By type
Three Phase Generators
Three phase sets for workshops, factories and larger buildings, where the sizing case is the largest motor start and the commonest fault is a set unbalanced across its phases.
Suits
- Workshops with lathes, compressors or welding plant
- Factories and light industry
- Cold rooms and refrigeration plant
- Buildings with lifts and large pumps
Sized by the biggest start, not by consumption
The commonest and costliest mistake on a three-phase installation is sizing from the electricity bill. Consumption tells you what the plant used over a month. It says nothing about the instant a 15 kW compressor starts direct-on-line and demands six to eight times its running current.
A set chosen on consumption dips its voltage when that motor starts, and the dip drops contactors across the whole plant. The symptom presents as a mysterious fault; the cause is arithmetic done on the wrong number.
So the sizing sequence is the largest motor start first, then the total running load, then a margin for what the business will add in three years.
Starters are often cheaper than kVA
Before buying the next size of generator, price a star-delta or soft starter on the largest motor. Reducing the starting current is frequently a fraction of the cost of the extra generator capacity that would otherwise be needed to absorb it, and it is kinder to the motor and the driven machine as well.
Balance across the phases
A three-phase set feeding a building full of single-phase loads needs those loads distributed deliberately. Left to chance they cluster, one winding runs hot, and the lightly loaded phases drift high enough to shorten the life of whatever is connected to them.
This is unglamorous work with a real payback, and it is the part most often skipped when a set is installed in a hurry.
Compliance
Three-phase generator work is electrical installation work: it requires an EPRA-licensed contractor and should be handed over with a certificate of compliance against the Kenyan electrical installation standards. For larger plant, a NEMA environmental assessment and county approvals may also apply, and bulk fuel storage brings EPRA storage requirements into scope.
FAQ
▸Do I need three phase?
If you run three-phase motors, yes. If everything you own is single phase, a three-phase set gains you nothing and introduces a balance problem. Note that on a budget import a 9.4kVA three-phase set is only about 5% more than the single-phase equivalent, which tempts people into buying three phase they cannot use.
▸What is phase imbalance and why does it matter?
Loading one phase much harder than the others. The set regulates on an average while one winding runs hot, the voltage on the lightly loaded phases drifts up, and equipment on them suffers. On a three-phase set feeding mostly single-phase loads, distributing those loads evenly across phases is real design work, not tidiness.
▸How do I size for a motor?
From the motor's starting current, not its rating. A direct-on-line start draws six to eight times full-load current for a second or two. A star-delta or soft starter reduces that substantially and is frequently cheaper than the next generator size up.