Why do bulbs blow all the time?

[bergie]

as andy said bad contact on the light fitting lampholder is the main culprit. many customers have told me the same thing and i replace the lampholder or fitting and the problem never reoccured.
on the bc lampholder the 2 pins have springs pushing it out ,if those springs are weak there will be a bad contact. on the es lampholders you can bend the centre and side tabs out again to make better contact.(if you are a cheapskate)

[Houses4Rent]

Thanks AndyD. I knew bad connections can make it flicker and eventually tire it out, but not blow it instantly. Learnt something

bergie, the centre contact is exactly what I am going to check first. Then the wire connections at that fitting.

Thanks all.

[AndyD]

Good luck. Please isolate the main supply at the DB if you're gong to fiddle with the fittings, rather be safe than sorry.

[gobbleteller]

"The aim of this part of SANS 10142 is to ensure that people, animals and
property are protected from hazards that can arise from the operation of an
electrical installation under both normal and fault conditions. An electrical
installation has to provide protection against
– shock current,
– overcurrent,
– fault current,
– overvoltage,
– undervoltage,
– excessive temperatures, and
– electric arcs.
If any of the above arises, the protection should automatically disconnect the
supply or limit currents and voltages to safe values....."

5.1.2 Temperature

5.1.2.1 Unless otherwise permitted by an applicable standard (see 4.3
and table 4.2), electrical equipment shall be so designed, positioned and
protected that accessible parts under normal operating conditions do not
reach a temperature (safe touch temperature) that exceeds
a) 70 oC in the case of metallic parts, and
b) 90 oC in the case of non-metallic parts.

There is no such temperature- regulating switch, apart from thermostats. But what the SANS is referring to is that the installation must be designed and installed in such a way as not to produce excessive heat. Installing too many socket outlets or lights on a single circuit will cause excessive current flow above the rated value of the cabling and components. Using an under rated cable to feed a motor will also cause excessive heat issues. Consider a 1.5mm2 cable that is rated at 19A carries 25A due to the amount of lights connected to it: not only will a lot of unwanted heat be generated, but after time the insulation will become brittle and break off (or even melt off). Also, loose connections are another source of unwanted heat from which the installation must be protected.

5.1.2, in my opinion will relate to the positioning of electrical equipment such as motors, geysers etc in that they must not be able to produce temperatures higher than those stipulated. For example, if an installation has a borehole or swimming pool pump, the pump should be positioned in such a way that the sun will not increase the motor's touch temperature to more than the above values.

[Houses4Rent]

Sure, at the very least I take all light circuit breakers down. Sometimes tenants have stuff plugged in or machines running which makes taking the mains out not feasible.

[ACEsterhuizen]

I beg to differ, the way I read it (and i might be wrong) is that:

"if any of the above arises, the protection (of the installation NOT the appliance) should automatically disconnect the supply or limit currents and voltages to safe values....."

That includes (excessive temperatures) as stated by SANS 10142. In fact it is the aim of it. To "...disconnect or limit currents and voltages..."

The "electrical installation" (which is from the point of control to the point of consumption") has to provide that "..by means of disconnecting..." and not the appliance (like the little temp switches mounted in the back of the newer ovens.

If the above is true then there is not one coc in this country that is valid. :-)

[Dave A]

How many installations provide protection against over and under voltage?

I suggest the intention of including under voltage, over voltage and temperature in the purpose statement is to ensure it is born in mind in setting the standards that follow, rather than requiring that there is equipment in place that specifically and continuously monitors the installation for these issues.