How to Test a Magnetic Contactor How to Test a Magnetic Contactor

What You'll Need
Clear tape
Volt Ohmmeter

A magnetic contractor or starter is uniquely made to produce power to electric motors. It has an overload relay which is attached physically and electrically, and can detect motor overload which triggers it the supply voltage to open and start. It is a switch that’s run by electricity and is used to operate electric motors, lighting, heating and other items loaded with electricity. This guide will aide you in testing a magnetic contractor.

Step 1 – Identify the L-side and T-side of the Contractor

First and important step is to turn off all power that leads to the L or the line side of the magnetic contractor. After that, you may pull out the wires located in the line side screws and you must recognize these wirings by using a pen or a clear tape as markers. Use your pen to write L-1, L-2 or L-3 on the clear tape and post it unto the respective wirings.

Next, also pull out the wires from the contractor’s T or terminal side and same with the L-side process, identify and put marks on each wiring using T-1, T-2, and T-3 as names. This will ensure that each wiring has its corresponding side and also to prevent any misreading in the next procedures.

Step 2 – Connect the Wirings to the Volt Ohmmeter

Turn the control switch to ON status to energize the coil in the contractor. Once you hear a clear clicking and humming sound from the contractor to know that it was successfully turned on. Although there are other magnetic contractors that when turned on have some sort of visual hint once the coil is energized.

Get the volt ohmmeter and turn it on and make sure that the ohm is positioned in front of the selector switch. Then set the red lead into the “ohm” connector, the black lead on the “common” and touch both leads together. The volt ohmmeter must read 0 ohms or a direct short.

Proceed to testing the L-side with its corresponding T-side L-1 to T-1 with the red lead to the L-side and the black lead to the T-side. Check if the wirings read 0 ohms and if it does not then that means that magnetic contact is bad and therefore the contact must be replaced.

Step 3 – Observe the Test

Always observe all the readings on the volt ohmmeter and must generate the same reading which is 0 ohms and direct short. If not, check if the coils are properly linked or try to cycle the control switch of the coil if you can hear a clear clicking sound. If you cannot hear a clear clicking sound then do check the voltage source of the coil.

Turn the ohm meter to volts and set the red lead into the volts connector of the meter and initiate power to the coil. Each lead must have direct contact with each coil connector. Reading of the meter must be the actual voltage supply; you may read the circuit specification to get the quantity of voltage. If the coil does not close even if the voltage is accurate then you need to shut off the flow of energy.

At this point, you can proceed to removing the wires to the coil using the screwdriver. Please reset the volt ohmmeter back to ohms. Then try to touch each leads that leads to the coil connector just like you reading the voltage awhile ago although with the meter now in the ohms position. Make sure that the ohm meter should read between 10 to 100 ohms and if it does not therefore the coil needs to be replaced because it is in bad status.

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