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A low-voltage distribution board is the panel every circuit in the building depends on, and it is the item most often specified by copying a previous project. The rating, the fault level and the form of separation all depend on this building and this network, and copying is what produces a board that is either undersized on fault rating or over-built on everything else.
This page covers the board as supplied: what the ratings mean, what the form of separation buys, and what has to be settled before it is built.
Start from the single-line diagram, not from a previous bill of materials
The board is an output of the distribution design. Three inputs decide it, and all three come from the design rather than from a catalogue.
- Load profile and diversity set the main busbar rating. The connected load is not the demand; a diversified commercial load is typically well below the sum of what is installed.
- Prospective fault current sets the short-time withstand, stated as a current over a duration such as 25 kA for 1 second. It has to cover the fault level with the transformer and any generation connected.
- Maintenance policy sets the form of separation. If the board can be shut down for work, a lower form is adequate. If parts of it must stay live, the form has to match.
Send the single-line diagram with the enquiry. A board quoted without one is being guessed at, and the guess usually shows up as a change order.
Specifications
Configuration reference
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| Parameter | Typical value | What it depends on |
|---|---|---|
| Rated voltage | Up to 690 V AC | Plant voltage and local standard |
| Main busbar current | 630 to 6 300 A | Load profile and diversity factor |
| Short-time withstand | 25 to 65 kA for 1 second | Prospective fault level at the connection point |
| Form of separation | Form 2b, 3b or 4b to IEC 61439-2 | How much must stay live during maintenance |
| Construction | Fixed, withdrawable, or a mix of both | Circuit isolation and approved replacement procedure |
| Protection devices | MCCB, ACB, or fuse-switch combinations | Protection study and discrimination |
| Cable entry | Top, bottom or side; cable or busway | Room layout and the cable route |
| Enclosure rating | IP31 to IP54 indoor; NEMA 3R outdoor | Room conditions or outdoor siting |
| Finish | Epoxy powder coat or galvanised | Environment and design life |
| Metering | Optional per-way metering and power quality | Whether you need per-circuit data |
| Standards | Confirm applicable assembly standards and required listing | Selected assembly type and destination-market requirements |
| Internal arc | Confirm required internal-arc test evidence and conditions | Project risk assessment, selected assembly and authority requirements |
Figures are selection references. Confirm the final ratings, dimensions, available certifications and warranty against the current datasheet and written proposal for the selected model or system.
What arrives in a typical order
- The board assembled, wired and routine-tested, with the form of separation built as specified.
- Routine test report to IEC 61439-2 or the applicable standard for that board.
- Single-line diagram, wiring diagram and the nameplate data.
- Protection device list with the settings applied and recorded.
- Installation, terminations and maintenance documentation.
Where the project needs it, the transformer feeding the board, the switchgear upstream and the sub-distribution boards are quoted on the same order, so the fault rating and the discrimination are settled once.
Where an LV board usually goes
- Commercial and industrial main distribution, fed from a transformer and feeding the sub-boards.
- Solar and storage projects, as the AC collection and distribution point.
- Plant rooms and substations where the board is the interface between the utility and the process.
- Replacement and extension where the new board has to match an existing footprint and busbar arrangement.
Sizing notes before you order
- Confirm the fault level from a study, not from the transformer rating alone. Generation on the board raises it, and the board has to withstand the result.
- Choose the form of separation from the maintenance policy. Higher forms cost more and take more depth, so specifying Form 4b on a board that is always shut down for work is money spent on nothing.
- Decide fixed or withdrawable per circuit. Withdrawable suits incomers and large feeders; fixed suits small feeders, and mixing them in one board is normal.
- State the spare ways and the future capacity now. Adding a section later costs more than leaving space in the first build.
Documentation to confirm for your order
- Routine test report to IEC 61439-2 or the applicable standard.
- Single-line and wiring diagrams, with the nameplate data marked.
- Protection device list, with the settings applied and recorded.
- Dimensional drawing and the termination details.
- Installation and maintenance documentation, and warranty terms.
Questions buyers ask
What does the form of separation actually buy?
Internal separation limits access between designated compartments; it does not by itself authorize work while other parts remain energised. Confirm the assembly design, isolation points and manufacturer maintenance procedure. Required circuits must be isolated before work.
Fixed or withdrawable?
Withdrawable construction can support replacement of an isolated functional unit while other sections remain in service, only where the equipment design and approved procedure allow it. Fixed construction can suit circuits that are maintained during a planned shutdown.
How is the short-circuit rating chosen?
From the prospective fault current at the point of connection, calculated in a fault study, and stated as a current over a duration such as 25 kA for 1 second. It has to cover the transformer and any generation connected.
Do we need internal arc containment?
Internal-arc performance is one design consideration, alongside isolation, protection settings and operating procedures. Confirm whether the project requires a tested internal-arc design and the test conditions; an incident-energy result alone does not establish a universal IEC 61641 requirement.
Can we add circuits later?
Yes, if the space and the spare ways are in the first build. State the future capacity at enquiry stage, because extending a board on site costs more than leaving space in it.
What to send us
Send the single-line diagram, the load profile or the connected load with the diversity you assume, the prospective fault level if you have it, and your target date. We confirm the rating, the form and the build date in writing.
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Send the ratings and the required listing
With the bus rating, the required short-circuit current rating, the enclosure type and the listing your authority requires, we confirm the build and the documentation set that ships with it.
Send your requirementsOr reach us directly: +86 136 7367 3267 · sales@gtpsolar.com