Consumer units house the main switch and circuit protection supplying accessories inside your home or business. Circuits need protection from:
Overload – over-current in a circuit that is otherwise OK. If you have ever got something stuck in your smoothie machine with your finger still on the blend button and the fuse blew – that is an overload. The fuse is designed to be the weakest link. Its job is to blow before the smoothie blenders flex has chance to warm up and pose a fire risk. But that’s all it will do.
Additional protection – for a user coming in to contact with a live conductor. Imagine you came in to contact with mains voltage through no fault of your own. Residual current devices were designed to reduce the risk of electrocution and fire. RCDs and RCBOS are ways of providing this additional protection and this article covers the benefits of installing a consumer unit with only rcbos.
Why install a consumer unit with only rcbos?
To understand why i always recommend installing RCBO consumer units i want you to take a look at a dual rcd consumer unit first. In the photo below you can see a consumer unit with two rcds (noted by the yellow “Test Regularly” button). Lets just assume a fault develops on the cooker (circuit number one in this instance) and the rcd trips. It will remove the power from the cooker, first floor lights and sockets. Bit of a pain until you get it fixed! If it’s an intermittent fault, it might not be obvious the fault is with the cooker. Until it has been diagnosed and isolated, repaired or replaced that means intermittent power issues with circuits two and three as well.
The other challenge with this type of consumer unit is that the more circuits protected by one device; the more natural earth leakage and therefore the greater chance of experiencing an rcd trip – loss of power. Some devices leak small amounts of current to earth even when new. Although the amount per device may not be harmful to a user, when added up in a busy household that can sometimes be close to the tripping threshold. Now take a look at a consumer unit from a much larger domestic property:
Lots of devices resulting at this property in Cathays (photograph, when added, together above). There was not one specific fault; just a lot of devices attached that when added together meant the rcd was near or on its threshold. The solution was to replace it with a full rcbo model like this:
How much more do rcbo consumer units cost?
The price of rcbos have dropped over the last few years. At the time of writing (November 2019) they are currently around £15 each. Circuit breakers are approximately £2.50 each with an rcd costing around £35. So, in a consumer unit with ten circuits the cost difference is:
Dual rcd AMD3 consumer unit. Two rcds with ten circuit breakers: £98
AMD3 consumer unit with 10 rcbos: £196
So, yes, a full rcbo consumer unit will cost more than a dual rcd type but worth it in my opinion. From the users perspective in the event of a fault, you will only loose the one circuit. It can also save you time and money on any troubleshooting; the circuit that is off is the one that needs to be investigated should you need to call an electrician.
If you need a new consumer unit installed in your Cardiff home or business please get in touch.