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Electric Float Switch

An electric float switch is a device that is designed to measure the water level in a tank. It can be used in a variety of electric devices from a pump to an alarm, indicator and more. Float switches vary in size and complexity. An example of a simple float switch is a mercury switch located inside a hinged float. While a complex float switch could comprise of a series of optical or conductance sensors that alert you as and when the liquid reaches different levels in a tank.

Listed below are a few questions answered by the electricians on electric float switches.

My cistern has a 200 volt submersible pump. Can I fix a float switch into one of the hot wires of either the submersible pump control box or the pressure switch? Will it be a problem if one of the hot wires is trying to operate the pump?

What you are contemplating doing is quite common. In most cases, a float switch would break both legs of power. But there are cases where a single pole float switch can be used to switch one hot leg of 220 volt power frequently. As long as the float wiring interrupts one leg of power it’s fine. However, if you can figure out a way by which one leg of pump power is always active at the pump, it would be useful in case you need to troubleshoot the system later.

Can I use a float switch in an underground cistern to control a shallow well jet pump that lies above the ground?

Case details: Pump specifications - 1/2 hp, max amp load of 12.4 amps at 115 volts, Float switch specifications - rated for a 1/2 hp pump, max pump run of 13 amps at 120 volts. The normally closed contact of a flexible 16 gauge three wire cable will be used to switch on a light when the water is low.

Since you’re float switch is rated for 1/2 HP, it means that the manufacturer has designed it to allow for higher start currents. When the pump is active, the lamp won’t light so the system won’t have more than 12.4 amps of power running through it.

I need to connect a 110 float switch to a 220 pump. How do I do this?

Case details: Pump motor specifications - 220 v 1/2 hp Franklin motor.

It’s quite simple. Just wire the float switch into one of the 220v legs. After you connect 220v to one side of the switch, connect the pump to the other side of the float.

My boat has a bilge pump with a 3 position switch. If I turn it to the right, it activates manual control, left is automatic and tuning it to the centre switches it off. When it’s in the automatic position and the water level rises, an integral float switch turns on the pump. Can I wire a relay into the circuitry to prevent it from draining my battery when the switch is not active?

To do this, first connect a common (12 Vdc -) wire to one side of the relay coil and a keyed hot wire—which is a wire that becomes hot only when the key is turned ON—to the other coil terminal.

The normally open (N.O) contacts, which are what the power for the float switch or the pump flows through, close once the key is turned on. If the pump is operated by the float, route one of the float leads through these N.O. contacts on the relay. When you examine the relay you will notice a common terminal on it that forms a part of a set of contacts. N.O. and N.C. (Normally closed) will be the other related terminals. Use the set of N.O. contacts to complete your job.

Do preventive maintenance regularly to ensure that your float switch doesn’t malfunction and cause considerable damage. For example if your pump float isn’t working well, it could lead to water damaging all the possessions stored in the basement due to a flood. However, ensure that you always wear rubber boots before troubleshooting the problem, since water is an excellent conductor of electricity. If you are unable to solve the problem yourself, ask an expert to help you find the right solution.

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