why do lights blow regularly on one circuit & very seldom on another, both supplied f

[harveya]

This is for those with much past experience!!
Could someone shed light on why lights on one light circuit fuse regularly and on other circuits almost never?
Consider this scenario:
A circuit on a 10A breaker, using FT&E 1.5mm^2 feeds a three lever 1w switch, 1st switches ceiling fan with 3 lamps, 2nd an outside floodlight and the 3rd 6 x lamps connected in parallel (60W bulbs) outside but under cover. It's the last mentioned circuit that is under question. These lights are constantly being replaced yet the others, as well as lights in the rest of the installation, hardly ever need to be replaced. All is correct as far as the wiring goes, the supply voltage acceptable at the time of measuring, although I can't say what the situation is like all the time. Can someone suggest a possible cause - other that poor quality lamps. CFL's have been tried as well and they don't last either.

[bergie]

if the fittings are old or have very low quality lamp holders then proper contact isnt made with the lamp. the contacts heat up and blows the lamp. try replacing some or all of the fittings.

[adrianh]

I've have had lights blow on the same circuit over at the moment the light is turned on.

I would hazard a guess that the switch is faulty. Could be that the contacts bounce.

[AndyD]

I've had similar problems a couple of times in the past. One was fixed by just remaking all terminations and connections on the circuit. The second one was caused by a poor connection on the incoming supply neutral in the main DB. Because it was a 3-phase DB the neutral bar was at a floating voltage which caused over-voltage damage to the lighting and a couple of appliances.

[harveya]

why do lights blow regularly on one circuit & very seldom on another

Thanks bergie, adrianh & AndyD.
It's fascinating posting a problem and getting such varied responses, which is the value of this forum. All possible causes suggested could apply and since the board in question is supplied from a 3ph source the post from Andy cannot be ruled out. An interesting point is that one of the six lights has just recently been added, is a brand new fitting with an ES fitting which should make good contact, a new bulb installed only lasted a couple of days! I will take all suggestions into consideration and apply as a process of elimination & see what turns out.
Thanks again.

[AndyD]

You're welcome harveya. I forgot to ask, does the unreliable circuit have a dimmer on it as well as a lever switch? Most CFL lamps won't run with a dimmer, there are a couple of models which you can use a specific leading or trailing edge PWM dimmer but these are few and far between.

Good luck sorting it out.

[harveya]

Morning Andy. No dimmer on this circuit, just a straightforward light circuit with 6 lamps on it!

[murdock]

i would do a loop impedance test on the circuit...megger the circuit and fit a recorder.

sometimes when there is a low insulation reading it will pop the lamps.

i assume they are on the same phase because they go thru a 3 lever switch?
are there big compressors or heavy loads close by?
is the building earthed correctly?
are the lamps rated for the correct voltage?
are the lights all on all day or do some switch on at night and others during the day...ie are they all on at the same time?
you said es lamps are they all connected to the correct polarity.
has this issue started recently since the new fitting was installted or has it been problem for a long time?

we can only guess without prior knowledge of the insallation

[Master Electrician]

I would like to suggest that there is a faulty capacitor or discharge resistor in the ceiling fan in circuit 1. It is discharging through the lighting circuit instead of the discharge resistor.

[mikilianis]

How would the capacitor discharge through the lighting circuit ?

[AndyD]

Not too sure mikilianis, usually the cap on a motor would discharge through the windings when the power is switched off. Also being a ceiling fan it should be on a 2-pole switch (assuming compliant installation) so both live + neutral would be isolated.

[Sparks]

Another possibility which has not been mentioned is cheap imported lamps. They do not have enough solder to make decent contact. I have found replacing cheap lamps solved the problem on a number of occasions.

[AndyD]

Good point, I assume you mean on the bottom tip of the lamp.

This problem could also be compounded by insufficient spring or travel on the center contact inside the lamp holder or previous over-tightening of a lamp in the fitting which is all too common.

[Martinco]

Another possibility which has not been mentioned is cheap imported lamps. They do not have enough solder to make decent contact. I have found replacing cheap lamps solved the problem on a number of occasions.

Sparks, you have a point there !
These imported jobs ( normally from China ) are really cheap and nasty and do not have a good life.
What about replacing one or two with CFL lamps and compare.

[Martinco]

While we are on the subject of lamps................has anybody ever found a "8000 hour" CFL to last even close to the 333 days (continuous) on nearly 3 years if only used 7-8 hours / night ?