Dying Energy-Saver bulb blew out my lighting circuit

[JohnGoingGreen]

An 11-watt mazda energy saving bulb about 5 years old, in the hall, about 12 hours use daily, gave up the ghost and blew out my downstairs light circuit. I changed the fuse (good website/instructions, thanks) and the lampholder just in case, everything now OK.

Point is, do I expect this every time one of my energy-saving bulbs wears out?

This is the only fuse that has blown in the last 20 years. The lighting circuit carries less than 200 watts even if everything is on.

[Steve]

expect to change the fuse. Many lamps of all varieties will take a lot of current upon failure.

Consider changing the fuse to a plug-in MCB, if you have a Wylex standard board. Then all you have to do is flick it back on. And why did you change the lampholder? Shouldn't have been ness.

http://www.tlc-direct.co.uk/Products/WYB6.html (click for a Wylex 5A MCB for a wylex standard fusebox)

[JohnGoingGreen]

Thanks for the tip. I have a Wylex CU but I don't know if it's "standard" or not - it's brown plastic (bakelite?).

Would I have to change all the fuses to MCBs? Also, I don't think the fusebox cover would fit over the switches on the MCBs - is it OK to leave the cover off?.

I changed the lampholder "just in case" because recently a c#@ppy supermarket own-brand incandescent bulb exploded (another lifetime first - they don't make them like they used to), dripped molten glass and metal on the floor and charred the holder and wire. (Funny though - didn't blow the fuse - same circuit as this one).

[RF Lighting]

From the sounds of it it is almost certain to be a standard wylex fusebox. You do not need to change all the fuses but this would be the better option if you can. The cover will not fit on with MCB's fitted as it is. You need to look inside the fuse cover (where the circuit designations should be written). Around the edge of the lid you will see a 'dimple' running all the way around. the middle of the lid can be carefully broken out (you will need to file down any sharp edges) The lid can now be refitted with the MCBs fitted.

Rob

[JohnD]

If it's Wylex, and brown bakelite, it's a "Standard" and probably over 30 years old (I installed my first cream plastic one in about 1976). It's also overdue for replacement by a nice new one!

You don't have to change them all at the same time, but it's not a bad idea. You have to change the plastic shields behind them at the same time, so you turn off the power, remove one old fuse, unscrew its old shield, screw in the new shield, fit the new MCB; then do the next one (this prevents you accidentally putting a new 5A in the slot where an old 30A used to be because you'd taken them both out at the same time and mixed them up). They are available at 99p upwards, used, on Fleabay, or about £7 new. You can change them like this without taking the CU cover off, but the live busbar is exposed when you take the plastic shields off, so you must turn off the power with the main switch of the CU.

The old fuse cover will not fit back on afterwards as the MCBs are bigger. there are various bodges you can use (I've cut a plastic sandwich box from Wilkinsons so it slips into the CU cover) but amazingly Wylex don't make a cover to fit (they must be mad) even though they still make these CUs and the MCB to go in them.

(Beat me to it, Rob)

[JohnGoingGreen]

Thanks, both of you.

I know I should get a new fusebox, but the expense would be prohibitive at the moment. I'm hoping it's OK to leave it for now because the biggest thing I have is the immersion, no electric cooker.

Just had a look inside the fusebox cover, there is nothing that can be called a dimple running round the edge of the box, just the little boxes where the descriptions should be but aren't. Though there is a note that says "60 amps max at any one time".

I've also had a look on tlc-direct and e-bay. There are Wylex MCBs on e-bay but they are all 6amp, 16 amp, and 32 amp - what happened to 5, 15, 30 amps?

[Adam_151]

JohnGoingGreen wrote:

I've also had a look on tlc-direct and e-bay. There are Wylex MCBs on e-bay but they are all 6amp, 16 amp, and 32 amp - what happened to 5, 15, 30 amps?

The same as has recently happened to red and black cable, EU harmonisationed away

[RF Lighting]

6, 16 and 32 are the new standard values and will be fine as replacements for 5, 15 and 30 A fuses
Can you remove the bit i have coloured in black?

(couldn't find a brown wylex)

Edit: Adam is harmonisationed a word? I like it

[JohnD]

it means playing one of those pedal-operated organ things used in methodist chapels, doesn't it?

[JohnD]

JohnGoingGreen wrote:

what happened to 5, 15, 30 amps?

I have some in my antique collection. They are £10 each due to their historical value as curiosities

[Adam_151]

RF Lighting wrote:

6, 16 and 32 are the new standard values and will be fine as replacements for 5, 15 and 30 A fuses

Actually a glance at the tables of max ELFI values indicates that this might not always be true

(using 80% values btw)

5A BS3036 8 ohms (14.8ohms for 5 sec) B6 breaker = 6.40 ohms
15A BS3036 2.13ohms (4.46 ohms for 5 sec) B16 breaker = 2.40 ohms
20A BS3036 1.48ohms (3.20 ohms for 5 sec) B20 breaker = 1.92 ohms
30A BS3036 0.91 ohms (2.20ohms for 5 sec) B32 breaker = 1.20 ohms

So, if we assume a worst case situation where the Z's are at the max allowed for the relevant disconnection time on the hot wire fuse, then if that disconnection time is 0.4sec, then anything upto a 20A device, then a swap out to a breaker is not acceptable, if the disconnect time allowed was 5 sec and the Z's were at the max for that, then a swap to a breaker becomes almost imposible, regardless of the current rating in question

[RF Lighting]

Ok, I should have written that in most cases the plug in breakers will be fine as a direct replacement, but you should get an electrician to check first.

Sorry

[Adam_151]

RF Lighting wrote:

Ok, I should have written that in most cases the plug in breakers will be fine as a direct replacement, but you should get an electrician to check first. Sorry

Lol, it supprised me when I first noticed it too, I used to think that it was just really heavy currents ( say > 6ka) that fuses (of the 1361 cartridge type though) protected against better than breakers (In the way of keeping I²t small, becuase they are fixed I²t, rather than fixed opening time, as breakers are)

Makes breakers look a bit weak pathetic, I suppose until you consider with a Z of 6.4 ohms a 5A Re-wireable might open in 0.2/0.3 seconds, and generally a B6 will manage it in about 0.01 seconds (though the regs assume that it might be upto 0.1s)

[JohnD]

Hi, Adam, my ignorance is profound, so i don't quite follow why the MCBs may not be acceptable. Is it that the current doesn't get high enough to trip the MCB quickly because the earth fault resistance is high? I don't see how the rewirable can trip faster then unless it is handling a big current. Have I misunderstood? Is it something you can explain or would I have to do some serious reading to grasp it? ta.

[Adam_151]

JohnD wrote:

Hi, Adam, my ignorance is profound, so i don't quite follow why the MCBs may not be acceptable. Is it that the current doesn't get high enough to trip the MCB quickly because the earth fault resistance is high?

thats exactly it

Quote:

I don't see how the rewirable can trip faster then unless it is handling a big current. Have I misunderstood? Is it something you can explain or would I have to do some serious reading to grasp it? ta.

Its because the tripping curve for the magnetic part of an MCB is a staight line, while a 20A re-wireable fuse will blow in 0.4 seconds at 155A, and 5 seconds at 71A, with a B20 breaker its absolute, at 100A (well actually the line could be anywhere between 60A and 100A but we have to assume worst case)it will trip in 0.1 seconds (actually nearer 0.01 seconds or even faster), the magnetic part is either triggered or it isn't, its not like a fuse where the wire will burn through eventually (though a similar effect will happen on the thermal part of the trip, but thats not used

I hope that makes sense, its getting late lol