[Question] Why do bulbs blow all the time?

[Houses4Rent]

I am managing a flat where the light bulbs in the one bathroom blow all the time. The tenants did not tell us and basically did not use the bathroom for three months as there is no window (no light). Now they moved out and we found out about it. I doubt the old tenant had bought a bulk pack of dodgy bulbs which might explain the problem, so there must be another reason.

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

[Justloadit]

Temperature

What kind of bulbs, incandescent, CFL or LEDs

[Houses4Rent]

Thanks, they are incandescent as far as I know (plain good all white standard bathroom ball type fitting), but could double check if need be.

Bulbs should withstand its own operating temperatures I would hope.

[adrianh]

Humidity. Our one bathroom light is the same. I think it happens in the paticular bathroom because the light fitting is very close to the shower. The moist hot air must be driven across the bulb given the airfow between the window and the door. A solution might be to ensure that the globe is housed in an airtight fitting.

Anyhow, call this lot my own theory on the problem.

[Houses4Rent]

Hm, you might have a point. However, there is no window, just a small extractor fan, not much air movement I would think. The bathroom next door also has no window and an fan, but just a bathtub which they fitted with a handshower. Difficult to say whether humidity levels are really different.

Either way you seem to agree with me that it its not an electrical problem?

[adrianh]

I doubt that there is an electrical problem. There is a tremendous amount of air movement in any bathroom even if it is totally enclosed. Remember that hot air rises due to its lower density. I think that one would find that the hot moist air first passes over the bulb before it cools and sinks down. I think that one could prove my theory by injecting a small amounts of smoke into different points in the expected path of the airflow and following the path that the smoke takes.

[Justloadit]

I say that it is temperature, especially with incandescence. The fact that the globe is designed to run at about 180 degrees, it still relies on the ambient to keep the globe cool. Remember that the filament is being driven hard to be able to light up with the current flow, and it too has a maximum operating temperature before metal fatigue plays a roll in its destruction.

There is also the number of switch on times to contend with. Being a mechanical device to create light, the cold resistance causing fatigue, and the mechanical 50Hz shock of every time being switched on probably all contributes to the demise.

How many times have you heard the globe element pop at switch on when it fails.

[Houses4Rent]

All makes sense, thanks. I also have seen many bulbs pop when the switching on spike hits it.
However, I just cannot get my head around the fact that it only happens in that particular bathroom so often. They said a few days and its gone again. No fatigue should set in so quickly and so regularly.

[ACEsterhuizen]

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.

[adrianh]

I say that it is temperature, especially with incandescence. The fact that the globe is designed to run at about 180 degrees, it still relies on the ambient to keep the globe cool. Remember that the filament is being driven hard to be able to light up with the current flow, and it too has a maximum operating temperature before metal fatigue plays a roll in its destruction.

There is also the number of switch on times to contend with. Being a mechanical device to create light, the cold resistance causing fatigue, and the mechanical 50Hz shock of every time being switched on probably all contributes to the demise.

How many times have you heard the globe element pop at switch on when it fails.

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.

[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.