Wiring switch on old Mark V with motor upgrade

[dwberry]

I was given an old Mark V (minus the motor) and am restoring it to make a shorty sanding station, and adding in the 1 1/8 motor I took out of my 2000's Mark 520 when I did the Power Pro upgrade. The switch is a toggle switch that had 4 wires connected (that had been cut) and had 3/4 HP on the switch. Do I wire all 4 wires to the switch with the 1 1/8 motor or just the black power cord to the switch and the blue to the motor and connect the white from the power cord straight to the motor as it was in my 510?

[dusty]

The four wire switch originally switched both the hot(black) and the neutral(white) wires. In other words there are two switches (in one). You can rewire the same way but that is not necessary. The new switch (if it is four wire) will function the same way if you connect the two white wires (motor and power cord) together and wire the black wires(motor and power) cord through the switch.

Note: the hot wire to the motor may be blue rather than black.

http://www.shopsmithacademy.com/SS_Arch ... Switch.htm

[DLB]

The switch is a toggle switch that had 4 wires connected (that had been cut) and had 3/4 HP on the switch.

A switch used with an induction motor should have a motor rating equal to or greater than the motor HP, so the 3/4 HP rating is not correct for this. (People use under-rated or non motor rated switches regularly, and with varying levels of success. I'm not suggesting it won't work.) If you look in the leftover parts from your PowerPro upgrade you may have the correct switch. My kit came with both switch types, a rocker for "C" headstocks and a toggle for the earlier headstock. IIWM, I would replace the switch with one adequately rated for the motor.

There are pros and cons to switching neutral. Overall, I favor the practice of switching because I would expect longer switch life for the most common failure modes. Opinions on this are going to vary.

I suggest you check your headstock for a ground and add it if not present by replacing the power cord. IIRC some early headstocks were not grounded.

- David

[RFGuy]

The switch is a toggle switch that had 4 wires connected (that had been cut) and had 3/4 HP on the switch.

A switch used with an induction motor should have a motor rating equal to or greater than the motor HP, so the 3/4 HP rating is not correct for this. (People use under-rated or non motor rated switches regularly, and with varying levels of success. I'm not suggesting it won't work.) If you look in the leftover parts from your PowerPro upgrade you may have the correct switch. My kit came with both switch types, a rocker for "C" headstocks and a toggle for the earlier headstock. IIWM, I would replace the switch with one adequately rated for the motor.

There are pros and cons to switching neutral. Overall, I favor the practice of switching because I would expect longer switch life for the most common failure modes. Opinions on this are going to vary.

I suggest you check your headstock for a ground and add it if not present by replacing the power cord. IIRC some early headstocks were not grounded.

- David

Neutrals should always be at 0V and must be physically bonded to Earth ground per NEC. Given this the load should see a smaller transient on power on because only the hot is being switched. If you switch both hot and neutral you are creating a situation where the neutral can have voltage on it from this switching transient. During the transient you may present higher than nominal line voltage to the load (due to the neutral floating in value from being switched). Either way, it likely wouldn't damage a motor load but if there are electronic involved all bets are off. Just my opinion though...

[dusty]

The switch is a toggle switch that had 4 wires connected (that had been cut) and had 3/4 HP on the switch.

A switch used with an induction motor should have a motor rating equal to or greater than the motor HP, so the 3/4 HP rating is not correct for this. (People use under-rated or non motor rated switches regularly, and with varying levels of success. I'm not suggesting it won't work.) If you look in the leftover parts from your PowerPro upgrade you may have the correct switch. My kit came with both switch types, a rocker for "C" headstocks and a toggle for the earlier headstock. IIWM, I would replace the switch with one adequately rated for the motor.

There are pros and cons to switching neutral. Overall, I favor the practice of switching because I would expect longer switch life for the most common failure modes. Opinions on this are going to vary.

I suggest you check your headstock for a ground and add it if not present by replacing the power cord. IIRC some early headstocks were not grounded.

- David

Neutrals should always be at 0V and must be physically bonded to Earth ground per NEC. Given this the load should see a smaller transient on power on because only the hot is being switched. If you switch both hot and neutral you are creating a situation where the neutral can have voltage on it from this switching transient. During the transient you may present higher than nominal line voltage to the load (due to the neutral floating in value from being switched). Either way, it likely wouldn't damage a motor load but if there are electronic involved all bets are off. Just my opinion though...

If the distribution system neutral line is properly bonded to earth ground, does switching the neutral (down stream) still have that negative effect. Stated another way - Does the neutral still float?

