AdvancedHigh risk

Safety switch trips only at night / at a set time

A safety switch trips at a consistent time (often overnight) — pointing at a time-controlled load (off-peak hot water, slab heating, irrigation, pool) with an earth-leakage fault that only runs then.

Start fault-finding

Safety first

A time-correlated trip still means real earth leakage — a shock risk. Don't bypass the safety switch. Isolate and test the time-controlled load.

Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

1
Off-peak hot water element leaking to earth
Most likely
The off-peak element only energises overnight; if it's leaking, the trip happens then.
2
Slab/space heating on a timer leaking
#2
Time-controlled heating with an earth fault trips when it switches on.
3
Irrigation/pool gear on a timer
#3
A timed pump/valve with leakage trips at its scheduled time.
4
Moisture/condensation worse overnight
Least likely
Cooler overnight conditions cause condensation/leakage in a fitting.

Reports are saved on this device to reflect what you actually find.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 2

Identify what's time-controlled to switch on at the trip time (hot water, heating, irrigation, pool).

Expected reading

A time-controlled load matching the trip time.

Your actual reading

If it passes

Isolate that load and see if the trips stop.

If it fails

If nothing's scheduled then, log and investigate as a random trip.

Often leads toRCD trips randomly with no obvious pattern Hot water system tripping the safety switch

View all expected readings at once

1. Identify what's time-controlled to switch on at the trip time (hot water, heating, irrigation, pool).

A time-controlled load matching the trip time.

2. Isolate the suspect time-controlled load and confirm the safety switch then holds through that time.

Safety switch holds with the load isolated.

Fault-finding flowchart

The same logic as a decision tree.

1
start
Trips at a set time
→ step 2
2
decision
Is something time-controlled to switch on at the trip time?
Yes→ step 3No→ step 4
3
decision
Does isolating that load stop the trips?
Yes→ step 5No→ step 6
4
result
Nothing scheduled — investigate as a random trip (log it).
5
result
That load is the source — insulation-test and rectify.
6
result
Still trips — broaden to wiring/condensation/other loads.

Common mistakes apprentices make

Not connecting the trip time to a scheduled load.
Bypassing the safety switch to stop overnight trips.
Overlooking off-peak hot water as the cause.
Not isolating the load to confirm.

When to stop & escalate

A leaking element/load is licensed rectification; never run on defeated protection. Controlled-load timing involves the meter/authority side too.

If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.

Related faults

RCD / RCBO faults Premium

RCD trips randomly with no obvious pattern

An RCD trips occasionally with nothing obviously changing — not tied to a clear appliance, weather, or time — the frustrating 'tripped again overnight' type.

4 causes3 test steps

AdvancedMedium risk

Hot water & heating