⚠️ SAFETY FIRST: READ BEFORE STARTING
Working on electric showers is dangerous. You are dealing with a high-voltage appliance (240V) and water.
ISOLATE POWER: Always turn off the electricity at the main consumer unit (fuse box) and pull the isolation cord before removing the shower cover.
VERIFY DEAD: Use a voltage tester to ensure no power is reaching the unit.
LEGALS: In the UK, major electrical work in bathrooms is "Part P" regulated. If you are not a competent person or are unsure of these tests, stop and consult a Part P qualified electrician.
DISCLAIMER: You follow these guides at your own risk. This site and its authors are not liable for any injury, loss, or damage caused by your repairs.
Is your electric shower tripping the electricity, MCB circuit breaker or RCD then it could be a break down of of the insulations resistance here i test the heating element to ensure its safe to use.
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Need a Multimeter for testing try on Ebay UK here
Because this involves testing live-style voltages (even if the unit is dead, the tester generates 500V), add this:
Warning: Never use the 1000V setting on an electric shower. 500V is the standard for 240V appliances.
Component Risk: Disconnect the PCB (Printed Circuit Board) before testing the element at high voltage. The 500V pulse from a Megger can instantly destroy sensitive electronics.
**Any insulation resistance testing is made on isolated dead equipment
If the insulation breaker down on your electric shower wiring or the element itself internally it can cause your MCB to trip but more likely before that the RCD to trip. Its not only a good idea to test the electrical installations insulation resistance values but its the law on any new installation or even when replacing an existing shower for a new one. it makes sense to do similar on the shower itself BUT only to the element as an insulation resistance use 250 or 500v to test, this can damage more sensitive electrical items and completely destroy electronics.
Why a Standard Multimeter Fails this Test
Many DIYers try to test for tripping faults using the Ohms setting on a standard multimeter. This usually fails because:
Low Voltage: A multimeter only uses 9V to test resistance.
High Voltage Leakage: Insulation breakdown often only "arcs" or leaks when full mains voltage (240V) is applied.
The Solution: An insulation tester (Megger) applies 250V or 500V to "stress" the insulation, revealing the leak that trips your RCD.
Critical Test Benchmarks:
Pass: 100 Mohm (Excellent insulation).
Advisory: 1-10 Mohm (Insulation is degrading; failure is imminent).
Fail: <1 Mohm (Dangerous; this is why your RCD/MCB is tripping).
The test itself is very easy connect one end of leads to the electrical terminal of the element and the other to the body of the unit itself then press test , do this to both side if the element and to both elements of the shower heater. The result should be high Mohms if its lower 10 Mohms then you have an issue somewhere. The resistance of the insulation is breaking down and you need to rewire or buy new element.
Below is a video of testing the insulation resistance of element
And below the video shows insulation resistance testing shower motor that was tripping the electric.
This shows importance of testing motors and heating elements for both continuity/resistance and insulation resistance values as this motor was tripping the electric MCB but it tests good on ohms reading but fails on insulation resistance testing
testing the installation video to follow ( TBC )
Here is insulation resistance testing on on a cooker wire install for now
See our post about working on electrical systems safely Here
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