Circuit training

Electrical contractors are the masters of electrical power. They are also responsible for protecting themselves, and millions of end-users, from its potential dangers.

According to government studies into fatalities and injuries involving electricity there are, on average, around 81 deaths per year, with 25 resulting from the 12 500 fires caused by faulty electrical installations. Serious injuries are now running at an all-time high – 4562 per year. 590 of these injuries result from fires caused by electrical faults, which leaves approximately 3970 people who are electrocuted each year and live to tell the tale.

With statistics like these, poor earthing, bad design, faulty equipment, incorrect installation and an uneducated selection of circuit protection devices is totally unacceptable.

The rcbo solution
To overcome the possibility of electrical fire or electrocution, a residual current device (rcd) could be installed. Even better still, you could use a residual circuit-breaker overload (rcbo), giving the same protection as a miniature circuit breaker (mcb) and rcd combined. But, I hear you cry, "both rcds and rcbos are two modules wide and therefore space would be a problem". Thankfully, Contactum has the answer – a one module rcbo. This is the same width as a mcb and therefore fits the same space.

RCBOs receive little in the way of editorial coverage, despite the fact that they can save lives and eliminate the risk of serious injuries. RCBOs are super-efficient safety devices that merit the most serious consideration by electrical contractors. The forerunner to today's rcbo was developed in the late 1950s. Although the latest generation, one module rcbo has been around for about ten years, I still meet electrical contractors who seem unaware of their existence, which makes me think that we manufacturers have failed to communicate the product benefits effectively.

One module rcbos work like any other mcb and rcd, with the magnetic characteristics available in B, C and D type and a thermal operation for overload, just like an mcb. The earth leakage side of the rcbo is dealt with by electronic detection and has the sensitivities that you would find on an rcd, eg 10, 30 and 100 mA for contractors to select, as they would when complying with our beloved Bible, the 16th Edition of the Wiring Regulations.

The one module rcbo is voltage dependent, so it will need a minimum of 120 V to operate. It has a switched live and a solid neutral. The latest generation Contactum rcbo is designed to go through some 4000 electrical and 20 000 mechanical operations. The mechanism is of a 'trip free' nature, so when it is subjected to fault conditions the dolly switch cannot close the contact until the fault is cleared. Positive contact status indication is in the form of a red and green flag, which is connected to the internal mechanisms and operates totally independently from the dolly switch.

The new Contactum rcbo is 17·5 mm wide. So, when space in the consumer unit or enclosure is getting tight and you need an mcb and an rcd, then an rcbo is a perfect solution.

A 950 mm flying neutral lead (sometimes called a pigtail) is attached to the neutral bar in the usual manner, with both load, live and neutral connecting into the top of the rcbo.

The Contactum one module rcbo can be released from its consumer unit or enclosures' full DIN-rail mount position without having to drop the busbar via the unique design of its three-position DIN-rail clip.

A one module rcbo is, in my opinion, the neatest and most cost-efficient solution in the circuit protection field. I therefore urge readers, as a matter of life and death, to give rcbos their closer study and consideration.