Why do bulbs blow all the time?

[AndyD]

What can be a possible reason why bulbs in one room/one fitting blow all the time?

The bigger question for me would be how anyone could go without using the bathroom for months

A poor electrical connection can cause lamps to blow. If it's just one fitting then it could be the lamp holder itself not making a good connection with the base of the lamp when it's screwed in. If it's an entire room or rooms with multiple fittings then it could be a poor connection on the wiring somewhere in the ceiling. I've also seen a case where the light switch was old and made excessive arcing inside when operated which caused lamps to blow frequently, when they're new they operate with a distinct snap action to prevent arcing but older switches can lose their 'snap' which means they make and break slowly. Finally if it's an entire house that's got a problem with lamps blowing it's possible the poor connection could be in the DB at the circuit breaker or on the neutral bar.

I'm not sure about the humidity theories, humidity could have an adverse effect on lamp longevity but I'd suspect it would be a much less than arcing. If it's halogen downlights they should be using the variety with the galss cover over the front of the lamp and this type should be protected from himidity and spalshing water by that extra cover.

Operating temperature has a big effect on the lifespan of energy saving lamps such as CFL's and LED's but some filament lamps, especially halogen lights require a temperature above a certain threshold to operate properly, if the lamp runs too cool the filament wears out faster than if it runs hot enough becaues the vapourised tungsten doesn't reassociate with the filament. For info on this google 'halogen cycle'.

High voltage can also negatively affect lamp live, even a 5 or 10% over-voltage can cause rapid lamp failures. This is kinda rare though and would probably only be the case if the property is very close to the main Eskom supply transformer. It's also possible though on a 3-phase installation with a loose neutral connection that the L-N voltage on one of the phases can become elevated and low on another phase depending on the balance of the load.

The problem is if it's caused by arcing, which I think would be the most likely, then it can also be a fire hazard. Arcing connections get very hot and are often the cause of combustion which causes house fires. I'd suggest it would be prudent to get a sparky to check the circuit connections on the enitire light circuit including the light fittings, any cabling in the ceiling, the switches and all the way back to the DB.

Talking about temperatures can someone please advise on how an installation would be protected against "excessive temperatures" by means of disconnecting or limiting as described below? I have never come across a "temperature switch" which protects the whole installation? or monitors it?

The electrical installation doesn't protect directly against excessive temperatures, only indirectly. The RCD or MBC on the circuit would facilitate disconnection at the point the excessive temperature became sufficient to cause an insulation fault resulting in a short circuit or an earth leakage current to flow.

[Justloadit]

Talking about temperatures can someone please advise on how an installation would be protected against "excessive temperatures" by means of disconnecting or limiting as described below? I have never come across a "temperature switch" which protects the whole installation? or monitors it?

Page 3(a):

"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.

They are talking about the equipment. You could use the following :-
Here is a 70Degree Switch
Here is a 90Degree

[Justloadit]

If it is temperature then why don't outside globes blow all the time. Surely they are exposed to far greater temperature extremes during their lives. Outside lights are sometimes turned on and off during the searing heat of day or the freezing cold of night yet they don't seem to blow that often.

There is movement of air which keeps the ambient temperature down, in the bathroom, in this particular application, there is no window, and the hot air remains close to the ceiling, and keeps on going up and up

[adrianh]

There is movement of air which keeps the ambient temperature down, in the bathroom, in this particular application, there is no window, and the hot air remains close to the ceiling, and keeps on going up and up

Fair enough.

[adrianh]

The bigger question for me would be how anyone could go without using the bathroom for months

A poor electrical connection can cause lamps to blow. If it's just one fitting then it could be the lamp holder itself not making a good connection with the base of the lamp when it's screwed in. If it's an entire room or rooms with multiple fittings then it could be a poor connection on the wiring somewhere in the ceiling. I've also seen a case where the light switch was old and made excessive arcing inside when operated which caused lamps to blow frequently, when they're new they operate with a distinct snap action to prevent arcing but older switches can lose their 'snap' which means they make and break slowly. Finally if it's an entire house that's got a problem with lamps blowing it's possible the poor connection could be in the DB at the circuit breaker or on the neutral bar.

I'm not sure about the humidity theories, humidity could have an adverse effect on lamp longevity but I'd suspect it would be a much less than arcing. If it's halogen downlights they should be using the variety with the galss cover over the front of the lamp and this type should be protected from himidity and spalshing water by that extra cover.

Operating temperature has a big effect on the lifespan of energy saving lamps such as CFL's and LED's but some filament lamps, especially halogen lights require a temperature above a certain threshold to operate properly, if the lamp runs too cool the filament wears out faster than if it runs hot enough becaues the vapourised tungsten doesn't reassociate with the filament. For info on this google 'halogen cycle'.

High voltage can also negatively affect lamp live, even a 5 or 10% over-voltage can cause rapid lamp failures. This is kinda rare though and would probably only be the case if the property is very close to the main Eskom supply transformer. It's also possible though on a 3-phase installation with a loose neutral connection that the L-N voltage on one of the phases can become elevated and low on another phase depending on the balance of the load.

The problem is if it's caused by arcing, which I think would be the most likely, then it can also be a fire hazard. Arcing connections get very hot and are often the cause of combustion which causes house fires. I'd suggest it would be prudent to get a sparky to check the circuit connections on the enitire light circuit including the light fittings, any cabling in the ceiling, the switches and all the way back to the DB.


The electrical installation doesn't protect directly against excessive temperatures, only indirectly. The RCD or MBC on the circuit would facilitate disconnection at the point the excessive temperature became sufficient to cause an insulation fault resulting in a short circuit or an earth leakage current to flow.

Makes good sense too.

[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.