Power Requirements

[abgiles]

Just breaking ground on a new 30x60 detached shop/garage (metal building). It will be used primarily as a personal workshop, but will also have a large mancave/guest suite in it for extended stays with guests.

I'm trying to determine what size panel I need. The main power pole to our property is on the street exactly 1/2 way between the house and where the shop will be, so my initial thought was to have a new 200A service and meter run to the shop, to make sure I have plenty of power.

However, the cost of installation of all of that is more than triple the cost of having 100A service run to the shop from the house.

Here is a list of major loads:

240v 6O gallon, 3.2HP Compressor
Central A/C or mini split system
4 large ceiling fans (continuously running when occupied)
240V welder
All shop lighting will be LED
Small water heater (probably 40 gallon 5500W)
4 post lift (240V motor)
Small Electric Range in the mancave/apt
Typical TV, etc.. small loads
Evacuation Fan for welding/painting

So, I guess my question is: Will having just 100A service ever be an issue? I'm willing to spend the extra if it's going to be in question, but don't want to if it's not going to be an issue.

There will be times when the welder, compressor, and A/C systems will be all running at the same time, but I doubt it will be often.

Thanks!

Brian

 

[sberry]

100A will be just fine.

 

[jgiles101982]

I would start out by finding out the FLA of each piece of equipment you plan to run at the same time to determine the size of service you will need. Some of the things you listed could easily go over 100 amps if they are running at the same time.

 

[DaDuck]

I only have half of the equipment from your list in my detached garage.

But I had a 200 AMP service installed by a licensed contractor and I will never have to worry about an "upgrade" down the road.

 

[Moto]

If you are burying conduit from your house to shop, use 2" conduit to allow for 200 amps should you need to upgrade someday.

 

[wyliesdiesels]

You didnt list the size of the service on the house.

What loads does your house have?

Best bet is to do a load calc.

Will you have more than yourself working simultaneously in there?

Is the comp really 6HP? Does it say that on the tank or the actual motor nameplate?

I would start out by finding out the FLA of each piece of equipment you plan to run at the same time to determine the size of service you will need. Some of the things you listed could easily go over 100 amps if they are running at the same time.

that is NOT how a load calc is done...

 

[abgiles]

You didnt list the size of the service on the house.

What loads does your house have?

Best bet is to do a load calc.

Will you have more than yourself working simultaneously in there?

Is the comp really 6HP? Does it say that on the tank or the actual motor nameplate?

Sorry, the compressor is 60 gallons, (3.2HP). Had a couple of number mixed up. There is 200A service to the house, and it's a 2400sqft house with typical loads. Gas water heater, all LED lighting, electric stove/oven, 2 refrigerators and a big freezer. Only major one that would be running would the the central A/C unit. It's a 3 ton unit and I live in Florida, so it pulls during the summer months (March through November here).

I usually will be working alone, but will occasionally have another working there at the same time. Not often though.

 

[wyliesdiesels]

Sorry, the compressor is 60 gallons, (3.2HP). Had a couple of number mixed up. There is 200A service to the house, and it's a 2400sqft house with typical loads. Gas water heater, all LED lighting, electric stove/oven, 2 refrigerators and a big freezer. Only major one that would be running would the the central A/C unit. It's a 3 ton unit and I live in Florida, so it pulls during the summer months (March through November here).

I usually will be working alone, but will occasionally have another working there at the same time. Not often though.

Gallons on a compressor is meaningless for sizing electrical loads.

Is the 3.2HP rating listed on the actual motor nameplate or the tank?

It sounds like 100a branch feeder would be fine.

How long will the wire run be?

 

[theoldwizard1]

Do to certain electrical codes and the type of wire you use, you may be limited to 90A. Still fine.

 

[wyliesdiesels]

Do to certain electrical codes and the type of wire you use, you may be limited to 90A. Still fine.

What on earth are you talking about?

No wire size has been mentioned that would limit feeder size to 90a.

The limiting factor is 200a...

 

[abgiles]

Gallons on a compressor is meaningless for sizing electrical loads.

Is the 3.2HP rating listed on the actual motor nameplate or the tank?

It sounds like 100a branch feeder would be fine.

How long will the wire run be?

That's from the motor nameplate. Tank quotes it as 3.6. The wire run would be about 100 feet, including all bends.

 

[Falcon67]

I have more than that running on 70A.

Buy a big box for the building, the more breaker spaces the better. I bought 20 - have like one left. Buy one with a main breaker - size matters little but 100A is OK, it's just there to shut down the building power. Your upline breaker is the protect.

FWIW - my shop is 960 sq/ft, 130' of 2-2-2-4 MHF, 20 space 100A box, 70A breaker at the house. About $250 worth of parts at HD at the time. I think the 20 space was on sale.

 

[nsula_country]

If you can afford it (installation and meter fee), I recommend a dedicated service. IF you ever run a business in the future, the utilities can be written off 100%. If fed from residence, it cannot. We have a 320 amp service at the house and a 200 amp service at the shop. Both all electric without any gas service. Shop meter is under our LLC name.

