ELECTRICS NEW LIGHTS ON EXISTING CIRCUIT (IN BACK OF STAIRS)

[QfanatiQ]

I want to integrate some lights into the sides of the back of the risers.

There is already a light switch to a the bottom and top of the stairs that operate the upper landing/hallway lights (up lighters at either end one standard bulb fixings)

Can I
1. Run my cable to the stair lights from the bottom light switch OR
2. Do I need to do something else
3. If I choose low voltage LED lights will this be ok
4. How do I work out loadings to make sure I am not overloading any circuits
5. Might I need to downgrade (voltage and therefore fittings and fixing) of the hallway down lights

I am ofay with fitting a plug socket on a ring mane, but not sure about adding to an existing lighting circuit

As usual, any info, pointers are welcome.

Finally, do I need one of those handheld electric meter testing (official word coming up) thingies? Please say yes!

Cheers…..Q

 

[riveralt]

I'm doing a similar job on a rewire at the moment.
The stair lights will come on only when the landing light is energised by either the landing or hallway 2 way switch.

Firstly your new lights will need both Live (S/Live), neutral and earth.
Secondly, they can only be around 25/35mm deep and most are 12v LED which means they need a transformer or transformers.

For my job I have run 1mm ² T&E from the ceiling rose bringing live, neutral and earth to the hallway switch.
I have then run 1mm ² T&E Switch Live, neutral and earth from the hallway 2way switch to the first transformer under the stairs then looping SL and neutral to each of the other transformers - I fitted one transformer for each lamp. Live and neutral are then fed to each lamp via the transformer's own cable.
A multi-meter is always preferable and they are relatively cheap in your local shed.

 

[PrenticeBoyofDerry]

Can I
1. Run my cable to the stair lights from the bottom light switch

To extend from the existing switch point, you will require line, neutral and CPC/earth. Often there is no neutral at the switch.

2. Do I need to do something else

Yes, you could loop in at another suitable point.

3. If I choose low voltage LED lights will this be ok

Low voltage or extra low voltage? They are different!

4. How do I work out loadings to make sure I am not overloading any circuits

Calculate the total load in Watts of the lamps, then divide that by the nominal voltage 230V, that will leave you with the current required on full load.

5. Might I need to downgrade (voltage and therefore fittings and fixing) of the hallway down lights

I doubt it!

I am ofay with fitting a plug socket on a ring mane, but not sure about adding to an existing lighting circuit

If you look here //www.diynot.com/wiki/electrics:lighting, plenty of useful advice.

Finally, do I need one of those handheld electric meter testing (official word coming up) thingies? Please say yes!

thingies are recommended, so Yes!

 

[QfanatiQ]

Someone has pointed out that this might be a bit overkill and we have an old house. So I will be fitting a light, but another uplight to the wall (stairs lead away from) to light the stair path.

This info is very good.

Cheers guys!

Q

 

[winston1]

- I fitted one transformer for each lamp.

Rather overkill. LEDs take very little power, one power supply (they were not transformers) would do for the lot.

 

[winston1]

[/quote]
Calculate the total load in Watts of the lamps, then divide that by the nominal voltage 230V, that will leave you with the current required on full load.
[/quote]

Wrong on 2 counts. UK voltage is not and has never been 230v, only the arse sitters in Brussels think that. It is 240v. Measure it.

More importantly these type of lights and power supplies will not have unity power factor so the current will be somewhat more than your simple formula implies.

 

[securespark]

Wrong on 2 counts. UK voltage is not and has never been 230v, only the a**e sitters in Brussels think that. It is 240v. Measure it.

I have. Over the years I have measured domestic single phase voltage thousands of times.

I have seen it as low as 198V and as high as 402V.

Admittedly, the lower figure was due to a severe loading issue on a local transformer and the higher figure due to an underground cable fault.

HOWEVER, we do use a nominal voltage in calculations. It is not 240. And neither is "UK voltage".

The voltage varies wildly and is within spec between 216 and 252V.

But, as you've argued this point before, you know all of this.

 

[riveralt]

- I fitted one transformer for each lamp.

Rather overkill. LEDs take very little power, one power supply (they were not transformers) would do for the lot.

This doesn't make any sense?

 

[JohnW2]

- I fitted one transformer for each lamp.

Rather overkill. LEDs take very little power, one power supply (they were not transformers) would do for the lot.

This doesn't make any sense?

Which bit doesn't make any sense?

Kind Regards, John

 

[riveralt]

Which bit doesn't make any sense?

What does

one power supply (they were not transformers)

mean?

There is only one power supply! That is coming from the CU.

What does 'they were not transformers' mean?

Winston seems to be someone who operates on the basis that you should fit as many lamps as you can on a single transformer - fine that is up to him/her.

I prefer to follow the manufacturers instructions and given the location of these lamps the knowledge that as and when a transformer goes it will take out only one light and not the lot.

Led drivers/transformers, as in this case, often have a limiting distance factor from the transformer due to voltage drop and/or a minimum and maximum lamps per transformer.

 

[JohnW2]

What does

one power supply (they were not transformers)

mean? There is only one power supply! That is coming from the CU. What does 'they were not transformers' mean?

I think it was a bit of a quibble about your use of what, although very common, some might regard as 'sloppy' terminology - i.e. calling a 'power supply' (unit) a "transformer" And that also addresses your other comment - 'power supply' is a widely accepted alternative to 'power supply unit' (as in 'bench power supply', 'regulated power supply', 'switched-mode power supply' etc.) - and therefore doesn't necessarily refer to the 'supply of (mains) power' coming from the CU, which is what you seem to have assumed. i.e. the 'power supply' to which he referred is what you are calling (techically incorrectly) a "transformer".

Kind Regards, John

 

[PrenticeBoyofDerry]

UK voltage is not and has never been 230v

Really? I have often taken readings that would prove that your comments are incorrect.

More importantly these type of lights and power supplies will not have unity power factor so the current will be somewhat more than your simple formula implies.

Which type of lights and power supplies?

So if your assumption was correct what calculations do you use?

 

[EFLImpudence]

UK voltage is not and has never been 230v

Technically it is even though it isn't.

 

[winston1]

UK voltage is not and has never been 230v

Really? I have often taken readings that would prove that your comments are incorrect.

More importantly these type of lights and power supplies will not have unity power factor so the current will be somewhat more than your simple formula implies.

Which type of lights and power supplies?

So if your assumption was correct what calculations do you use?

It appears I have caused some confusion. First UK voltage. As I said it has been nominally 240v for a long time, 230v in NI. Europe including the Irish Republic 220v. Harmonisation has come along and the nominal voltages have not changed, only the tolerances have changed. However to please the Eurocrats it is now incorrectly referred to as 230v. To base calculations on this incorrect figure is madness, no real engineer would do it. I've just measured the voltage at home and it 242v.

LED lights and LED drivers are unlikely to have unity power factor. The correct formula is current = watts/volts x power factor or I=W/Vcos phase angle. The best way to know load current is to measure it.

Whether you want one driver per LED is up to you, but it does seem wasteful considering LEDs use so little power. All lights out if the driver fails is irrevelvant in this case as the lights are not in the same place as the driver anyway.

 

[riveralt]

All lights out if the driver fails is irrevelvant in this case as the lights are not in the same place as the driver anyway.

Like most of what you have said, this doesn't make sense.