RCD circuit breakers are also referred to as residual current circuit breakers. In the case of intact electrical devices, the electric currents in the outgoing and return conductors are always the same strength. If an incident occurs, such as if someone touches live parts, there is a difference between the outgoing and return current — and the RCD interrupts the circuit completely.
This is usually done even in very low differences around 30 milliamps. The lower the value, the quicker the shutdown. Common residual current circuit breakers react in less than 40 milliseconds. Normal fuses fuse and line circuit breakers normally only interrupt the circuit at current levels above the specified rated current, as in the event of short-circuits for example.
This is sufficient to avoid cable fires. However, they do not protect people effectively against life-threatening electric shocks. When carrying out alterations to a switchboard, where a amp MCB was installed on a 2. Clause 2. When determining what an increased risk of electric shock is, what guidelines do I use? When determining what type of electrical equipment or appliance that is permanently connected to supply will cause an increased risk to the user, the following steps are recommended:.
If yes to any of the above, then install an RCD on the final sub circuit. Question 6. Do I need to provide the 1m clearance from the end of the open door of the switchboard?
No, clearance from the end of a switchboard doors in non-domestic and non-residential is are as per clause 2. In a domestic electrical installation this distance may be reduced to 0.
Do I need to provide an RCD on a car hoist in a mechanical workshop? Answer: -. Yes, an RCD is required on the final subcircuit as the steel hoist with the motor attached is deemed to represent an increased risk of electric shock to the user. This applies to a final subcircuit supplying the hoist up to and including 32 Amps. However, if you look at Chapter 13 of BS you will find that it contains copious warnings about external influences on an installation to help you ensure that what you do does not make an installation unsafe or compromised.
Regulations Appendix 5 External Influences contains lots of items that can affect an electrical installation. So, do you think with all the onslaught of modern technology and the drive for smart homes, we are adequately considering and taking all precautions required in terms of our methods of protection? With all the modern technology that is now installed into domestic installations, would you ever have thought that DC current could be a real issue for you?
DC has a tendency to leak to earth. When it does, it immediately becomes an AM7 external influence under the categories in Appendix 5. If this does happen, your RCD, in whatever form you use, will NOT perform to the requirements of the standard it is made to. In a nutshell, it becomes less safe —the greater the DC current the bigger the effect. AC: this device ensures tripping for residual AC currents whether sudden or rising; this is standard in most domestic installations.
The marking for this is shown below. Disconnection of the circuit would create a greater danger traffic lights iii. The final sub-circuit is used for specific equipment where tripping is unacceptable, provided that the outlet is in a position not likely to be accessed and is clearly marked Alterations and switchboard replacements all installations : a.
If an alteration to an existing circuit or a switchboard replacement is undertaken, RCD protection is required b. Where socket outlets are added to an existing circuit, the RCD need only be installed at the commencement of the new additional wiring c.
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