Photograph of a well pump relay switch The Water Pump Relay Switch on Private Well and Pump Systems

  • WATER PUMP RELAY SWITCH - CONTENTS: Well pump relay switches: How to Find & Use the Water Pump Relay Switch, will one be installed on your system? if so where is it? what does the pump relay do? Why is it needed? Well pump relay switch diagnosis & repair procedures
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Heavy duty switching relays for well pumps:

This article describes how to find, use, diagnose, install and wire-up or repair the a water pump relay switch (well pump relay).

The page top photo shows a typical wall-mounted Goulds ™ relay switch used to power a submersible well pump. The well pump relay switch is used to turn on and off higher horsepower well pumps. The pump pressure control switch operates the pump relay switch that in turn operates the pump.

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How to Locate & Use the Water Pump Relay Switch

Where will I find the pressure control switch and where is the pump relay switch?

The water pump pressure control switch (orange arrow in photo at below left) and the pump relay switch (below right) are two different devices. As we explain below, all well pump systems require a pressure control switch to sense the water pressure and turn the pump on and off as needed. But when a higher horsepower submersible pump is used, a separate pump relay (red arrow in photo below right) is used to actually control turning the pump on and off.

Pump pressure control switch (C) D Friedman Well pump relay switch and power control (C) D Friedman

Well Pump electrical power switch: In the photo at above right, you'll note a third control marked by the white arrow. This is the main electrical power shutoff for the well pump. Some pump relay covers, when removed, include a pull-out switch that cuts electrical power to the pump. This is a handy detail to know: if your well pump relay switch is of that type, and if the cover of the switch is not securely installed, your well pump could lose electrical power and the building will have no water.

Watch out: while the pressure control switch is usually easy to find (located on or close to the water pressure tank) the pump relay switch might be found nearby, say on a wall (photo below left) or it might be hidden away in a closet or crawl space (photo above right).

Photograph of a water pressure tank air valve

How to Recognize and Locate a Pump Relay Switch

In this photograph a pump relay switch is mounted on the wall to the left of the blue water pressure tank. You'll notice that an electrical conduit can be seen running down the wall below this gray switch box. The relay is usually mounted on a wall near the water pressure tank.

How are Water Pump Relay Switches Wired & Controlled?

Electrical power, either 120V or 240V, is brought into the relay switch from the electrical panel and is connected to one side of an internal relay switch inside the box. Wiring to the water pump, usually a submersible pump located inside the well, is connected to the other side of the relay switch.

A separate pair of wires will run from the relay switch to the pump pressure control switch. (See that little gray box at the lower end of the conduit below the larger, wall-mounted gray pressure switch box?).

When the pump pressure control switch detects that the water pump should turn on, a light-duty switch inside of the water pump pressure control switch senses this pressure drop and turns on the heavy-duty electrical relay switch inside of the wall mounted pump relay.

The wall mounted relay thus is sending power to the water pump.

When do we use a pump relay switch

A pump relay switch such as the relay switches shown in photographs in this article is used to power a water pump when the voltage/amperage combination would be too much to switch on and off by the simple pump pressure switch.

Larger horsepower submersible well pumps draw more than 15A, sufficient amperage that if they were wired through a little pressure control switch at the water tank that switch would burn up pretty quickly.

Well pump relay cover (C) D Friedman Well pump relay cover (C) D Friedman

The specifications and load handling capacity of the pump relay switch are found on the switch cover or body, or sometimes on a sticker located inside the switch cover. A closer examination of this data (above right, click to enlarge) indicates the horsepower rating of the pump that the switch is intended to handle - in the case of our photo, it's a 1/2 hp submersible well pump wired for up to 230V (and at 5this voltage drawing just 7.7Amps).

Technical note: if the well pump offers the option of wiring at either 120V or 240V, we prefer to wire for 240V service. If you need help sorting out the definitions of current (amperage or amps), voltage, and watts, see DEFINE AMPS VOLTS WATTS.

When are pump relay switches not used?

Many well pump installations use only the pressure control switch to operate the system, so separate pump relay switches are not installed on every water pump. Separate pump relay switches are usually not found when the water pump is above ground such as when a one line or two line jet pump is installed at or near the water pressure tank and they are generally not used on smaller horsepower submersible well pumps that draw 15A or less of current. For those installations,

Photograph of a water pressure tank air valve

Combined Heavy Duty Pump Relays and Pressure Controls

Some heavy duty submersible pump relays such as the Homat™ switch shown in this photograph combine the pressure control sensor and the heavy duty pump electrical relay switch.

Notice the copper tube entering the pump relay box at the lower right in this photo? Also notice that this switch has a pressure gauge right on the switch box face.

This pump control switch has combined a water pressure sensor and switch with the relay to send power to the water pump.

So inspecting the rest of the water equipment at this building we won't expect to find that ordinary littlegray box which controls pump operation on a lower horsepower water pump.

Where is the "electrical ON-OFF switch" when a wall mounted heavy duty pump relay is installed?

We may not see a separate wall mounted electrical switch by the pump controls when a heavy duty relay such as those discussed here is installed. Rather, on at least some of these switches, pulling off the cover of the relay box will actually disconnect internal components and thus serves as a local electrical switch for the water pump.

Safety warning live voltage is inside of all of these pump switches - and is a shock hazard. When you don't see an ordinary wall switch to turn off the water pump you're probably safer going to the electrical panel where you can turn off power to the water pump by switching off the appropriate circuit breaker or pulling the appropriate fuse.


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