A Magnetic Moment

Recent e-mail from a customer calls to my attention that it's very easy to be confused about what constitutes a "magnetic starter" and how to identify one on a machine. Here's what's what.

A "magnetic starter" is what I've often called a "safety switch". The word "starter" just means "switch", nothing fancier than that. "Magnetic" means there's an electromagnetic relay built into the switch which keeps it in the ON position when you punch the ON button. If power is interrupted, the electromagnet shuts down and the relay physically opens the circuit—so the switch is in the OFF position when power is restored.

On machines here in the store we have seen two kinds of magnetic starters: low voltage and high voltage. On machines with a low voltage starter (such as on Delta Unisaws up through the mid '90s or thereabouts), there's a large transformer box, separate from the switch, which sends easily managed low voltage to the switch itself. The switch activates a relay within the transformer box that sends high voltage to the machine's motor.

Most magnetic starters today are high voltage switches; incoming 220 volt current goes directly to the switch, eliminating the need for a separate, expensive transformer/relay box. This is good news, for as the cost comes down we should see more and more machines equipped with this excellent safety feature.

Zach Etheridge