Lighting trip and MCBs

[Ovation]

Hi All,
I'm getting a little fed up with the lighting ring in my house and I thought I'd give you all a shout for some help.

The problem is simple: Every time a light bulb blows the MCD trips and plunges the entire house into darkness. I have a suspicion that this may be considered a 'saftey' feature, but as far as I am concerned, I am far more likely to hurt myself trying to get to the consumer unit in total darkness!!!

I've been looking at different MCBs and I was wondering if I could perhaps change mine to a less sensitive one. I believe I have an 'MK' consumer unit, but I'll have to check it tonight and report back about the model of MCB that's installed - I only know that it is 6A.

Originally I was suffering for the loss of about one bulb per week; then I discovered that the PIR for my front courtesy light was full of water. This has since been replaced and I have only had one bulb go since then - Sure enough when it blew the entire house went dark.

Can anybody recommend a means of dealing with this that will not get me sued by a future owner of my house???

I should mention, that I assume this behavior is common and normal as many people I know get exactly the same behaviour from their lighting MCB - Perhaps we all have faults?

Thanks in advance to anyone who can lend a hand.....

 

[mapj1]

This is common in houses where hot-wire fuses have been replaced by MCBs without too much thought for the surge rating, or where there are really rather too many lamps on the circuit.
It may be possible to split the circuit into zones controlled by separate trips, or possibly to fit a C type (higher surge rating) as opposed to a B type (more common) trip, but this requires some checking of the nature of the wiring. (it may even be possible to substitute a fuse, but this might be seen as a backward step.)
Substituting a larger breaker may sound tempting, but may not be safe if the wiring is not up to the larger fault currents that could pass before the breaker trips.
Note that the use of cheap bulbs tends to excerbate the problem, but the use of expensive ones is not a guarantee of a cure.

can you tell us,
1) total load controlled by the breaker (add up the lamp wattages)
On a 6A breaker around 1000Watts is getting to the danger mark for nuiscence tripping.
2) Is the wiring in 1mm or 1.5mm cable, (or something else)
(you'll need to look at the cable)
3) an estimate of the cable length between breaker and furthest fitting.
This information is needed to deduce which approach may be best for you.

 

[Ovation]

Hi Mike,
Thanks for your response..... I'll try and answer your questions as best as I can:

1) total load controlled by the breaker (add up the lamp wattages)
On a 6A breaker around 1000Watts is getting to the danger mark for nuiscence tripping.
2) Is the wiring in 1mm or 1.5mm cable, (or something else)
(you'll need to look at the cable)
3) an estimate of the cable length between breaker and furthest fitting.

1) If all lights were to be on at once:
Kitchen = 4x 50W 12V Halogens = 200W?
Lounge = 6x ses Golf Balls on 2x IQ Dimmers@ 40w ea = 240W
Hall = 100W
Toilet = 60W
Utility Room = 100W
Landing = 60W
Office = 60W
Bedroom1 = 60w
Bedroom2 = 100W
Bathroom = 3x GU10 Halogen at 50W = 150W
**** Front Outside Light = 100w
**** Backdoor Outside Light = Unknown - Probaly 500W
Loft Light = 50w Tube
Total based on the above = 1780w !!!

2) It's all 1.5mm cable - Regular contract lighting cable in grey pvc.

3) The furthest light is probably the office, I'd estimate that it is approximately 10metres going on a distance of 3.5metres up from the CU to the loft and then about 6m across.


**** These lights probably need my attention - I need to check the regulations about them. At present the front light is on the lighting ring with a single pole switch to control the live feed to the PIR. The back light is a cheap PIR Halogen spotlight which appears to have been wired directly into the lighting ring with no switch. I need to pull up the carpet in our bedroom to try and find what and where they have done!!
Any advice on the regs for this?? Thanks

 

[Ovation]

I've just checked my Consumer Unit - It's actually a Contactum unit with 100A main switch. The lights are on a 6A Contactum 7106B MCB which says it is 'B6' (I assume Class B and 6A).

There's space for a further 3 MCBs if need be.

 

[mapj1]

Well as a first up you can split the circuit into two, thats rather an overloaded little circuit, and relies on not all being on for the breaker not to trip! Thats not sensible. For convenience, many people recommend keeping inside and outside light separate, and high wattege ones, like the 500W, may be better run from the power ring via a fused spur fitted local to the socket it comes from. Without seeing the building, only you will know what split is appropriate in terms of logical grouping.

If you are sure about the 1.5mm wiring, and the length you describe, you should be fine with a C6 or a B10 circuit breaker, but I'd not recommnd anything bigger without a more thorough survey of what exactly goes where, and checking about the earth fault loop impedances. In saying the earthing is OK to go up to a C6 or B10 I have presumed you have non-RCD protected lights, and at least one B 32A or B 16A non RCD protected trip for something else in the box. If the earth impedance was good enough when that was installed, then there will be no problem with supply earth for what I propose.
If not, however, you should check earth impedance anyway (or have it checked), as it may not be low enough to clear a fault fast enough with the larger breaker (but I doubt it very much, otherwise my advice would be much less positive.)
Contactum 9006C, or 7110B are the likely part numbers. See here
http://www.alertelectrical.com/product_subcat.asp?typeID=99&SubID=153 Do they look the right sort of shape?
Come back if this makes no sense.

