How can a circuit still be energised when it is clearly switched off? ….Answer ? when it is an incorrectly installed Ring Circuit! This week we have had the not so unusual occurrence of a ring circuit that when installed or modified the conductors have been mixed up with another Ring Circuit. For the circuit to be fully isolated two MCB’s* would be required to be switched off making the protective device ineffective for its purpose.
The Ring Circuit was introduced in the early 1940’s due to its efficient use of copper and its flexibility for installation. It is still the most common circuit used for sockets in the UK to this day! Installed correctly the circuit makes use of two conductors running in parallel for the Line, Neutral and Earth conductors. In the instance of our fault of the week, one single conductor from one leg of the circuit had been mixed up with another leg of a completely different circuit.
A Ring Circuit that has been incorrectly wired in this manner poses a number of hazards. Firstly in the event of a fault to an appliance the circuit protection (MCB) would not operate therefore leading to a possible overload. Also, during maintenance, should **Safe Isolation not be correctly undertaken the circuit would remain live even though appearing switched off to the maintenance personnel.
Veriserv recommend that only competent electricians undertake maintenance work on electrical circuits.
Photograph(s)
MCB for the fuseboard that is clearly switched off and the microwave oven that is plugged into the circuit that remains switched on & energised.
Our mission is to provide every single customer with an outstanding service that is fit for purpose and delivered by experts to reduce risk. As you can see from our other faults of the week, regular visits from a professional can cut down the risk of electrical faults, fire and disrupted security, to you and your workplace.
So if you know you are due a service, or have some concerns about your premises, please call 01543 225306, or fill out one of our contact forms to arrange a free assessment of your premises, with one of our fully trained engineers.
References
*MCB- Miniature Circuit Breaker (as shown in the photograph) also referred to as “over-current protective device”
**Safe Isolation- proving dead (not energised) in accordance with Electricity at Work Regulations 1989 regulation 12
