QualifiedHigh risk

No power to a shed or outbuilding

A shed or outbuilding has lost power — points at the sub-circuit/sub-board feeding it, the submain, a tripped protective device, or moisture.

Start fault-finding

Safety first

Isolate and prove dead. Outbuildings often have their own sub-board and a submain — confirm what's live. Damp outbuildings increase shock risk.

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
Protective device feeding the shed tripped/off
Most likely
The breaker/RCD at the main board (or the shed's sub-board) has tripped or is off.
2
Submain fault
#2
The cable feeding the outbuilding has a fault (damage, moisture, rodents).
3
Moisture/earth fault tripping protection
#3
Damp in the shed wiring or fittings trips the safety switch.
4
Sub-board fault
Least likely
A fault at the shed's own sub-board/devices.

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

Check the protective device feeding the shed at the main board (and the shed sub-board) for a trip/off.

Expected reading

Devices on; nothing tripped.

Your actual reading

If it passes

Not tripped — check the submain and shed wiring for supply/faults.

If it fails

Tripped/off — find why before resetting (don't just re-trip).

Often leads toNo power to the whole house Safety switch (RCD) keeps tripping at the switchboard

View all expected readings at once

1. Check the protective device feeding the shed at the main board (and the shed sub-board) for a trip/off.

Devices on; nothing tripped.

2. If tripped, isolate shed circuits/appliances and reset to localise; if not, trace the submain for supply.

Cause localised (a shed circuit, appliance, or the submain).

Fault-finding flowchart

The same logic as a decision tree.

1
start
No power to shed
→ step 2
2
decision
Has the device feeding the shed tripped/off?
Yes→ step 3No→ step 4
3
decision
Does isolating shed circuits let it reset and hold?
Yes→ step 5No→ step 6
4
result
Not tripped — trace the submain and shed wiring for supply/faults.
5
result
The shed circuit/appliance that drops it is the fault — rectify.
6
result
Trips with all off — submain/feed or earth fault; have it repaired.

Common mistakes apprentices make

Repeatedly resetting a tripping device feeding the shed.
Forgetting the shed may have its own sub-board.
Overlooking moisture/rodent damage to the submain.
Working in a damp outbuilding without isolating.

When to stop & escalate

Submains, sub-boards, and outbuilding wiring are licensed electrical work. A submain or earth fault must be found and repaired before re-energising.

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

Switchboards & safety switches

No power to the whole house

The entire home has no power — nothing works. Could be a supply outage, the main switch/main safety switch, or a main fault, and the first job is to tell which.

4 causes3 test steps

QualifiedHigh risk

Switchboards & safety switches

Safety switch (RCD) keeps tripping at the switchboard

The safety switch trips repeatedly — instantly on reset, randomly, or when certain appliances run. It's detecting earth leakage somewhere; the job is to find where.

5 causes3 test steps

QualifiedHigh risk

Outdoor & garden