A 3 HP Conveyor on a Lighting Circuit

Full-load current. Input power = output / efficiency = (3 × 746) / 0.85 = 2,238 / 0.85 ≈ 2,633 W. For a three-phase motor:

I = P / (√3 × V × cos φ) = 2,633 / (1.732 × 415 × 0.80) ≈ 4.6 A

Assessment of the 32 A fuse. That is roughly seven times full-load current. It is not a protection device for this motor at all - it is a switch that will one day fail to operate. The 2.5 mm² cable is comfortably rated for 4.6 A, so the fuse is not there to protect the cable either.

What should be done instead:

1. Find the cause of the trips. A motor that stops under load is usually telling you something: a jammed belt, an over-tight belt, a dry or failed bearing, product build-up at the skirt, single-phasing, or a voltage dip on a long lighting circuit. Uprating the fuse converts a nuisance trip into a burnt winding or a fire.
2. Protect correctly. A dedicated 3-phase circuit with a 6 A (or 10 A) MCB and a thermal overload relay set at the motor's nameplate full-load current; an isolator at the machine.
3. Record it. Note the nameplate current; if it differs materially from 4.6 A, the motor has been rewound or the phase supply is unbalanced and the machine should come out of service pending a supply test.

Risk order (worst first):

1. Damaged flexible cable with taped live cores - potential electrocution of anyone handling the cable or standing in water. Control: take the conveyor out of service immediately, isolate and lock off, and replace the cable. A taped repair on a trailing cable in a wet godown is never acceptable.
2. No residual-current protection on a portable appliance circuit. Control: 30 mA RCCB on the circuit, and an earth continuity test before the machine is returned to use. The intact earth core is the only thing that has prevented a serious incident so far - it is not a control, it is luck.
3. Plug-top adaptor from a 15 A plug into a 20 A lighting circuit. Control: industrial plug and socket matched to the machine, on a dedicated circuit, with the cable routed overhead or in a cable ramp rather than across a truck path.
4. Bare nip point at the discharge head pulley. Control: fixed guard, interlocked if access is needed; guarding is a machine-safety requirement, not a housekeeping preference.
5. Emergency stop only at the tail end. Control: stops at both ends, or a pull-cord along the full length, so an operator at the discharge end can stop the belt without walking past the moving belt.
6. Operator competence. Control: only a trained, authorised operator starts the conveyor, and the start-up alarm or call-out is used because the belt cannot be seen from the tail end.

Required rate. 600 bags in 3 hours = 200 bags per hour.

Offered rate. 15 workers × 8 bags per hour = 120 bags per hour, i.e. 360 bags in the three hours.

Shortfall. 600 − 360 = 240 bags, which at 8 bags per worker-hour needs 30 more worker-hours - or 10 more workers for the same three hours.

Minimum viable crew = 200 / 8 = 25 workers (15 + 10). Any figure below 25 means the trucks wait or the last 240 bags are moved in a rush at the end of the window, which is exactly when 50 kg manual handling injuries happen.

Advice, in order:

1. Repair and re-commission the conveyor - it moves 600 bags in a fraction of the time and removes the manual handling exposure altogether. That is the correct answer to a 3-hour window; more labour is the fallback.
2. If manual work is unavoidable, engage 25 workers with staggered rest, two supervisors, a clear walkway and no stacking above shoulder height during the rush.
3. Do not accept the contractor's 15 and 'make up the balance later'. The rate stated by the contractor is itself an average that assumes rest; squeezing it is how the rest gets dropped.