7.9 Electrical wiring and earthing
Key idea: Correct supply, protection and earthing keep the installer, the user and the compressor safe.
A heat pump draws high current, has a compressor motor and often an inverter drive. Undersized cables, missing earths and wrong protection cause trips, burnt terminals and electric shock. All electrical work must follow the Indian Electricity Rules / CEA regulations and the earthing code IS 3043, and be done by a licensed electrician.
Main items
- Dedicated circuit from the distribution board (DB) with its own breaker.
- MCB (miniature circuit breaker) rated for the unit. Motor loads often need C or D curve; follow the manual's MOCP (maximum over-current protection) value.
- RCD / RCCB (residual current device), typically 30 mA for personal protection. Inverter units may need a Type B or another type the manufacturer specifies.
- Local isolator within sight of the unit, lockable for service.
- Phase sequence check on three-phase units. Scroll compressors run backwards on the wrong sequence, get noisy and fail.
- Earthing: a low-resistance earth conductor to the unit frame and a tested earth pit. Bond metal pipework.
- Control and sensor cables run separately from power cables, or shielded, to avoid noise.
- Glands and drip loops: cables enter from below with a drip loop so rain does not run into the panel.
| Check | Typical acceptable value | Tool |
|---|---|---|
| Supply voltage, single-phase | 230 V ± 10% | Multimeter |
| Supply voltage, three-phase | 415 V ± 10%, phase imbalance under ~2% | Multimeter |
| Neutral–earth voltage | Under ~2 V (typical good practice) | Multimeter |
| Earth resistance | As low as practical; follow local inspector (a few ohms or less is common) | Earth tester |
| Insulation resistance of compressor | Above 1 MΩ typical (check manual) | Insulation tester (megger) |
| Voltage drop along cable | Within ~3–5% typical | Calculation / measurement |
Worked example — current and breaker for a three-phase unit
A unit in Ahmedabad draws 10 kW electrical input at full load on a 415 V supply, power factor 0.9.
- I = 10,000 ÷ (1.732 × 415 × 0.9) = 10,000 ÷ 647 = 15.5 A per phase.
- Breaker: next standard size above full-load current, but not above the manual's MOCP. A 20 A C/D-curve MCB is a typical choice.
- Cable: 4 mm² copper is a typical choice for 20 A on a short run. Check voltage drop on runs over about 30 m and upsize if needed.
- Confirm with the nameplate maximum current, which can be higher than the rated current.
Remember
- Dedicated circuit, correct MCB, RCD and lockable isolator.
- Check phase sequence before first start on three-phase units.
- Test earth resistance and insulation resistance; record the values.
- Separate control cables from power cables.
Common mistake: Using the neutral as earth, or no earth at all. The frame can become live and the electronics fail.
Correct supply, protection and earthing keep the installer, the user and the compressor safe.
Rating
There are no comments for now.
to be the first to leave a comment.