Ampcontrol 115161, User Manual

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ELDB006R9 15/07/2015 17:44
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Ampcontrol Electronics
ELDB006R9 ELD V2 USER MANUAL
Rev 9
– 03/14, ECN: 10573
A definite time operating characteristic is provided with adjustable trip sensitivity and time delay.
Time delay between protective units is introduced to allow the unit close to the fault to isolate the faulty
circuit without causing the healthy part of the system to be de-energised.
4.2 Earth Leakage Systems
Desirable though it may be, it is impractical to provide automatic protection against electrocution as a
result of direct contact with a live conductor, particularly where the electrical reticulation is exposed to a
humid or damp atmosphere.
The table below (taken from IEC Standards) indicates the current values affecting human beings.
Current mA Symptom
1 or less Causes no sensation - not felt
1 to 8
Sensation of shock, not painful, individual can let go at will, as muscular
control is not lost
8 to 15 Painful shock, individual can let go at will, as muscular control is not lost
15 to 20 Painful shock, muscular control of adjacent muscles lost, cannot let go
20 to 50 Painful, severe muscular contractions, breathing difficult
50 to 100
(possible)
100 to 200
(certain)
Ventricular fibrillation (a heart condition that may result in death)
200 and over
Severe burns, severe muscular contractions; so severe that chest
muscles clamp the heart and stop it for the duration of the shock (this
prevents ventricular fibrillation).
It can be seen from the previous table that the passage of a current of as low as 15mA through the
human body can cause loss of muscular control to the extent of preventing the recipient from
disengaging from the live conductor. Whereas a current in excess of 50mA is sufficient to produce a
critical heart condition from which there is little or no chance of recovery.
It follows that as an effective safeguard against electrocution resulting from direct contact with a live
conductor, it would be necessary to introduce earth leakage protection designed to operate with a fault
current below 15mA, which in the majority of cases, would be impractical.
The automatic protection of circuits is not intended to take the place of sound installation practice and
the regular maintenance and testing of electrical apparatus.
Care must be taken in the selection and installation of all electrical equipment with due regard to its
required duty and the conditions under which it may be called upon to operate.
Where automatic earth leakage protection has been installed it is essential that its operation be tested
often, and to facilitate this, a means for testing is incorporated in all approved earth leakage relays.
4.3 Methods of Earth Leakage Protection
Earth Leakage Protection Relays for use in mining applications have to be designed and tested to
AS/NZS 2081:2011 for use on fault limited systems.
There are two methods of protection used, Core Balance and Series Neutral earth leakage protection
systems. A relay installed in Core Balance applications performs the primary protection in an installation,
protecting the outlet supplying power to a machine. In this application the time delay is set at
instantaneous. Series Neutral earth leakage provides backup protection for the installation and can have
a time delay up to a maximum of 500mS.