Lights tripping 6A MCB

[pcboffinuk]

Just trying to sign off a nightmare job, and one or two little quibbles are still being raised by the owner.

One is that on occasions the mcb trips when switching lights off at the switch. Since I have not been there they are not too clear but it would appear that at the same time a bulb blows in one of 3 fittings they have in the lounge, with 5 arms each running 20W globe bulbs.

The wiring is all new and has been insulation tested. The switches are new and tightness checked (no dimmers). I've also specified Osram bulbs though I don't think all of them are changed yet.

The lights downstairs all run 5x40 W so 200W a light point, and potentially 5 all on at once, along with 4 36W flourescent fittings in kitchen/utility room and a 100W light in the portch, so it may be getting close to the trip rating for 6A.

Obviously is is inconvenient for this to keep happening, so I have a couple of options I'm considering.

Upgrade the MCB to a B10 (1.5mm cable laid in open in the loft so still protecting cable)

Upgrade the MCB to a C10 to avoid surges when a lamp blows causing a short surge.

I will probably also put the kitchen lights on the upstairs circuit so that they do not trip and the homeowner can see to flick the mcb back on.

I realise the issue with C type is meeting the Zs requirement, but as this is a TT installation none of the circuits meet the type B requirement either (Zs is ~22). The source of installation is protected by a type S 100ma rcd, and the db with this lighting circuit on has 30ma protection for all circuits.

I'm open to other advice - the light fittings in the lounge are the sort with 'petal' shades so get very hot with the globe lights in (I would have expected candle lights but apparently globe ones were specified). On inspection some of the SES terminals also show signs of pitting, suggesting that they were not firmly screwed in and perhaps arcing. One of these fittings in the past has ejected a blown bulb across the room, though I think that was down to cheap bulbs (and probably the fact that it was on a 16A circuit when I started the job).

Gavin

 

[Lantash]

If bulbs are popping, have you checked for an excessive supply voltage? Even a few percent overvoltage will drastically reduce lamp life.

IMLI these specialist SES or 'candle' bulbs in very small luminaires are prone to overheating and random popping. I think if they want to use this type of fitting they may have to put up with the short bulb life.

Also, I've never yet seen an quick-acting MCB that won't trip when a GLS bulb pops. They all do. Use of slow-acting types might solve the problem... but I think the better approach is to tackle the problem at source.

The best choice these days is low-energy (fluorescent) lamps, or if they dislike the appearance of those, then low voltage halogen offer reasonable efficiency and longer lamp life.

Topical point as a friend is trying to persuade me to install oldstyle SES 'eyeball' spots in her kitchen. I'm doing my best to convince her this is a Bad Idea, but so far no joy.

 

[Spark123]

MCB trips when the switch is turned on or off? Sounds strange that it would happen when the power is disconnected?
There are some regs re the protective device rating and SES lampholders, wether this luminaire is suitable to be fused above 6A needs to be determined.
Are the lamps a good brand i.e. osram with balotini fuses? Can you fit energy saving type lamps?

 

[Steve]

low voltage halogen offer reasonable efficiency and longer lamp life.

No they dont.

 

[plugwash]

halogens offer slightly better efficiacny (in terms of lumens/watt) than normal incandescents BUT downlights at least have a terribbly narrow beam spread which tends to counteract this in a domestic situation.

Flourescents (compact or otherwise) give high efficiancy but have poor CRI so don't use them if you need to be sure that colors of everything will look right. LEDs are even worse in this regard.

as for the original problem i'd reccomend a C6 or a B10 mcb, B6's are just too sensitive (obviously check out the circuit specs first but i can't imagine many domestic lighting circuits being unsuitable for a C6 or B10).

 

[JohnD]

it has SES fittings so can't be 10A

I have a C6 for my kitchen lighting (SES spots) still trips sometimes, but not as often as the B6 did. I am replacing with CFL spots as they die.l

 

[pcboffinuk]

According to the client, they have tripped when they turn the switch OFF, generally at night, when the lights have all been on for some time. Naturally I can't get it to repeat the feat whatever I try.

I have suggested osram bulbs and they are gradually replacing them all. I've also told them that shorter life is to be expected. However, its the nuisance tripping that is the larger problem as the wife is not so mobile and resetting the mcb is difficult for her.

The voltage is a little high (242) or so, but because its in the sticks and fed via overhead lines it may well go higher at times.

Given that before I arrived all these light fittings were running on rubber cable and a 16A breaker (for at least 10 years), I guess they have been tested as suitable for 10A

Plug, any reason why a C10 wouldn't be acceptable, given the circuit is 30ma rcd protected so disconnection times are ok? The reason I ask is that RS don't stock a B10 and they are the only reliable source I've found for MEM. Given this client's penchant for lots of light I can see a C6 being overloaded at some point in the not too distant future.

Gavin

 

[JohnD]

... the only reliable source I've found for MEM...

put your email address in your profile for today...

 

[plugwash]

nothing wrong with a C10 as long as the figures for the circuit check out.

 

[Spark123]

There is one of the regs which goes along the lines of SES/SBC lampholers shouldn't be fused above 6A, it also gives some exceptions to this rule though. I'll see if I can find the exact wording later.

 

[securespark]

Given this client's penchant for lots of light I can see a C6 being overloaded at some point in the not too distant future.

Then the circuit is being overloaded and you need to suggest installing a new one to carry the extra load.

 

[plugwash]

if you wan't to go to 10A and have some SES fittings you could always replace the lightswitches for those fittings with FCUs

 

[pcboffinuk]

if you wan't to go to 10A and have some SES fittings you could always replace the lightswitches for those fittings with FCUs

Not a bad idea Plug, although that would require a neutral at the switch too, as I would assume using a FCU just to break the phase would be considered bad practise?

Just done some more searching and Spark123 is right....

Reg 553-03-01 states that lampholders with SES os SBS cannot be used on a circuit with above 6A overcurrent protection, unless they are enclosed in earthed metal or insulating material with ignitability rating 'P' (unless separate overcurrent protection is provided).

Credit to Adam on another post for pointing me at that one...

The wording suggests that they are concerned about the fittings melting and bursting into flames.

Fortunately, the luminaires with SES in this place are earthed metal (brass or brass effect at least) so I think I am ok with a C10 but may try a C6 first....

Thanks for the responses.

Gavin

 

[Spark123]

It is still a concern that you say it only happens when it is switched off? Thinking back, I remember someone saying about a customer who had wired the neutrals to the L2 terminals in the switch. Phase must have been to L1 and switch to Com otherwise they would have has a dead short! Worth checking if you haven't already.

 

[Lantash]

halogens offer slightly better efficiacny (in terms of lumens/watt) than normal incandescents BUT downlights at least have a terribbly narrow beam spread which tends to counteract this in a domestic situation.

I'd have to agree with everything you say, however we are in the "Spot Fad" era of lighting. Hopefully this will pass and commonsense will once more prevail.

If people insist on 'spots' (floods, actually) then LV halogen are at least a reasonably sensible choice. Though I'd always try to persuade them to go for something that lights the room instead of lighting circles of carpet.

As for the popping problem, one solution may be LE fluorescent lamps, these are available in SES although you may have to search around for them. The spiral type will fit quite small luminaires.