Need some help with electrical design!

[Gota66]

I have been reading this forum for some time and have already got tons of great info here. The time has finally come to start my new detached garage! Yes! I am going to build a 24' x 30' x 10' walls and am going with pole type construction to save some money. I am working with an electrician and he is asking me basically what I need. I am waiting to get the garage built before buying equipment for it i.e air compressor, welder, wall A/C unit. All these things have different current/amp requirments that I had not figured in yet. Is there any standard electrical package that I could put in that would cover these things or am I going to have to decide on all these components first so I can supply him with the correct needs? Also any other general electrical issues to think about?

 

[DIGGER_DAVE]

I have been reading this forum for some time and have already got tons of great info here. The time has finally come to start my new detached garage! Yes! I am going to build a 24' x 30' x 10' walls and am going with pole type construction to save some money. I am working with an electrician and he is asking me basically what I need. I am waiting to get the garage built before buying equipment for it i.e air compressor, welder, wall A/C unit. All these things have different current/amp requirments that I had not figured in yet. Is there any standard electrical package that I could put in that would cover these things or am I going to have to decide on all these components first so I can supply him with the correct needs? Also any other general electrical issues to think about?

A couple of KEY QUESTIONS;

Will your shop be fed from a SEPARATE SOURCE? i.e. - Are you located on property that would allow a DIRECT feed from a/your power pole?

OR, if you have to take the power for your shop from your residence (the panel at/in the house) WHAT CAPACITY is it? (100 AMP, 200 AMP, etc.)

If it is 100 AMP or smaller; you may have to replace it with a larger panel. And the size will be governed by the utility company you use.

If the power can be feed from a SEPARATE source, then a PANEL of at LEAST 200 AMPS should cover all your needs. (and this is assuming you only receive SINGLE PHASE power)

When it comes time to install 110/120 volt outlets around the shop; forget code (it usually calls for outlets every 10 or 12 feet) and install outlets about every SIX FEET! (you will find there is never enough of them!)

Start with a layout of your shop; decide where welders, air compressors, etc. will be located and be ready to pull a LOT of wire!

 

[AndrewM]

All it takes is (1) 50A circuit for a 7.5 HP compressor, (1) 40 A circuit for a light welder, and (2) 10A circuits for lights, and you blow through a 100A panel real quick. My vote goes for 200A service if you can do it.

I'd plan on a 50A breaker for the compressor, a 60A breaker for the welder, and fill out the rest with lights and outlets, using 20A circuits for the 110 stuff.

Me, I have 80A service to my little shop, and while I've never tripped a breaker (knock on wood), I do my share at trying. I wish I had bigger than 40A/240VAC breaker to feed my compressor, welder, and lift (they don't ever run at the same time tho - welder and compressor share a plug).

 

[sjsfire]

Digger Dave gave good info. I will add that when we built our house I had the electrician wire in a couple of ceiling fan brackets in the garage. Put them on a separate switch so you can add fans later on. Also put your outlets about waist high or as high as your building codes allow.

 

[Gota66]

All great information! Thanks. I never knew there was so much to consider with the power. I will have to determine the answers to the questions DiggerDave brought up and then figure out from there. I guess I got some more planning to do.

 

[bmwpower]

Keep in mind when determining panel size, amperages are not always additive. Also, you really have to do a demand load calculation to determine what your garage load will be and if the feed will adequately supply you with power.

 

[boiler7904]

This has all been good info. I've got a couple more to add.

Some things that we tell commercial / industrial clients from a construction / architecture point of view:
* Research equipment as much as possible. If you know the manufacturer and model number, great - get their specs and build accordingly. If you don't know the manufacturer or exact model number, look at various models and figure what the most likely (not average) requirements are and build accordingly.
* Figure what you know you'll need now and allow for future expansion.
* Multiple lighting circuits allow flexibility. You need a lot less light to walk through the garage to grab something out of the car than you do to detailed work.
* IIRC, garage receptacles have to be GFCI protected - either at the receptacle or at the breaker.
* There are numerous codes on locating receptacles in houses but I can't recall if they apply to residential garages or not:
- Receptacles placed so that no point on a wall is more than 6' from a receptacle i.e. receptacles at 12'-0" on center.
- Receptacles within 2'-0" of doors.
* Put at least one box on the exterior of the front wall (with overhead doors). You'll eventually need to run a tool or a vaccum outside. By the way, the National Electric Code now requires that all exterior receptacles have covers that can be closed while the outlet is in use. The covers are big, ugly, and likely to break; but's the code.

