An equipment specification is a message. It tells a manufacturer what the equipment has to do, where it will work and how it will be checked, so that the offer received matches the project’s real need. When the message is clear, offers can be compared on the same basis and the equipment that arrives is the equipment that was needed. When it is vague, copied from another project or built around one product’s datasheet, the result is either offers that cannot be compared or equipment that is restricted for no technical reason.
This article answers the question: how do you prepare an electrical equipment specification that communicates the actual technical requirements, without unnecessary restrictions or ambiguity, so that offers are comparable and the equipment can be verified on delivery?
Key takeaways
- A specification has three readers: the manufacturer who designs and quotes, the evaluator who compares offers, and the inspector who checks the delivered equipment. Write each requirement so all three understand it the same way.
- State the need first (operating duty, system data, site conditions), then the ratings that follow from it. Prescribe construction details only where the project genuinely requires them.
- Separate mandatory requirements, preferences and acceptable alternatives. Only the first group should decide whether an offer is compliant.
- Name the applicable standards precisely, IEC first, and add IEEE/ANSI or regional rules only where the project or destination market requires them.
- Every mandatory requirement should have a way to verify it: a type test report, a routine test, a factory acceptance test, a document review or an inspection on delivery.
- A clear specification makes offers easier to compare. It does not replace engineering judgment: deviations and alternatives still need a reasoned technical review against the project’s actual requirements.
What a specification is for
A specification does four jobs in sequence:
- It defines the requirement. What the equipment must do, in which system and under which conditions.
- It is the basis for offers. Each manufacturer designs and prices against it, and declares where its offer differs.
- It is the basis for comparison. The evaluator checks each offer against the same requirements, so differences in price can be traced to differences in scope or performance.
- It becomes part of the contract and the acceptance basis. After order placement, the agreed specification, together with approved deviations, is what the equipment is checked against.
A requirement that fails at any of these steps causes trouble later. “Switchgear of good quality” defines nothing, cannot be priced consistently and cannot be checked. “Rated short-time withstand current 25 kA for 3 s” can be designed, priced, compared and verified from a type test report. The value itself must come from the project’s fault-level study, not from habit.
Performance requirements and prescriptive requirements
There are two ways to write a requirement:
- Performance (functional) requirements state what the equipment must achieve: ratings, duty, environment, interfaces, availability. The manufacturer chooses how to achieve it.
- Prescriptive requirements state how the equipment must be built: a particular material, layout, component or design feature.
Performance requirements usually give better results, because they leave room for manufacturers to offer their proven designs while still meeting the need. IEC equipment standards are written mostly in this way. IEC 60076-1 for power transformers, for example, includes guidance on specifying a transformer by its functional requirements.
Prescriptive requirements are justified where the project has a real reason. Typical reasons are compatibility with existing equipment, a utility or operator requirement, a maintenance policy (for example common spare parts across a site), or a proven safety or reliability concern. When a prescriptive requirement is used, it helps to state the reason in a short note. A reviewer can then judge whether an alternative meets the same intent.
The structure of a clear specification
The exact layout varies by equipment type and by company practice, but a clear specification usually answers the same questions in a predictable order.
