Question 1

What is the difference between a fuse, an MCB and an RCD?

Accepted Answer

They protect against different dangers, and the crucial point is that **only one of them protects people**.

**Fuses and MCBs protect the wiring.** Their job is to prevent cables overheating and causing fire when too much current flows.

**A fuse** is a thin wire that melts when current exceeds its rating, breaking the circuit. Simple, reliable and single-use — it must be replaced. Rewirable fuses in old consumer units are obsolete and were a genuine hazard, since people replaced the wire with whatever was to hand.

**An MCB (miniature circuit breaker)** does the same job mechanically and can be reset. It has two mechanisms: a thermal element for sustained overload, and a magnetic element for instantaneous disconnection on a short circuit. MCBs are more accurate than fuses and cannot be defeated by improvisation.

**An RCD (residual current device) protects people.** It works on a completely different principle. It continuously compares the current flowing **out** on the live conductor with the current returning on the neutral. In a healthy circuit these are equal. If some current is escaping — through a person touching a live part, or through damaged insulation to earth — there is an imbalance, and the RCD disconnects within milliseconds.

Typical domestic RCDs trip at a residual current of **30mA**, chosen because it is below the level that causes ventricular fibrillation in most people.

**Critically, an MCB will not save you from electrocution.** A person can receive a fatal shock at a current far below what it takes to trip a 32A breaker. This is why RCD protection is now required on most domestic circuits.

**An RCBO** combines both functions in one device, which is why modern consumer units often use them — an RCD fault then trips only the affected circuit rather than half the house.

**Test RCDs quarterly** using the test button. Electrical work should be done by a qualified electrician.

Question 2

What do the fuse ratings in a plug mean?

Accepted Answer

The fuse in a UK plug protects the appliance's flexible cable, not the appliance itself and not you. Its job is to melt before the flex can overheat and cause a fire. This is a peculiarly British

Question 3

What is the difference between a ring main, a radial circuit and a spur?

Accepted Answer

They are different ways of wiring sockets, and the distinction matters because it determines what you may safely add. A ring final circuit (ring main) is a loop. Cable runs from the consumer unit,

Question 4

Does my house need rewiring, and what does it involve?

Accepted Answer

Probably not on age alone. Rewiring is sold on the basis that wiring "expires" after a fixed period, and the honest answer is that condition and safety standards matter, not the calendar. The genuine

Question 5

Why do my circuit breakers keep tripping?

Accepted Answer

A breaker tripping is protection working, not failing. The useful question is which of three conditions triggered it, because they mean different things. An overload means the total current on that

Question 6

What is the difference between a stopcock, an isolation valve and a service valve?

Accepted Answer

They all shut off water, at different points and for different purposes — and knowing where each one is before you need it is one of the more valuable pieces of household knowledge. The external

Question 7

What is the difference between MDF, chipboard and plywood?

Accepted Answer

All three are engineered boards made by bonding wood together, but the form the wood takes is completely different and it determines what each is good for. MDF (medium-density fibreboard) is made

Related Questions