The importance of Fuses

Failure to fit the fuse and or reverse polarity may lead to damage to your controller Pump and or wiring which will invalidate the manufacturer's warranty on the control.

Why is fitting a fuse important

A fuse(s) is needed in any electrical system (AC or DC). These protection devices react to the amount of heat being produced by electricity passing through wires and/or components. They are used so as to protect wires and components from the extreme heat produced should there be an electrical overload or short circuit.

When a short or overload occurs, the amps being drawn spike and this increases the heat produced in the wiring and components. When this occurs, a fuse or circuit breaker reacts almost instantly to stop the flow of electricity in the circuit and thereby stopping heat production.

You should never exceed the fuse rating advised by the manufacturer. For a fuse to open in a fault condition almost instantly (a few hundred milliseconds ) it can require a current of 2.2 to 3 times the rating of the fuse. We recommend 7.5 amp fuses so the actual current to open the fuse may be as high as 22.5 amps overrating the fuse is dangerous.

In very rare cases if a current is only slightly above or close to the rating of the fuse for prolonged periods there is not sufficient heat or current to blow the fuse, in this case, the heat can build up and cause the fuse to melt.

For example, a 15 amp fuse will happily supply current up to 15 amps but will not blow. (to blow it could require current of up to 45 amps) The fuse will however gradually get hot over time in testing at Spring I have seen a 7.5 amp fuse heat to 62C and not blow

Without PROPERLY-SIZED FUSES, this quick break in the circuit would not be possible, and damage to components and even FIRE could result.

If you are having a problem with fuses "blowing" please know that these devices are doing their job! It is important that you NOT replace a fuse or breaker with a higher-rated one. Check the circuit for shorts or overloads.


  • Damaged, rusted or worn connectors
  • Damaged cable
  • Bare cables touching
  • Poor connection (example would be insulation not stripped back)

Why then place the fuse close to the battery?

To reduce the risk of overheating in either the cable or device in the event of an electrical fault. The shorter distance current can travel between the battery and fuse means that the amount of cable that may get overheated is reduced to a minimum. For Example, It is possible the insulation on the red (positive) cable can become chaffed allowing the core or poorly installed cable to come into contact with the chassis creating a fault condition. Without a fuse fitted close to the battery, the wire will heat to red hot, burn off all the insulation and potentially cause a fire. Fitting a fuse close to the battery protects the cable run plus control and pump.

We recommend fitting cable into a conduit to provide double protection

It is the same with electrical goods, for example, you go out a buy a new Laptop or TV, the unit is supplied with a fused power lead. The Fuse is in the plug so it is close as physically possible to the power source in the case the wall socket. In both cases, the fuse is as close to the power source as possible to reduce the risk of
overheating and fire.

What then is the difference between DC (direct current) and AC (alternating current)?

A short history lesson most people know that Thomas Edison is the man credited with marketing Direct current power to the masses, However, what is less known is that his associate Nikola Tesla (

Tesla disagreed with the principle of large-scale DC as it requires every property to have its own generation plant. Tesler proposed AC was much more efficient as large stand-alone generation facilities could be built and the power could be transferred over long distances easily. Tesler, in fact, is responsible for the way power in
generated and transferred to this day.

Batteries, Fuel cells and solar cells all produce something called direct current (DC). The positive and negative terminals of a battery are always, respectively, positive and negative. Current always flows in the same direction between those two terminals. On the other hand, the power that comes from a power plant is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) or 50 times per second (in Europe, for example). The power that is available at a wall socket in the
United States is 120-volt, 60-cycle AC power.

The term positive terminal describes which of the two connection terminals on direct current (DC) equipment supplies or is meant to receive a positive electrical charge. DC power supplies always feature a positive to negative electron and always have a negative and positive terminal. Most DC appliances or machines also have a positive and negative terminal which should always be connected to terminals of same orientation on the power supply. Failure to do so can cause severe damage to the equipment and power supply. This positive/negative relationship is commonly known as the polarity of a supply or device.

Any source of direct current electrical power flows from a positive source to a negative source. This applies to the DC side of rectified power supplies, batteries, and Solar panel outputs. Each of these DC power sources features a positive terminal and a negative terminal. The permanent relationship between positive and negative
sides of DC power supplies is referred to as the polarity of the supply.

The universal colour code and symbol for a positive terminal is red and a plus (+) sign. The colour code and symbol for a negative terminal is black and a minus (-) sign. The polarity relationship, colour codes, and symbols for positive and negative terminals are also used on the devices powered by DC power supplies. The connection terminals on DC power supplies and devices will always be marked with one or both of these identifiers. When connecting DC devices to a power supply, it is crucial to observe the correct polarity. In other words, the positive terminals of the supply and device should be connected to each other with the same applying to the negative terminals.

In effect, the current can only travel in one direction around the circuit. Think of it as a one-way valve if you try to force the current the wrong way through the valve it will break and fail.

Our controls have a reverse polarity diode so in the event of reverse polarity the diode will blow, however, without a fuse the current can still flow onto the PCB Processor and pump drive stage causing further damage to the controller.

Fitting a fuse even in the event of reverse polarity will provide additional protection even as the current passes the wrong way around the circuit with the fuse now on the output part of the circuit it will still blow preventing further damage to the processor and pump drive stage as described above. The circuit is broken and current is no longer able to flow.

Please always be aware of Correct polarity when connecting your controller and please always ensure the correct rated fuse is fitted.