After yarn, power is often a weaving unit's biggest running cost. The bill comes for the whole unit, so many units never know how much power went into a metre. This guide covers the formula, a full worked example, getting the real load from the bill, and ways to bring the cost down.
The formula
Power is sold in units (kWh): a 1 kW load running for 1 hour is 1 unit.
₹ a day = units × ₹ per unit
₹ per metre = ₹ a day ÷ (one loom's metres a day × looms)
₹ a month = ₹ a day × days
Example
24 waterjet looms, 2.5 kW each, running 24 hours a day. Power at ₹8 a unit — an example rate only; use the rate on your bill. Each loom weaves 373 m a day (600 RPM, 50 picks, 85%, two 12-hour shifts).
- Units a day: 2.5 × 24 × 24 = 1,440 units
- ₹ a day: 1,440 × 8 = ₹11,520
- Metres a day: 373 × 24 = 8,952 m
- ₹ per metre: 11,520 ÷ 8,952 = ₹1.29
- Month (30 days): 11,520 × 30 = ₹3,45,600
Put your own numbers into the Power cost per metre calculator. If you don't know the metres a day, get them first from the Loom Production calculator.
Get the real load from your bill
The kW on the motor plate is not the real load — a loom draws more at some times and less at others. The best way is a sub-meter on one loom. Without one, use the monthly bill:
Example
The bill shows 43,200 units for 24 looms, 30 days, 24 hours: 43,200 ÷ 24 ÷ 30 ÷ 24 = 2.5 kW per loom. This includes lights, fans and pumps — which is right, because that cost lands on the cloth too.
Besides the energy charge, a bill has fixed / demand charges and duty. So check once more: the bill's total ÷ the month's total metres. Say the bill is ₹3,60,000 (example) and the metres 8,952 × 30 = 2,68,560 — the real power cost is ₹1.34 a metre, above the ₹1.29 from the unit rate alone.
The compressor and pump share
On airjets, the compressor takes a large share of the power. Divide the compressor's units (from its sub-meter) among the airjet looms running and add that to each loom's kW — otherwise the airjet costing comes out far too low. On waterjets, the water pump, filters and treatment motors run too; share those over the looms as well. The right share depends on the loom model and setup — measure it on your meter, don't guess. For the difference, see the Waterjet vs Airjet guide.
Lower efficiency means more power per metre
If the same loom runs at 75% instead of 85%, its metres a day fall from 373 to 329.18 m. The power stays about the same — compressors, pumps and lights keep running. Per metre: one loom's ₹480 a day ÷ 329.18 = ₹1.46, ₹0.17 more on every metre. That's why the biggest power saving is often raising efficiency.
Ways to cut power
- Switch off idle looms. Waiting for a beam or a mechanic? Turn off the loom and its pump or air line.
- Air leaks. On airjets, leaks keep the compressor working for nothing. Listen to the air line at night when the looms are off.
- Only the pressure you need. Compressor pressure above what's needed costs extra power. Set it as the loom's maker advises.
- Power factor. Look for the power factor on your bill. If it's low there may be a penalty — have an electrician check the capacitors / panel. Your connection's rules are in the power company's tariff.
- Maintenance. Loose belts, dry bearings and dirty filters all add load to the motor. Oil and clean on a fixed day.
- Contract load. Take the load you need — too much wastes fixed charges, too little brings penalties. Read the tariff on your bill.
- Lights and fans. Swap old bulbs and tubes for LEDs — a small cost that saves every month.
Common mistakes
- Using the motor's kW. The plate kW isn't the real load. Take it from the bill or a sub-meter.
- Counting only the unit rate. Leave out fixed charges and duty and power per metre looks lower than it is.
- Forgetting the compressor or pump. The loom motor isn't all the power.
- Measuring once and assuming forever. When the quality, RPM or season changes, check again.
- Taking metres at 100%. Work out power per metre from metres actually woven.
In Loomiro
In Loomiro's Costing, set the loom's kW and your ₹ per unit once as defaults. The loom's metres a day come from RPM, efficiency and shift hours, and power per metre is worked out on them — in the full breakdown with yarn, wages and overheads. The "What if…" table shows how much the cost moves when efficiency changes.
The kW, ₹8 a unit and bill amount in this guide are examples only. Use the numbers from your own bill and meter, and confirm tariff rules with your power company.