Basic Lighting Questions Ask questions and find answers to many subjects relating to electrics and electrical work

[DIYvirgin1975]

What is a contactor switch ? Whats the difference between a normal light switch and a contactor switch and how is it wired ?

[ericmark]

I am guessing you are working on something big? With large building three phase is used for lighting and so a contactor is fitted and the switch only powers the contactor. This takes the load away from the switch. Also used with time delay etc. It also could be just a switch after all in all the old films they never shouted "turn ignition switch on" they shouted "Contact". So where have you heard the term "Contactor Switch"?

[DIYvirgin1975]

They usually call it contactor, so contactors are used on large sites. What's wrong with having a normal wired two way or three gang switch. Explain please

[sparx]

Hi don't know who 'THEY' are, but as ERIC said two or more reasons for using a 'contactor',
First would be in the same way as you have one in every motor vehicle only mechanics call it a solenoid, it acts as a slave device ie it would not be practical to wire the starter motors main cable through an ignition switch so there is a remote contactor/relay/solenoid on the starter whoes contacts are made by a small circuit from ignition switch energising a coil to 'pull-in' the main contacts to put 100Amps or so to starter.
Another use of a contactor would be to allow small switch / timer / sensor only capable of switching a 5A load to operate several kilo-Watts of lighting such as used to floodlight a building from one dusk-to-dawn sensor.The contactor could have 4 contacts each one carrying a different circuit.
hope this is helpful,
regards SPARX

[DIYvirgin1975]

I get confused with the following tests
Earth loop impedence
Continuity
and insulation resistence

What would be the most populiar test you would do if their were lights that were not working ?

[ericmark]

Earth loop impedance. Is the resistance measured that will stop current flowing to earth should there be a short circuit. It is measured in ohms between live oops not called that now I mean Line Conductor and earth. It needs a special Earth Loop impedance meter that measures and calculates the parameters and displays directly as Earth Loop impedance and plugs directly into the 230 volt supply. According to the MCB’s or RCD’s in the consumer unit it must be below a set figure taken from a table for example if the biggest MCB was a B32A then 1.44 ohms or lower would be required at the furthest socket from the consumer unit. It is normally measured with a special meter with the power one.
Continuity. Again measured in ohms means basically something is connected. This can be measured with a low ohm ohm-meter which must use not less than 200mA at between 4 and 24 volt (i.e. not a multi-meter) and can be added to the value of earth loop impedance given by the supply authority to give the final earth loop impedance before power is put on the circuit. We talk about R1 + R2 where this is the resistance of the Line Conductor + Earth Conductor.
Insulation resistance This is resistance to flow again measured in ohms or more likely meg ohms and controls the amount of current that can leak away to earth. Nothing is a perfect insulator there is always a little current that can flow we hope in an insulator it is very low. We look for a value in excess of 1MΩ and it uses a special meter able to produce 500 volt to take this measurement with.
All three use special meters the last two normally use the same meter which is normally duel function. There is a third meter used to test RCD’s which both measures mA required to trip and time taken. The first meter is normally also able to measure the prospective short circuit current as well.

[DIYvirgin1975]

So if my lights were not working the insulation resistence would be the first test i would do to check their is supply coming in ?

[ericmark]

No the Earth loop impedance, and Insulation resistance are tested to insure safety. You may test Continuity but fault finding there are different tools. The first is ones eyes and looking for faults, when a quick look fails then the test lamp. The simple test lamp draws current enough to ensure it’s a real supply not a return but also we used a neon tester these draw very little current and we can test without tripping the earth leakage trip. We also have a proving tester this tests the neon tester is working so if we are looking to test something is dead we can be sure the testers OK. We also use a multi-meter these often have a clip on part so we can test current so we can see remote from what we are testing if it has switched on. And also often a buzzer on the continuity test handy when ringing out wires. Plus the volt meter which in real terms is very little used.
So if your lights are not working first I would ask questions has anyone been working on them, did they flicker etc then to visible test. Has the MCB tripped out, or is the fuse OK. You may put millimetre buzzer across fuse once removed. Also look for any new lamps where the customer may have tried some DIY often they will not admit what they have done. Always walk the whole circuit in case someone is working on it. Assuming you sockets were OK then you would switch off the lighting circuit easiest is switch off whole supply and tape the switch so people can see switched off on purpose and not tripped the look at closest lamp and gently pull each wire to look for bad connections. This would be repeated with any other lamps likely to be first in the chain. If this failed then the power would be switched on and voltage checked at the lamp with a test lamp or meter with GS38 type leads not the cheap leads that come free with many meters. (GS38 leads have only 1mm of probe showing and guards to stop fingers slipping forward onto connections and fuses built in and are designed for mains)
The tests for health and safety use completely different meters to those to repair the installation. There is of course an over lap and if for example an earth leakage device would not hold in then stage one would be to test Insulation resistance then if that was OK the trip its self. And once a repair is complete one would test to ensure one had not made any mistakes for a socket the earth loop impedance tester and prospective short circuit current would test for polarity, and bad connections, plus extras like if there is a good earth in the house. This is one reason the minor works certificate has to be filled in. It forces the electrician to check type of supply, size of protective device, Insulation resistance, Earth fault loop impedance, Polarity, and RCD times. This will high light any faults in the system as well as what he has just worked on and there was a famous court case where the electrician was found guilty of manslaughter not just for his mistake but also for missing mistakes made by those who had worked on the house before him. At that case it was stated if an electrician fits a plug in the premises it is to be used in he should also check the socket it is to be plugged into.
The same applies to any DIYer in that if he causes injury to someone other than himself he can also be taken to court very likely if injured person is young. And now with Part P he can even be taken to court for injury to himself.
From your posts I can see you are trying to learn and we will all help but a lot more people read these than you and the idea of a lot of DIY people sticking meter leads in holes makes me very nervous. I will not allow apprentices to have any ammeter other than a clip on as ionisation of the atmosphere is one of the biggest dangers to electricians and using a meter which is switched onto an amps range by mistake is one of the biggest causes. Electricity bits!

