Polarity: Testing at light switch

[Dambo]

Polarity does my nut in!!! headbang

When testing polarity at a light switch why is the test carried out between L and E? And is this a dead test?

 

[green-hornet]

The live is going to be continous throughout its length, unless it is not connected somewhere. As is the earth.

When you do a temporary connection between live and earth the circuit MUST be dead.

If not you would hear a little bang and a click.

There are normally only Live and Earth at a light switch that is why the temp connection is needed to test continuity between live and earth.

 

[Badger]

the test is done to make sure that it is switching the live cable and not the neutral.

 

[Dambo]

The live is going to be continous throughout its length, unless it is not connected somewhere. As is the earth.When you do a temporary connection between live and earth the circuit MUST be dead.

If not you would hear a little bang and a click.

There are normally only Live and Earth at a light switch that is why the temp connection is needed to test continuity between live and earth.

What about the neutral?

 

[Dambo]

the test is done to make sure that it is switching the live cable and not the neutral.

What's to say that the L and E aren't crossed?

 

[ianmacd]

Not sure I follow. You mean if the switch was on the cpc (BAD)? Then if the light was wired to line and neutral then the light would never switch off and if it was wired to cpc & neutral then your RCD will probably trip but no light.

 

[Dambo]

Not sure I follow. You mean if the switch was on the cpc (BAD)? Then if the light was wired to line and neutral then the light would never switch off and if it was wired to cpc & neutral then your RCD will probably trip but no light.

When carrying out the polarity test on a lighting point, with the test being carried out between L and E, how can you tell that L and E aren't wired the wrong way round?

 

[ianmacd]

As above.

 

[Risteard]

When carrying out the polarity test on a lighting point, with the test being carried out between L and E, how can you tell that L and E aren't wired the wrong way round?

Don't forget the Inspection part of Inspection and Testing. Inspection will reveal faults that Testing cannot.

 

[m4tty]

...............and remember Inspection always comes before testing :|

 

[Dambo]

I'm still not getting it guys, sorry.

I'm studying to be an electrician and doing a question now on polarity. The question asks: Describe, with the aid of a labelled diagram, how a polarity test may be conducted on a wall light with an ES lamp holder.

I've looked through my study material and it shows how to carry out the test but I just don't understand it.

 

[Bez]

Inspection should reveal any wrong wiring at the board, think thats what the guys are saying

 

[ianmacd]

ES lamps are polarised too. So you need to test from center pin to cpc in rose via loop in CCU (L & E linked) and it should be a complete circuit depending on the switch position.

 

[Dambo]

ES lamps are polarised too. So you need to test from center pin to cpc in rose via loop in CCU (L & E linked) and it should be a complete circuit depending on the switch position.

Aye, I know that part, but what I can't understand is why between L and E???

 

[ianmacd]

As you can confirm switches are only in the L conductor and not the N conductor and also proving that cpc is continuous too.

 

[androiduk2002]

And also if using the switch it confirms the switch does actually work correctly rather than the embarrisment of saying to customer all done switching a light on and nothing happening ! ! ! .

If I am correct ................

If not i will be told so soon enough Pray Pray Pray

 

[Risteard]

If you test between the cpc and switched line conductor at the light then operate the switch you have confirmed that a single-pole device is connected in the line conductor only.

As others have said you must also verify that ES lampholders (apart from certain types of insulated E14/E27 types) have the centre-pin connected in the line conductor only.

 

[green-hornet]

Aye, I know that part, but what I can't understand is why between L and E???

It is possible to switch a light using the nuetral but it is not allowed for obvious reasons.

When the temp connection is made from earth to the live cable (power off), then test at the switch between live and earth you should get a continuity reading this confirms that the switching is on the live conductor and not the nuetral.

The same tests can be carried out at the lighting points by tempory connecting the earth to the nuetral, you will not be able to test at a switch though because normally there is no nuetral at the switch.

The other method is to do the wander lead test where you connect a long lead to one of the conductors or earth and test at each point until you get the highest reading.

 

[PC Electrics]

Aye, I know that part, but what I can't understand is why between L and E???

Because, the reading you obtain, in ohms, is R1+R2 for that light point.

With your meter connected (at the light) switch all switches for that light to test all line conductors. This proves continuity (of L & E), polarity and provides R1+R2 all in one test. Don't forget on an ES to check the line is on the centre contact. Kewtech do adaptors for that.

Your IR test (at the board end) will have already proved there is no cross connection between any of the 3 conductors.

 

[Risteard]

Your IR test (at the board end) will have already proved there is no cross connection between any of the 3 conductors.

Except that insulation resistance is carried out AFTER continuity tests!