| Section | The question it answers | Typical content |
|---|---|---|
| 1. Scope and boundaries | What is included, and where does supply end? | Equipment list and quantities; terminal points; items supplied by others; services excluded or separately arranged |
| 2. System and operating requirements | What will the equipment do, and in which system? | Nominal voltage and frequency, earthing system, fault level, load and duty, operating philosophy, future extension |
| 3. Ratings | Which declared ratings must the equipment have? | The ratings defined by the relevant equipment standard, stated as values with their basis (for example duration, cooling method or reference conditions) |
| 4. Applicable standards | Which rules define the ratings and tests? | Equipment standards (IEC first), any IEEE/ANSI standards the project requires, regional or utility requirements |
| 5. Site and service conditions | Where will it work? | Ambient temperature range, altitude, humidity, pollution, indoor or outdoor, seismic data, enclosure protection (see Defining Site and Service Conditions) |
| 6. Interfaces | What does it connect to? | Cable or busbar connections, control and protection signals, communication protocols, auxiliary supplies, mechanical and civil interface information |
| 7. Construction and features | Which design features are genuinely required? | Only features with a project reason: for example withdrawable execution, interlocking scheme, metering, accessories |
| 8. Documentation | What must the manufacturer provide, and when? | Offer documents, approval drawings, datasheets, test reports, manuals, final documentation |
| 9. Testing, inspection and acceptance | How will compliance be shown? | Type test evidence, routine tests, any special tests, factory acceptance testing and witness points, delivery inspection |
| 10. Packing, transport and spares | How does it arrive and how is it supported? | Packing for the transport route and storage period, marking, recommended spares, special tools |
| 11. Compliance and deviations | How should the offer respond? | A compliance schedule to fill in, and a deviations list with the reason for each deviation |
Two practical points make this structure work:
- Put each requirement in one place. If the fault level appears in section 2 and again, with a different value, in a datasheet appendix, the manufacturer has to guess. Conflicting clauses are among the most common sources of non-comparable offers.
- Use a datasheet for values and the text for intent. A datasheet or schedule of technical particulars, with “required” and “offered” columns, keeps the values easy to compare. The text explains the purpose and any conditions behind them.
Mandatory requirements, preferences and acceptable alternatives
Not every line in a specification carries the same weight. Mixing them is the main reason specifications become either too restrictive or too vague. Three kinds of statement are worth keeping apart.
| Type | What it means | How it is usually worded | How it is used in evaluation |
|---|---|---|---|
| Mandatory requirement | The equipment is not suitable without it | “shall” | An offer that does not meet it is non-compliant, unless the deviation is reviewed and accepted |
| Preference | Desirable, but the equipment can still be suitable without it | “should” or “preferred” | Considered in evaluation, but does not on its own make an offer non-compliant |
| Acceptable alternative | A different solution that the project would consider if it meets the same intent | “alternatives may be offered”, with the intent stated | Assessed on technical merit against the stated intent |
This wording follows the convention used in IEC and ISO documents, where “shall” expresses a requirement, “should” a recommendation and “may” a permission. Using the same convention in a project specification makes the intent clear to manufacturers who work with those standards every day.
Some practical guidance:
- Keep the mandatory list short and real. Each mandatory item should trace back to a system requirement, a site condition, a standard, a regulation or a documented project decision. A long list of “shall” clauses copied from another project often contains requirements that do not apply, and it pushes offers towards deviations that then have to be reviewed one by one.
- Say why a preference exists. “Front access preferred, because the switchroom has no rear clearance” gives a manufacturer the information needed to offer a suitable design. If rear clearance is in fact unavailable, it is a mandatory requirement and should be written as one.
- Invite alternatives deliberately. Where more than one solution could meet the need, say so, and say what the alternative must achieve. This is often where better-value solutions come from.
- Ask for deviations to be declared. A deviations list with a short technical reason for each item is more useful than an offer that claims full compliance without evidence.
Writing ratings and requirements that can be compared
A rating is only comparable if it is stated with its basis. The table below shows typical weak wording and a clearer alternative. The values are illustrative and show the form of the requirement, not recommended values for any project.
