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Isolator Switches

KATKO is an electrical switch manufacturer based in Finland that specialises in safety switches, load break switches and switch fuses. KATKO use the most up-to-date materials to produce the best quality switches at a competitive price and to produce the widest possible range to suit customer requirements.



A mechanical switching device capable of making, carrying and breaking currents under normal circuit conditions which may include specified operating overload conditions and also carrying for a specified time current under specified abnormal circuit conditions such as those of short circuit.

Note: A switch may be capable of making, but not breaking, short-circuit currents.



A mechanical switching device which, in the open position, complies with the requirements specified for the isolating function.

Disconnector: (working definition) device without on-load making and breaking capacity.


Switch disconnector/load break switch

A switch capable of making, carrying and breaking currents under normal circuit conditions and which, in the open position, complies with the isolating requirements specified for a disconnector.


Switch disconnector fuse

A switch-disconnector in which one or more poles have a fuse in series in a composite unit.


Why are they so safe?

All of our Safety Switches have a door interlock system, which not only prevents the cover from being removed when the switch is in the ‘ON’ position, but also when the switch is ‘PADLOCKED OFF’.

Traditional Isolator Switches have always been open to abuse due to the fact that their covers can be removed, or doors opened, when the switch is ‘PADLOCKED OFF’. This allows the switch to be turned ON manually, leaving the switch vulnerable to tampering, which is very dangerous for the person working on the plant involved. However, KATKO has overcome this by fitting a mechanical interlock which operates in both the ‘ON’ and ‘PADLOCKED OFF’ positions throughout their range of products.


KATKO switches are mounted inside enclosures made of various materials to suit specific applications: ABS, Polycarbonate, Aluminium, Steel and Stainless Steel. The minimum IP rating for all KATKO enclosures are IP65.


The switches inside the enclosures are Load Break Switches, not no-load isolators.


Utilization category

The standards give the following utilisation categories:

  • AC-21 – Switching of resistive loads including moderate overloads
  • AC-22 – Switching of mixed loads, inductive and resistive loads including moderate overloads
  • AC-23 – Switching of motor loads or other highly inductive loads

KATKO switches have ratings of AC-21, AC-22 and AC-23 for each switch.

As AC-22 is the most commonly used, KATKO uses this rating as the basis for parts numbering. For example, the KEM316 is a 3-pole 16A switch with an AC-22 rating. The AC-21 rating of KEM 316 is 25A, and most of our competitors use code 325 for a corresponding switch.


AC-23 rating

The AC-23 rating of KATKO switches ensures that the switch can break 8 times the full-load motor current, so the switch can break a stalled motor load.

Most other manufacturers allow 2.5 times the full-load motor current – and hope that the end customer fits other motor protection devices between the switch and the motor. If the customer does not, then the switch could weld if attempting to break a stalled motor load.


Protection against overvoltage

Overvoltage protection is ensured by choosing the equipment according to Uimp. The 2 impulse withstand categories used for most of the Katko switches is 6kV (Equipment placed in distribution networks) 8kV (Equipment placed at the head of an installation).



IEC60 947-3, ATEX, FI, KEMA, CE, UL Listed, BBJ, ESC, RINA, EMC Protected, IP65 or IP66.


Short-circuit rating

Most manufacturers claim a 50kA short-circuit rating for their switches, but the important point is the size of the back-up fuse recommended to maintain the 50kA short-circuit level.

The lower the fuse rating, the quicker the fuse will blow under short-circuit conditions – and will thus reduce the time the switch has to withstand 50kA.

KATKO tests short-circuit ratings with the fuse recommended by the motor manufacturers to protect their motor, but without nuisance tripping. For example, on the 25A switch, KATKO uses a 63A back-up fuse on short-circuit tests, whereas most other manufacturers use a 25A fuse. So, what difference does this make?

The difference is this. Virtually all switch manufacturers claim that their 25A switch is suitable for use with an 11kW motor, but the motor manufacturers recommend a 63A back-up fuse.

The reason for this is that the full-load current of an 11kW motor is up to 22A, and the starting current is up to 8 times this value, i.e. 176A. Therefore, if you have a 25A back-up fuse, the chances are it will blow, causing nuisance tripping. To overcome this nuisance tripping the customer must fit a 63A fuse, and by doing so the 50kA short-circuit rating no longer applies unless a switch with a short-circuit rating of 50kA with a 63A fuse is applied.

Katko isolators

Operating temperature

The operating temperature for KATKO switches ranges from –40°C to +80°C. For instance, it is quite normal to have switches mounted outdoors in Finland, where in winter they are subject to ice, snow and temperatures of –40°C. At the other end of the scale, in the Gulf Area the temperature can easily climb to over +50°C.

For higher ambient temperatures than +40°C the maximum load of the switch might be de-rated. For the right application, please contact KATKO for further information.



Products can be tested either in-house or by an accredited testing station. All KATKO switches are tested by independent, accredited testing institutes for compliance with the relative standards, and we can supply these independent test certificates if required.

All KATKO switches are designed to comply with both national and international standards, and we have third-party certificates complying with IEC and NEMA standards from FIMKO, KEMA, GOST, UL, etc.



Katko Isolator Switches and Switch Fuse Range


KE Side Operated Aluminium Enclosed Switches 16-63A

KEF Firefighter Side Operated Aluminium / Polycarbonate Enclosed Switches 16-63A

KEA FR / FR3 Fire Rated Aluminium Enclosed Isolator 16-200A

KEM Polycarbonate Enclosed Isolators 10-630A

KEM ABS Enclosed Isolators 10-100A

KSM Side Operated Switches Polycarbonate Enclosed 16-25A

KER Stainless Steel Enclosed Isolators 16-1600A

KER R/RS Stainless Steel Enclosed Isolators 16-200A

KE Side Operated Switches Polycarbonate Enclosed 16-63A

KEM/KEA/KET EMC Protected Enclosed Isolators 16-630A

TKM Motor Control Switches 16-40A

TKM/KEM/KEA Changeover Switches 16-200A

KEA Aluminium Enclosed Isolators 25-250A

KET Sheet Steel Enclosed Isolators 16-1600A

PV Photovoltaic DC Switches

KEA/KER ATEX Isolator Switches 16-200A

Enclosed Switch Fuses 16-630A

TKA/KUT/KUM Bypass Switch For Frequency Inverter 16-100A

KU Load Break Switches 100-160A

KUE Load Break Switches 16-125A Toggle Switches

EVA Load Break Switches 80A-250A Toggle Switches

KKV Switch Fuses 16-32A

KVKE Switch Fuses 20-160A

KVKE Switch Fuses 200-630A

KU Load Break Switches 16-125A

VKA Load Break Switches 125-250A

VKE Load Break Switches 160-630A

Cable Connectors

Switches and Switch Fuses Accessories


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