

Either will be fine as long as you don't plan on running multiple welders at the same time ! Worst case would be AC, plasma cutter and compressor. You might have to turn off the AC for the few minutes you have the plasma cutter fired up.

 

[sberry]

They make wire just for this, 90A in the main to a 100 panel. I mostly use 60 in the main though as it is simply cheaper, never had anyone call and said they tripped it.

 

[75gmck25]

If you search the site you will find that a very common wiring solution is 2-2-2-4 AL MHF, which is good for 90 amps. You can always run that wiring and just use a 60 amp breaker in the main panel for now (they are more commonly stocked at the big box stores). Dual rated MHF must be run in conduit inside a building, and you have a choice of direct bury or conduit for the underground run. Larger gauge wire would also work fine, but you might change your mind after you compare the cost, especially if you use copper.

Buy a 100 amp sub-panel with about 12-24 breakers and you will have plenty of space for what you have planned. The sub-panel breaker only serves as a disconnect at the garage, so there is no problem with the 100 amp sub-panel and a 90 amp feed. The main panel breaker is the one that has to match the wiring amperage. You will also need two ground rods at the barn.

Bruce

 

[laser3kw]

If you search the site you will find that a very common wiring solution is 2-2-2-4 AL MHF, which is good for 90 amps. You can always run that wiring and just use a 60 amp breaker in the main panel for now (they are more commonly stocked at the big box stores). Dual rated MHF must be run in conduit inside a building, and you have a choice of direct bury or conduit for the underground run. Larger gauge wire would also work fine, but you might change your mind after you compare the cost, especially if you use copper.

Buy a 100 amp sub-panel with about 12-24 breakers and you will have plenty of space for what you have planned. The sub-panel breaker only serves as a disconnect at the garage, so there is no problem with the 100 amp sub-panel and a 90 amp feed. The main panel breaker is the one that has to match the wiring amperage. You will also need two ground rods at the barn.

Bruce

^^^ this is how my garage is done.
My electrician convinced me to try 60 amp to see if would be ok. He did install cable that will carry up to 100 amp, but the breaker in the house panel is only 60 amp ( by local code I guess).
To date, never have tripped the house breaker. I have a 5 hp compressor, 30 4' florescent tubes, a couple of outlets, a 130 amp mig and a 100 amp tig, 240v lathe and a Bridgeport running off a vfd. Of course, I do not run more than one thing at a time. I keep the breakers off until needed.

 

[ard]

#2 will handle 90A. Buy a 100A subpanel. Doesnt matter that the circuit is 90 and the panel is 100.

 

[cvairwerks]

Run the numbers on what you might be running at the same time and then provide some growth. A quick calc yields the following

Lights: 10 amps max
Lift: 20 amps max
Compressor 20 amps average depending on motor...

At this point, you have the potential to be out of power on a 50 amp feed, should you have the lights on, the compressor kicks in and at the same instant you start the lift..If you end up with fans or other power hungry devices, you could be out of power real quick, should more than one big item kick on at the same time.

 

[Lariatstang]

Thanks everyone, there’s some good input in here. I think I’m going to go with 100A. Looks like the total cost to upgrade isn’t a whole lot higher and i’d Rather have room to grow. Especially if I decide to add on to the building later on.

 

[Bigblockyeti]

How big is your pole barn going to be? As others have mentioned, the big draw down the road if not already would be welding. Is there any chance you might have a wood shop? That could mean a 5hp dust collector and a 5hp planer running at the same time. Is there any chance of insulating and HVAC down the road, that would need more power too. I've never heard of anyone regretting going too big but plenty of people going too small. I had a 420sqft. insulated shop at my last house and it already had a 60A subpanel which I quickly outgrew even in a small space. Had I taken care of the electrical for that shop I probably would have gone 200A just to make sure I'd never be left wanting.

 

[sberry]

For some reason 60A seems more popular than 50A.

Either will be fine as long as you don't plan on running multiple welders at the same time ! Worst case would be AC, plasma cutter and compressor. You might have to turn off the AC for the few minutes you have the plasma cutter fired up.

Reason 60 is more popular is you can use 60 breaker or fuses on 6 wire. Despite some speculation I rarely see common garages under powered and very few with 420 sq ft will find they need 200A. What does happen is lack of spaces in small panels, this is very common. 6 spaces go fast but I have fed a couple dozen garages, maybe more with 60A breakers and NEVER had one call about a trip, used them myself.
My bud worked a career in auto repair with 1 and a real 5hp comp, never tripped it.

 

[Jazz1]

60amp is plenty. I’ve never tripped a breaker. Electrical inspector recommended 60 as I had initially said 100 which inspector felt was overkill and costlier

 

[sberry]

The thing is that with alum wire a guy can get 90A wire cheaper than 60 copper and a fair number of these garages have longer runs by the time they get panel to panel.