Too many lights on a single circuit?

[OscarLomax]

Hi all, after a bit of advice here.

My builder's 'electrician' is in the process of adding lights to a new extension. I want to check what he's doing is ok (I don't quite trust him for various reasons!)

We have a radial serving about 24 GU10s in a large room (intention is to use 1W to 3W LEDs). Another radial serves about 12 GU10s (kitchen, again LEDs). Both these radials wire back to a grid switch box, each with a dimmer. The power to these is the end of the existing 1.5mm radial that serves the downstairs lights. This originates from a 6A MCB in the CU.

I can see that with all 32 lights on the current will still be very low with LED lamps. But if someone replaced them with 36x 50W halogens it'd be overloaded. Electrician says "it's all fine as the 6A MCB adequately protects the 1.5mm cable so all is good."

Is that correct? Has the old '10 lighting points maximum' for radials gone away now with people installing rows of low power lamps?

Thanks in advance!

 

[securespark]

In the good old days, before the advent of energy-efficient lighting and recessed fittings, the general rule was (and still is) to assume current demand for each lamp holder as the "current equivalent to the connected load, with a minimum of 100W per lampholder" and on a standard 5A (as it was then) circuit, you were limited to 12 fittings.

It was common to fit just one lighting circuit and in the majority of houses (with one ceiling rose or batten lampholder per room) this was sufficient.

But these days, things have changed just a tad.

You say you have 36 GU10's of maximum 3W fed from the end of the GF lighting circuit which in turn supplies more fittings?

So what is the total current demand for all light fittings fed by that 6A breaker?

Your dimmers will get fried if the type or size of load is exceeded.

 

[OscarLomax]

Hi, thanks for reply. I've had a look and that MCB feeds the following:

1.5mm radial:
- toilet light fitting (3x 1W GU10 LED)
- garage light fitting (3x 1W GU10 LED)
- utility light fittings (2 fittings, each 3x 1W GU10 LED)

radial then feeds grid switch box where it splits. It feeds two grid dimmers, one cables off to 24 GU10s and the other to 12 GU10s (intention is all 1W LED).

So ignoring dimmer efficiency, on the face of it it's only about 50W all in! (144W if 3W LEDs were used and 2.4kW if someone were mad enough to install 50W halogens!). I suppose what didn't look right to me was the end of the radial splitting into two further radials at the grid dimmer switches - but I guess this is reasonable? And is he right that as 6A MCB adequately protects the 1.5mm cable all is ok?

 

[Taylortwocities]

All is OK. In fact a 10A MCB could be used, providing all of the wiring is 1.5mm² - and subject to one or two other factors, like EFLI.

 

[OscarLomax]

Thanks TTC,

That's a relief. Actually, I think he may have used 1.0mm² (no writing on side). I assume that'd be ok on 6A MCB?

Cheers, Osc

 

[Taylortwocities]

Again, it depends. But in general a qualified yes.

EDIT.
You do not need to worry. The 6A MCB is there to protect the cable from overload. The whole idea is that even if somebody were to change the 32 LED lamps for 50watt halogens - a total load of nearly 8 amps - then the MCB should do its job and would trip before the cable overheated.

 

[OscarLomax]

Thanks TTC!

What I'm not used to is these grid switches so looked a bit odd that cable splits to feed multiple further circuits but I can see that all cables can happily carry more current than the breaker will allow.

Cheers!

 

[OscarLomax]

Also, am I right in saying that when there's no earth connection on the GU10 fittings he should still be continuing the earth continuity along the length of the radial? I don't think he's done that...

 

[ban-all-sheds]

We have a radial serving about 24 GU10s in a large room

"Large"? It must be gigantic if it needs 24 lights.

But if someone replaced them with 36x 50W halogens it'd be overloaded.

Don't be surprised if Building Control refuse to give you a completion certificate when they find that you've used lights which can have halogen lamps put in them.

 

[OscarLomax]

Well, yes it's fairly gigantic!

Part-L? We did consider LED luminaires that could not have other lamps stuffed in them, but was getting extremely expensive.

BCO should be fine, by the time this is finished 50W halogens won't exist...

 

[Taylortwocities]

am I right in saying that when there's no earth connection on the GU10 fittings he should still be continuing the earth continuity along the length of the radial?

Yes. The earth should be continued through from supply to the end luinaire.
There are several reasons, firstly the cpc (that bare conductor in the middle of the cable) is there to protect the wiring in the event of fault/damage. Secondly, when the installation is finished, he will test the circuit and produce a figure (of the EFLI )that goes on the installation certificate. This is ameasurement essentially done between the line and earth conductor. If there's no earth at the end, he cannot do the test. If he cannot do the test he cannot sign the cert to say he has tested the work!!

 

[ban-all-sheds]

Well, yes it's fairly gigantic!

Over 200m²?

Part-L? We did consider LED luminaires that could not have other lamps stuffed in them, but was getting extremely expensive.

BCO should be fine, by the time this is finished 50W halogens won't exist...

Well - it's your financial risk, if you're sure.

Did you say how you would comply, when you applied for approval?

 

[OscarLomax]

Did you say how you would comply, when you applied for approval?

Sorry, could you expand on that? Do you mean did we say on our submitted plans how the lights would comply with Part-L?

 

[ban-all-sheds]

Not just lights - all of the requirements of Part L, but lights come under

 

[ericmark]

You can get GU10L2 fittings which will only take LED bulbs. There is a little pip in the holder and dimple in the LED bulb, however not all LED bulbs have the dimple so tend not to use the L2 holder unless the LABC inspector insists. In the main they are reasonable.

As to number of lamps that has already been covered, the trip will fail safe, as to using a 10A or 16A trip for lights, that is only an option if there are no junction boxes or ceiling roses rated 6A. In the main since the standard ceiling rose is rated 6A we are stuck with 6A MCB's. I will admit it is unlikely having over 6A MCB would cause a problem, but it would not tick the boxes.

Good point about the allowing for 100W, but it was the on-site guide which gave these figures not the regulations and there were special notes for fluorescent fittings which today would cover the LED fittings where you can't get over a set size of lamp.

Every installation shall be divided into circuits, as necessary, to take account of danger that may arise from the failure of a single circuit such as a lighting circuit, and to avoid hazards and minimize inconvenience in the event of a fault plus to facilitate safe inspection, testing and maintenance. To comply with this you need the earth wires in all low voltage installation and although the OSG allows diversity of 66% I know in my house with LED lighting nearly everywhere there is a tendency of not switching off the lights until we retire at night.

With so many lights I would use at least two switches, when cooking in the kitchen I want light, but to make a cup of coffee all I need is enough to see where the kettle is, same with living room, to watch TV the small up lighter is ample, but to read a book or do craft stuff we want more light. Switching lights on and off in general works better than dimmers, in general the dimmer switch is used where the wiring is already in place as an after thought where it was not planned correctly to start with.

With home automation yes having the lights auto dim when the TV is switched on is a nice option. But unless worked with a remote I would never use.