Should I run a sub panel or another garage breaker

[cincinnati_kid]

Right now my house panel (100 A) has a 220 V 30A breaker running to the garage. In the garage there is a sub panel with 3 20A breakers in it. However, I am going to be adding a lot of things to my shop and I think I need more power. I have my 220 welders, 3 phase converter for my mill and lathe; air compressor (120 V but draws a lot), and Im adding a lot of lighting.

Do you guys think I should run a line to have a new sub panel in the garage or do you think I should just run another 220V 30A breaker to the garage split to some 20A breakers?

I am a mechanical engineer so by no means am i an electrical guy haha.

 

[Aceman]

If your garage is detached you can't have more than one feeder(line) to it. So that only leaves you with replacing and upsizing it.

If it's attached you can do it however you want. I like simple so I'd probably run one big feeder to a garage subpanel that could handle everything and abandon the existing circuit you have out there.

It's good to know when something trips or needs to be shut off in the garage, the breaker is IN the garage, not in the house or wherever else...

 

[cincinnati_kid]

The garage is connected with a breezeway. Here are a couple pictures. The main line comes in up near the AC unit on the house.

 

[pattenp]

I'm with Aceman on this to upgrade the existing sub-panel. Is is possible to take the same route from the house panel to the garage sub-panel that the 30A feed takes and replace it with a larger wire without a bunch of hassle? Also if the existing 30A feed to the sub-panel is only 3 conductors it would be best to update it using 4 conductors (adding a neutral). Using a #6 Cu SER cable will give you up to 70A providing you aren't running it within insulation, if within insulation you should go no more than 60A on it.

 

[cincinnati_kid]

I'll take a look tonight to see how it was run. I might be able to use the 30A 220 currently run for my heater which draws a lot. Lots to think about.

 

[signcrafter]

From what you listed for machinery and heater and lights you sound like you need a whole new service. You only have a 100 amp panel in the house. Running another line with "a couple more 20 amp circuits" in the garage isn't going to work for you. These 20 amp circuits won't cut it for your 220 welders and phase convertor. My welder takes a 50 amp plug itself. I realise you won't be using everything at once but it sounds like you don't even have what you need coming into your house. To do it right I would look into upgrading your whole service to 200 amps and then put a 100 amp sub panel in the garage so you can have all your 220 you are going to need right at the garage. So you can run your heaters, lights, air compressor and welder without worrying about not having enough power. You sound like you are trying to set up a small machine shop, which takes a good deal of power, which means atleast a 100 amp panel.

 

[jvitez]

Please do a proper load calc. You're an engineer. Come on, do the math!

The proper way to determine the size of a subpanel feed is to add the up the load in wattage, then divide by 240 to equal total amperage. Add up every possible thing you can think of that would be requiring power at the same time. Eg.: all the lights on, your compressor running, the lathe running, any electric heat or AC running. People often overestimate the amount of power they use. It's what's running at the same time that matters.

Addendum: forgot to mention that once you've got this total in watts, do a proper load calc using the NEC method for your entire house, adding in the extra load of the subpanel. This will tell you whether you need to upgrade you're entire service. A

 

[cincinnati_kid]

Please do a proper load calc. You're an engineer. Come on, do the math!

The proper way to determine the size of a subpanel feed is to add the up the load in wattage, then divide by 240 to equal total amperage. Add up every possible thing you can think of that would be requiring power at the same time. Eg.: all the lights on, your compressor running, the lathe running, any electric heat or AC running. People often overestimate the amount of power they use. It's what's running at the same time that matters.

Addendum: forgot to mention that once you've got this total in watts, do a proper load calc using the NEC method for your entire house, adding in the extra load of the subpanel. This will tell you whether you need to upgrade you're entire service. A

I am a mechanical engineer. I know enough about electric to get myself hurt. haha

I know when a piece of machinery is about to kill me because I see it coming electric on the other hand by the time you find out its too late.

I am not sure how much the lathe would draw run off a phase converter. It is only a 1.5 hp motor.

I would think the 2 things that will draw the most are the heater, compressor and welder. It would be possible that all 3 of these could be running at the same time as well as the lights, radio etc. I will try and do some calculations to see what I will need.

 

[cincinnati_kid]

The psnel has 10-3 running from the main panel to the garage

 

[toler234]

upgrade to 200A, saves you alot of headache, don't have to worry bout it, ive got a 400A meter combo at the house 200a to the house and 200a to the shop, all underground, 1500sf house and 2800sf shop, 10/3 of course wont do any garage favors, im surprised it hasn't burned down yet, and dont forget about voltage drop, don't want to burn anything up

lisc journeyman

 

[rodm1]

I personally would run a 100amp feed to the garage then deal with the other problems if they show up. Do everything to code you won't have to worry about burning the house down.

220 welders probable 50amp
3 phase converter for my mill and lathe; probable 20amps
air compressor (120 V but draws a lot) at most 20amp

A 60amp service probable will serve you well.

 

[garboui]

I am not sure how much the lathe would draw run off a phase converter. It is only a 1.5 hp motor.

1hp =~ 750W

1.5HP*750 = 1125W

now 1125W is what the drive can supply to the motor. This does not account for inefficiencies of the drive and also power factor. Both these factors should be available in the manual. If its a good quality drive/PC (not rotary a PC) it will likely have some PFC (power factor correction) built in. If you cant look up either I would divide your 11125W by 0.7 making your drive have a maximum load of roughly 1600W.

 

[E.Marquez]

I had much the same needs when we bought our current house in 2009. I knew my Shop build was 3~5 years down the road, so the 20x28 5th room that had a garage door in it was my shop for some time to come.

I was lucky in that I had a 200 amp service and open breaker spots...to work with.

While I had 120v receptacles every 6 feet in the garage.. I needed more and required at least 4 240v 50amp plugs for the welder, late/mil, air compressor and a spare alt location plug for the welder.

I chose to go with a 100 amp sub panel.
All of the equipment, both 240 and 120v are on breakers in this panel.. I can shut down the "shop equipment" from drill pack battery charger to welder from inside the garage.

It also allows me to shut off "shop" power for work, while maintaining lights... Or I can shut off the main panel breaker to that room (lights and built in 120v recep) and use surface mounted 120v recep for temp lighting, tool usage.