Main Distribution Boards
A main distribution board (MDB) takes power from the LV switchgear or transformer and splits it into the large feeders that run to sub distribution boards, MCCs and major equipment across a building or plant. NLS Power sources MDBs built to IEC 61439-1/2, with breaking capacity and busbar rating matched to the site's fault level.
The main distribution board is the second tier down from LV switchgear: where the switchgear carries the full incoming supply on one or two busbar sections, the MDB takes a large feeder from it and splits that current into the handful of major outgoing ways that serve a building floor group, a process unit, or a set of sub distribution boards further down the chain. On a mid-size commercial or industrial building it's common for the MDB itself to be part of the main LV switchgear lineup rather than a separate room, while larger sites run MDBs in each building or block, fed from a central switchgear room.
Breaking capacity on the incoming and outgoing devices has to be checked against the actual fault level at that point, not against a generic assumption carried over from a different project. An MDB installed one floor away from the transformer sees a different fault current than one at the switchgear room itself, because cable and busbar impedance between the two points reduces the fault current the further downstream you go; sizing an MDB breaker without that calculation either wastes money on unnecessary breaking capacity or, worse, under-rates it.
Arc flash exposure is a real consideration at MDB level because technicians open these boards more often than switchgear, for metering checks, breaker maintenance, and load additions. Incident energy calculations, arc flash labeling, and a documented safe working distance are becoming standard requirements on Saudi hospital and data centre specifications even though the formal driver, NFPA 70E, is a US standard; IEC-based projects reference IEC/TR 61641 for the equivalent internal arc consideration.
NLS Power sources main distribution boards to IEC 61439-1/2, with incoming ACB or MCCB, form of separation matched to the project spec, and busbar and breaker ratings confirmed against the protection study rather than assumed. Quoting works from the single line diagram, the outgoing feeder schedule, and the fault level at the board; NLS Power returns pricing in USD with delivery phased to match the building's floor-by-floor handover schedule where relevant.
Specifications
- ✓Type tested to IEC 61439-1/2, form of separation matched to project specification
- ✓Incoming device: air circuit breaker (ACB) or moulded case circuit breaker (MCCB) sized to the transformer or switchgear feeder
- ✓Breaking capacity (Icu/Ics) verified against fault level at the actual board location, not assumed
- ✓Busbar rated current sized to the sum of outgoing feeders plus spare capacity
- ✓Arc flash incident energy labeling available on request per project specification
- ✓Outgoing feeders sized to sub distribution boards, MCCs and major fixed equipment
Frequently Asked Questions
What's the difference between a main distribution board and LV switchgear?+
LV switchgear carries the full incoming supply directly from the transformer or generator. The MDB sits one step downstream, taking a large feeder from the switchgear and splitting it into the major outgoing ways that reach sub distribution boards and equipment.
Who supplies main distribution boards in Saudi Arabia?+
NLS Power sources MDBs built to IEC 61439-1/2, with breaker ratings verified against the actual fault level at the board rather than assumed, for commercial, industrial and healthcare projects across KSA.
Does an MDB need arc flash labeling in Saudi Arabia?+
It depends on the project specification. Hospital and data centre clients increasingly ask for incident energy calculations and arc flash labels even on IEC-based designs, since technicians open these boards routinely for metering and maintenance work.