Article
When dealing with low, medium, or high AC voltages (or DC voltages for that matter), removing power from the circuit is crucial for any maintenance, servicing, or installation operation. Most of the disconnects I've dealt with through the years have been fused and non-fused safety switches, switchgear disconnects, and disconnects mounted on starter buckets. Of course, circuit breakers are also a form of disconnect, but not normally designated as such.

Disconnects Come in All Shapes and Sizes

Steve Maurer, IME
When dealing with low, medium, or high AC voltages (or DC voltages for that matter), removing power from the circuit is crucial for any maintenance, servicing, or installation operation.

Most of the disconnects I've dealt with through the years have been fused and non-fused safety switches, switchgear disconnects, and disconnects mounted on starter buckets. Of course, circuit breakers are also a form of disconnect, but not normally designated as such.

Panel or door mounted disconnects are also common in industrial and commercial settings. But whatever type of actuator used—rotary, pull down handle, or other—one common factor remains. The disconnect completely removes power from the circuit and is lockable, permitting lockout/tagout safety procedures.

Now, most of the disconnects I've worked with have been rather large. But even small panel or door mounted switches are forms of disconnects.

A compact fused switch is one that's mounted inside a panel. This type can be used as either a main/feeder device or branch circuit protection.

Most mount in the interior of a panel box via DIN rail mount. With a smaller footprint than larger versions, it saves space in the enclosure.

Many of the compact versions accept UL class CC fuses of up to 30 amp. For those I researched, single pole disconnects were rated for 347 VAC or 125 VDC, while 2-3 pole disconnects were rated up the 600 VAC.

As deadfront switches, they provide "finger safe" operation and can be operated safely, preventing exposure to live components.

With an integrated lockout/tagout feature and IP20 rating, additional safety is built into the design while still allowing switch functionality.

These compact units have a smaller footprint than traditional Class CC disconnects with a maximum interrupt rating of 200KVA.

When used as motor disconnects, a properly rated time delay fuse must be used. This is to allow for the inrush voltage encountered at startup.

Other Disconnects for Low Voltage Applications
For motor protection and power distribution, vertical fused switch disconnects are available. These units clamp directly to horizontally installed buss bars. Many of these units are modular, allowing for a variety of configurations. One unit I checked out was rated for 800 VAC at 160 amps.

The modular units can be fitted with one triple pole switch for a three phase application or motor and similar controls or with three single pole switch to feed branch circuits.

When a series of modules is use, the switch configuration can be different on each one.

Some of these disconnects are made to IEC/EN standards, and are available for most applications.

Whether you're a panel builder or designing an MCC for motor control, you have more options than ever before.
Photo courtesy of Mersen
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