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ET351 · Earthing and Residual Current Protection

Experimental Apparatus for the Study of Earthing and Residual Current Protection

A modular apparatus for the study of earthing and of the 30 mA residual current circuit breaker in a domestic installation. Diagrams printed on the modules trace the supply from a medium/low-voltage transformer substation to a house. The student plugs resistive dipoles into the modules to set two earth resistances and two fault resistances, then sees from an LED on a printed human figure whether the leakage current would be dangerous. Everything runs at safety extra-low voltage from an isolating transformer, so nobody touches mains voltage during an experiment.
Description
    The ET351 builds a TT supply chain from panel modules on a mobile frame. The transformer module carries a printed diagram of the public network, with the MV/LV substation and its earthed neutral. Two transmission-line modules take the supply to a domestic installation. Two modules with a 30 mA residual current circuit breaker simulate a washing machine with a metal enclosure. On the human-figure module an LED at the heart lights when a dangerous leakage current flows through the person. The student moves dipoles on the dipole holder module to set the earth resistance and the fault resistance, and measures every current and voltage on 4 mm safety sockets.
Features
  • modular panels with printed synoptic diagrams and 4 mm safety sockets
  • safety extra-low voltage from an isolating transformer, 230 V AC / 24 V AC
  • two earth resistances and two fault resistances, set with plug-in dipoles
  • four free dipole positions for the user's own resistors
  • 30 mA residual current circuit breaker with washing-machine simulation
  • human figure with an LED at the heart that lights on a dangerous leakage current
  • mobile frame with cable holder and single-phase power console
  • measurements possible in dusty conditions
Specifications
    Power supply 230 V, 50 Hz
    Transformer module 230 V AC / 24 V AC, isolating
    Fault resistances 1 × 10 Ω and 1 × 2 kΩ
    Earth resistances 100 Ω and 5 Ω, plus 4 free positions
    Residual current device 30 mA, on 2 modules
    Mobile frame H 1610 × L 940 × W 600 mm, with cable holder
    Power console single-phase; 16 A thermal-magnetic circuit breaker, key-operated emergency stop button, push-button with LED indicator
    Outlets 1 single-phase 230 V output on 4 mm safety terminals; 2 × 230 V AC (2P+E) sockets and 12 × 230 V AC (2P+E) sockets at the rear
    Mains connection 3 m cable with 2P+E plug, 230 V, 50/60 Hz
230V
L 940 W 600 H 1610 mm
Learning objectives / experiments
  • risk of electrocution on indirect contact
  • how the quality of the earth connection changes that risk
  • role of a 30 mA residual current circuit breaker in a domestic installation
  • TT system, with the neutral earthed at the substation and the exposed conductive parts earthed at the consumer
  • experiments with earth and insulation faults
    • insulation fault with no earth connection
    • earth below 100 Ω with a dead insulation fault, where a fault current above 30 mA trips the residual current device
    • earth below 100 Ω with a partial insulation fault, where the fault current stays below 30 mA and the student measures the current through the person
    • earth above 100 Ω with a partial insulation fault, with measurement of the touch voltage and of the current through the person
Scope of delivery
  • 1 transformer module 230 V AC / 24 V AC with printed public-network diagram
  • 2 transmission-line modules, substation to domestic installation
  • 2 modules with 30 mA residual current circuit breaker and washing-machine simulation
  • 1 module with printed human figure and heart LED
  • 1 dipole holder module with earth resistances 100 Ω and 5 Ω, fault resistances 10 Ω and 2 kΩ, and 4 free positions
  • 1 set of safety measuring leads
  • 1 mobile frame with cable holder
  • 1 single-phase power console
  • 1 set of instructional material

All components and accessories listed under Scope of delivery are supplied, whether or not they are visible in the illustrations.

Required for operation
  • 230 V, 50 Hz, 1 phase, socket with protective earth