| Weak wording | Why it causes problems | Clearer wording (illustrative values) |
|---|---|---|
| “11 kV switchgear” | 11 kV is a nominal system voltage; equipment is rated by its rated voltage and insulation level | “Rated voltage Ur 12 kV for an 11 kV nominal system, rated insulation level as per IEC 62271-1 for 12 kV” |
| “Breaking capacity 25 kA” | Duration and the related ratings are missing | “Rated short-circuit breaking current 25 kA; rated short-time withstand current 25 kA for 3 s; rated peak withstand current to IEC 62271-1, based on the project fault-level study” |
| “1 000 kVA transformer” | Voltage ratio, vector group, cooling, losses basis and tappings are undefined | “Rated power 1 000 kVA, ONAN, 11/0.4 kV, Dyn11, off-circuit tappings as per project requirement, losses stated at the reference temperature defined in IEC 60076-1, with any loss limits or capitalisation values given” |
| “Suitable for site conditions” | The manufacturer does not know the site | “Indoor, maximum ambient 45 °C, 24 h average 40 °C, altitude 1 800 m, see site conditions schedule” |
| “IP65 throughout” | May be unnecessary indoors, and a sealed enclosure can need thermal derating | “Enclosure degree of protection as required for the location: IP3X minimum in the dry switchroom; outdoor kiosk per site conditions schedule” |
| “Make X type Y or equal” | Restricts competition and leaves “equal” undefined | “Performance as stated in the datasheet; proposed equipment to be identified with evidence of compliance. Where existing-site compatibility requires a specific range, state the reason” |
| “All relevant IEC standards” | Every manufacturer may read a different list | “IEC 62271-200 for the switchgear assembly, IEC 62271-100 for circuit-breakers, IEC 62271-1 common specifications; edition as stated in the project standards list” |
When a value comes from a study (fault level, maximum demand, voltage drop), give the value and, where useful, the study it comes from. Manufacturers can then raise a question if the value looks inconsistent with the rest of the system.
The meaning of the main MV switchgear ratings is explained in Specifying MV Switchgear: Key Ratings Explained. For LV equipment, keep device ratings and assembly ratings apart, as described in Choosing LV Circuit Breakers: a breaker’s ratings are not the ratings of the switchboard it sits in.
Applicable standards: naming them usefully
Standards define the meaning of ratings and the tests that prove them. A specification uses them in three layers:
- IEC equipment standards are the primary reference. They define ratings, construction requirements and tests for each equipment family: for example IEC 62271 for MV switchgear, IEC 60076 for transformers, IEC 61439 for LV assemblies and IEC 60947 for LV switching devices.
- IEEE/ANSI standards apply where the project or destination market requires them. If a project specifies them, say so clearly for each item. Do not mix rating systems for the same item without an engineering review, because ratings and test conditions are not always directly interchangeable.
- Regional, national and utility requirements apply where relevant. Examples are national wiring rules, utility connection requirements or EU Ecodesign requirements for transformers placed on the EU market. State where they apply. They do not automatically govern projects in other markets.
Good practice is to list the standards once, in a project standards list, and refer to it from each section. If a specific edition matters, for example because a national standard or a utility requirement is based on it, state the edition. Otherwise, state that the edition in force at the date of the offer applies, or agree the edition during clarification.
Interfaces: the requirements that fall between packages
Many problems on site come from what sits between two pieces of equipment rather than from the equipment itself. A specification should state:
- Electrical interfaces: cable sizes, number and type of cables per phase, cable entry direction, busbar connections between assemblies, earthing connections.
- Control and protection interfaces: signals exchanged with other equipment, interlocks between units, protection relay functions provided by whom, auxiliary supply voltage.
- Communication interfaces: protocol and data points, if remote monitoring or control is required.
- Mechanical and civil interface information: dimensions, weights, lifting points, foundation loads and cable trench positions. The supplier provides the information; the project’s own design and installation teams use it.
Where several items come from different manufacturers, for example a transformer, MV switchgear and an LV switchboard for the same substation, the interface data must match on both sides. This is easier to coordinate when one specification covers the whole package, or when interface schedules are shared between packages.
Documentation, testing and acceptance
A requirement that cannot be checked is, in practice, a preference. For each mandatory requirement, the specification should make clear how compliance will be shown.
The main verification methods are:
- Type tests (or design verification for LV assemblies). Tests carried out on a representative design to prove its ratings, for example temperature rise, dielectric withstand, short-time withstand and, for switchgear, internal arc classification where specified. The evidence is a type test report. The specification should ask for reports that cover the offered design and ratings.
