The use of 30 milliampere RCDs has been commonplace.RCDs used to be called ELCBs –
earth leakage circuit breakers.
Safety switches
monitor the leakage of electrical current to earth through faulty
appliances or incorrect wiring and disconnect the power quickly.
A safety switch can cut off power in 30 milliseconds - a 30th of a heart beat.
If
a fault occurs in an appliance or wiring causing current to flow to
earth - perhaps through a person - the switch's earth leakage sensor
responds to the imbalance of current and cuts the power.
However, the passage of 30mA through a person, even for only 30 milliseconds,
may be painful. Unfortunately, for the RCD to work when a person is
involved, this has to happen! If the person affected is on a ladder or
in a similar elevated situation this shock may cause a fall, which could
lead to further injuries!
Over the years the mining and quarrying
industry has become familiar with, and in some cases, over-dependent,
on these devices. It appears as if people are relying purely on the RCD to
protect them rather than ensuring that the equipment is being used
correctly. One incident occurred recently where a contractor using a
portable device which had no "Test or Tag" label stated emphatically
that it was not necessary as the outlet he was using was protected by a
30mA RCD! There have been several reported incidents where portable
appliances and/or their power leads have been subject to excessive
moisture and the operator felt a tingle. Fortunately the RCD worked and
no long-term ill effects occurred.
An RCD is an electro-mechanical
device that is inherently extremely reliable, however, they can fail
and in this case the tingle may become more serious!
An RCD is there to isolate faulty electrical items; the primary barrier to prevent inadvertent contact with dangerous electrical conductors is the integrity of the insulation.
The
users of portable electrical appliances and/or electrical leads must
ensure that they are not subject to mechanical abuse or the ingress of
water. Testing and tagging should weed out damaged items but will not
eliminate misuse particularly if moisture is present. The user has the primary responsibility and obligation to visually check and use portable appliances in a safe manner.
NB: An RCD will not provide protection against a live to neutral fault!
Courtesy: Queensland department of mines:
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