Author: Josie

When choosing your transfer switch, a less understood factor is how many poles you need. A pole is a discrete switching position on the contactor where the utility, generator and load can be connected for one lead.

2-Pole

A 2-pole switch has two hot wires coming into it for 120/240 single phase. This also is a solid neutral design – the utility, generator and building neutral are permanently connected.

3-Pole

A 3-pole switch has three hot wires coming into it for 120/208, 120/240, 277/480, and 346/600 three phase. This is also has a solid neutral design – the utility, generator and building neutral are permanently connected.

3-Pole Switched Neutral

A 3-pole switch has two hot wires coming into it for 120/240 single phase plus an additional pole for the neutral. A switched neutral will only allow the utility or the generator neutral to be connected to the building at a time.

4-Pole Switched Neutral

A 4-pole switch has two hot wires coming into it for 120/208, 120/240, 277/480, and 347/600 three phase, plus an additional pole for the neutral. A switched neutral will only allow the utility or the generator neutral to be connected to the building at a time.

When choosing a transfer switch, you will have to decide if you need an open or closed transition transfer switch. Basically, you need to ask yourself if you have critical loads that cannot have disruption of power, not even for a split second.

OPEN TRANSITION

You may have heard this called a break-before-make transfer switch. With this type of transition, the transfer switch breaks contact with one power source before it makes contact with the another. The flow of electricity will be interrupted, therefore preventing backfeeding. This is a split second transfer with an automatic transfer switch. If you have a three position manual transfer switch, utility and generator are on their own sides with the middle position being the full disconnect ‘off’ position.

CLOSED TRANSITION

You may have heard this called a make-before-break transfer switch. With a closed transition, your generator is momentarily running in parallel with utility power. Typically, you will install this in a hospital or critical care facility that requires zero interruption of power. If neither power sources are available, the transfer switch must operate in a open transition mode, ensuring back feeding cannot occur.

While searching for the right transfer switch, you will want to know how your application requires the neutral to be handled. The rules vary by application and in some cases depend upon the authority having jurisdiction (Local electrical inspector).

Solid Neutral

A solid neutral switch provides basic load switching. The neutral of the generator, utility and building are permanently connected inside the transfer switch. The transfer only switches the hot (power) leads. In this application you need one pole on the switch for each hot lead.

Switched Neutral

A switched neutral transfer switch only allows the utility or generator neutral to be connected to the building load at a time. Since the neutral is switching between sources another pole on the transfer switch is required.

The National Electric Code (NEC) requires a way for disconnecting the electrical service where it enters a building. This main circuit breaker prevents the building from demanding too much current from the utility creating a dangerous conditions. This circuit breaker may be in a separate panel or part of a service entrance rated transfer switch.

Non-Service Entrance Rated

There isn’t any over-current protection within a non-service entrance rated transfer switch. Therefore, when you install this type of transfer switch, it will be after the service disconnect panel.

If you find a non-fusible manual transfer switch, it does not have over-current protection. Non-fusible switches are not service entrance rated and cannot have the over-current protection added.

Service Entrance Rated

Service entrance switches will have a service disconnect at the utility side. This installation requires less components, making it ideal for new construction, which can be more cost effective.

At WINCO, we offer ASCO service entrance rated switches equipped with an additional disconnect breaker.

First, lets discuss what GFCI protected means. GFCI stands for ground-fault circuit interrupter. You will recognize the outlets in your home, they are the ones with test and reset buttons. This is to eliminate the risk of an electric shock. On many of our generators, GFCI protection is part of the main line circuit breaker.

You can use a transfer switch with a full panel GFCI protected generator. When looking at transfer switches, you will need one with a switched neutral.

3-POLE SWITCHED NEUTRAL

A 3-pole transfer switch with a switched neutral is single phase. The switching mechanism will break the two hot legs of the circuit, in either direction, before the neutral is broken. It will then close the neutral before the two hot legs close, preventing the generator’s circuit breakers from nuisance tripping and protects inductive motors and sensitive loads.

This style of switched neutral transfer switch is also recommended for safe use with any generator that has a bonded neutral.