Is a 15 amp circuit enough?

[Richard Wagner]

I suspect that in one form or another this question has been asked and answered many times here on the forum. Please indulge me and my stubbornness but I must ask it again in my own words.

I have a Shopsmith Mark V. The manual states that this device can be operated on a 15 amp circuit. Quote: "The wall receptacles and wires in the circuit must be rated for at least 15 amps". It goes on to state, "The Mark V 115-volt motor is rated at 1 1/8 horsepower. It develops more than 1 1/2 hp in use and "pulls" 13-14 amps when running under a heavy load. The headstock motor runs on a standard U.S. house current - 120vac 60hertz. The wire size in the circuit you use must be rated for at least 15 amps, using wire and receptacles rated to handle 20 or 25 amps will give you an even greater safety margin".

If I operate this device on the 15 amp circuit that is available in the garage, am I testing fate? Is it likely that I shall have problems?

I have operated this way for some time and do not seem to be having any difficulty but I don't know for sure. If the service is marginal, what signs would I see that indicate I am pushing it.

[Eric DeSilva]

If it says it can be operated on a 15A standard household circuit, and you are operating it on a 15A standard household circuit, why do you think problems may arise? I'm not sure I understand the question.

Do you suspect the wiring may not be rated for 15A? 15A is about the smallest household circuit, so I have a hard time seeing anyone try to cheat on the wire for that...

[Scott Wigginton]

If I operate this device on the 15 amp circuit that is available in the garage, am I testing fate? Is it likely that I shall have problems?

I have operated this way for some time and do not seem to be having any difficulty but I don't know for sure. If the service is marginal, what signs would I see that indicate I am pushing it.

I'm not an electrician but everything is fine as far as sizing. Would 20amp be better? Only if you're gonna have other things operating simultaneously on that circuit. The real question I have is do you know all the outlets on that circuit? If not then the only concern is you might run into a future condition when you add or move your DC/air cleaner/ac/heater/fridge and you'll start tripping the breaker.

[Eric Roberge]

You will be ok so long you do not run anything else off that circuit. I owned a Shop Smith for several years and operated it on a 15A circuit and never had a problem.

[Richard Wagner]

I'm not an electrician but everything is fine as far as sizing. Would 20amp be better? Only if you're gonna have other things operating simultaneously on that circuit. The real question I have is do you know all the outlets on that circuit? If not then the only concern is you might run into a future condition when you add or move your DC/air cleaner/ac/heater/fridge and you'll start tripping the breaker.

I have looked at the wiring and I believe that it is 14 ga wire. There are two circuits in the breaker panel that appear to have smaller wiring (16 ga) but they serve light fixtures and a single outlet in each of the the doorways to the house.

I have determined which outlets are serviced by the same breaker that protects the circuit I use for the table saw and I have learned by experience that nothing can be plugged in there while I am using the table saw. Example: the air compressor. If it kicks on while using the table saw the breaker trips so the air compressor now gets plugged into a different circuit or is unplugged.

My real concern is whether or not I really need to rewire. I can not afford to take on that expense right now but I also cannot afford to burn down the garage.

[Rob Russell]

As long as the circuit is at least #14 with a 15A breaker, you should be fine. Like the table saw, you should leave the compressor unplugged or on a different circuit when using the Shopsmith. There is nothing about what you have posted that would make me beleive you have to rewire anything in your garage.

On the other hand, if you truly do have circuits wired with conductors that are smaller than #14, I'd rewire those. The smallest circuit breaker I'm aware of is 15A and the minimum conductor size for 15A is #14. If you have 15A circuits wired with #16, that's a fire hazard.

As an aside, I noticed recently that the 30A dryer circuit in our cottage home was wired with #12 - not #10. I'll be replacing that this spring when I replace the main panel.

[David G Baker]

I did not know that there was a standard electrical wire designed for residential use that was smaller than #14.

[Rob Russell]

I did not know that there was a standard electrical wire designed for residential use that was smaller than #14.

For house wiring - there isn't. Lamp cord is frequently #16 (or 18).

[David G Baker]

Rob,
I knew about the lamp cord sizes but couldn't visualize anyone in their right mind using wire smaller than #14 in a breaker box.
I do know folks in my area of Michigan that use 100' 18 gage extension cords to power some of their out buildings. The wire is on the ground Winter, Spring, Summer and Fall. It even crosses the driveway and they frequently drive over it. Extension cords are cut into shorter pieces and used to wire light switches for overhead lights and plugs. I cringe every time I see it but I keep my mouth shut because there isn't a thing I can say that will change anything..

[Richard Wagner]

I don't know that there is anything less than 14 ga. I'll have to check now to make sure. There are two circuits that appear to me to be lighter gauge and I have checked to see what they service; they provide power to the two entry lights and one outlet in the front doorway. The outlet is up high, about 6' off the ground (near the ceiling). I think the only thing that has ever been plugged into it is a lighted Christmas wreath.

I'll keep watching for additional information but as of now I feel that I probably don't have a hazard condition but rather just a nuisance in that I am limited as to what can be plugged in.

Since I seldom have others in the shop powering equipment when I am, I am not likely to overload the available circuits.

However, even with 20 amp circuits, it seems that this could remain a lasting limitation unless I bring in multiple service lines. Three or four different feeds and now we are talking major expense because I don't have that many unused breaker positions in the main junction box.

[Darius Ferlas]

While nominally 15amps should be OK you are likely to hit those times when it's not.

On a 15amp line I managed to trip the breakers with an 11amp router and 3 amps worth of light at the time of the mishap.

I added two 20 amp circuits.

[Rob Russell]

Richard,

If you have 2 slots open in your main panelboard, you could run a subpanel out to the garage. That could be a 240v, 60A subpanel and would allow you to run pretty much whatever you want out there. The only reason to go to a 100A subpanel would be if you had a big welder and big 240v compressor that you'd be running at the same time.

The subpanel circuit looks like a big (in terms of amps) branch circuit in the main panelboard but terminates in a smaller panelboard out in the garage. You'd then run whatever circuits you needed out in the garage from the subpanel. The subpanel would be fed by a total of 4 wires - 2 hots, 1 neutral and 1 equipment grounding conductor. The subpanel circuit doesn't take up any more room than a 240v dryer or range circuit would use in the main panelboard.

[Richard Wagner]

I thank you all for your comments. You, collectively, have put my mind at ease. Being confident that I am not likely to burn the garage down, I shall continue as I have been until I can afford to do some rewiring.

When that time comes, I will most likely install a sub-panel, making 60 amps available for use in the shop and then redistribute it there with the proper breakers to each of the work areas.

It would be nice to be able to allow someone to use the belt sander or jointer at the same time some one else is using the table saw.;)