Double-pole single toggle switch vs. 3-way switch?

In alt.engineering.electrical East Coast wrote: | I have looked in a couple of wiring books and I don't see double-pole | single toggle switches addressed. What is the difference between a | Double-pole single toggle switch and a 3-way switch? I see in the | Leviton catalog these are two different items.

A 3-way is a single pole double throw. It switches one common terminal between 2 other terminals.

A double pole is like 2 switches latched together, but with separate wiring circuits. A single throw would just be an on-off for a 2-pole circuit, such as 240 volts in the US.

| If you have a single light, like in a hallway, and want to be able to | switch it on and off from two different locations, you use a 3-way | switch I've been told. How is a double-pole single toggle switch used?

It doesn't have much common use in a home. It could be used to turn on and off smaller 240 volt loads.

A Three-Way switch is identical to a SPDT switch in every respect. If they are listed separately it might be because one is generally intended for a particular application.

The three say switches are routinely used in homes to permit, for example, a hall lighting fixture to be controlled from both the top and the bottom of the stairway. Any "home center" type store will carry this type of switch.

Double pole (DPST) switches are ofen used to switch 240 volt loads (I use one at my water heater as a "vacation" switch.) These switches are also carried by Lowe's and Home Depot type stores.

There is another switch call the Four Way switch. Internally, it is a DPDT switch which is internally connected as a 2 pole reversing switch. The

4-way switch is used in combination with 2 three way switches (above) to switch a light fixture from 3 separate locations. Actually, you can add as many 4-way switches as you care and any switch will turn the light on or off. These switches (4-way) are a little harder to find but they are out there.

A true DPDT switch with reasonable ratings (240 volts, 20 amps) is hard to find. They have an obvious application is switching a load between two power sources. When sold as "transfer switches" they are quite expensive. Some power panel makers use mechanical interlocks to cause two circuit breakes to act as a transfer switch.

I see in the

The 4-way (reversing switch) is placed BETWEEN the two 3-way switches. Operation of the 4-way has the same effect as operating one of the 3-ways. As mentioned above, you can put in a many 4-ways as you care.

Double-pole single throw switches are used for switching of (2) hot legs. Here in the U.S., 480V 1-phase or 208/240V 1-phase. Example: You need a disconnect switch for a 240V water heater, or you have 480V lighting in a warehouse. Your (2) hot leads will be switched with a

2-pole, single throw switch.

There are also 3-pole, s>I have looked in a couple of wiring books and I don't see double-pole

A SPDT switch can come in On-Off-On or On-On configurations. Any 3-ways I've ever seen have been On-On only. Other than that, excellent answer.

And some come in momentary contact while others are not.