Temporary Electricity Use On Construction Sites: How To Calculate How Many Large Generators Need To Be Purchased (or Rented)? Even Beginners Can Understand If They Read Carefully.

Temporary electricity use on construction sites: How to calculate how many large generators need to be purchased (or rented)? Even beginners can understand if they read carefully.

 

Many contractors choose diesel generator sets based on intuition, either ending up with equipment that can't be powered or incurring excessive costs. Now, Xiao Huang, drawing on years of experience, summarizes and personally teaches newcomers how to calculate the total equipment power and determine the reserve power for starting current, so that after reading it they are no longer confused.

 

Ⅰ. Step 1: List all construction electrical equipment.

 

Common load classifications on the site are registered, and the rated power is recorded against the nameplate. Do not omit lighting, dormitory air conditioners, or small power tools.

 

1. Motors (impulse load): air compressors, mixers, water pumps, cutting machines, with very high starting current;

 

2. Resistive loads: welding machines, lighting, heaters, which start without shock;

 

3. Small single-phase equipment: dormitory fans and chargers; if power is low, they can be consolidated together. Here's a simple site checklist:

1pcs 15kW air compressor,

2 pcs 7.5kW mixers,

3 pcs 5kW welding machines,

total lighting power 4kW.

 

Ⅱ. Step 2: Calculate the total steady-state operating power

 

Sum the rated power of all equipment to get the total normal operating load.

Example calculation:

15 +7.5×2 +5×3+4 = 44kW.

 

Tip: Not all equipment on the site will run 24 hours a day. Multiple devices are used staggered, multiplying by a coefficient of 0.7~0.9 to reduce overpriced selection.

 

Ⅲ. Step 3: Focus on calculating the motor startup peak value (most common pitfall).

 

The motor's power at startup is 2~3 times normal operation; directly starting an old air compressor can reach up to 3 times or more. If the unit's power cannot withstand the peak, it will trip directly and shut down.

 

Rule: The unit's rated power must exceed the maximum single motor starting power

The largest equipment in the example is a 15kW air compressor, with a startup peak value = 15×3 = 45kW.

This step can filter out many smaller units; even if the total load is only 44kW, 40kW units should not be selected.

 

Ⅳ. Step 4: Stack safety margin to determine final unit power.

 

When construction site units operate at full load for long periods throughout the day, a 20%-30% safety margin must be reserved to offset line losses, power loss due to high temperatures, and later equipment additions.

 

General calculation formula: Demand power = Steady-state total power ×1.2 (base margin) Example: 44×1.2 = 52.8kW, so the unit is recommended to be 60-75KW

Ⅴ. Three key points for beginners to avoid when choosing a model

 

1. Distinguish between kW and kVA: The generator nameplate is marked with kVA, industry power factor is 0.8, 100kVA = 80kW, don't confuse the unit with sellers;

 

2. Add extra capacity at high-altitude construction sites: Above 1000 meters altitude, engine output decreases, increasing power by an extra 10%;

 

3. Prioritize commonly used power; backup power is only for emergencies and cannot be used for long-term full load construction.

 

Conclusion

Many business owners rent units only by adding total equipment power, which can cause frequent trips and delay construction periods, while severe overhauls can increase costs due to high temperatures. Using this three-step calculation method, you can match the construction load without spending extra money renting high-power units and wasting fuel.

 

For issues such as generator selection, load balancing, and fuel consumption calculation on construction sites, feel free to leave a message in the backend for inquiries and continuously update practical information on construction site power supply.