- Routine tests (or routine verification). Tests carried out on every unit before dispatch, as defined by the equipment standard. The evidence is the routine test report for each unit.
- Special tests. Tests beyond routine tests, agreed between purchaser and manufacturer. IEC 60076-1, for example, distinguishes routine, type and special tests for transformers. If a special test is required, it must be named in the specification, because it affects price and programme.
- Factory acceptance testing (FAT) and witness points. If the purchaser or a third party wishes to witness tests, state which tests and how much notice is required.
- Document review. Datasheets, drawings and calculations checked against the specification during the approval stage.
- Inspection on delivery. Visual and documentary checks at receipt: correct items, nameplate data, no transport damage, documents present.
The documentation list should state what is needed at each stage: with the offer, for approval after order, before shipment and at handover. Asking for everything with the offer slows the process and adds cost without improving the comparison.
A clear specification supports engineering judgment
A well-structured specification makes offers easier to compare, but comparison is not a mechanical exercise. Two offers can both show “compliant” in every line of a schedule and still differ in ways that matter: design margins, maintainability, the service experience of the design in similar conditions, or how well the equipment fits the rest of the system. Equally, an offer with a declared deviation may be the better technical solution.
For this reason:
- Equivalence is a professional judgment. Whether an alternative is technically equivalent is assessed by engineers who understand the project and the equipment, informed by project experience. It is not decided automatically by matching catalogue values or by the lower price.
- Value engineering is not price reduction. A value-engineering proposal is worth considering when it maintains or improves technical suitability, functionality, quality and reliability against the actual project requirements. A cheaper option that removes a margin the project needs is not value engineering.
- Deviations deserve a reasoned answer. Each declared deviation should be accepted, rejected or clarified with a short technical reason, and the outcome recorded so it becomes part of the agreed basis.
Framework: reviewing a specification before it is issued
Before sending a specification to manufacturers, a short review against these questions catches most problems:
- Need: Is the operating duty described, including future extension, so that the ratings can be traced back to it?
- Values: Is every rating stated with its basis (duration, reference temperature, cooling method, insulation level)? Do values that come from studies match the latest study?
- Conditions: Are site and service conditions stated in full, or explicitly confirmed as the normal service conditions of the relevant standard?
- Weight: Is every “shall” justified? Are preferences marked as preferences? Are alternatives invited where they make sense?
- Standards: Is there one project standards list, IEC first, with any other standards and their scope of application stated?
- Interfaces: Are all interfaces with other equipment and with the site defined, and do they match the other packages?
- Verification: Does every mandatory requirement have a verification method? Are special tests and witness points named?
- Consistency: Do the text, datasheets and drawings agree? Is there a single place for each value?
- Response format: Is there a compliance schedule and a deviations list for the offer?
Illustrative example: improving one requirement
Scenario (illustrative, not a design): a project needs a distribution transformer for an industrial building, supplied from an 11 kV network and feeding a 400 V main switchboard. The first draft of the requirement reads:
“Transformer 1 000 kVA, 11 kV/400 V, high quality, best losses, suitable for local conditions, to IEC standards, make X or equal.”
What is missing or ambiguous
- Cooling method, vector group and tappings are not stated.
- “Best losses” cannot be priced or compared. Losses need either stated limits or a stated evaluation method.
- “Local conditions” gives the manufacturer no data.
- “IEC standards” does not say which ones.
- “Make X or equal” restricts the offer without explaining what makes X suitable.
An improved version (values illustrative, chosen only to show the form):
- Mandatory: liquid-immersed transformer to IEC 60076-1 and the relevant parts of the IEC 60076 series; rated power 1 000 kVA, ONAN; 11/0.4 kV; Dyn11; off-circuit tap changer with the tapping range stated in the datasheet; short-circuit impedance as required by the LV fault-level study (value stated in the datasheet); load and no-load losses within the limits stated in the datasheet, or evaluated by the capitalisation values stated; site conditions as per the site conditions schedule; routine tests to IEC 60076-1 on each unit.
