Selecting a Float Switch – What Should You Consider?

Float switches


Firstly, it’s important to understand how a liquid level sensor, or float switch, works.  The products supplied by Alan Butcher Components contain a reed switch within a stem.  An external float, with a magnet inside, passes over and activates the reed switch, depending on the level of the liquid.  No power supply is required to operate these switches.

Float switch operation


When selecting a liquid level sensor, you should consider the following:


Contact Form – do you need the switch to turn on when the liquid level reaches a certain point (Form A NO) or do you need the switch to turn off (Form B NC)?

                Form A – Normally Open                                                       Form B – Normally Closed

        Float Switch NO                         Float Switch NC


Mounting Position – identifying where your level sensor will be positioned within your application is important, as it will also determine whether you need a vertical or side mounting/horizontal float switch.  Please note, when mounting “stem up”, operating functions are reversed.

              Top Mounting          Bottom Mounting                                                            Side Mounting

       Float Switch Mounting                                Side Float Switch Mounting

Housing Materials – When selecting a float switch it is essential to establish the type of fluid the level sensor will be required to operate in.  Our products are available in Polypropylene, Polyamide and Stainless Steel materials.  It is strongly advised that a sample switch is tested for suitability during the early stages of the design phase, as the incorrect material choice may lead to product failure.  More detailed information on the chemical resistive nature of materials can be found on the PIC website –



Other considerations include the cable type and length, size of the tank/container, electrical rating of the switch (the PLS series rates up to 250V/50W with a maximum current capacity of 2A depending on the switch) and whether there is likely to be deposit build up, for example lime-scale within the application as this can adversely affect the operation of the switch.


Typical Applications –

Refrigerators – modern refrigerators with ice cube makers require a water tank.  The water level inside the tank can be monitored with a level sensor.  If the water level drops below a certain point, a warning will be issued and the machine will stop producing ice cubes.

Condenser Tumble Dryers – a float switch or float/sensor combination inside the condenser tank will active a pump when the liquid reaches a certain level.

Coffee Machines – these can use a customised float with an integrated magnet.  The float sits inside the water tank and if the level drops, the magnet activates a reed sensor located in the machine housing.  A signal to re-fill is issued and the machine will stop producing coffee to avoid running dry.

Steamers and Steam Cleaners – If the water level drops below a certain point, a warning will be issued and the machine will stop producing steam.


The float switches on our website are our most popular items –  If your application has specific requirements which cannot be met by standard parts, please contact us on 01258 456360 or email  We will do our best to help!