Push-Button Switches and Disconnects

Momentary or maintained: how the switch should behave

A momentary pushbutton closes or opens its contacts only while you hold it, which suits start buttons, horns and jog functions. A maintained switch stays in position until you act again, as selector switches and latching mushroom heads do. Panel-mounted operators fit a round cut-out, usually 22 mm or 30 mm, so measure the hole first; the visible head, such as a 60 mm mushroom, can be much wider than the hole behind it. Contact blocks, lens caps and lock-off kits are often sold separately from the operator.

Amps, volts and AC or DC: rating the contacts for the load

Contact ratings are stated per voltage and current, and they only apply to the type of supply named. A switch rated 250 V AC may be rated far lower on DC, because a direct-current arc does not die out at zero crossing and burns the contacts. For 12 V systems, look for an explicit DC rating at the current you draw, and stay comfortably below the stated amps for motors and lamps, which pull a large surge when they start.

Disconnect switches add a second job: isolating equipment so it can be worked on safely. A lock-off kit lets a padlock hold the handle in the off position, but kits are built for one disconnect family, so match the model number. Count the poles too: a three-pole (3P) unit switches all three conductors of a three-phase supply, while single-pole parts only break one line.

Questions about Push-Button Switches and Disconnects

How do I size a switch for a motor?

Use the motor's nameplate current as your starting point and pick a switch with margin above it. Motors draw several times their running current for a moment at start-up, so look for a horsepower or motor-load rating rather than a resistive-only amp figure.

What is a lock-off kit for?

It lets a padlock hold a disconnect handle in the off position, so nobody can switch the circuit on while equipment is being serviced. Kits are made for specific disconnect series, so check the model number against the kit's compatibility list rather than guessing from the look of the handle.

Is a mushroom-head pushbutton the same as an emergency stop?

No. Mushroom is only the shape of the head. A genuine emergency-stop device is a safety component with latching action and direct-opening contacts, and its listing says so. Do not use a plain mushroom pushbutton for that duty, even if it is colored red.