Independent comparisons. We may earn from shop links. More info

How to test a fuse box

Updated: October 2026

You test a fuse box differently once you know which box is on the wall. A garage consumer unit has a button marked T or Test, and that is the check you can do without taking the cover into a wiring job. A 12 V blade block has no such button. You change a blade fuse, and you stop if the terminal still looks live. This page is those two user checks, and the line where you call a competent person. It is not a ranking. The products themselves are on the [fuse box comparison](/hub/electrical-equipment/fuse-box). The six-month interval below is the IET reading of Regulation 514.12.2. Prices and review notes are from amazon.co.uk on 20 October 2026.

You test a fuse box differently once you know which box is on the wall. A garage consumer unit has a button marked T or Test, and that is the check you can do without taking the cover into a wiring job.

Our top picks

Tawveml Tawveml 6-way 12 V fuse box

Best overall

Tawveml Tawveml 6-way 12 V fuse box
8.5/10about £11.39
View offer
KAOLALI KAOLALI 12-way 12 V fuse box

Best value

KAOLALI KAOLALI 12-way 12 V fuse box
7.9/10about £14.57
View offer
Lifegogo Lifegogo 2-way IP65 consumer unit

Rank 3

Lifegogo Lifegogo 2-way IP65 consumer unit
6.3/10about £14.99
View offer
On this page
  1. 1.Identify the box before you touch it
  2. 2.The six-month RCD test
  3. 3.A breaker that is off
  4. 4.Changing a blade fuse

Identify the box before you touch it

Look for the test button before you look for a fuse. The four 230 V units in our set are consumer units with a 30 mA RCD. The eight other listings are blade holders for 12 V to 32 V DC. If you can see a button marked T or Test, you are on the mains board. If you can see a row of ATC or ATO blade fuses, you are on the battery board and you skip the RCD section. Pressing Test on the mains board does nothing to a 12 V pump. Fitting a new garage circuit sits on the garage consumer unit page. The fuse box buying guide separates those products before you buy. Do not open the board to have a look as the test. If the label and the cable colours disagree, stop.

The six-month RCD test

On a consumer unit, the user test is the button. The IET's note says you press T or Test, the supply should switch off, and you then reset. Regulation 514.12.2 puts that check at least every six months. Write the date down. Press the button. The RCD should open. On the 2-way units in this set, one RCD sits over both MCBs, so the light and the socket drop together. Reset, and note the date. If the button does nothing, the test has failed. Do not hold it down. The IET's advice is to get a contractor. The same stop applies if the RCD will not reset, if it trips again at once, or if you smell hot plastic.
Tawveml Tawveml 6-way 12 V fuse box

Testsieger

Tawveml Tawveml 6-way 12 V fuse box
8.5/10about £11.39
View offer

A breaker that is off

A breaker that is off is a clue, not yet a repair. An MCB opens because that circuit drew too much current or saw a short. The RCD opens because it saw an imbalance, or because you pressed the button. If the RCD is off, everything downstream of it is off. On a 2-way unit both the 6 A lighting breaker and the 16 A socket breaker lose supply together. Unplug the extra load before you reset once. A heater and a kettle on one 16 A socket is a common trip, and the cure is less load, not a larger breaker. If it trips again at once, leave it off. If there is no T button, you are not in this section.

Changing a blade fuse

Switch the load off. Pull the blade fuse for the dead circuit. ATC and ATO are the same outline. Fit the same amp number you removed. A 20 A fuse where a 10 A fuse was is not a repair, because the fuse protects the cable. Most blocks here that state a limit say 30 A per circuit, which is the holder's maximum. If the new fuse blows at once, the fault is still in the cable. Seat the fuse fully. Tawveml buyers report fuses that fall out. If the fuse does not click home, do not load the circuit. A red LED is the other trap. ENDARK and KAOLALI reviewers found voltage on the output with the fuse removed. A lit LED does not prove the terminal is dead. If a meter still shows volts, stop.

Common questions

How do you test an RCD without opening the board?
Press the button marked T or Test. The supply it protects should switch off, then you reset. You do not remove the cover. If the button does not drop the supply, the test has failed and the next step is a contractor.
How often is that test due?
At least every six months, which is the interval the IET ties to Regulation 514.12.2. Note the date when the RCD opened and reset. A 12 V blade block has no test button, so the six-month habit does not apply to it.
What if the button does nothing?
Treat the RCD as failed and leave it with a competent person. Do not wedge the button, bypass it, or move the circuits onto a blade fuse box. A unit that will not reset, or any smell of heat, is the same stop.
What does a tripped MCB mean compared with a tripped RCD?
An MCB has opened on too much current on that one circuit. An RCD has opened on an imbalance, or because you pressed Test, and everything after it is off. On these 2-way garage units both ways share one RCD. If it trips again immediately, leave it off.
How do you change an ATC or ATO fuse?
Switch the load off, pull the blade, and fit the same amp value. Do not fit a higher number because it plugs in. Push it fully home. If it falls out, as QWORK reviewers reported, do not load the block.
Why might a red LED be on while a meter still shows volts?
The LED on some of these blocks does not isolate the terminal. ENDARK and KAOLALI reviews report voltage with the fuse removed. A glowing LED hints that a fuse has opened. If you still measure volts, stop.
Which jobs are not in this how-to?
Installing a new circuit, replacing a house consumer unit, isolating meter tails, and choosing the earth for a detached garage. Those sit with a competent person, and in England a new circuit is notifiable. The user check stops at the test button or a like-for-like blade fuse.

Related pages

Best fuse box

12 V fuse box or consumer unit

Fuse box

Fuse box buying guide: voltage, then ways and trip

Garage consumer unit: 2-way, 4-way and who fits it

Sources

Public UK sources are listed below. Shelf prices and star lines are the amazon.co.uk figures checked on 20 October 2026.

  1. Approved Document P (2013, England) (retrieved 20 October 2026)
  2. IET: consumer units and protective devices FAQs (retrieved 20 October 2026)
  3. Electrical Safety First: wiring regulations help (retrieved 20 October 2026)
  4. Electrical Safety First: How safe is your home (2025) (retrieved 20 October 2026)
  5. IET: supply to a detached outbuilding (retrieved 20 October 2026)
  6. IET: external consumer units (retrieved 20 October 2026)
  7. ISO 8820-3:2026, blade fuse-links for road vehicles (retrieved 20 October 2026)
  8. 12 Volt Planet: Blue Sea 5026 12-circuit fuse block (retrieved 20 October 2026)