From my experience building my house (currently at drywall phase):
* My house will be slab on grade. Conduit in the slab *****. Every conduit was installed in the wrong location at each end of the run (once at the panel and once at the termination). Consequently all conduits had to be cut off, sealed, and fed overhead. The same thing happed to the water and drain lines for the kitchen sink and ice maker.
* Do not use 15 amp receptacles in the garage. Many power tools draw close to that. Start up amperage is usually more than that.
* Install the receptacles at 42" or 48" above finish floor. This is taller than most base cabinets, but lower than most upper cabinets.
* Prewire for an overhead door operator(s) and control pad(s) even if you aren't installing the operator(s) now. The cost now is nothing compared to the time, money, and frustration in the future.
* Install a light and switch in the attic right above the access hatch (if you are going to have an attic)

I'm sure that are other things that haven't been mentioned, but is what came to mind right away.

 

[Gota66]

Thanks for all the info Boiler7904 and everyone else. Most of this stuff I would have never considered.
Thanks again.

 

[sberry]

Not many home garages need more than 100A service and most could get by on 60 provided there wasnt a great deal of arc welding going on. We can go on and on about what is ideal but its hard to beat 2-2-2-4 alum wire supplied with a 60 breaker for garages like this. I have wired dozens of garages like this and in 25 years NEVER had one call back with a tripped breaker. My auto mechanic bud runs a working garage from this setup including AC and comp. A good benifit of this setup is you could upsize the breaker if needed and the wire size is helpful with voltage drop, even on long runs this works well. This is very economical when feeding from existing services. You can have some stuff in the garage but it isnt running all at the same time, with a garage like that the AC will be fairly modest as will be the comp and it isnt like you are tooling for a dozen heavy fabricators with a couple welders going at the same time. 99% of the time the lights are running and thats it.

 

[sberry]

I have fed garages from homes with 100 services and the owner never had a problem. This is especially true if the major appliances are gas especially hot water. In a common garage, especially one not much bigger than a mobile home its a one or 2 guy show when woirk is going on, 90% of the time 30A service would do, even in a modest home 30A would run the place if it was divided up with all gas and no air cond. One of the main things for system performance anyway is to avoid all that 120V ****, comp, welding machine, air cond unit and stick with the 240 stuff, another hundred bucks a unit and its own outlet and stuff works so much better. I know another guy that runs a small make a living welding shop from a 100A service drop. When someone asks for advice for an install I would try to give something that applies to their typical situation, who I am talking to, where the install is going, what type of building, a lot of factors including where its being fed from. This is a modest garage likely being fed from a modest home, the main factor would be can that service handle the load when needed. Another common thing is to upgrade the garage to 200A and backfeed the house if it is 100A, you can kind of get 2 for one there, maybe even reroute the well on to the new panel. A lot of ways to look at this and there is no blanket answers untill there are more known factors.

 

[sberry]

I set a 100A service drop after a building fire as a temp, 100A, run a full size plasma, welding machine, pressure washer, 5 hp, 3 hp well on all the time, migrant camp with 4 units and a house, I kind of kept an eye on it about cutting and welding at the same time, never a trip. If we are talking to a guy setting up a full size machine shop then its a different story or if the wife has a pottery biz on the side with a couple of kilns, then the needs are different.

 

[indyjps]

think about adding outlets in the ceiling, they work great for retractable extension cords. try to plan out where your compressor/grinder/welder etc will be.

 

[Charles (in GA)]

Go ahead and put in a 40 space/40 circuit panel (don't get a smaller 30 space/40 circuit panel) These panels are huge, take 40 full size 1" wide breakers, and have lots of room to run wires, and heavier stuff like 6 gauge wire for welder and compressor circuits. The difference in price between a smaller panel and a larger one is insignificant compared to the aggrivation in future years of having to deal with something that is too small to work with.

Charles