IF you plan for a large backup genset, one service will feed both structures. May not be practical with multiple HVAC units and electric ranges. 2 services, 2 generators or maybe shop will not need one. You did mention an apartment.

As said, 100 amp service to the shop should handle most people's needs. But, as said a load Calc needs to be done for the current house and the shop loads to determine if your current 200 amp service is sufficient.

 

[SOB Racing]

I went with a dedicated 200 amp service separate from the house for my 30 x 30. The price difference in cable/circuit panel etc wasn't much and I'll never have to worry about power. You do have to pay for a separate meter (in IL) monthly

 

[jgiles101982]

You didnt list the size of the service on the house.

What loads does your house have?

Best bet is to do a load calc.

Will you have more than yourself working simultaneously in there?

Is the comp really 6HP? Does it say that on the tank or the actual motor nameplate?



that is NOT how a load calc is done...

True, but I wasn't trying to lead the OP into any calculation rather a general idea.

 

[sberry]

I have never seen a small garage overload 100, in fact have wired a couple dozen with 2 alum wire with a 60 breaker, never had a call about a trip. I have never seen a common residence overload 200. A new service is expensive , a continious bill.

 

[abgiles]

Thanks for all of the support. I'll get the load calc done, and see what "spare" I have to go with. I'd like to stick to dedicated service, and will get a few estimates (and speak with the local electric company about minimum monthly charges while I travel for work) to see what the best route is.

 

[Bretny]

With just what you have listed your taking up 19 spaces or so in a pannel. Im prety sure code now requires the fridge and microwave to be on separate circuits, at least here i think.
So you add a few strings of outlets and you will be in the 25 spot range. Want garagr door openers, outside lights, a RV plug or any thing else?
I would do a 200a sub pannel just for the space. Your also really asking alot of a 100a service with all the 240v loads you list.

 

[Falcon67]

I would do a 200a sub pannel just for the space. Your also really asking alot of a 100a service with all the 240v loads you list.

240V loads in my shop:
12x36 lathe
Two post lift
60 gallon air compressor
5kw electric heater
Square column mill on a VFD (240 single to 240 3 phase)
3/4 HP well pump

120v loads:
Drill press
5 plug runs
Two light circuits
One dedicated AC run, two actual AC units
120V lathe
Currently 120V welder
Bench grinder
Belt Sander
Band saw
Beer fridge
misc support gizmos for mill and lathes, battery chargers/maintainers

Zero trips on the 70A feed.

Dedicated drop here is $35 min charge for the meter. That's 7 months payback on the materials not even counting any power that would have been used at .16/kwh. At our old house - at that time, different now - the 2nd meter was billed at commercial rates plus the meter charge. Cost of wiring that garage/shop to the house paid back in 4 months.

 

[mm08822]

If you can afford it (installation and meter fee), I recommend a dedicated service. IF you ever run a business in the future, the utilities can be written off 100%. If fed from residence, it cannot. We have a 320 amp service at the house and a 200 amp service at the shop. Both all electric without any gas service. Shop meter is under our LLC name.

IF you plan for a large backup genset, one service will feed both structures. May not be practical with multiple HVAC units and electric ranges. 2 services, 2 generators or maybe shop will not need one. You did mention an apartment.

As said, 100 amp service to the shop should handle most people's needs. But, as said a load Calc needs to be done for the current house and the shop loads to determine if your current 200 amp service is sufficient.

All you need is revenue grade meter. Does not have to be typical poco meter pan format.

Read the kwh's for the shop and take that % from the total cost of residential bill.

 

[Bretny]

240V loads in my shop:
12x36 lathe
Two post lift
60 gallon air compressor
5kw electric heater
Square column mill on a VFD (240 single to 240 3 phase)
3/4 HP well pump

120v loads:
Drill press
5 plug runs
Two light circuits
One dedicated AC run, two actual AC units
120V lathe
Currently 120V welder
Bench grinder
Belt Sander
Band saw
Beer fridge
misc support gizmos for mill and lathes, battery chargers/maintainers

Zero trips on the 70A feed.

Dedicated drop here is $35 min charge for the meter. That's 7 months payback on the materials not even counting any power that would have been used at .16/kwh. At our old house - at that time, different now - the 2nd meter was billed at commercial rates plus the meter charge. Cost of wiring that garage/shop to the house paid back in 4 months.

All your 240v loads are mostly momentary or sunning with someone standing there. Hes got a electric water heater and AC. Adding a apartment to yours and i bet you would be tripping that 70a breaker.

 

[rburke65]

A 100amp. service for a residential, one man shop is a lot of juice!

 

[sberry]

Yes it is. I could make a list of all the connected equipment I ran from 100 at one time and itvwould be way longer than these,,,, with lotso people on it too.

 

[bob_mp]

I have never seen a small garage overload 100, in fact have wired a couple dozen with 2 alum wire with a 60 breaker, never had a call about a trip. I have never seen a common residence overload 200. A new service is expensive , a continious bill.

I generally agree that 100A is plenty for a garage. It’s not plenty if you want to run a large rotary phase converter. The inrush current of RPCs can be very high.

My RPC trips a 100A breaker every once in a while when starting. It has for the last 18 years.