In short. A temporary distribution panel takes the output of a rental generator and splits it into protected, isolatable feeders for the loads on site. Specify it by incomer current, number and rating of outgoing circuits, fault level at the generator terminals, earth-leakage protection, enclosure IP rating and the connectors the site cables actually use. A panel sized for the project, not borrowed from the yard, is what keeps a temporary installation safe when the site changes.
What the panel has to do
A generator has one set of outgoing terminals. A construction site, shutdown or event has dozens of loads in different places, owned by different contractors, switched on at different times. The distribution panel turns one source into a managed network: a main isolator so the whole temporary system can be made dead, overcurrent protection for each feeder so a fault on one cable does not trip the generator, earth-leakage protection where people and portable tools are involved, and metering so the operator knows how much capacity is in use and on which phase.
In the Indian rental market the common pattern is a main panel at the generator with an incomer MCCB and four to eight outgoing MCCBs, feeding sub-distribution boards nearer the work with MCBs and RCCBs for final circuits. The architecture matters more than the brand of breaker. See rental and temporary power for where the panel sits in the overall system.
Specifying the incomer and feeders
Start from the generator rating. A 250 kVA set at 415 V delivers about 348 A at full load, so the incomer and busbar should be rated at least 400 A. Each outgoing feeder is then rated for its own cable and load, not for the generator. The table below is a practical checklist.
| Item | What to decide | Typical temporary-power practice |
|---|---|---|
| Incomer | Current rating, breaking capacity, isolation | MCCB rated above generator full-load current, lockable in the off position |
| Outgoing feeders | Number, current, cable size each will protect | One MCCB per feeder, rated to the cable, with spare ways for site growth |
| Fault level | Breaking capacity of every device | Generator fault current is low, roughly three times rated, so 10 to 25 kA devices are usually adequate; confirm if a transformer or utility can also feed the bus |
| Earth leakage | Where RCDs are required and at what sensitivity | 30 mA RCCB on socket and hand-tool circuits, 100 to 300 mA upstream for fire protection |
| Metering | Phase currents, voltage, kWh | Three ammeters or a digital meter on the incomer; per-feeder metering on larger projects |
| Enclosure | IP rating, mounting, cable entry | IP54 or better outdoors, on a stand or skid, bottom entry with glands |
The breaking capacity point deserves care. Rental generators have limited fault current, which is why protection coordination on generator supply is slow and why breaker selection should follow earthing and neutral grounding practice for the system in question. A panel that is also connected to a DISCOM supply through a changeover must be rated for the higher utility fault level.
Neutral, earthing and phase balance
A temporary panel on a 415 V three-phase four-wire system carries a neutral, and that neutral must be bonded to earth at one defined point, normally at the generator, with the panel earth bar connected to both the generator earth and a local electrode. Earth-leakage devices only work if the fault current has a return path, so the earth continuity from every socket back to the generator neutral-earth link should be tested before the system is energised, and the earth electrode resistance recorded.
Phase balance is the other recurring problem. Site loads are largely single-phase: lighting, welding sets, small pumps, cabins. If they are connected to whichever phase is convenient, one phase can reach the generator’s limit while the others are lightly loaded, and the generator trips on single-phase overload well below its rated kVA. Allocate single-phase feeders deliberately across the three phases, label them, and check the ammeters after each new load is added. Where UPS, drives or LED lighting dominate, third-harmonic currents add in the neutral, and the neutral conductor should be sized at least equal to the phase conductors. More on this in UPS and non-linear loads.
Connectors and terminations
Most temporary-power failures happen at a termination, not in a cable. Loose lugs heat up under load, the insulation discolours and eventually the joint fails or starts a fire. Good temporary panels use either bolted lugs that are torqued and checked with a thermal camera after the first hours of load, or industrial plug-and-socket connectors rated for the current and IP class. Mixing connector systems that look alike but are not interchangeable is a known hazard on multi-contractor sites. Every cable should enter through a gland that provides strain relief, so that a trip over a cable does not pull a live conductor off its terminal. Cable practice is covered in temporary power cables.
Designing for a site that changes
A shutdown on day one needs lighting and a few pumps; by day ten it needs welding sets, compressors and commissioning loads. A construction site grows from site cabins to tower cranes and batching plants. The distribution system should be able to absorb these changes without someone adding a cable under a breaker that is already feeding something else. In practice this means spare outgoing ways at the main panel, sub-boards positioned by zone rather than by whoever asked first, a simple record of which feeder supplies which load, and a rule that nobody connects to the panel without the operator’s knowledge. Load shedding is also easier when the loads are already grouped by priority on separate feeders; see load shedding.
Commissioning the temporary panel
Before the generator is loaded, test the panel as a small switchboard: tightness of every termination, phase sequence at the incomer and each socket, insulation resistance of each feeder with loads disconnected, earth continuity, and every RCCB on its test button. Energise with all outgoing breakers open, check voltage and rotation, then close feeders one at a time while watching the ammeters. Record the results on one sheet that stays with the panel and is updated when loads are added and at demobilisation.
Common mistakes
- Choosing the panel by whatever is free in the yard rather than by the project’s feeders. The site ends up with daisy-chained extension boards and no selective protection.
- Rating outgoing breakers for the load instead of for the cable. An undersized cable can carry a sustained overload without the breaker ever tripping.
- Putting all single-phase loads on the red phase. The generator trips on phase overload at half its nameplate kVA and the operator blames the machine.
- Omitting the neutral-earth link or bonding the neutral at two places. Earth-leakage protection either does not work or trips at random.
- Skipping the RCCB test and the thermal check after first load. A faulty device or a loose lug is only discovered when it fails.
What to send us
Send the generator size you expect to hire or already have, a list of the loads with their location on a simple site sketch, the number and rating of circuits you need in each zone, and whether any part of the system connects to a DISCOM supply or an existing building board. Photographs of the connectors on your existing site cables help us match the panel outlets. Send a generator rental enquiry with these details and we will propose the panel and sub-board arrangement.
Questions engineers ask
Do I need RCCBs on a construction site panel?
Yes, on every circuit that feeds socket outlets, hand tools or portable lighting. A 30 mA device is the usual choice for personnel protection. Fixed motor feeders can be protected by a higher-sensitivity device upstream so that nuisance tripping from normal leakage does not stop production.
What breaking capacity do the breakers need on generator supply?
Generator fault current is usually around three times the rated current, so for a 500 kVA set the prospective fault current is a few kiloamperes and 10 to 25 kA breakers are sufficient. If the same panel can also be fed from the utility through a changeover, every device must be rated for the utility fault level, which can be far higher.
Can I use my building’s existing distribution board instead of a rental panel?
Often yes, if it has a suitable incomer, its neutral earthing is compatible with the generator and the breaker ratings suit the lower generator fault current. The connection must go through a proper changeover so the generator can never back-feed the DISCOM supply.
How do I know when the panel is overloaded on one phase?
Read the three phase ammeters, or the digital meter, after each load is connected. A difference of more than about 15 to 20 percent between phases on a loaded generator should be corrected by moving single-phase loads to another feeder, because the generator’s protection acts on the highest phase current, not the average.
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.