BUILDING SERVICES TWO (BLD60503)

ELECTRICAL INSTALLATION

Prepared by Tan Hee Chai

BUILDING | SERVICES | TWO (BLD60503)

Earth Straps

•All metal works in electricity hazardous areas •All electrical outlet points must have a screwed terminal earthing point.•Must be bonded together and strapped to a tested earth leakage point.•Also to taps, waste outlets, grab handles, and any metal work•This is to prevent significant voltage differences at any point contact.

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

Cables

May be flexible or rigid & consist of conductors, insulation and mechanical protection.

•Portable appliances – use flexible•Permanent wiring installations – rigid.

BUILDING | SERVICES | TWO (BLD60503)

• Conductors must be material of low electrical resistance which convey current with smallest voltage drop.

• Regulation requires voltage drop from consumers’ terminal to any point not exceed 2.5% of declared nominal supply voltage when carrying full current load.

BUILDING | SERVICES | TWO (BLD60503)

Copper most common used as conductors due to •tenacious (firm hold) •highly resistant to atmospheric corrosion. •Malleable and ductile (easily bend into shape like wire)when in anneal state•Very low electricity resistivity•Resistance increased when hot•Copper wires easily joined by soldering

BUILDING | SERVICES | TWO (BLD60503)

Aluminium as alternative conductors

•Cheaper than copper though not so corrosion resistant.•25% large in diameter that copper required to carry same current load.•Less dense, so lighter than copper.•Larger circumference require more material for insulation.

BUILDING | SERVICES | TWO (BLD60503)

Insulating materials used for internal circuits include:

PVC •A good insulating material•Good resistance to moist oils, acids and alkalis•Not greatly affected by sunlight but soften at high temperature above 80º Celsius and brittle at low temperature.•Water resistant and self extinguishing in event of fire.•Become corrosive at high temperature above 115º C

BUILDING | SERVICES | TWO (BLD60503)

Insulating materials used for internal circuits include:

Butyl rubber and silicone rubber•Both used as insulators particularly in high temperature

Paper•Common for underground cables and in industrial buildings as an additional means of insulating/sleeving cables

BUILDING | SERVICES | TWO (BLD60503)

Insulating materials used for internal circuits include:

Magnesium oxide powder•In a compressed form and must contained in sheath which protects it from moisture.•Sheath is of copper

BUILDING | SERVICES | TWO (BLD60503)

Insulating materials used for internal circuits include:

Mineral insulated copper sheathed (MCIS) cables•Used below ground provided adequate precautions are taken against ingress of moisture. •Copper sheath maybe covered with PVC as protection against environment which is corrosive to copper.•Suitable for high temperature situations and those contact with oil or grease•Requires special joint and technique for sealing cables

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

Fixing of cables:•Termination must not subject to strain•Regulation requires degree of support when run in accessible situations.•Unsheathed cables in conduits must be supported by bends with proper radius when cable length exceeds 5m.•Non-armoured, lead sheathed cables must be supported at intervals not exceeding 2m•Cables are enclosed in conduit and trunking for commercial buildings, hospitals etc

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

BUILDING | SERVICES | TWO (BLD60503)

The End