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TM063 701, 702 & 703 Series Boiling Water Unit Service Instructions
Revision D: Feb 2017
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Electrical Safety Testing
There are some basic test procedures that should be carried out when the operation and function
of a BWU electrical system is in doubt.
Wear Personal Protective Equipment (PPE) when conducting step 1 of these
procedures to reduce the risk of electric shock. Refer to the safety warning on
electrical testing on page 3.
Procedure 1: Insulation resistance test of the water heater.
1. For 3 – 15L models: Isolate power by switching off at power point and unplugging BWU
3 pin plug from power point.
For 25 & 40L models: Isolate power by turning isolation switch off and then removing
fuse (or switching off circuit breaker). Disconnect Active, Neutral and Earth wires from
BWU terminal block.
2. For 3 – 15L models: Connect one test meter lead to the Phase and Neutral conductors
(bridging them), and the other to lead to the Earth pin of the BWU 3 pin plug.
For 25 & 40L models: Connect one test meter lead to bridge out the Phase and Neutral
conductors and the other to lead to the Earth terminal of the BWU terminal block.
3. Operate insulation resistance tester. A reading above 1 mega ohm should be obtained.
4. If a reading below 1 mega ohm is indicated, all component parts will need to be individually
tested to locate the fault. Refer to Fault Finding Chart 1.1 on page 33.
Procedure 2: To check “Earth Continuity” of the water heater.
6. Set test meter to x1 Ω (ohms) resistance scale.
(3-15L models)
7. Measure between the earth pin on the 3 pin plug and the water heater jacket. The reading
should be less than 1 Ω ohms.
(25-40L models)
8. Measure between the earth terminal and the water heater jacket. The reading should be less
than 0.5 Ω ohms.
9. If a reading greater than this value is obtained the earthing connection should be checked for
corrosion/tightness and the power lead earth wire tested, if necessary replace the power lead.
Procedure 3: To check “Continuity” of the water heater electrical circuit.
Note: If continuing with any diagnostic procedures do not perform this step (3) until
diagnostics are complete.
10. Set test meter to x1 Ω (ohms) resistance scale.
11. For 3 – 15L models: Measure between the Active and Neutral pins of the BWU 3 pin plug. The
resistance should be approximately 1.5 kilo ohms.
For 25 & 40L models: Measure between the Active and Neutral terminals of the BWU terminal
block. The resistance should be approximately 1.4 kilo ohms.
12. If a reading outside these resistance values is obtained, all electrical component parts will
need to be individually tested to locate the fault. Refer to Specifications table on page 6 for
indicative resistance values of components.
13. For 3 – 15L models: Plug BWU 3 pin plug back into power point and switch on power point.
For 25 & 40L models: Reconnect Active, Neutral and Earth wires to BWU terminal block,
replace fuse (or turn on circuit breaker) and turn isolation switch on.
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