Power Distribution

Power distribution takes electricity from the main switchboard to the points of use: sub-main cables and busducts in risers, distribution boards on each floor or tenancy, final circuits to outlets, lighting and equipment, residual current devices (RCDs) and other protection, metering for tenants and services, and the trays, ladders and conduits that carry cables. It is the most altered part of a building's electrical system, because every fit-out touches it.

Metering and ownership vary by building type. In multi-tenant commercial buildings the owner may meter tenants with check meters or recharge by area. In apartment buildings, residents are either supplied by the network directly or through an embedded network owned by the building, which carries its own regulatory and consumer obligations.

What shortens life:

• Heat: cables bundled together, run through insulation or in hot ceiling spaces and plant rooms lose capacity and age faster.
• Overload from added equipment, power boards and extension leads.
• Alterations by tenants and contractors without records or proper protection.
• Harmonics from electronic loads overheating shared neutrals.
• Mechanical damage by other trades in ceilings and risers.
• Moisture in basements, car parks and external areas.

Insulation breakdown

Rubber insulation hardens, cracks and falls away with age and heat, leaving bare conductors in light fittings, switches and ceiling spaces. Disturbing old cables during renovation accelerates the breakdown. PVC insulation that has been overheated becomes brittle and discoloured around terminations and in bundles.

Connection failures

Terminals at outlets, switches, joint boxes and boards loosen with thermal cycling and poor workmanship; resistance and heat rise until the accessory scorches or ignites. Aluminium branch wiring in United States houses of 1965 to 1973 does this at devices not rated for aluminium; remediation with approved connectors or rewiring is the accepted fix.

Absent or failed RCD protection

RCDs disconnect a circuit when current leaks to earth, protecting people from electric shock. Older installations often have none, or only on some circuits; devices that are never tested can fail to trip. Wet areas, outdoor circuits and portable equipment circuits are where the absence matters most.

Busduct joint failure

Busduct sections are joined with bolted connections that must be torqued and checked. Loose joints overheat and fail; tap-off units opened or moved by tenants are a common source of faults.

Undocumented alterations

Fit-outs add circuits and sub-boards, remove or bypass protection, reuse old cables, and leave boards without circuit schedules. Over time nobody knows what a breaker controls, and isolation for maintenance becomes unsafe.

Harmonics and neutral overheating

Computers, LED drivers and variable speed drives draw distorted current. On three-phase circuits that share a neutral, some harmonic currents add rather than cancel, so the neutral can carry more current than the phases and overheat, particularly in older installations with reduced neutrals.

Fire-stopping breaches

Every time cables are pulled through fire-rated walls, floors and riser slabs, the fire stopping is disturbed. Unsealed penetrations let fire and smoke spread between compartments; risers in older buildings are often riddled with them.

At distribution boards

• Board type, age and maker; rewireable fuses, cartridge fuses or breakers; RCDs present on which circuits.
• Circuit schedules present and accurate; boards added by tenants.
• Discolouration, burn marks, melted insulation, a smell of hot plastic.
• Missing blanks and covers exposing live parts.

In ceilings, risers and occupied spaces

• Rubber-insulated cables, especially at light fittings and old switches.
• Unsupported cables draped over ceilings; damaged sheathing.
• Unsealed cable penetrations in risers and walls.
• Scorched or warm outlets and switches; flickering lights.
• Daisy-chained power boards and extension leads, signs that circuits are too few.

In the records

• Periodic inspection and test reports with observations and their codes.
• RCD test records.
• Circuit schedules and as-built drawings.
• Thermographic surveys of boards and busducts.
• Metering arrangements and any embedded network documents.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A licensed electrical contractor or electrical engineer carries out a periodic inspection and test.

• Visual inspection of boards, a sample of accessories and accessible wiring, with covers off where safe.
• Testing of a representative sample of circuits: insulation resistance, earth continuity, polarity, earth fault loop impedance, and RCD operation times.
• Wiring type survey to identify rubber-insulated, aluminium or other at-risk wiring.
• Thermographic survey of distribution boards and busduct joints under load.
• Load and harmonic measurement where overload or neutral heating is suspected.
• Fire-stopping survey of risers and penetrations.
• Documentation review: circuit schedules, drawings, metering.

The report should list observations by severity code, sample results extrapolated to the installation, wiring types and extent, boards needing replacement, fire-stopping breaches, and the next inspection date.

• Rewiring of rubber-insulated and other end-of-life circuits, usually floor by floor or tenancy by tenancy.
• Aluminium wiring remediation with approved connectors at every device, or rewiring.
• RCD protection added to circuits without it, or boards upgraded to RCBOs.
• Board replacement where devices are unsupported or boards are unsafe.
• Busduct maintenance: torque checks and joint replacement.
• Neutral upgrades or harmonic filtering where neutrals overheat.
• Fire stopping of every penetration with tested systems, recorded with photographs.
• Documentation: circuit schedules, labelling and as-built drawings.
• Additional circuits where loads have outgrown the installation.

• Load management: redistribute circuits and add submains where boards are overloaded.

Periodic inspection and testing is a recurring lump sum. Rewiring is priced per circuit, per floor or per tenancy, with ceiling access and making good often the largest component. Boards are priced per board. RCD upgrades per circuit or per board. Fire stopping per penetration or per riser. Busduct joint work per joint.

Testing and safety rectification are code compliance; rewiring and board replacement are lifecycle; repairs are repairs and maintenance. Rewiring is usually best timed with fit-outs, when ceilings are open.

• Australia. Installations follow AS/NZS 3000, with periodic verification to AS/NZS 3019; RCD protection is required on new and altered circuits; electrical safety regulators in each state set licensing and notification. Embedded networks in residential buildings are regulated by the Australian Energy Regulator and state rules.
• United Kingdom. BS 7671 governs installations and requires RCD protection on socket circuits; periodic inspection results in an Electrical Installation Condition Report, required at least every five years for privately rented homes in England; the Electricity at Work Regulations 1989 require installations to be maintained safe.
• United States. NFPA 70 (the National Electrical Code) governs installations, including GFCI and AFCI protection; NFPA 70B sets maintenance; the Consumer Product Safety Commission publishes guidance on aluminium branch wiring remediation.

• Periodic inspection and test reports with observations.
• RCD test records.
• Circuit schedules and electrical as-built drawings.
• Thermographic surveys of boards and busducts.
• Rewiring records and dates.
• Fire-stopping records for risers.
• Metering and embedded network arrangements.

• Records of electrical fires, scorching or tripping incidents.
• Tenant fit-out electrical certificates.