Metering, Service Connections and Consumer Installations
Domain 9 - Metering, Service Connections and Consumer Installations. Expect questions on service line sizing, meter selection and connection, sealing and accuracy testing.
Rules and practice
- A service connection starts with the application, sanctioned load and the test report of internal wiring; supply is released under IE Rule 50 only when the installation is safe.
- Single-phase 240 V two-wire for small loads; three-phase 415 V four-wire for motors and larger loads; CT-operated meters where current exceeds the direct-connected range, commonly above 60–100 A.
- Meter types: static single-phase and three-phase, kWh or kVAh, TOD, prepaid, and net metering for rooftop solar. Accuracy classes 1.0 and 2.0; the meter constant in rev/kWh or pulses/kWh verifies accuracy.
- The meter is sealed, the service cable is sized for the sanctioned load, and three-phase installations need two earths plus an RCCB.
Worked example
A meter marked 3200 rev/kWh is tested on a 2 kW load. Expected revolutions per hour = 2 × 3200 = 6400, so 10 revolutions should take 10 × 3600/6400 = 5.6 s. If the disc completes them in 4.5 s the meter is fast by (5.6 − 4.5)/5.6 ≈ 20%, and it must be replaced and the account adjusted.
Traps
- Inverting the meter constant, so a fast meter looks slow.
- Testing with a load that varies during the count.
- Connecting the meter with the load on the supply side, bypassing registration.
- Breaking seals without recording it, which is a serious irregularity.
- Forgetting the CT multiplier on a CT-operated meter, so readings are wrong by the ratio.