HT Panel Specification for a Factory: VCB, Relays, Metering and What to Demand

An HT panel specification for a factory should state the fault level at your point of supply, the breaker and busbar ratings that follow from it, the construction (metal-clad, compartmented, draw-out vacuum breaker), the protection relays, the metering classes, and the type-test evidence you will accept. Get the fault level from the DISCOM first. Every other rating follows from it.

What do you fix before you write the specification?

Five inputs go in the document header, and a bidder cannot price honestly without them.

• Fault level at the point of supply. Ask the DISCOM for the prospective short-circuit level at your incomer in writing. The breaker's breaking and short-time ratings must exceed it, with margin for growth.
• System voltage and earthing. 11 kV or 33 kV, and how the neutral is earthed at the transformer.
• The single-line diagram. Incomer, metering, bus section, transformer feeders, capacitor or DG feeders, and which breakers are spare.
• Site conditions. Ambient temperature, altitude, dust, humidity, and whether the room is indoor, ventilated or air-conditioned.
• Auxiliary supplies. The DC supply and battery charger for tripping and closing, and the control voltage you will provide.

Our notes on HT connection and substation approval and on transformer undersizing cover the load side. The HT and LT distribution page shows the full substation scope.

What should the switchgear and breaker clauses say?

A distribution company's own specification is a good model of how detailed a clause can be. Maharashtra's MSEDCL specification for 11 kV, 25 kA indoor switchgear with control and relay panels, issued in 2020, is written for its substations, not for a consumer plant, so do not copy its ratings. Copy its discipline. It names IEC 62271-100 for breakers and IEC 62271-200 for the switchgear assembly, and it writes down each requirement a bidder can be tested against.

On interlocks the rule is statutory. The CEA Safety Regulations, 2023, regulation 47, require isolators and their controlling breakers to be interlocked so the isolator cannot operate with the breaker closed, earthing switches to be interlocked so they cannot close unless the isolator is open, and access doors to live parts to be interlocked so they cannot open until the parts are dead, discharged and earthed.

How do you specify relays, current transformers and metering?

The same MSEDCL specification requires numerical relays with three over-current elements and one earth-fault element, with high-set, draw-out construction with automatic shorting of the CT circuit when the relay is removed, and a standard communication protocol for remote monitoring. Current transformers carry a 0.2 class metering core and a protection core, a short-time rating equal to the panel's, and an instrument security factor of not more than 5 for the metering core. These are good clauses to ask a bidder to meet or to state a deviation from.

The regulations add protection that the panel and its feeders must provide. Regulation 47 requires over-current and earth-fault protection on all circuits, Buchholz, pressure-relief and winding and oil temperature protection on transformers of 1,000 kVA and above, earth-fault protection on generators of 100 kVA and above, and restricted earth-fault or differential protection on generators of 1,000 kVA and above.

Billing metering is a DISCOM matter. Ask the DISCOM for its metering cubicle drawing, the CT and PT ratios and the sealing arrangement before you finalise the incomer. Metering accuracy is set under the CEA metering regulations; Odisha's supply code, restating them, puts meters above 650 V and up to 33 kV at class 0.5S or better, with CTs and PTs no worse than the meter, but confirm the class and ratios in force with your DISCOM.

What does protection coordination mean for the buyer?

Relays are only as good as their settings. The incomer's settings must grade with the DISCOM's upstream protection, and each feeder must grade with the incomer, so a transformer fault trips its own breaker and not the whole plant. Make the settings study a deliverable: a coordination study with time-current curves, the fault levels used, and a settings schedule for every relay. Require secondary-injection testing of every relay at commissioning with the results in the handover file, and ask for the settings to be recorded so a replacement relay can be set identically. For the hazard side, our note on arc flash studies explains why the incident energy at the panel depends on the clearing time you set.

What type tests and site tests do you ask for?

MSEDCL's specification asks for type tests at an accredited laboratory within the last five years, on the offered design: lightning impulse, power-frequency withstand, short-time and peak withstand, short-circuit duties, single-phase breaking, cable-charging breaking, temperature rise and the internal arc test on the panel; a mechanical endurance test on the breaker; and tests on CTs and PTs including partial discharge and accuracy. If the reports are older than five years, it requires the tests to be repeated before supply. Ask for the same, with routine tests witnessed at the works.

At site, specify insulation resistance and contact resistance, breaker timing, interlock operation, relay secondary injection, CT ratio and polarity, and a functional trip test from the relay to the breaker. Then the Electrical Inspector inspects before energisation; our guide to CEIG approval for factories lists the file. Our guide to electrical testing and commissioning covers the site tests in detail.

How Secured Engineers helps

We design HT and LT distribution and write the equipment specifications in-house, file Fire NOC, CEIG and DISCOM applications in-house, and deliver MEPF and solar under one contract, so the HT room, the transformer yard and the solar interconnection are specified together. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

Send your single-line diagram, the DISCOM's fault level and the specification or quotation you are comparing, and we will review it line by line and tell you what is missing or under-rated. See our electrical infrastructure page, message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.