Shopsmith Forums

I think that most of us have probably turned the Mark V off and back on at higher than factory recommended speeds, and with no ill effects. I personally have and I also have seen the TA instructor do it. I believe that it is safer for the motor to not do so, and so we are all risking damage to the motor, but IMHO, it is a small risk, unless there is a great load at start-up.

As long as the subject of what gauge wire and what size breaker to use is being discussed here, with apologies to Nick for his earlier post, #5 of this thread, I will put in my 2 cents: The factory manual that came with my Mark V 510 (purchased in 1995) makes the following statement.

....The wire size (gauge) 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 bigger safety margin.

In the next paragraph, the manual makes the following statement (SS uses the bold lettering).

....Do not use fuses or circuit breakers larger than 15 amps.

Those of us that are plugging the Mark V into a 20 amp circuit are not following these instructions. What that means is we are risking damage to our SS motor. It can overheat without "blowing the fuse". This overheating can shorten the life of the motor.

In the state of Washington, it is completely legal to "oversize" the wiring in a circuit; in other words, using a 15 amp fuse or circuit breaker, you MUST use a minimum of 14 gauge wire, but you MAY use 12 gauge (this is what SS is recommending) or even larger wire (anything larger than 12 guage would be overkill).

Using 12 gauge wire is the minimum that you MUST use with a 20 amp fuse or circuit breaker. If you are using a 20 amp fuse or circuit breaker with 12 guage wire, it is a legal circuit, but it will not protect your Mark V until it may be too late. So, that is why you don't trip your 20 amp breaker.

Having said that, know this: My Mark V is plugged into a 20 amp circuit utilizing 12 guage wire. I do not believe I have ever strained the motor, but who knows? If you are using a 20 amp circuit and this concerns you, all you have to do is replace the fuse or circuit breaker with a 15 amp one. (Never do the opposite; i.e., never put a larger breaker on a circuit with smaller wire then the breaker is rated for) No other "rewiring" is necessary, but care must be taken to NOT have any other load on that circuit, as the Mark V will use.... (also from the 1995 owners manual)

....13-14 amps when running under a heavy load.

which only leaves 1-2 amps left before tripping the breaker or burning your fuse.

Ed in Tampa's use of a 12 guage power cord would be perfectly acceptable according to the SS manual: It is just oversizing the wire.

Tim
I think the warning in the your second quote is not warning against the use of a 20 amp breaker but rather a warning to the owner not to arbitrarily change the 15 amp to 20 amp breaker.

Contrary to most popular belief a breaker is not designed or sized to protect what is plugged into the circuit, it is sized to protect the circuit itself. Hence if you have 14 gauge wire the biggest breaker you can safely use is 15amp however if you have 12 gauge wire you can use a 20 amp breaker. If you plug something into the circuit that draws more than 20 amps the breaker will protect the circuit. Inversely if you plug a motor into the circuit and it has no internal protection and draws less than 20 amps you can burn the motor up and breaker would care less.

I believe the Shopsmith motor has an auto reset thermal breaker in it which is there to protect the motor. Should your motor get too hot it should break the circuit until the temperature comes down.
Ed

Hi Ed,

If the motor does indeed have it's own internal protection, I see no need to worry about using 20 amp circuits with the SS. Do you know this for a fact? Anyone?

Ed in Tampa wrote:Tim
I think the warning in the your second quote is not warning against the use of a 20 amp breaker but rather a warning to the owner not to arbitrarily change the 15 amp to 20 amp breaker.

I am not getting that message when I read the manual; however, I agree with your concern of people doing just that. Doing that is a time bomb waiting to go off.

a1gutterman wrote:Hi Ed,

If the motor does indeed have it's own internal protection, I see no need to worry about using 20 amp circuits with the SS. Do you know this for a fact? Anyone?

a1gutterman
I can't say I know it for a fact but I believe I have both read the motor label which stated it was thermally protected, and I believe I have read other posts in perhaps other forums that stated that.

I will try to verify this by checking the motor label or finding where I read it in the first place.

In any case you can still fry the motor using a 15 amp circuit.

Ed

My manual from 1989/90 say the following:

This is formated as in the manual (safety section page 2), but the red I have added. So what amperage to use?

They do recommend going to a larger wire size than standard 14 AWG.

Circuit- Before you plug in your Mark V, check the output and the amperage of the circuit you'll be using. The output of the circuit must meet or exceed the electrical requirements of the Mark V power plant.

The amperage must be rated high enough to handle the load (in amps) of that motor plus any other tools or appliances you may have plugged into the same circuit and running at the same time.

• The Mark V 115-volt motor is rated at 1-1/8 hp. It develops more than 1-1/2hp in use and 'pulls' 13-14 amps when running under a heavy load. this motor runs on ordinary U.S. house current--115 volts, 60hz. The wire size (gauge) in the circuit you use must be rated for at least 15 amps. Wire rated to handle 20 or 25 amps will give you an even bigger safety margin.
• We recommend you install circuit breakers or use time-delay fuses. Fusetron T-15 fuses are recommended. Do not use fuses or circuit breaker larger than 15 amps. When you first turn on the machine, the motor pulls high amperage to get up to running speed. A time delay fuse won't blow during this initial surge.
• If you need to run a new circuit to operate the Mark V, be sure that the wire you use is rated to handle the amperage of the circuit.