[RFGuy]

If the distribution system neutral line is properly bonded to earth ground, does switching the neutral (down stream) still have that negative effect. Stated another way - Does the neutral still float?

Ideally neutral and ground are 0V and connected all the way from the service panel to the load (Mark V in this case). My comment about the neutral floating is related to switching the neutral meaning that during that switch transient the switched neutral can have a voltage on it until the transient settles out. My only concern was during the transient...once at steady state it doesn't matter.

[dusty]

If the distribution system neutral line is properly bonded to earth ground, does switching the neutral (down stream) still have that negative effect. Stated another way - Does the neutral still float?

Ideally neutral and ground are 0V and connected all the way from the service panel to the load (Mark V in this case). My comment about the neutral floating is related to switching the neutral meaning that during that switch transient the switched neutral can have a voltage on it until the transient settles out. My only concern was during the transient...once at steady state it doesn't matter.

OKAY I can see that.

[RFGuy]

OKAY I can see that.

It would probably not be a problem either way for this application, but I am never a fan of switching neutrals. Floating neutrals are dangerous. Water coming out of the sink can shock you if house wiring isn't properly bonded to Earth ground. My parents lost a tv because of a floating neutral back in the 70's. He had to argue with the power company before they finally put a 24 hour monitor on the pole transformer. They found out that the neutral tap on it had become disconnected causing the neutral voltage to vary widely up or down. I think my Dad had measured like a 170V going into the tv at one point when it should have been 110V nominal (now 120V nominal). Not too hard to see why the tv failed. The power company fixed the issue but never paid for the tv.

[DLB]

I did say pros AND cons. And that opinions will (not might) vary... Most of the Mark 5/V's I've seen are wired to switch neutral. Also always true for the PowerPro except when neutral is not present (230V U.S.). Neutral is normally bonded to earth ground only outside the facility. Everything downstream of that has a measurable voltage potential on neutral compared to ground because neutral is carrying current and ground is, ideally, not. That potential includes transients, regardless of whether neutral is switched. I'm not sure what is meant here by floating neutral. Aren't there going to be switching transients on neutral when the Mark is powered on regardless?

But I agree that the decision to switch neutral or not is up to the engineer responsible for the design at the time. Or in this case, the person doing the repair/upgrade. So the hard question is: do they follow the guidance of the engineer responsible for the headstock they are modifying or the one responsible for the donor headstock? IMO, either is okay.

- David

[RFGuy]

I did say pros AND cons. And that opinions will (not might) vary... Most of the Mark 5/V's I've seen are wired to switch neutral. Also always true for the PowerPro except when neutral is not present (230V U.S.). Neutral is normally bonded to earth ground only outside the facility. Everything downstream of that has a measurable voltage potential on neutral compared to ground because neutral is carrying current and ground is, ideally, not. That potential includes transients, regardless of whether neutral is switched. I'm not sure what is meant here by floating neutral. Aren't there going to be switching transients on neutral when the Mark is powered on regardless?

But I agree that the decision to switch neutral or not is up to the engineer responsible for the design at the time. Or in this case, the person doing the repair/upgrade. So the hard question is: do they follow the guidance of the engineer responsible for the headstock they are modifying or the one responsible for the donor headstock? IMO, either is okay.

- David

Thanks David. Yeah, I didn't intend to start a new debate on it, but I guess I did. Well in the ideal world there are no parasitics so neutral would be at 0V and always stay at 0V. Unfortunately in the real world there will be R, L and C created on that neutral wire so even if it is bonded to Earth ground close to the Mark V there will be a nonzero voltage on neutral...probably only in the few mV or less. This voltage arises because as you point out there is an AC current flow in the neutral wire for a single phase 120V system like this. AC current plus wire resistance equals voltage rise. By switching both hot and neutral, the load (Mark V) is fully disconnected from power and on paper this is safer for the end user. My concern was more related to the long term health of the Mark V. Having 2 switches, one on hot and one on neutral can cause a higher overall transient to be exposed to the load, e.g. if their transients superimpose. This may be a worse case that never happens. If it were mine, I would hard tie neutral and not switch it for this reason. A "floating neutral" is what it is called when a neutral is not tied to ground and is allowed to float above or below ground potential. This should never happen but sometimes houses are wired improperly (or when a pole transformer is malfunctioning as in my anecdote above).

I agree with you...I think either way is okay, but I just wanted to share my opinion of why I would only switch one.