Detached Garage Wiring

64mgb · #1 IP: 12.217.200.82 December 3rd, 2002, 05:57 PM

I'm preparing to wire my newly built detached garage and have several questions. First, the situation. The new garage is 24 x 28, and the wiring will enter it approximately 30 feet from where it exits the home. The exit from the home is approximately 20 feet from the home's circuit box. There are no noncurrent carrying metallic connections between the 2 structures. I intend to install a 220v outlet for a welder, and have a compressor and a radial arm saw. Other than that all loads should be typical garage/workshop power tools and such. I want to install a circuit box in the garage with at least 4 circuits besides the 220 for the welder. Now the questions: What size wire do I need to use between the home's service panel and the garage? What's the best way for the wire to exit the home...I intend to bring it out about a foot above ground...what materials should I use? (I've buried flexible plastic conduit in the concrete for the wires to enter the garage). Should I use direct bury, or run it in PVC? Do I need to install a grounding rod at the garage? If so, how do I do that?

Sorry if these questions are repeats on this forum...I just discovered it and it looks like a great resource.

All advice is greatly appreciated!

Thanks,
Rich

**Wgoodrich** · #2 IP: 148.78.243.121 December 3rd, 2002, 07:03 PM

Is this a 20 amp wire welder or a 50 amp arc welder. What size horse power and voltage is your air compressor. Are you planning on an electric water heater or any type air conditioner window or central.

This flexible conduit was it approved for contact or buried in concrete?

Curious

Wg

64mgb · #3 IP: 205.175.225.24 December 4th, 2002, 05:30 AM

Hi Wg -

I plan on being able to use an arc welder. The compressor is 110v...I meant to check the horsepower but forgot...I think it's 5HP. I'm not planning on installing a water heater or air conditioner. I'm not sure about the flexible conduit...my brother gave it to me and said his company uses it all the time for burying cable, although I think it is used for communications cable, not ac cable. I've been concerned about it's proper use, since we didn't check ahead of time. Worst case, we plug it up and enter the garage a different way.

Thanks,
Rich

**Wgoodrich** · #4 IP: 148.78.243.122 December 4th, 2002, 02:41 PM

A 5 horse power motor 120 volt would make your garage service size jump way high. Confirm the horse power and voltage of that motor before we can come up with an accurate service size for your garage.

Also confirm is you are the only person planned to use equipment at any one given time in your garage. This also would make a difference in service size required.

Curious

Wg

64mgb · #5 IP: 12.217.200.82 December 4th, 2002, 06:16 PM

I just checked the compressor...it's actually 5.5 HP, and it's 120v (plugs into a standard receptacle). As a rule, I'll be the only one using the garage at any one time.

Thanks for your time.

Rich

**Wgoodrich** · #6 IP: 148.78.243.123 December 4th, 2002, 07:19 PM

You are not looking on the right location. You need to look on the name plate of the motor for your horse power and voltage. The sticker on the tank has nothing to do with motor horse power. That is compressor horse power rating not motor horse power rating. I am expecting your electric motor name plate found on the motor yourself to say either 1/2 horse power or 3/4 horse power. Look again you used the sticker on the tank and you don't have the proper horse power rating yet.

Wg

64mgb · #7 IP: 205.175.225.24 December 5th, 2002, 05:50 AM

Thanfor your patience and attention to this Wg. I'll check again tonight.

Rich

**Wgoodrich** · #8 IP: 148.78.243.122 December 5th, 2002, 01:06 PM

See you then

Wg

64mgb · #9 IP: 12.217.200.82 December 5th, 2002, 05:32 PM

I was unable to find any other markings...I suspect I need to take the plastic cover off the motor/compressor (but it's cold here in Iowa!). But, here's what it says in the manual:

======================================
These compressors can be operated on a 15 amp circuit if:
1. Voltage supply to circuit is normal.
2. Circuit is not used to supply any other electrical needs (lights, appliances, etc.)
3. Extension cords comply with specifications in owners manual.
4. Circuit is equipped with 15 amp circuit breaker or 15 amp time delay fuse.

If any of the above conditions can not be met, or if operation of the compressor repeatedly causes interruption of power, it may be necessary to operate it from a 20 amp circuit. It is not necessary to change the cord set.
======================================

Does this tell you what you need to know? If I need to, I can go out and figure out how to get the cover off and see if there are markings on the motor. The compressor normally works fine, even on a circuit used for lights, except when it's cold out. Then it will occasionally trip the 15 amp breaker.

Thanks again for your help!

Rich

**Wgoodrich** · #10 IP: 148.78.243.123 December 5th, 2002, 06:49 PM

If you welder is a wire welder with 240 volts then most likely it will be 20 amp 240 volt.

If your welder is an arc welder then most likely it is a 60 amp 240 volt welder.

You are compresser we will take as 15 amp load but advise you install a 20 amp branch circuit from your garage panel to that air compressor for reliable service of that air compressor.

Also chances are if you install that air compressor in an accessible location you should be able to unplug your air compressor and plug in your wire welder.

If you have an arc welder then you will need 6/2wGrnd [no neutral wire used reidentify the white as a hot wire for this arc welder] Then use a 50 amp welder plug and a 50 amp double pole 240 volt breaker.

To size your service we would take the 50 amp arc welder as your largest load increasing it 125% = 62.5 amps then add you air compressor load of 15 amp to that. I picked up no other loads that would be used at the same time other than general lighting. so lets add approximately 10 amps for lighting say. This would require a garage service 87.5 amps adjusted up to a 100 amp service.

If you do not have an arc welder and only have a wire welder at 20 amp 240 volt then you would take that welder at 20 amps increase 125% = 25 amps add 15 amps for the air compressor and 10 amps say for general lighting and you have a minimum service size of 60 amp service.

Now you need to decide how much more than minimum service size you want to install.

Keep in mind that you garage may be served using TAble 310.15.B.6 allowing 4 awg coppper or 2 awg aluminum wire to serve a 100 amp panel in your garage.

You may use a 6 awg copper or 4 awg aluminum feeder to serve a 60 amp panel in your garage.

Suspect that you can buy with little cost difference between the 60 amp service and the 100 amp service in the garage, the 4 awg wire in a conduit using 4 awg copper wire using three conductors as your feeder in a 1 1/4" PVC conduit buried a minimum of 18" deep using a 100 amp service panel in the garage and marry the neutral bar and hte grounding bar together due to no equipment grounding conductor ran with the feeder between the two buildings due to no metal water pipes etc. connecting the two buildings.

Let us know what you decide

Good Luck

Wg