[DIYvirgin1975]

I was connecting a light fitting in India and i asked were the neutral and live connection was and i was told it doesnt matter . can someone explain why is this ?

[ericmark]

The word "Live" refers to both "Line" and "Neutral" so you question could have well been "were the neutral and neutral connection was" many countries do not use polarity with there plugs and sockets and use double pole switches on everything something we now have to do in order to be harmoised with Europe. The reason we have to ensure Line and Neutral are the correct way around is because of the fuses in our plugs, we only fit one fuse which is the main problem in not identifying which is which as fuses should only go in the Line and not in neutral so linked trips have to be used. Well they would if they followed the regulations. Portable appliances if they require fusing should not rely on the fuse in the plug as if used in Europe the plug could be changed for one without a fuse. The same does not apply to fixed appliances like central heating boilers where it is acceptable to fuse in the FCU. Some times even big firms get things wrong I worked on a small Honda duel voltage generator and on 110v all was OK but on 230v we had 57 - 0 - 173v giving an un-fused 57v I switched to 110v (55 - 0 - 55) and removed change over knob.

[DIYvirgin1975]

What's the diifference between single pole and double pole switches and when will each one be used ?

[ericmark]

Because in this country we use a star supply the centre point is connected to earth. This gives us a number of safety features mainly in if the high voltage should ever get connected to the low voltage it would give a massive short circuit and blow the fuse before anyone gets injured. Since our single phase supplies are taken from the star point to a Phase putting fuses and switches in the Phase only will produce very few problems and is easier and cheaper. This relies on all plugs and sockets being of a non reversible type. From the 1st July all plugs and sockets in the UK must be non reversible (So much for harmonisation?) but in the rest of Europe there is no requirement to even indicate which is Line and which is neutral and as a result from the plug onward everything must switch both Line and Neutral since we also are not permitted to switch the neutral without the Line. Switches or overloads must be used in linked pairs. This leaves a problem with fuses and means no volt relays will be required to ensure both Lives are removed if either Line or Neutral fuses blow. This has been done in three phase supplies for many years to stop single phasing of motors etc. With the introduction of current earth leakage devices neutral earth faults became a big problem and over the years more and more twin pole switching has been used, also to harmonise with Europe we have insisted that portable equipment has twin pole switching and that the fuse in the plug is only to protect the cable again so if used in Europe it will not cause danger with their inferior system. 553.1.2 says must be non reversible type 553.1.5 give exception for shaver plugs and sockets if to BS EN 61558-2-5 Cable couplers also are allowed to be reversed only with Class II equipment 553.2.1 I am not sure how this will affect imported equipment from Europe as it has been common to provide Europe type sockets inside electrical cabinets to plug in the likes of Laptops to allow programming of the machines.
But the real problem is we follow the rules but the rest of Europe only pay lip service to the regulations.

[DIYvirgin1975]

How do you work out the amount of lights needed for a circuit to prevent over load.

[ericmark]

Most ceiling roses are only rated my manufactures as 5 or 6 amp so that is normally the limiting factor. Watts = Joule/sec but in electrical terms Watts = Volts x Amps so at nominal volts of 230 thats max 1380 Watts. Each switch should control no more than 1/3 of the total to avoid the problems with the extra current used on switch on but it is simply a matter of adding all the watts and ensuring it does not exceed the 1380 total. Because it is unusual for all lights to be switched on together some people exceed this limit and use something called diversity but when doing that all normal fitting have to be considered as 100W where in real terms most fittings restrict the bulb size to below that figure so in real terms there is very little difference between real max and max with diversity taken into account.
Biggest problems today is with the move from fuse to MCB inrush especially to extra low voltage transformers can trip MCB's on switch on if too many are switched together and also the ionisation which takes place when a bulb blows within the bulb should blow the bulbs built in fuse but now often takes out the MCB. Under the new regulations it is more careful to say how the same protection device should not be used for lights and power outlets in the same area so lights and sockets in the same area can't use same RCD.
Old houses would have one single lighting circuit but latter houses split them upstairs and downstairs with modern houses not sure how lights will be split because they may need to follow the power socket split so we may see some side to side splitting. Because it is likely that either upstairs or downstairs sockets are used but not at same time so side to side split of sockets gives more even demand to ring mains also it reduces cable length and so volt drop. With new RCD rules lights may need to follow socket wiring.

[DIYvirgin1975]

What is the list of checks you need to do in the correct order to test why a light is not working ?