Electrical safety in houses

There are a few issues with electrical safety in a house. Old electrical wiring. Overloaded electrical circuits. Fuseboxes.

1. Old electrical wiring

The first Nelson houses were not connected to electricity. Electrical lighting only became available to most houses during the 1920s. It was surprisingly late, in the 1950s, that laundry coppers that required considerable manual effort were replaced by electrically powered washing machines, complete with a ringer, and refrigerators were installed in most houses. Few power outlets were provided in homes because there were few electrical appliances available. Usually it was a solitary power outlet per room.

Electrical cabling was initially copper wires that were then coated in rubber sheathing, then wrapped in fabric, and run in 12 mm steel conduit which provided protection to the cables as well as the electrical earthing. This type of wiring is known as VIR, or Vulcan Indianised Rubber. The rubber was perishable, particularly affected by oxygen and ozone in the atmosphere, or by sulphur. Over time the rubber dried out and became brittle. Black steel conduit in the roof-space is indicative of this type of cabling, but often any wiring has been disconnected and replaced by newer cabling. This type of wiring is now illegal and houses that once relied on it should have been completely re-wired.

Immediately after the Second World War, 1945, TRS or Tough Rubber Sheath cabling was used. This can be identified because conduit was not used. Instead the insulation protection was provided to the electrical cables by a thin black rubber sheath.

Use of TRS was discontinued by the early 1960s due to the use of PVC sheathed cables. Initial attempts at the chemical formulation of the polyvinyl chloride from about 1955 had a low softening temperature and so the cabling wasn’t suited to handling much power.

Later formulations of what has become known as TPS, thermoplastic sheathed wiring, has proved to be long lasting and safe. TPS has been standard building practice since the late 1960s.

2. Overloaded electrical circuits

Many older houses have insufficient power outlets for modern electrical requirements.

The diameter of the internal copper wire may not be sufficient for modern electrical needs within a house, and the cable can become overheated and cause house fires.

Overloading electrical circuits can cause frequent blowing of fuses, or flicking of circuit breakers.

The solution is for an electrician to install additional power circuits that take into account the number and type of electrical devices drawing current so as not to cause overloading.

3. Fusebox vs switchboard

Electricity enters the house via a mains cable, either overhead or underground. It is then distributed around from a central location.

Initially this was a fuse box. In recent years switchboards, with RCDs, or residual current device, have become required in all new houses.

The fuses, or switches, are deliberate weak points in the circuit so that if there is a problem with the circuit it fails at the board, rather than short-circuiting at an unknown location in the house.

Fuseboxes are less safe than switchboards because fuses take some time to burn through. If someone is being electrocuted via, for instance, a faulty toaster, a considerable amount of current can pass through the body before the fuse has melted through.

With a fusebox you are required to remove the fuse and replace it once a new wire is installed. Hands are in close proximity to the full electrical current, a particularly unsafe operation.

Switchboards are much more effective in cutting off the power in a hurry, and can be reset very much more safely. You simply flick a switch.

It is a requirement to install an electrical safety switch, RCD, on each power circuit in new homes. This electronically tests each power circuit for earth leakage, and can work out that any plugged in appliance is faulty. It automatically switches any unsafe circuit, whether or not a faulty appliance is switched on.

It is recommended to replace an existing fuse box with a switchboard due to the substantially increased level of safety.

As a compromise fuses can be replaced with electrical switches available from major hardware stores. Ensure that the correct power rating for the circuit is installed. Lighting is usually 10 A, power 15 A, and the stove and air-conditioning circuits have a higher rating, often 30 A.

← Do I need a LIM, Land Information Memorandum, report from the council? High moisture levels in a house? →