Why were only some of my tools damaged when connected to a 240V receptacle?

Question

I live in the US and recently bought a home. There are several electrical outlets in my garage. I have recently had two tools that have burned up and gone to an early grave. It turns out that the previous owner put in a 220 volt outlet but used a 20 amp 110 receptacle. I figured this out after my shop vac motor burned-up and died. Also, my belt sander emitted sparks, flames, and died. A quick check with a multimeter determined that some goof ball put 220 into a standard outlet designed for 110v.

Of course, I will be wiring this outlet correctly. For now, it is covered with tape.

So, here is my question. Some tools, like my air compressor and table saw were not damaged by this outlet. I used the outlet for these tools and they don't seem like they were harmed. Why did some tools die and others survive ? ? Is it a difference between brushed and brushless motors ? ?

Answer 1

Many devices are rated for either 110 or 220. There should be a tag on the device which says this. In some appliances its done intentionally so that one model can be sold and safely used in countries which use either voltage. In other cases its simply dumb luck that the component parts can tolerate either voltage.

I'm not sure if this fully answers your question. "The device is rated for it" doesn't really cover what aspects of the device make this possible.

Answer 2

It's not going to be about brushed vs. brushless motors but the quality and grade of the parts used in the tools. Heavy duty equipment like a compressor or table saw are likely to use heavier wiring and components which can take the higher voltage, where the lighter weight tools are overheating with the voltage they weren't designed for.

Answer 3

Because over voltage tolerance is a complex matter and the susceptibility of any individual device is highly dependent on the design of that particular device.

Into a resistive load twice the voltage means four times the power. Depending on where that heat goes that may or may not be enough to make the device go up in smoke but there are many other effects that can either mitigate or worsen the effect. On the worsening side we have.

1. Magnetic saturation. If too much energy is stored in an iron-cored coil the core will saturate and the effective inductance will fall through the floor. If the device was relying on the inductance of the coil to limit current this can result in a massive increase in current.
2. Electrical breakdown. High voltages can rip electrons off atoms which can then start conducting leading to high currents where there were not supposed to be high currents. Normal wire insulation will not break down with a mere 2x overvoltage, but electronic components like diodes, transistors and capacitors may well break down at this level. Electrical breakdown can also happen with deliberately-placed spike protection devices that were designed to break down and shunt away short spikes of overvoltage, but were not designed to handle sustained overvoltage.

On the mitigating side we have.

1. Some things self-regulate. A motor (if it has not suffered from magnetic saturation) will draw less current as it's speed increases. A device with a thermostat will heat up quicker but assuming nothing breaks down the thermostat will mean the final temperature ends up approximately the same as normal.
2. Some devices have protection that will trip out under over-voltage or over-temperature conditions. This protection may or may not be self-resetting and it may or may not act fast enough to save the device.

Answer 4

You'll probably get a better answer on physics or electronics, but it's mostly a matter of voltage and damage not being that simple, especially when there are magnetic fields involved.

More voltage will drive more current through the same circuit. More current generates more heat. What happens from there depends quite a lot on exactly what the circuit is and the physics of any moving parts.

In the case of your drill and belt sander I would guess that what burned out was most likely the speed control. Speed controllers use semi-conductors to flip the power on and off with the cycles of the AC current. Semi-conductors (Silicon Controlled Rectifiers in this case) really don't like being subjected to voltages higher than they're rated for or excessive heat and tend to melt, explode, catch fire, or do other, violent things in response.

Your table saw and air compressor don't have speed controllers though. So if you subject them to a higher voltage, that drives more current, but nothing immediately faults and burns up. The more current results in more heat, but also creates stronger magnetic fields inside the motor. The stronger magnetic fields spin the motor faster. The motor spinning faster makes its fan push more cooling air. It's not actually that uncommon for motors to run cooler at higher voltages with the same load because the field effects are more efficient and the higher speed cools them off better. Couple that with most of the larger tools' electric motors being designed to run at either 110 or 220 because that makes them significantly more useful for an insignificantly higher cost and it's not terribly surprising that your heavy-duty tools could handle the higher voltage.

In fact, you might want to consult their owner's manual and/or the spec sheet of the motors they contain and see about just switching them over to 220v permanently. If they were designed to to that they'll run cooler and last longer plus they'll use the electricity more efficiently so it will cost you less to operate them, and you already have 220v available, you just need to put a proper socket on it.