How to Choose the Right Model for the Job

Posted by Celtic Water on 12th May 2025

The Mac3 Brand is well known for its float switches and for good reason. Since developing the first float switch in 1971, Mac3 have gone on to develop a comprehensive range of high-quality float switches for use in many different situations.

What do Float Switches Do?

In simple terms, a float switch is used to monitor the level of a contained liquid, so that a subsequent action can automatically be triggered when the liquid rises or falls within designated levels. For example, to start/stop a pump, to fill/empty a tank etc.

How Float Switches Work

How Float Switches work A Float Switch consists of a length of electrical cable which is attached to the Float Switch itself. The float switch sits in the liquid and as the level rises and/or falls, a microswitch inside the float switch opens and closes, sending a signal to the electronic equipment it is attached to (pump, controller etc.), for subsequent action. E.g. to start a pump.

Image Right: Example of how the Mac3 ‘Key’ float switch can be installed inside a tank, to turn a pump on and/or off.

How to Choose the Right Float Switch.

There are a few elements to consider, when choosing a float switch for a particular installation…

What type of liquid and environment will it be used in?

Some float switches are designed to work in clean water only, whereas others are specifically designed for use in more viscous liquids, such as dirty water or sewage. Choosing the correct model to suit your liquid, will ensure you get the desired performance from the float switch.

What type of cable do I need on my float Switch?

The type of liquid and the environment the float switch is being installed in, will also determine which type of cable would be best on your float switch:

‘PVC’ is the standard lightweight cable supplied with Mac3 float switches and is suited to most situations. It can be buried, exposed to heat (up to 60°C), inclement weather and sunlight, however, it can become brittle and less flexible if exposed to high or low temperatures over time.
‘H07RN-F’ cable, also known as Neoprene, is suited to applications which require a sturdier cable than the PVC. It tolerates low and high temperatures without becoming brittle and stiff and is generally more wear resistant than the PVC.
‘H07BN4-F’ cable is, in most respects, like H07RN-F except that it has a greater resistance to oil and is more wear resistant. Note: this cable is only available for the Mac5 model. however, it is also available for the E-Fly on request.

Choosing the cable length for your float Switch

As well as selecting the appropriate cable type for your float switch, it’s also important to consider the length of cable used…

Too short and the cable can suffer from connection strain, resulting in not enough slack for the float switch to operate to its full potential (this can become an issue when the float switch is installed outside the tank).

Too long and the cable can become entangled in pipework and other obstructions, which again can impede successful operation and in some cases, can even lead to total failure.

If there is no space for a cable, consider a compact float switch like the Agma 22 (for clean water) or Agma W Evo (for dirty water and sewage).

How much space do you have in your tank, well, etc?

It’s important that the float switch has enough room within the environment it is installed in, to rise and fall without being impeded. Considering the size of the float switch (along with the cable length) is therefore also helpful, especially where space is limited.

The following Reference Guide provides a overview of the different Mac3 float switches available for quick comparison…

Product	Small	Key	Mac3	E-Fly	Mac5
Picture
Suitable For:	Clean Water		Clean water, dirty/sewage water	Sewage type liquids and turbulent water
Size:	82 x 111 x 48mm	81mm x 131mm x 41.5mm	106mm x 154mm x 54mm	110mm x 156mm	117mm x 222mm
*Cable Lengths:**	2m, 5m, 10m, 15m, 20m			5m, 10m, 20m
Cable Types:	PVC, H07RN-F			PVC, H07RN-F. H07BN4-F (on special request)	PVC, H07RN-F, H07BN4-F
Angle of Movement:	+45° / - 45°	+45° / - 45°	+20° / - 45°	+10°/-10°	+10°/-10° or +45°/-45°
Max Depth:	2 bar	1 bar	1 bar	2 bar	2 bar
Uses:	Start / Stop electrical equipment (pump/solenoid, valve, alarm etc)	Good general purpose clean water float switch.	Start / Stop electrical equipment (pump/solenoid, valve, alarm etc)	Start / Stop electrical equipment (pump/solenoid, valve, alarm etc)	Start / Stop electrical equipment (pump/solenoid, valve, alarm etc)
Counterweight:	Optional			Built-in
Approvals:	ENEC / EC			ENEC / EC (ATEX approved version also available)
Installation Types:	Good for confined spaces and small tanks, with clean water.	Good general purpose float switch for clean water.	Good for both clean water and dirty/sewage water.	Good for sewage water, industrial wastewater with suspended residues, turbulent water or other dense liquids such as liquid animal feed.	Good for sewage water, industrial wastewater with suspended residues and in turbulent water.