 

[delmel]

This is a common happening and is generally due to cheap lamps from the far east. It is to do with the way that it is manufactured they use a cheap method missing a part out used on quality lamps, this causes the trip to activate when they blow. Try using a good brand of lamp. Its difficult because so many use these lamps and have them branded for them.
Its a cost issue, and hard to find a decent GLS lamp now. Suggest Bell lamps if you can find them

 

[felix]

Start with that rear 500 watt halogen spot light. It's badly wired anyway if there's no switch. Put it on a switched fused spur on a ring main as Mapj1 suggests. You can run this spur from a socket using 2.5mm cable as long as the socket itself is not a spur.

A lot of those lights have an override feature built in. If you switch off and on again within a few seconds they stay on permanently until switched off for over ten seconds. If yours has this useful feature you can't use it at present. Also, have you considered how you would go about replacing its bulb?

To get your total lighting current down why not replace some of your standard bulbs with compact fluorescent ones. These are now so cheap that they pay for themselves within a year. They last longer too. They can cause problems with dimmers and some security switches so use them only with simple on-off switches. For a somewhat higher price you can get them in more aesthetic shapes than the utilitarian folded tube.

 

[Ovation]

This is a common happening and is generally due to cheap lamps from the far east. It is to do with the way that it is manufactured they use a cheap method missing a part out used on quality lamps, this causes the trip to activate when they blow. Try using a good brand of lamp. Its difficult because so many use these lamps and have them branded for them.
Its a cost issue, and hard to find a decent GLS lamp now. Suggest Bell lamps if you can find them

I was using OSRAM Bulbs that I bought from my local hardware store, but because these were blowing all the time I bought a 10pack of cheap ones from Wickes.
Now that these have all gone, I have bought a pack of 'Triple Life Plus GLS Light Bulbs' from CPC. These are made by Crompton Lighting and cliam to have a 3500hr Lifetime.
Hopefully these will be better than my previous lamps.

Since I discovered that the front light's PIR was full with rain water (and hence the entire circuit was badly corroded) and replaced it, the freqency at which lights bulbs blow has dropped significantly.
However, when a bulb did finally go the other night - POP! Out went all the lights

 

[Ovation]

Well as a first up you can split the circuit into two, thats rather an overloaded little circuit,

I think I shall investigate doing this. It only makes sense to me to separate the Upstairs and Downstairs zones... Heck, I've done it with my heating - Lets do it with the mains!

like the 500W, may be better run from the power ring via a fused spur fitted local to the socket it comes from.

felix:
Start with that rear 500 watt halogen spot light. It's badly wired anyway if there's no switch. Put it on a switched fused spur on a ring main as Mapj1 suggests. You can run this spur from a socket using 2.5mm cable as long as the socket itself is not a spur.

What a shame it was all bodged in the first place. I actually want to fit quite a bit of extra outside lighting, so I may investigate the posibility of a dedicated ring for this.

To get your total lighting current down why not replace some of your standard bulbs with compact fluorescent ones.

I'd get my manhood chopped off if I suggested that in my house Me and the missus both hate the 'energy saver' bulbs - They're not bright enough and the flicker apparently aggrevates her headaches. The problem for me is that in order to get at bright enough light I have to buy a stupidly big energy saver - I'd quite happily have a 6ft strip in some of the rooms, but she ain't havin' none of it! (N.B. Please don't start picking me up about the use of double negatives

Contactum 9006C, or 7110B are the likely part numbers. Do they look the right sort of shape?
Come back if this makes no sense.

Yup! They're the babies. I think I'll investigate splitting the load first of all.
I'm not entirely sure how to test the earth impedance accurately.. I have been looking at a few diagrams, but can you give me a basic procedure. I've got a decent Tektronix DVM that has been calibrated - I'm hoping that this will be good enough for the test?

I have presumed you have non-RCD protected lights, and at least one B 32A or B 16A non RCD protected trip for something else in the box.

The lights are not on an RCD and I assume that an RCD would guarantee a blackout every time a bulb goes?
I can't remember what is where now, certainly the Ring main is RCD protected and the lights are not. I also have MCBs for:
- A double socket immediately next to the CU
- Immersion Heater
- Cooker
I cannot remember the individual ratings of the MCBs off the top of my head, but I can remember that they are all 'B' Rated.

The main isolation switch is rated at 100A.

----
thanks to all of you for your help..... If you have any other information please do let me know.
I will probably be back here very soon as I've got a few projects to play with.

Regards
Jonathan

 

[Ovation]

Whoops! Didn't mean to duplicate my preious message... This text is its replacement.
Please ignore.

 

[plugwash]

I've just checked my Consumer Unit - It's actually a Contactum unit with 100A main switch. The lights are on a 6A Contactum 7106B MCB which says it is 'B6' (I assume Class B and 6A).

There's space for a further 3 MCBs if need be.

B6s are notorius for tripping on bulb blows

easist thing to do is probably to change it for a C6

http://www.tlc-direct.co.uk/Products/CM9006C.html

 

[Damocles]

Lots of people seem to go round saying you just can't get quality bulbs nowadays. Rubbish. It is not a problem with bulbs, it is a problem with B6 mcb which are not good enough for the job. Chosen to be guaranteed failsafe, but fail is the operative word.

 

[plugwash]

mostly type B breakers are appropriate for domestic cuircuits

but a B6 seems to have the fast trip point just too low for lightbulbs blowing

a C6 or a B10 (c6 and B10 have about the same fast trip point) should solve this and your lighting cuircuit would have to be insanely long to have an earth fault loop impedance problem with one of theese devices.