common

[Anonymous]

I recently installed a bunch of single pole pilot light toggle switches. There were three screws beside the ground screw, a black, marked common, a brass and a sliver. To make sure I asked my buddy. He said the common is always the hot. So black is line, brass load & silver neutral. I said yes but isn’t the neutral sometimes called the common? He said no. Now today I installed a bunch of single phase three speed fan motors. The speeds were wired blue, black & red (high, med, low), with a purple wire marked common. Now my question – aren’t the blue, black or red the line according to what speed is selected the motor the load and the purple (common) the neutral and if so can a neutral be purple? Thanks for your help in my education.

[imported_Ron]

Common is the neutral.

[Anonymous]

Common is the neutral.Thanks. A little more detail if possible. Is the common always the neutral or is it sometimes the hot (line)? Is purple a NEC color for neutral? I don’t think so. On the switch the silver screw has got to be the neutral so the black screw marked common can’t be, can it?

[imported_Ron]

White is generally the code required color for neutral. The term "common" is not defined by the code, but generally is reffering to the neutral.
Silver screw is for the neutral, brass is for the hot.

[Wgoodrich]

The term COMMON is a generic term that can be a neutral, a grounded leg or even a hot wire.

Common by electrical terms are often referring to a neutral or grounded leg becuase this white wire is pretty well common throughout the home as a white or gray wire being a neutral [carrying unbalanced load between to hot wires back to the panel] or grounded leg [carrying the path back to the panel for only one hot wire.

Now if you look in the dictionary you would find commong means one with other entities in common with each other or electrically connected in common with each other.

When you are dealing with a piggy back single pole switch or a three way switch then you will find a common HOT connection in common with other points on or within that certain device.

If you have a fan that has four hot colors declared by the NEC to be hot wires [which you do] but one has a tag saying it is a common wire [even if a purple wire] then if that purple wire is truly marked [COMMON] then that is the one you would connect the white wire from you house wiring to. In this case you have the same word common meaning both in common with each winding inside the motor and meaning grounded leg [aka neutral conductor].

Are we having fun yet. Boy I am surprise that this fan has a UL approved listing. Purple by the NEC is a hot wire not a ground wire [aka neutral conductor or grounded leg]. However you have a tag declaring it COMMON. This may be approved and listed because the power can enter the three windings of this three speed motor from either end of the windings and considering that the purple wire is the one wire connected to all three windings with the three hot colored wires connecting to the other end of those motor windings separately to create the three speeds of that motor. This would make that purple wire to be common but not necessarily a neutral conductor.

This leads to one concern that I am having. If this is a foreign made motor such as in Europe then most likely this motor is rated 200 volts 50 cycles. If so then your 120 volts will burn out this fan motor.

Check the name plate on that motor and confirm that it is 120 volt rated 60 cycle American made and not 200 volt 50 cycle Euroupean made.

Let us know what you find.

Concerned

Wg

[Anonymous]

Thanks for your in-depth answer. There is nothing special about the motor. It’s just a single phase, 120, three-speed blower replacement motor ordered from Grainger. It’s a Dayton, there house brand, probably mfg. by Emerson. If you want any more details I’ll get them Monday.

[Wgoodrich]

The motor you discribe come in 120 or 240 volt single phase. Just make sure you have a 120 volt motor by reading the voltage rating on the name plate. Quite often these motors are dual rated voltage where you change a couple of wires to convert from 120 volt to 240 volt. It should show on the voltage box on the name plate 120/240 volt if your motor is a dual voltage motor.

If you have a 120 volt only motor then that purple wire is marked common because that purple wire is connected to the end of each of the three windings in that motor in the run mode. This would make that purple wire in common with all windings in the run mode. This purple wire would be connected to the white wire of the house wiring system. Then a three speed switch will take the black power wire with three hot wires [switched] going to the motor's three wires connected separately on the other end of the motor windings from that purple wire called common that is connected to all the windings on the opposite end of those windings.

Good Luck

Wg

[Anonymous]

Thanks. It's a 120 volt only motor.