Determining if Power Supply is Adequate

[dusty]

I watched Dusty's video and have a much more clear idea of what I'll be looking for when I do my testing.

If I understand correctly, if I feed my Shopsmith with a 15 amp breaker connected to 12 AWG wire, there's a chance I'll blow the breaker because the Shopsmith is trying to draw more amps than the breaker's rating, but I probably won't damage the Shopsmith.

On the other hand, if I were to feed my Shopsmith with a 20 amp breaker connected to a really long run of 14 AWG, I probably wouldn't blow the breaker, but I could damage the Shopsmith because the long run of thin wire wouldn't be able to transmit the amount of amps required to drive the Shopsmith.

I'm wonder what kind of damage would be caused in the second scenario, and why.

Thanks!
Rob

Oh... I am going to follow Dusty's suggestion on replacing the Shopsmith's power cord with a heftier SO cord and suspect I'll end up running a new 20 amp circuit with 12 AWG wire to a new electrical outlet on the side of the house closest to the garage, and then use a 20 amp 50' extension cord whenever I work with the Shopsmith. I believe the 20 amp extension cord is made with 10 gauge wire.

Unless you persist in trying to run under this condition, you most likely would do no damage to the Shopsmith. The extension cord, however, might be another story. It would get hot and your power meter will be spinning faster. The power company will be happier.

Again, watch the voltage and listen to the Shopsmith to see what it is doing. If the voltage stays up at or near to 115 vac, the Shopsmith will be content.

[JPG]

. . .

I don't think you are allowed to protect 14 gauge wire with a 20 amp breaker. To use a 20 amp breaker you need at least 12 gauge wire. More specifically, 14 Gauge wire is not allowed on a 20A branch circuit.

Remember the breaker protects the circuit, it does not control the circuit. It 'controls' the circuit by shutting it off if excessive current is drawn too long and thus 'protects' the structure containing the wiring from fire.

BTW larger sized wire is allowed, and is required for long runs(to prevent excessive voltage drop!).


. . .

See de blue!

[beeg]

I don't think you are allowed to protect 14 gauge wire with a 20 amp breaker. To use a 20 amp breaker you need at least 12 gauge wire. More specifically, 14 Gauge wire is not allowed on a 20A branch circuit.

See de blue!

Also some inspectors are knot happy with 12ga wire with a 15 amp breaker.

[dusty]

Also some inspectors are knot happy with 12ga wire with a 15 amp breaker.

Why? It is safer. The breaker limits the current to 15 amps while the wire is capable of carrying more than 15 amps.

[robfish]

I know that a 20 amp breaker and 12 AWG wire is going to keep my SS happy. What I'm curious about is exactly what damages the electric motor when a combination of undersized wire and an overly long run prevent enough amps from getting to the SS to do the job.

[dusty]

I know that a 20 amp breaker and 12 AWG wire is going to keep my SS happy. What I'm curious about is exactly what damages the electric motor when a combination of undersized wire and an overly long run prevent enough amps from getting to the SS to do the job.

That question is difficult to answer (safely) without taking some voltage readings.

The current will flow no matter how long the wire. The question is, how much voltage will be dissipated by the wire and therefore not be available for the motor.

I just did a couple quick voltage checks in the shop (with about a 12' power cord on the Mark V) and either the belt sander or the belt sander and sanding disk mounted. I could not distinguish a difference in voltage drop between the two configurations.

The normal 122vac line voltage dropped momentarily to about 80.8vac and then rose to 119.5vac. That means that approximately 3vac is dropped do to the line cord.

You want to do the same test with your long extension supplying power to the Mark V. While watching the line voltage, turn the Mark V on (slow speed to be safe) and watch the voltage.

As a general rule of thumb, you do not want more than about 6% to 8% of voltage drop when the Mark V is turned on.

In my example above, I would hope that with the long power cord the voltage would not drop to less than about 104.68 volts (122vac-(.06x122vac)).

The voltage indicated above (104.68vac) is the voltage after the Mark V has come to run speed. At startup, the voltage will drop momentarily to 80vac there about. You saw the video.

[beeg]

Why? It is safer. The breaker limits the current to 15 amps while the wire is capable of carrying more than 15 amps.

Don't know why, but somebody here did that and HAD to change to a 20 amp breaker. Seems that "code" says that a 20 amp breaker has to be used with 12ga wire. So the inspector took it literally. That if ya use 12 ga it HAS to have a 20 amp breaker. Knot realizing that those are minimums. You could use 4/0 if ya could figure out how to get the wire safely under the outlet screws.

[dusty]

Don't know why, but somebody here did that and HAD to change to a 20 amp breaker. Seems that "code" says that a 20 amp breaker has to be used with 12ga wire. So the inspector took it literally. That if ya use 12 ga it HAS to have a 20 amp breaker. Knot realizing that those are minimums. You could use 4/0 if ya could figure out how to get the wire safely under the outlet screws.

I don't know about the code elsewhere but here a 20 amp breaker must be connected to no less than 12 ga wire. Simultaneously, I know of no requirement to install 20 amp breakers simply because I have 12 ga wire.

[beeg]

Simultaneously, I know of no requirement to install 20 amp breakers simply because I have 12 ga wire.

As far as I know, it's KNOT a requirement. It's a LACK of being able to understand what he read or heard.

[JPG]

As far as I know, it's KNOT a requirement. It's a LACK of being able to understand what he read or heard.

Had he read more, he would have 'discovered' that length of the wire involved is also a determinate of 'minimum' wire size.

In addition to protecting the structure from fire(overheating the wiring), the code is also concerned with proper voltage available at the far end of the circuit.


i.e. The 'inspector' is either ignorant, misinformed, an idiot, or most likely all three with control freak thrown in.

The proper size definition is more than a single chart, but involves several sections etc.