- Preferred: a low-loss design where the evaluation shows a lifetime benefit; plug-in cable terminations on the MV side to suit the existing switchgear.
- Acceptable alternative: a dry-type transformer may be offered if it meets the same ratings and the site’s environmental, climatic and fire-behaviour requirements, with the effect on footprint and ventilation stated.
- Verification: routine test reports for each unit; type test report or special test, where required, named in the datasheet; document review of the rating plate drawing and outline drawing at the approval stage.
What changed: the improved version is not longer for its own sake. Every line can now be designed, priced, compared and checked. The manufacturer also understands which items are fixed and where a better proposal is welcome. The detailed transformer rating questions are covered in Sizing a Distribution Transformer.
Relevant standards
| Standard | What it covers | Why it matters |
|---|---|---|
| ISO/IEC Directives, Part 2 | Rules for drafting IEC and ISO documents, including the meaning of “shall”, “should” and “may” | Using the same verbal forms in a project specification makes the weight of each requirement clear |
| IEC 60050 (International Electrotechnical Vocabulary) | Standard terms and definitions for electrotechnology | Consistent terms reduce misreading between purchaser and manufacturer |
| IEC 62271-1 | Common specifications for AC high-voltage switchgear and controlgear above 1 000 V: ratings, normal service conditions, type and routine tests | The basis for stating MV switchgear ratings such as rated voltage, insulation level and short-time withstand current |
| IEC 62271-200 | AC metal-enclosed switchgear and controlgear from above 1 kV up to and including 52 kV | Defines assembly-level requirements and tests for MV switchgear, including internal arc classification where specified |
| IEC 60076-1 | Power transformers: general requirements, ratings, tests and guidance on specification | Defines transformer ratings and the routine, type and special test categories referred to in a specification |
| IEC 61439-1 and IEC 61439-2 | LV switchgear and controlgear assemblies: general rules and power switchgear assemblies | Defines assembly ratings, design verification and routine verification for LV switchboards |
| IEC 60947 series | LV switchgear and controlgear devices, including circuit-breakers (IEC 60947-2) | Defines device ratings used in LV specifications |
| IEC 60038 | IEC standard voltages | Helps relate nominal system voltages to the equipment voltages a specification should state |
National, utility or regional requirements, and IEEE/ANSI standards where a project uses them, are added to the project standards list for the market concerned.
Common mistakes
- Copying a specification from another project without checking that its ratings, conditions and standards apply.
- Building the specification around one product’s datasheet, so that only that product can comply.
- Stating nominal system values where equipment ratings are needed, or ratings without their basis (duration, cooling method, reference temperature).
- Leaving site conditions as “to suit site” or omitting them, so offers assume different conditions.
- Marking every line as mandatory, so every offer shows deviations and real differences are hidden.
- Repeating the same value in several places, with different numbers.
- Asking for “all relevant standards” instead of naming them.
- Specifying tests or witness points that are not needed, or omitting ones that are.
- Treating a fully ticked compliance schedule as proof of suitability, without engineering review of the offer.
Conclusion
A clear electrical equipment specification starts from the need: the system, the duty and the site. From these follow the ratings, the standards that define them, the interfaces with other equipment and the tests that prove compliance. Separating mandatory requirements from preferences and acceptable alternatives keeps the specification focused on what the project actually needs and leaves room for manufacturers to propose suitable designs. Linking every mandatory requirement to a verification method makes the specification useful after order placement, not just at tender stage. A clear specification makes offers comparable, but the final assessment of suitability, equivalence and value remains a matter of engineering judgment applied to the project’s real requirements.
When the specification is ready, the next step is the request for quotation. Preparing an RFQ for Electrical Power Equipment explains what to send with it, and what can be clarified later.
Related AdepaTrade solutions
AdepaTrade sources MV switchgear, transformers, compact / package substations and LV distribution equipment to project specifications from manufacturers in Türkiye and around the world, and works with customers to clarify requirements before offers are prepared. Medium Voltage Distribution & Protection · Transformers
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