What kind of electrical protection do you have in your home?
Electricity is amazing, but it can be dangerous. Well designed modern electrical installations have many built in ways to protect you in the event of a fault occurring. They are generally referred to by acronyms which can be confusing, so let’s look at what each one is and how they can protect us.
Fuse
There can be many separate fuses of different types in your electrical installation. The main incoming supply has a fuse, typically rated at 60-100A (amps). Older fuse boards then have individual fuses for each circuit, and mains powered appliances also have a 3-13A fuse fitted in the plug. Fuses protect against over-current – that is where too much electricity flows, either because too much power is being used (e.g. too many things plugged in), or because a fault is causing a short circuit. A typical 100A BS88-2 main supply fuse will ‘blow’ in about 6 seconds with a fault current of 500A. This is because they are primarily designed to protect the fixed wiring, and to help prevent it heating up and catching fire as a result of excessive electricity flow for a prolonged period.
MCB – Miniature Circuit Breaker
This device is found in consumer units, and replaced circuit fuses from the 1970s onwards. Like fuses, they protect against over-current. They have a significant benefit in that they can be reset after operating, and do not need to be replaced like fuse wire or a cartridge fuse. This means the correct rating will be reset – no more fuse wire replaced by paperclips!! A typical 32A type B MCB (commonly fitted to protect socket circuits), will operate in around 0.1 seconds with fault currents of 160A or more.
RCD – Residual Current Device (also known as RCCB – Residual Current Circuit Breaker)
The latest version of the wiring regulations requires RCD protection for the majority of domestic circuits. They measure the electricity flowing down the live and neutral conductors, and automatically disconnect the supply if there is an imbalance between the two. This is important, because any difference could be due to a fault causing electricity to flow to earth, potentially due to a person touching a live wire and receiving an electric shock. RCD’s typically operate at fault currents of 0.03 amps or more, and should disconnect the supply within a maximum of 0.3 seconds. RCDs do not themselves protect against overcurrent, so they tend to be used to protect a number of circuits, where each circuit has its own fuse or MCB. The TEST button should be checked at least every 6 months, to ensure it is is still operating properly.
RCBO – Residual Current circuit Breaker with Overload protection
This combines the features of an MCB and and RCD in a single package. The main benefit of this is that if a fault causes one circuit to ‘trip’, power will still be available on all other circuits, so you’re not left completely in the dark! When fitted, they look similar to MCBs, but have a TEST button, like an RCD.
SPD – Surge protection device
Fitted in the consumer unit or at the origin of the supply, this device helps protects your electrical equipment from high voltage spikes that may be caused by lightning strikes or other electromagnetic phenomena. The SPD module will tend to have a little window, showing a green 'flag', this tells us that the SPD is working and does not need to be replaced. They do not have any switches or buttons.
AFDD – Arc Fault Detection Device
This relatively recent development to RCBO modules identifies the signature of an electrical arc – essentially where a bad connection is sparking. This is a dangerous situation that can easily cause fires, particularly in wooden framed buildings. AFDDs appear very similar to RCBO modules, but they do cost significantly more!
FCAH – Fingers Crossed And Hope!
Okay, so I made this one up. Despite that, many people do not know about their electrical protection, so this becomes the default. If you don’t know what kind of protective devices you have in your home, this could be you!
Why it's important
Let's put some of the above numbers into context. Whilst fortunately it is quite unlikely, the worst case scenario is an electric shock that involves passing mains electric current directly through the human body. If this was to occur, a fault current of more than just 0.1 amps would sadly most likely result in death.
However small the chances of this occurring, there is a simple, inexpensive and reliable way to avoid such a catastrophe. Fit RCD protection to every circuit in your home. RCDs (and RCBOs) are specifically designed to automatically disconnect the supply before a potentially fatal shock occurs. I strongly recommend RCD or RCBO protection for all domestic circuits, as part of a well designed and maintained system. Fuses and MCBs do a great job of protecting wiring and reducing the likelihood of electrical fires, but if the worst should happen, they do not offer sufficient protection for the most important part of your home - you and your family.
If you have any questions about the safety of your electrical installation, give me a call. I’ll happily come and inspect your home, and give you my honest opinion about what (if anything) you might want to consider doing to upgrade your protection.