I cannot find a Special Application Pressure Switch rated for 5 HP, Single Phase Power. What can I do to protect my pump?

You are correct, many of the special application pressure switches, such as Reverse Action, High-Gard, Gard-all, Auto-Off and the Low Pressure Cut Off Switches are limited to 2 – 3 Hp depending on the Voltage. You will not find these special switched rated for 5 HP, Single Phase Power. This is true for the BOSHART, SQUARE D, or FURNAS (HUBBELL) brands, none of which offer these special switches with this high of a HP rating when using single phase power.

SOLUTION:

The good news is that there is a simple solution to allow the installation of a special applications pressure switch with a lower HP electrical rating in conjunction with a relay. Let’s use the low pressure cut-off switch as an example.

In this application the switch is installed where it is normally located, typically on the tank tee plumbed to the pressure tank.

However, the switch is only used as a signaling device, to send a signal to a relay, telling the relay when to open or close. The relay is equipped with heavy duty contacts to conduct the current to run the higher HP pump. The high amperage power supply goes directly from the power source (electrical panel) through the relay to the pump. The low special application pressure switch does not carry the load to run the pump.

Make sure to have your electrical wholesaler or electrician select the proper relay, the relay must be rated for the Higher horse power (HP), the voltage (V) a of the pump motor, and phase of the power supply (1-phase "Single Phase" or 3-phase which is sometimes refered to as "Poly Phase") 

Always follow the National Electric Code (N.E.C.) in the U.S., or the Canadian Electrical Code in Canada, as well as all state, provincial, or local codes. All electrical work must be performed by qualified personnel. Some local laws require installation by only “licensed installers”.