Wiring and Connection Practices
Domain 6: Wiring and Connection Practices
This domain tests correct meter wiring for single-phase and three-phase services, CT connections and safe isolation.
Core rules
- Single-phase: supply phase to line-in, supply neutral to neutral-in; load phase and neutral from load-out terminals. Polarity must not be reversed.
- Three-phase: connect R, Y, B and neutral in sequence; confirm phase sequence and voltages of about 415 V between phases and 230 V phase-to-neutral.
- For CT-operated meters, CT secondary leads go to meter current terminals; use shorting links before removing the meter. Never open a live CT secondary.
- Use correct cable size, ferrules, crimped lugs and torque; keep CT burden within the meter rating.
- Test continuity and insulation before energizing.
Worked example
A CT-operated meter reads 10 kWh on a 200/5 CT. The CT ratio is 40, so primary energy is 10 × 40 = 400 kWh. If a PT ratio of 100 is also present, primary energy is 400 × 100 = 40,000 kWh. Reasoning: the meter registers secondary quantities; both ratios multiply the register.
Traps that cost marks
- Opening a CT secondary under load, which creates dangerous high voltage.
- Reversing CT polarity.
- Connecting load to supply terminals.
- Sharing a neutral with another consumer.
- Ignoring the PT ratio.