Technical specification for switchboard equipment: a customer checklist

Author: Volodymyr Ledok, Production Technical Director at LK Energy Group.
He is responsible for the manufacture of switchboard equipment — assembly of NKU, KRU and KSO units and busbar systems. Customers' technical specifications pass through his engineers: from checking the input data to factory testing of the finished product.

A technical specification (ToR) for switchboard equipment is the document in which the customer records the input data for the manufacturer: what product is required, in what network it will operate, what has to be inside it and under what conditions it will stand. The format can be anything — a completed questionnaire sheet, a single-line diagram with a table, a specification letter or a section of the design documentation. What matters is not the format but the completeness: the selection of devices, the cabinet layout and the price calculation all start from the ToR. This article is a checklist of the parameters worth collecting before you approach the plant, whether you are ordering a 0.4 kV distribution board, 10 kV cubicles or a packaged substation.

Why a clear ToR matters

Switchboard equipment is a project-based product: two identical main distribution switchboards (GRShch) or substations are almost never built. That is why the enquiry "we need a 400 amp switchboard, how much is it" has no answer — the price depends on the diagram, the devices, the metering and the enclosure design. A clear ToR delivers three practical results:

An accurate price and lead time

with complete input data the manufacturer prices a specific bill of materials rather than a "range" padded for the unknowns. The manufacturing lead time is also fixed in concrete terms — the devices are known, and so is their availability.

Protection against errors

a discrepancy found on paper costs one line in the specification. The same discrepancy found after assembly means reworking the cabinet: different devices have different dimensions, and the layout has to be "reassembled". And an error found on site brings installation to a halt.

A fast approval cycle

without a ToR the same data is gathered by correspondence: the manufacturer asks — the customer investigates — the designer answers. Each round takes days. A complete ToR removes most of the questions before production starts.

Checklist: what to state in the technical specification

1. Type of equipment and its purpose

First and foremost — what the product is and what it does in the power supply scheme: an incoming distribution unit (VRP), a main distribution switchboard (GRShch), ShchO-90 panels, an automatic transfer cabinet (AVR), a capacitor bank (UKRM), KSO or KRU cubicles for 6–10 kV, a packaged transformer substation (KTP). Add the purpose of the facility — a production plant, a pumping station, a residential building, a SES: the redundancy requirements and the set of protections depend on it.

2. Network parameters

Three figures without which devices cannot be selected:

• rated voltage — 0.4 kV for NKU (low-voltage switchgear assemblies) or 6/10 kV for cubicles and substations; the number of busbar sections;
• rated current of the incomer and of the busbars — it determines the busbar cross-section and the frame size of the incoming devices;
• expected short-circuit current at the connection point — it is used to verify the electrodynamic and thermal withstand of the busbars and the breaking capacity of the devices. If the TKZ has not been calculated, say so: an honest gap is better than a figure pulled out of thin air.

3. Main circuit diagram

How many incomers there are, whether there is a bus-section device, how many outgoing lines there are and what their ratings are. For each feeder — its purpose: "ventilation", "chiller", "spare". This is not a formality: the purpose is what the logic of the scheme, the selectivity and the need for an AVR are checked against. The best way to present it is a single-line diagram, even a sketch.

4. Protection, automation, metering

For 6–10 kV — the set of relay protection and automation (RZA) for each cubicle, and the need for an AVR on the incomers and the bus-section breaker. For 0.4 kV — the type of devices (a circuit breaker or a switch-disconnector with fuses) and the trip unit settings, if they are defined by the design. Metering is a separate item: whether a commercial metering unit is required, the ratio of the current transformers (accuracy class 0.5S for commercial metering), the type of meter and who supplies it, and the need for an ASKOE system.

5. Enclosure and installation conditions

Indoor or outdoor installation — this determines the enclosure protection rating (typically IP31 for dry rooms, IP54 and above for outdoor sites and dusty workshops) and the climatic version (U3 for heated premises, U1 for the open air). For outdoor installation, state right away whether heating, lighting and compartment ventilation are needed — this is part of the design, not an option to be added "later".

6. Cable entry and dimensional constraints

Where the supply comes in from: bottom or top cable entry, or an overhead entry through wall bushings. The number and cross-sections of the cables per feeder — the size of the cable compartments depends on it. And, without fail, the space constraints: the dimensions of the switchgear room, the width of the doorways, the ceiling height. The layout is determined at the very start, and "the cabinet does not fit through the door" is a real problem that is easily avoided with one line in the ToR.

7. Special requirements

Everything that goes beyond standard practice: remote control and dry alarm contacts, reserved space for future feeders, a RAL colour, a reinforced anti-corrosion coating for aggressive environments, requirements for specific device manufacturers if the design calls for them.

Summary table of the ToR sections

How to pass the data to the manufacturer

For standard products the most convenient form of ToR is a questionnaire sheet: the form already contains a single-line diagram and a table of parameters, and all that is left is to fill in the fields. Forms for KTP, KSO/KRUN cubicles, ShchO-90 panels and RUNN cabinets are collected on the questionnaire sheets page. For non-standard products, a free-form ToR following the checklist above plus a single-line diagram is enough — and if the design includes one, be sure to attach it: the diagram removes most of the questions about the configuration. Designers will find the standard solutions with drawings and RZA diagrams in the section for designers useful — a ToR is put together faster on that basis.

What we do next

Once the ToR is received, the production engineers first check the input data: the withstand of the devices against the stated short-circuit current, the consistency of the ratings, the completeness of the diagram. If there are gaps, we come back with specific questions rather than a refusal. Next come device selection and layout, a specification with prices and lead time, and a dimensional drawing and diagrams for the customer's approval. The product goes into production only after your approval, and before shipment it undergoes factory testing. That way the errors stay on paper, where correcting them costs nothing.

Frequently asked questions

LK Energy Group manufactures switchboard equipment at its own plant in Odesa — from 0.4 kV distribution boards to KSO/KRU cubicles and packaged substations. Send us a completed form from the questionnaire sheets page or a free-form ToR with a single-line diagram, and we will prepare a specification with a price and a lead time; designers will find ready-made standard solutions in the section for designers.

See also

• RUNN cabinets
• ShchO 90 type distribution board panels for currents up to 4000 A
• KSO-E type single-side service cubicles (frame size 393)
• Case study: KRP-4000/0.4 U1 — a 4000 A substation in a container unit
• Manufacture and assembly of switchboard equipment