Multimeter,

How to Test a 5-Pin Relay with a Multimeter (4 Tests)

Using a multimeter to do a series of 5-pin relay tests saves time and helps prevent damaging your equipment.

Relays are sophisticated but fragile devices. They can become faulty and need regular testing to maintain good working order. Checking whether a 5-pin relay works correctly may be necessary for diagnosing electrical issues and during general maintenance checks.

You can easily check a 5-pin relay with a multimeter by conducting continuity tests between its coil terminals (85 and 86) and the normally open (NO, 87) and normally closed (NC, 87a) terminals with the common terminal (COM, 30), as indicated in the table below.

The coil test should give a resistance value within the manufacturer’s specified range, whereas NO with ground should be OL and NC with ground close to zero.

Type of 5-Pin Relay TestTerminals to Attach the Probes toExpected Result (resistance value when not energized)
Relay’s Coils (85 is – and 86 is +)Coil terminals (85 and 86)Within specified range
Normally Open Terminal (87)NO (87) and COM (30)OL (no continuity)
Normally Closed Terminal (87a)NC (87a) and COM (30)Close to zero
NO and NCTerminals 87 and 87aOL (no continuity)

You can test a 5-pin relay with a multimeter and repeat it whenever needed. I’ll show you how to test it in detail.

Testing a 5-pin Relay with a Multimeter

mechanic testing car engine with multimeter

A 5-pin relay has 2 pins (85 and 86) that control a coil and three (87, 87a, and 30) that switch power between the circuits.

The switching pins include ‘normally open’ (NO) and ‘normally closed’ (NC) connection pins, typically numbered 87 and 87a, respectively. When supplying power to the coil, these three pins switch the current, and the normally closed pin becomes a normally open one.

We will conduct the following 2 types of tests (coil and terminals) on a 5-pin relay using a multimeter (4 tests in total):

  • Testing the relay’s coil (between 85 and 86)
  • Testing the following relay terminals:
    • Normally open terminal test (87 with COM)
    • Normally closed terminal test (87a with COM)

Another 4th test you can do is to ensure no continuity between pins 87 (NO) and 87a (NC). You should get an OL reading.

Are All Relays Tested the Same Way?

A relay is a switch that assists in opening and closing circuits electronically.

The switches use a small amount of current to control bigger and larger currents. 5-pin relays provide 2 control pins (87 and 87a) and 3 pins (30, 85, and 86) for switching the power between circuits. It differs from a 4-pin relay with only a single control pin (87).

However, the testing procedure is similar.


Testing a 5-Pin Relay’s Coil

This first step will measure the resistance passing through the relay’s coil.

Set the multimeter to the resistance measurement mode and the dial knob to the 200Ω or 400Ω position depending on the tolerance range specified in the relay’s datasheet. This setting should be a little larger than the range’s upper limit.

For example, if the datasheet specifies a resistance value of 320Ω ± 10% (288Ω–352Ω), 400Ω or a little higher would be a suitable setting.

Resistance is unaffected by polarity, so it doesn’t matter which pin is connected where on the multimeter’s jacks. Place the two lead probes across the two coil terminals to test the relay’s coil.

If the relay is in good working order, the multimeter will show a reading within the range specified in the datasheet.

If you get a reading outside this range, the relay coil test has failed, and it should be replaced immediately. Since a coil is not repairable, you must change it.

yellow color multimeter at 0 reading


Testing a 5-Pin Relay’s Terminals

I will show how to conduct 3 terminal tests using the general procedure described below.

Step 1: Set the Multimeter

As described earlier, set the multimeter to continuity (resistance) mode for a continuity test.

Step 2: Attach the Probes

A continuity test measures the continuity between the pair of terminals attached to the multimeter’s probes.

Place the two lead probes firmly on the relay’s metal contacts (pins) while taking a reading. Which terminals to attach the probes to depends on the type of terminal test. However, it doesn’t matter where each lead probe comes from on the multimeter’s jacks, as in the previous or any continuity test.

Step 3: Interpret the Reading

There should be very little resistance between the two selected relay terminals.

If the multimeter shows a high resistance reading, it means the two terminals are not connected to each other, or else the connection between them is poor. This is because the terminals are connected by a coil, which has most likely worn out or weakened.

Step 4: Take Action

Continue using the relay if all terminal tests are positive, i.e., you get low resistance readings. If any relay coil is faulty, you must replace the relay with one that works.

It’s time to test the continuity between three pairs of terminals on the relay. Remember that we will measure the resistance between them.

a person testing the coil terminals with a multimeter
Video | AJ Electric


Testing the Normally Open Terminal of a 5-pin Relay

When testing the normally open terminal, place one of the lead probes on the normally open terminal (87) and the other on the relay’s COM terminal (30).

Then, read the resistance on the multimeter. If it is several milliohms (a high or OL reading) while the circuit is not energized, the relay works fine because it is meant to be open.

If you get a low resistance reading from the multimeter while the coil is energized, the relay is working fine because it indicates that current can pass due to becoming a closed circuit. A high reading in this case would indicate the relay is faulty and needs to be replaced because it remains open, whereas it should be closed.

A person is drawing a diagram on a piece of paper to illustrate the process of testing a 5 pin relay with a multimeter
Video | AJ Electric


Testing the Normally Closed Terminal of a 5-Pin Relay

Keep the multimeter set to the resistance setting.

Place one of the lead probes on the COM terminal (30) and the other on the normally closed terminal (87a). Then, read the resistance on the screen.

If it shows a resistance close to zero ohms again, i.e., very low resistance, the relay works fine and doesn’t need to be changed.

If you get a very high resistance reading, it means the normally closed terminal is faulty. The resistance should only be high when the terminal is open.

A pair of hands drawing a diagram on a piece of paper
Video | AJ Electric


Testing Continuity between the NO and NC Terminals

Keep the multimeter set to the resistance setting.

Place the two lead probes on the relay’s NO and NC terminals, which are terminals 87 and 87a. There should be infinitely high (OL) resistance between them.

If the resistance value is zero or close to zero, the relay is faulty and must be replaced.


References

Website Resources:

Video References:

AJ Electric

Electro University

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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