Ceramic Fuses, Circuit Breakers and Safety Switches: What's in Your Switchboard?

Open the door on most switchboards and you’ll find a row of switches, a bigger switch on one end, and maybe some little white fuse holders. Here’s what you’re looking at, and which parts are actually protecting you.

The main switch

The biggest switch, usually on the end, turns off everything in the house. It’s the one to use in an emergency, and everyone in the house should know where it is.

Ceramic (rewireable) fuses

If you see small white or brown porcelain holders with a bit of fuse wire inside, you have an old-style board, commonly 40 years old or more.

• What they do: if a circuit draws too much current, the wire heats and melts, cutting the power.
• What they don’t do: protect you from electric shock. They only react to overload, not to current leaking through a person or a fault.
• The problem: they’re easy to replace with the wrong wire, or worse, with something that doesn’t melt at all. That defeats the protection entirely.

If you have these, the board is a candidate for an upgrade. See the signs your switchboard needs upgrading.

Circuit breakers (MCBs)

These are the small switches that replaced fuses. When a circuit is overloaded or short-circuits, the breaker trips and you reset it by flicking it back on. They protect the wiring from overheating. On their own, they still don’t protect a person from shock.

Safety switches (RCDs)

A safety switch is different. It constantly compares the current going out with the current coming back. If some of it is leaking, for example through a person touching a live part, it cuts the power very quickly. That’s what protects people from electric shock.

• They usually have a Test button, often marked “T”.
• Press it about every three months. It should trip straight away. Reset it after. If it doesn’t trip, it needs attention.
• Queensland rules require safety switches protecting power and lighting circuits in many homes, including ones that are being sold or leased. Ask your electrician what applies to yours.

More on testing in how RCD testing works.

RCBOs

An RCBO combines a circuit breaker and a safety switch on a single circuit. The benefit is that a fault on one circuit only trips that circuit rather than a group of them. It’s more precise, and it’s why modern boards often use them.

How to tell what you’ve got

You see	What it probably is
White porcelain holders with wire	Ceramic fuses (old board)
A row of small switches	Circuit breakers
One or more switches with a Test button	Safety switch(es)
Switches with a Test button on each circuit	RCBOs

If you can see fuses, and no Test button anywhere, your board isn’t protecting you from shock, and it’s worth getting it checked.

The catch: it depends on coverage

Having a safety switch isn’t the same as having your whole house covered. Some older upgrades protected only part of the house, leaving other circuits unprotected. A licensed electrician can tell you which circuits are covered and which aren’t.

Don’t DIY it

Working inside a switchboard is licensed electrical work. Testing the Test button is fine. Opening the board isn’t. If something looks wrong, get an electrician in to assess it, and you’ll get a written quote for any switchboard upgrade that’s needed.