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Health and Safety
Published in Trevor Linsley, Electronic Servicing and Repairs, 2014
An RCD is an electrical safety device which constantly monitors the balance of the current through two coils connected to the live and neutral conductors of the load. In a healthy circuit these live and neutral currents balance, but if a fault occurs the balance is lost and a trip circuit opens a double pole switch to isolate the load. Modern RCDs designed to protect people have tripping current sensitivities of 30 mA and, therefore, a faulty circuit can be isolated very quickly before the lethal limit to human beings of 50 mA is reached. (See the section on Electric Shock later in this chapter.)
Health and safety in electrical installation
Published in Peter Roberts, Electrical Installation Work, 2017
A further safety device, known as a Residual Current Device (RCD), operates if it senses that current is travelling down the earthing system, rather than being returned to the supply through the neutral conductor as it would normally. Various ratings of RCD are installed in different locations. For instance, socket outlets must be protected by an RCD rated at 30 mA, but other ratings such as 100 mA are also used when safeguarding the input supplies to 110 V safety transformers.
C&G Unit 203: Electrical installations technology and renewable energy systems
Published in Trevor Linsley, Basic Electrical Installation Work, 2018
An RCD is a type of circuit-breaker that continuously compares the current in the line and neutral conductors of the circuit. The currents in a healthy circuit will be equal, but in a circuit that develops a fault, some current will flow to earth and the line and neutral currents will no longer balance. The RCD detects the imbalance and disconnects the circuit. Figure 3.33 shows an RCD’s construction.
Calibration of Residual Current Device (RCD) Testers
Published in NCSLI Measure, 2018
The schematic diagram of an RCD is shown in Figure 1. The RCD monitors the unbalanced current of the live and neutral terminals of the electric circuit. If there is a leakage current flowing from the live terminal to the earth terminal, as illustrated by the dotted line, the current that flows between the live terminal and the neutral terminal will become unbalanced. When this unbalanced current exceeds the residual current setting of the RCD, an out-of-balance flux is created in the current sensing toroid. This will induce a current in the sensing winding, and will trigger the relay to disconnect the load from the power line. Depending on the end users’ applications and requirements, different RCD types are available in the market. Some commonly used RCD types are listed in Table 1.