Load break switches

We offer a range of Load Break Switches, covering everything from 16A to 630A. The switches also comes as 3 pole, 3 pole and neutral and 4 pole versions. They can also be made into 6 pole and 8 pole versions by the use of a parallel kit or into changeover versions using a changeover kit.

Safety is the prime factor of Katko's switches. They are designed to break 8 x full load current when used on AC23 duty, and are tested at 50kA short circuit capacity using the fuse back up recommended by the motor manufacturers. (AC rating explanation.)

Current calculations

For example, the normal running current of a 7.5kW motor (used for, say, a ventilation system) is 14.8A.

The starting current is 116.9A, calculated by taking the running current of 14.8A and multiplying by 7.9 (motor manufacturers state 7.9 as the ratio of the start current to the running current ).

If a fault occurs, a 16A Load Break Switch, breaking at 8 x full load current has a breaking current of 128A and will therefore turn the motor off even during start up. In this scenario, the best switch is the KU 316N.

We sell both Rotary and Toggle load break switches: Rotary (16A-250A) | Toggle (16A-250A) | Rotary (200A-630A)

Short circuit

There is another factor in choosing the right switch: a motor's back-up fuse.

Using the same scenario as above, motor manufacturers recommend a 63A fuse for a 7.5kW motor. This value ensures that the motor is protected but at the same time prevents nuisance tripping (the fuse blowing) during start up.

In short circuit tests, many switch manufacturers use a smaller fuse (sometimes even as low as 25A) to achieve the set-standard 50kA rating during the test. A smaller fuse blows much faster than a larger one, reducing the time that a switch is subject to the 50kA through-current.

It means that the switch can pass the test, but in a real-world situation (where a much larger fuse is likely to be installed) it would not meet that rating i.e. it will blow up (or weld itself together), leaving you with a disabled motor and the need to buy and install another switch.

Product range

Visit our online catalogue to view the entire Load Break product range, or if you need further assistance in locating which switch is right for you, visit our Product Guide.