How-To Troubleshoot a B/W Controls 1500 Series Liquid Level Control System


At Nelson Northwest, we're frequently asked to help troubleshoot liquid level control systems with B/W controls Relays, and in this guide we're going to provide some tips, and a step-by-step guide for troubleshooting these systems.

1500 relays are very reliable, but they've been around since the 1980s, so there's been plenty of time for systems with these relays to develop problems. To figure out why a system is not working, we'll isolate the various elements of the assembly. When liquid level control systems with 1500 relays fail, by far the most common cause is the electrode circuit, rather than the relay itself; however, operating with a faulty electrode circuit can cause premature wear and ultimately failure of the relay.

Remember, there are hundreds of volts on the terminals, so this should be done by a qualified technician.

What We'll Need

  • Slotted Screwdriver
  • Multimeter
  • Lengths of insulated wire

Checking the Relay Itself

  • Does the relay have the correct line voltage on terminals three and four?
  • Are the connections on the relay secure and corrosion-free?
  • Are the electrodes in the tank clean and reasonably corrosion-free?
  • If you're using an electrode holder with connections: are these connections in good shape?
  • Is there a good signal ground from the relay to the liquid? This should be either a ground electrode or a solid connection from the relay to a metal tank.
  • If this is a new installation, remember that the load contacts on this relay just provide a dry contact closure. Hooking the two terminals of a contact to the two terminals of a starter coil or single-phase pump won't work.
    • It's a bit like a light switch: you have to put power on one side and it will switch it on and off.
  • For new installations, also make sure that the electrodes are within the acceptable distance from the relay. If they are too far away, the relay may not drop out correctly, or may fail prematurely.

The Jumper Test (Ruling out Faults in the Relay)

  1. Turn off the power to the relay
  2. We'll have to disconnect the wiring, so make a wiring diagram of the relay. Mark any unmarked wires, and take a good photo showing the connections.
  3. Disconnect all the wires from the relay, except the line voltage on terminals 3 and 4.
  4. Measure continuity for each of the contacts:
    • Normally open (N.O.) contacts should read open, and normally closed (N.C.) contacts should read very low resistance.
    • If the continuity is incorrect, the relay is probably defective. Replacing bad contacts may be an option if the rest of the relay is in good shape; otherwise, replace the relay.
  5. Now turn the power back on to the relay. The relay should NOT pull in. Continuity of the contacts should be the same.
  6. Measure the voltage across the secondary terminals 7 and 8. It should be roughly equal to the rated secondary voltage. A bit higher or lower is okay, but if the voltage is significantly lower than the rated voltage (with no other connections on the secondary coil), the relay is probably defective.
  7. Turn off the power again
  8. Put a jumper wire across the secondary terminals 7 and 8.
  9. Turn the power back on.
    • The relay should now pull in.
    • If the relay does not pull in with jumpered secondary coils, it's defective.
  10. Measure continuity for each of the contacts.
    • Normally open (N.O.) contacts should read very low resistance, and normally closed (N.C.) contacts should now read open.
    • If the continuity is incorrect, the relay is probably defective. You'll need to replace contacts or replace the entire relay.
  11. Now turn the power off again.
  12. If no problems were found with the relay, remove the jumper and reconnect the wiring. The problem is most likely in the electrode circuit.

The Electrode Test (Checking the Electrode Circuit)

If the relay tests okay, make a thorough inspection of the electrode circuit.

  • Electrodes should be clean and free of corrosion.
  • Check all connections inside and outside of the tank for low resistance. This includes wire connections on wire suspension electrodes.
  • Make sure the signal ground from the relay goes either to a dedicated ground electrode or has a good connection to a metallic tank.
  • One trick you can use to check electrode circuits is as follows:
    1. Power off the relay.
    2. Connect two electrodes together at the tank.
    3. Disconnect the electrodes at the relay, and test the resistance between the two ends.
    4. If the resistance is high, the wiring is suspect

The Bucket Test

One final trick, if no problems have been identified so far, but the system is still not working, is to simulate the electrode circuit in a bucket. This will help to isolate problems with the relay from problems with the electrode circuit.

  1. First, fill a bucket with the same water that you're sensing.
  2. Cut lengths of insulated wire to simulate your electrodes.
  3. Strip both ends of the wires and wire the relay per your wiring diagram.
  4. Suspend the ends of the wires in your bucket, and remember that when we turn on the power, these will have high voltage, so exercise caution.
  5. Move the wires up and down to simulate the changing water level, and verify if the relay actuates at the correct points.

In addition to the tips we'eve provided here, you can find troubleshooting information in the 1500 Relay Installation Manual. The manual also ships with new relays.

If you get stuck, contact us! We're always happy to answer questions.

Nelson Northwest Alaska • 2115 SW 152nd St. • Seattle, WA 98166 • 800-726-1884
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