How To Use a Multimeter to Test a Pool Pump Motor - Voltage

In this "how to" we will guide you through how to use a multimeter to measure the AC voltage to your pool pump motor. If you are installing a new pool pump or you have to troubleshoot a failing pump, you will generally want to measure the motors supply voltage, its running amperage and its line continuity. 

1. VIEW MULTIMETER - This picture show you the different measurement options available on a standard multimeter.  Each meter is designed for a max Voltage level, specified as Cat I to Cat IV. See the lower right corner of this picture. This meter is designated a Category II level meter designed to handle up to 300 volts. This is sufficient for measuring the two supply voltage used for pool pump motors; 120V or 230V. The different test options are shown around the yellow selection dial. Voltage test options are shown at the top of the dial - DC voltage (shown with a solid bar and 3 dots) is on the left; AC Voltage (shown with a ~ line) to the right. Since pump motors are run on AC Voltage we will want to set the dial to 300 or 200 on the right side. This picture shows it set at 300V since most motors are set up on 230V. If you have 130V supply voltage, you would set the meter to 200V.

2. SELECT TEST POINTS - Voltage to the motor can be measured anywhere between the circuit breaker and the motor terminals One convenient test point is at the output terminals of your pump's timer, shown here. This picture shows the wiring inside the timer box. Three wires come in from the left of the box. Two are labeled INPUT and one GROUND. Generally, but not always, color of the wire is significant. If the two INPUT wires are red and black, they are both load wires and provide 240VAC. If they are white and black, white is neutral and black provides 120VAC. The green wires provide GROUND. The GROUND WIRES SHOULD BE ATTACHED TO THE GROUND SCREW JUST ABOVE TERMINAL "A". IT IS WRONGLY SHOWN IN THE CURRENT PICTURE AS GOING TO "A". There are 5 terminals in the timer box. The left most is A. The other four are labeled 1 to 4. The INPUT wires are connected to 1 and 3. The OUTPUT wires to 2 and 4. The OUTPUT wires are currently wired to the pump. Note: Not all timers are wired the same. This is the terminal configuration for an Intermatic timer. Check your timer to make sure which leads are the output lines.

3. TURN POWER OFF - In preparation for measuring your power, TURN OFF THE POWER TO THE TIMER BOX. There should be a circuit breaker before the timer box.

4. REMOVE TERMINAL COVER - With power off, remove the cover that is over the terminals inside the timer box.

5. TURN POWER ON - To measure the pump's voltage, you will have to turn the power back on.

6. MEASURE SUPPLY VOLTAGE - Set your digital multimeter to 300 VAC and place the meter's probes on the OUTPUT terminals, 2 and 4. It does not matter which probe is placed on which terminal. USE EXTREME CAUTION. These wires have 240V on them. And be careful not to let the probes short out between two adjacent terminals. The meter should read within 10 %  of the nameplate voltage. If the nameplate voltage is 230V, the voltage should read between 207V and 253V.

7. REPLACE COVER - TURN POWER OFF at the breaker and replace the cover.

8. OTHER CONSIDERATIONS - If you have a long wire going to the pump from the timer, you may want to measure the motor's voltage at the motor. If the wire is too long or too small, you may be dropping significant voltage to the motor on the supply line. This drop in voltage can increase your motor's amperage to above its max amperage causing your pump to heat up and fail. To measure voltage at the pump, place the meter's probes on L1 and L2. These terminals are usually labeled on the motor. USE EXTREME CAUTION. These wires have 240V on them.

If you have any other questions about pool and spa products please do let us know - we are here to help! 

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