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Basic Lighting Questions

Postby ericmark » Sat Jun 14, 2008 4:20 am

With any electrical testing there are two methods adopted.
1) Jumping to likely faults
2) Sequential testing
The former can be quicker but also can fail the latter will find the fault. Working in a factory where there are plans and all cables are accessible using the latter makes good sense but in a house with many cables buried one can only guess on routes and one has to jump to likely faults.
Some pointers though are:-
1) Check the bulbs are good.
2) Do not use energy saving bulbs to fault find with.
3) Invest in a cable finder and good meters.
4) Make notes.
5) Enquire about work undertaken in house.
As time goes on one finds repeated faults for example one whole sale outlet in my area was selling populated consumer units and they would place the MCB’s in the unit. In theory the electrician fitting the unit should check the tightness of all screws but in fact they would only tighten those they had used and it became a common fault to find the screw connecting the MCB to the bus bar was lose. So it for a time became first item to check. An old poor quality transistor radio is a good tool as it will crackle with sparks from bad connections especially if off channel. In industrial premises we often used a heat gun to find faults where items were hard to access. There is really no magic wand just a lot of thought on each system.
With domestic lights one would try to work out the likely route and check the lamp before the one not working.
So there is no real correct order as such.
You must also remember on forums like this you may get 100’s of people reading a post and acting on it even though it is aimed at you. It I suggested the first place to look is the consumer unit and explained how to remove the protective covers and test the output from the 6 amp MCB there would be a high chance others with little or no experience will also try that method and be unaware of the dangers from ionisation try measuring with the meter on the wrong range and suffer very nasty burns as a result. Because of this I don’t recommend methods which if I was answering the same post on the IET forum designed for the trade would be recommended without much hesitation. The other point is you have talked about India and although they may follow some of our practices I could very easy direct you completely wrong.
Having worked in Algeria, Falklands, and Hong Kong plus working on Dutch, German and Turkish systems I realise how easy it would be to give completely wrong information. For example the Dutch system I worked on had the switch after the bottle fuses so fuses always connected to a Phase and there were special tools to allow live working. Your general questions are good but will get very general answers.

All best Eric


Simply Build It

Postby DIYvirgin1975 » Sat Jun 14, 2008 9:21 am

I have a basic idea on the list of checks that need to be made in the UK in domestic premises when a light is not working they are as follows:-

Change the lamp
Take a visual check
Isolate the circuit and check for loose connections.

if this fails then testing needs to be done on a instrument but which tests need to be done and why ?
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Postby ericmark » Sun Jun 15, 2008 7:01 am

In a house because it is hard to trace wires one jumps to easy points. So at lamp not working testing at rose is there a supply Line / Neutral and if not is there a supply Line / Earth if not and neon screwdriver is available any supply to Line. It is common to lose neutral which is why we try to test the line against something else it not showing live to neutral. Because the black wires are often used as switch wires it is easy to get them mixed up. Any faults at rose then you need to return to last working lamp if no faults at rose then go to switch. Here we have a danger that when removing the switch wires can come out so it is never removed live. Also we have a problem of nothing to measure against often plastic switches on plastic back boxes do not have earths connected so we must isolate on a double pole switch not just at MCB and one wire will need removing and the switch belled out with ohm or buzzer setting on meter once the test is completed ensure the meter is returned to volt or off position as making any mistake and trying to measure volts on any other range than volts can both burn out meter and cause an explosion. Meters used on mains should have leads to GU10 but only really expensive ones come with them as standard. If this fails to find the fault one has to use experience to work out the next likely point where it may have failed main thing is to look for new work. Remember you may have floor boards nailed through the cable etc. So turn off power before lifting any boards etc. Those nails may be live. The same goes for pictures on the wall etc.
All this is not really a DIY job and I would strongly advise you don’t do it your self. I have told you how as better you do it in a safe manor than like bull in china shop but even electricians can make mistakes and if you initiate ionisation of the atmosphere burns can be horrific plus the chance of getting a shock. A simple mistake like leaving meter on wrong range can cause this.
I hope you can see your own limitations and keep within them.
Yours Eric

Postby DIYvirgin1975 » Sun Jun 15, 2008 7:52 am

Is the name of the test (Insulation Resistence) that needs to be done when finding the fault ?
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Postby ericmark » Mon Jun 16, 2008 10:31 am

Sorry to say your well off the mark. It is because people make mistakes like the one you have made but unlike you don’t write themselves and just read other posts that we get uneasy at giving advice with could involve unseen dangers.
There are a hundred and one ways to test a system and still come out with the same result so when teaching an apprentice we have to explain the basics then guide them to find their own method to fault finding.
We explain how the power requires two wires not one and how it has a feed and return starting with a battery switch and lamp we explain how it is wired and why then slowly move them to AC and then from the extra low voltage to the low voltage house hold mains.
To try and jump all the basic training and go directly into fault finding in most cases does not work mainly because of the technical terms. Earth Fault Loop Impedance or EFLI most electricians will understand but to most DIY’ers it is some magical thing which electricians talk about and if they nod their head it will go away. If however we talked about the resistance of a circuit when it has a fault to earth and explain we are working out if enough current would flow to blow a fuse in 0.5 seconds if we should get a fault there may be some understanding but EFLI has grown to a paragraph and unless we were to basically write a whole text book and put it on these pages it can’t be done.
I can see your trying to learn but you need to read a few text books first and get some of the basics.

Sorry Eric

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