Automatic Transfer Switch Buyer's Guide

How To Pick the Perfect Automatic Transfer Switch

By  | Generator Product Expert

A standby generator is basically brain dead without an automatic transfer switch.

They are similar to the thermostat in your house. Instead of monitoring temperature, an automatic transfer switch monitors utility power.

When the power goes out, the automatic transfer switch tells the generator to start.

1. Select a Size
200 amp main breakerAutomatic transfer switches come in a variety of amps, ranging from 50-amps to 400-amps.

In most cases, you simply match the transfer switch to the main breaker in your electrical panel. For example, if you have a 200-amp main breaker, you'll need a 200-amp automatic transfer switch.

2. Select a Style
Automatic Transfer Switches come in one of three styles:

Standard Switches
These prehistoric automatic transfer switches are usually custom ordered by older electricians who love installing unnecessary sub-panels. Standard automatic transfer switches are rarely bundled with home standby generators any more. Stay away if possible.

Load Centers
Instead of installing an automatic transfer switch AND a sub-panel, most manufacturers combine the best of both worlds into a single switch.

Load centers are ideal for standby generators powering small homes with 100-amp inbound service. Your electrician simply connects the load center to 8-16 mission critical circuits.

Unless you own a really small home, youíll still experience a mini-blackout with a load center. When a high-demand appliance Ė like a central air conditioner Ė turns off, the extra electricity generated cannot be diverted to other circuits.

Service Disconnect
If 16 circuits just arenít enough, you can opt for an automatic transfer switch with service entrance disconnect, which energizes your entire electrical panel. They are best suited for larger generators powering homes with 200-amp service.

Your electrician installs it between your meter and electrical panel. While their initial cost is usually greater than a load center, you donít need to purchase a sub-panel. Plus, they are typically easier to install than a load center.

2 Air Conditioners
Air Conditioner Shedding

In the past, home standby generators couldnít power two central air conditioners because they would overload if both started at the same time. As a result, one air conditioner was always locked out.

There are two types of automatic transfer switches with A/C Shedding capability:

Load Center + AC Shedding
Automatic Transfer Switch + AC SheddingNew sophisticated load centers will always energize 16 essential circuits during an outage.

Two of the circuits could be connected to central air conditioners, allowing either to start but not simultaneously.

Service Disconnect + A/C Shedding
A better option is to use a service disconnect switch to power the entire panel and lock out a few high-demand appliances instead.
Service Disconnect + AC Shedding
If the system doesn't have enough juice, the service disconnect will lock out up to four individual HVAC loads, preventing them from starting.

In addition to the built-in A/C shedding functionality, you can install Power Management or Smart Management Modules (PMM)(SMM) that will manage up to 8 additional loads to cycle, so you'll never have to worry about those higher-voltage appliances tripping the system.


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