5.9.1 - Why do we need residual current devices?
{5.3}
has stressed that the standard method of protection
is to make sure that an earth fault results in a fault current
high enough to operate the protective device quickly so
that fatal shock is prevented. However, there are cases
where the impedance of the earth-fault loop, or the impedance
of the fault itself, are too high to enable enough fault
current to flow. In such a case, either:
1. - current will continue to flow
to earth, perhaps generating enough heat to start a fire,
or
2. - metalwork which is open to
touch may be at a high potential relative to earth, resulting
in severe shock danger.
Either or both of these possibilities can
be removed by the installation of a residual current device
(RCD).
In recent years there has been an enormous
increase in the use of initials for residual current devices
of all kinds. The following list, which is not exhaustive,
may be helpful to readers:
| RCD |
residual current device |
| RCCD |
residual current operated circuit
breaker |
| SRCD |
socket outlet incorporating an RCD |
| PRCD |
portable RCD, usually an RCD incorporated
into a plug |
| RCBO |
an RCCD which includes overcurrent
protection |
| SRCBO |
a socket outlet incorporating an
RCBO |
|