Changing an MCB

So a 6A MCB ought to be ample for either, unless there are other loads not metioned on those MCBs.

With 55 tungsten lamps at 2,000 hrs life each that's one going pop every 36 hrs of use... I guess with 11 in each chandelier untill three or four have gone it doesn't notice but all the same, that number of bulbs and 1.4 kW of power when all on, they must have money to burn...

Did a bulb blow at the same time?

To do blindly yes, you really need to know the size of the cable used to wire the fittings and how it's installed. IANAE either and don't have the figures off the top of my head. 6 to 10 A might be OK but if it's tripping due to in rush at switch on rather than a bulb blowing then a 6 A type C would be better.

That would depend... to just swap without knowing details of the circuit certainly would be.

Also if (as I suspect) he is just trying to lower the chances of a nuisance trip on a bulb failure, a better way to do it would be to change the type of MCB from a B to a C. While having the same thermal response curve, a A 6A type C will need a higher fault current of 60A to trip "instantly" (compared with the normal of 30A). A 10A type B will only need 50A to trip instantly for comparison.

There are three "standard" lighting circuit protective device sizes, 6,

Here is the list:

There are implications of say swapping from a 6 to a 10

Say the circuit was wired in 1.0mm T&E, its TN-S and not RCD protected. Your maximum circuit length with a 6A device is 59m in most cases. The same circuit with a 10A MCB, would have a maximum length of on 35m. So to safely swap from one to the other, you need to know the maximum cable length from CU to furthest light fitting on the circuit. (if wired in

Generally going from a B to a C device is a much safer gambit. On a

On average - which means nothing if you change all the bulbs at the same time. Lamps are usually pretty consistent in life IME.

Indeed - it will also help on bulb failure. Some bulb types are worse than others IME. Small golf ball types and GU10 mains halogens being more likely to cause a trip on failure compared to normal GLS. Candle lamps seem somewhere in the middle.

Odd the landlord does not change them to LE lamps - but it might be that the switches depend on some let through current to power the switch. Perhaps suggesting PIR control of them instead would make more sense. Or use vacuum switches.

Another factor is the lampholders. SES and SBC allow 6A max circuit protection. BC and SES are higher (I can't recall exactly what, without the regs).

Change the lamps to LEDs. If necessary, change the control switch to one which will work with them, although the power reduction may be so much that it's still cheaper even if they're left on (particularly if they add in your relamping and call- out charges).

It won't make any difference if its the blown bulb syndrome blowing it I'd imagine, which makes me wonder they the other 10A ones do not blow as well, its suspicious. Brian

That used to be the case, but ISTR they removed the restriction on using the small lamp holders with 10A circuits in the 17th edition...

Yup...

The 10A one will take a higher fault current to trip... so depending on how hard the "short" the lamp presents on failure, you may see a discrepancy in performance.