In short. A low-voltage generator system produces power at 415 V three-phase, 50 Hz, the utilisation voltage of almost every Indian factory and building, and feeds the main switchboard directly without a transformer. It is the simplest and cheapest arrangement up to about 1,000 to 1,500 kVA. Above that, line currents of 2,000 A and more make cables, busbars and breakers expensive and fault levels hard to manage, which is where medium-voltage generation starts to make sense.
Why voltage sets the current, and current sets everything else
The alternator in a 415 V generator set is wound to deliver its rated kVA at 415 V between lines. Because the power is fixed by the engine, a lower voltage can only mean a higher current, and current is what sizes every conductor, joint and switching device downstream.
I = (kVA × 1000) ÷ (√3 × VLL)
Here I is the line current in amperes, kVA is the apparent power the set delivers and VLL is the line-to-line voltage in volts. A 500 kVA set at 415 V therefore delivers about 696 A at full load, a 1,000 kVA set about 1,391 A and a 2,000 kVA set about 2,782 A (illustrative). The same 2,000 kVA at 11 kV would be only 105 A. That single comparison explains the whole low-voltage versus medium-voltage decision. The current calculator gives the figure for any rating and voltage.
Where low-voltage generation is the right answer
For the great majority of installations we see in Hyderabad, from a 62.5 kVA set behind a clinic to a 1,000 kVA set at a pharmaceutical unit, low voltage is correct and nothing else should be considered. The loads are at 415 V, the existing switchboard is at 415 V, the DISCOM metering is often at 415 V, and the generator breaker simply becomes another incomer. There is no transformer to buy, energise or maintain, protection is handled by moulded-case or air circuit breakers that every electrician understands, and a licensed LT contractor can carry out the installation.
Low voltage also remains the right choice for multi-set plants up to a few MVA when the sets sit close to the switchboard, because paralleling breakers and busbars at 415 V are standard products. The question only becomes serious when currents pass about 2,500 A per circuit, when the generator is more than about 100 metres from the load, or when the plant already has an 11 kV ring.
Cables, busbars and the cost of amperes
The cost of a low-voltage installation rises faster than the kVA because conductor cross-section must grow with current while voltage drop must stay within limits. The table shows how the conductor arrangement typically changes with set size at 415 V; actual sizes depend on cable type, installation method, ambient temperature and run length and must be calculated for the project.
| Set rating at 415 V | Full-load current | Typical conductor arrangement | Practical note |
|---|---|---|---|
| 125 kVA | 174 A | Single 3.5 core aluminium or copper cable | Straightforward; voltage drop rarely limits short runs |
| 500 kVA | 696 A | Two single-core cables per phase or one large multicore | Glanding and bending radius start to matter |
| 1,000 kVA | 1,391 A | Three to four single-core cables per phase | Unequal current sharing between parallel runs becomes a risk |
| 2,000 kVA | 2,782 A | Six or more cables per phase, or busduct | Busduct usually cheaper and safer than a cable trench |
Parallel single-core cables share current equally only when they are the same length, the same size and arranged symmetrically in trefoil or a transposed flat formation. Four cables per phase laid side by side in a trench will not share equally, and the outer cables run hotter than the calculation assumed. Above about 1,500 A a sandwich busduct from the alternator terminals to the switchboard removes that problem. The cable sizing guide and the cables, busbars and distribution page cover the selection in detail.
Voltage drop on a weak source
A generator is a much softer source than the DISCOM transformer it replaces, so voltage drop in the cable adds to voltage dip in the alternator when a motor starts. On a long low-voltage run the two together can take the voltage at a motor terminal below the point where its contactor holds in. The usual design limit is a total drop of about 3 to 5 percent from alternator terminals to the farthest load at full current, with the motor-starting case checked separately. Where the generator cannot be placed near the switchboard, the options are a larger conductor, a busduct or, for large plants, generating at medium voltage and stepping down close to the load. The voltage drop page gives the calculation method.
Fault current and breaker selection
A low-voltage generator contributes less fault current than a utility transformer of the same kVA, typically six to ten times rated current in the first cycles decaying to a sustained value of about three times rated current with a permanent-magnet excitation system. That is good news for the breaker’s breaking capacity and bad news for protection, because a downstream fuse or breaker set for the utility fault level may not operate quickly on generator supply. Breakers on the generator incomer must be selected for the higher of the two fault levels and their settings checked for the lower one. For multi-set plants the contributions add, and the switchboard fault rating must cover all sets in parallel plus any motor contribution. The fault current page explains the calculation and when a formal study is needed.
Common mistakes
- Running six parallel cables per phase in a flat trench to save the cost of busduct; the outer cables overheat because current does not share equally.
- Placing a 1,000 kVA set 150 metres from the switchboard to keep the noise away; voltage drop at motor starting trips contactors across the plant.
- Reusing the existing incomer breaker without checking its generator-mode settings; a downstream fault on generator supply is cleared slowly or not at all.
- Specifying a transformer and 11 kV switchgear for a 750 kVA set because the DISCOM supply is at 11 kV; the cost doubles for no electrical benefit.
What to send us
Send the single-line diagram or a photograph of the main switchboard nameplate and incomer breaker, the distance from the proposed generator position to the switchboard, the connected load list with the largest motors, and the DISCOM supply voltage and transformer rating. If the plant already has an 11 kV intake, say so, since that changes the comparison. Use the generator sales enquiry and we will confirm the voltage, the conductor arrangement and the breaker requirement with the set recommendation.
Questions engineers ask
What is the largest practical low-voltage generator?
Alternators are built for 415 V up to about 2,500 to 3,000 kVA, but above roughly 1,500 kVA the current exceeds 2,000 A and the installation cost of busduct, breakers and switchboard rises steeply. Most engineers move to 11 kV for single sets above 2,000 kVA or for multi-set plants above about 4 MVA.
Can a 415 V generator be connected to an 11 kV plant?
Yes, through a step-up transformer, and it is a common arrangement for sets up to about 1,500 kVA on campuses with an 11 kV ring. The transformer must be sized for the set, its inrush checked against the alternator capability, and the protection designed for both directions of power flow.
How far can a low-voltage generator be from the switchboard?
There is no fixed limit, only a voltage-drop budget. For a 500 kVA set, runs up to about 50 to 80 metres are routine with correctly sized cable; beyond that the conductor cost grows quickly and a busduct or a closer location should be considered.
Does a low-voltage generator need its own earthing?
Yes. The alternator neutral must be earthed through its own electrode system in accordance with the CEA regulations and IS 3043, and the arrangement must be coordinated with the DISCOM transformer earthing and the transfer switch so that the neutral is never left floating or doubly earthed in a way that defeats earth fault protection.
Is 415 V generation less efficient than 11 kV?
The alternator efficiency is similar at either voltage. The difference lies in distribution losses, which rise with the square of current, so a long 415 V run loses more energy than the same power at 11 kV. For short runs the difference is negligible and the transformer losses of a medium-voltage scheme would outweigh it.
Looking for a specific rating? See the generator full-load current chart for every common size from 7.5 to 3,000 kVA at 415 V and 11 kV.
Generators by rating
- Under 15 kVA generators
- 15–50 kVA generators
- 50–125 kVA generators
- 125–250 kVA generators
- 250–500 kVA generators
- 500–1000 kVA generators
- 1–2 MVA generators
- 2 MVA and above generators
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.