Embed Size (px)
Citation preview
Earth leakage clamp applications Application note
Earth leakage clamp applications Causes of leakage currents Since there is no such thing as perfect insulation, if any conductor is raised to a potential above that of earth some current is bound to flow to earth from that conductor. The amount of current that flows is dependant on
� Voltage on the conductor
� The capacitive reactance between the conductor and earth
� Resistance between conductor and earth Currents that flow to earth are called leakage currents and are usually very small values. However the amount of current that is required to cause distress or harm to a human
being or animal is also small, these currents must be limited by circuit design to safe values. If this is not possible then an RCD (residual current device) is fitted for personal protection. An earth leakage clamp is generally a lightweight pocket size clamp meter designed to measure a.c. earth leakage currents. They enable earth leakage faults to be detected and located without having to isolate and disconnect circuit wiring. In addition, most of these clamps are capable of performing a.c. current tests like any normal clamp meter. The measurement of earth leakage can be conducted on single or three phase systems. .
The following applications show positions of conductors in respect to the jaws of the clamp.
Single Phase / Two Wire Circuits
This diagram illustrates the method of leakage measurement utilising the live and neutral.
The phase and neutral currents should ideally cancel each other out, showing zero leakage..
3 Phase circuits
3 phase circuit leakage can be conducted using a similar test to the single phase application.
For 3 wire circuits, clamp all 3 phases. For 4 wire circuits, include the neutral in the jaws.
.
Earth leakage clamp applications Application note
Earth Conductors
The diagram above illustrates earth leakage measurement by utilising the earth conductor only. The same principle can be used for 3 phase circuits.
It should be mentioned that this method will only measure the leakage current in the earth conductor, not the total leakage on the system.
A.C. Current
As previously mentioned some earth leakage clamps can be used as a standard current clamp meter by simply clamping the phase in the jaws.
UK
Archcliffe Road Dover
CT17 9EN England
T +44 (0) 1304 502101
F +44 (0) 1304 207342
UNITED STATES
4271 Bronze Way
Dallas TX 75237-1019 USA
T 800 723 2861 (USA only)
T +1 214 333 3201
F +1 214 331 7399
OTHER TECHNICAL SALES OFFICES
Valley Forge USA, College Station USA, Sydney
AUSTRALIA, Täby SWEDEN, Ontario CANADA,
Trappes FRANCE, Oberursel GERMANY, Aargau
SWITZERLAND, Kingdom of BAHRAIN, Mumbai
INDIA, Johannesburg SOUTH AFRICA, Chonburi
THAILAND
CERTIFICATION ISO
Registered to ISO 9001:2008 Cert. no. Q 09250
Registered to ISO 14001-2004 Cert. no. EMS 61597
DET300E_AN_en_V02 www.megger.com
Megger is a registered trademark
