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Ovi-Scan
Appendix B – Safety devices
Residual Current Devices (RCDs)
A Residual Current Device has two specific purposes:
1. To protect plant and equipment from fires started by (usually) low fault currents passing from
live to earth.
2. To prevent fatal electric shock to personnel by reducing to “safe” levels (not eliminating) the
value and length of time a person is exposed to current flow through the body.
An RCD does not detect over currents or short circuits and must be used in conjunction with
conventional circuit protection devices, which may be included in the same physical package. The most
common value of operating current for an RCD is 30 milliamps (mA).
An RCD should be tested by stimulating an earth fault condition which is independent of any test
facility within the device. The test push should be used at regular intervals in order to test the function
of the tripping mechanism. It does not test if the device will operate in the event of an earth fault.
Anti-Surge adapter
The function of the anti-surge adapter is to reduce the possibility of equipment damage caused by
voltage transients appearing on mains supply lines. These transients can be extremely large and if
the anti-surge device is not quick enough (nano-second operation) the transient can get through.
Transients can also be induced on local supply cables and extension leads. Therefore, fit the anti-surge
device close to the scanner.
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