Snag 4

A householder complained of an acrid smell of burning. Upon investigation, it was found that a 100 watt incandescent lamp had been fitted in a bulkhead luminaire with a maximum rating of 60 watts. The insulation of the fixed wiring had degraded and the moulded connector block had melted. The excessive temperatures were likely to cause a fire.

Solution

The solution to this problem is to:

• Effect repairs to the damaged equipment (the cable, the connector block and, probably, the luminaire).
• Consider selecting a replacement luminaire that can safely operate continuously with a 100 watt lamp.
• If this is not possible, ensure that the 100 watt lamp is replaced by a lamp with a dissipation not exceeding 60 watts.
• Consider using a Compact Fluorescent Lamp (CFL) or luminaire
• Ensure the luminaire is suitably marked and, if possible, all users of the installation made aware that, should a higher rated lamp be fitted, a risk of fire exists.

Good practice requires that, as far as possible, cables are routed away from sources of heat. Heat resisting sleeving should be installed to protect fixed installation cabling and, if necessary, the connecting cables within the luminaire. The means of connection, such as a connector block, must be suitable for the temperatures likely to be encountered. A porcelain/ceramic connector block may be required. The use of CFLs, provided such a lamp will physically fit and is suitable for the particular mounting position, will significantly reduce the heat production, the lamp should have a longer life and consume less energy.

Compact Fluorescent Lamps (CFLs).

The light output from a compact fluorescent lamp comes from phosphors that convert energy from a low pressure discharge into visible light. The colour temperature and colour rendering are determined by the phosphor mix coated on the inside of the tube. CFLs have the characteristics and advantages of linear fluorescent lamps but with compact size which is achieved by folding the discharge path while retaining high efficacy.

The two main groups of CFLs are those with external control gear and those with internal control gear. High frequency control gear is now available integrated into the CFL lampholder making luminaire conversion from General Lighting Service (GLS) to CFL relatively simple. A fluorescent lamp operated at high frequency (typically at or above 30 kHz) results in a reduction of losses both in the lamp and the control gear. The control gear size and weight are less, the efficiency is higher, dimming - if required - is easier and operation is almost silent.

Regulation 522-01-01

A wiring system shall be selected and erected so as to be suitable for the highest and lowest local ambient temperature likely to be encountered.

Regulation 522-02-01 (part of)

To avoid the effects of heat from external sources including solar gain one or more of the following methods, or an equally effective method, shall be used to protect the wiring system:

(i) shielding
(ii) placing sufficiently far from the source of heat
(iii) selecting a system with due regard for the additional temperature rise which may occur
(v) local reinforcement or substitution of insulating material.

Regulation 522-02-02

Parts of a cable or flexible cord within an accessory, appliance or luminaire shall be suitable for the temperatures likely to be encountered, as determined in accordance with Regulation 522-01-01, or shall be provided with additional insulation suitable for those temperatures.

This common problem is extracted from Snags and Solutions Part 1 published by the NICEIC.