Eric, I hope that you aren't suggesting that we can ignore EFLI if RCDs are installed?
Ignore no but the permitted parameters do change. With a RCD table 41.5 note 2 advises the permitted EFLI should not exceed 200 ohm however we also have volt drop to consider so the cable lengths are still limited.
It will be noted that many RCBO's are provided in the C rather than B magnetic release.
We did in the past use LOADMASTER MCB's which had no magnetic release and at the time it was felt these were an improvement on the fuse.
However the damage which could be caused under short circuit when considering the let through was of course a problem the main one was the blowing of up stream fuses and the problem of using D rated large MCB's in domestic does present the problem that before the MCB trips is can take out the incoming fuse.
However this is not a problem with 6A devices.
I would agree the BS7671 does not really explain what we may use a RCD for when it allows the use of an RCD when the earth loop impedance is high in TT systems 411.8.3 does state "or" not "and" but 415.1.2 The use of RCDs is not recognised as a sole means of protection and does not obviate the need to apply one of the protective measures specified in Sections 411 to 414.
However because there is a thermal trip the RCD is not the "sole" means of protection.
What does worry me is the use of passive RCD's remote from main incomer where under fault conditions volt drop may mean there is not enough volts for the RCD electronics to work and trip the device. I note the earth wire fitted to RCBO's to assist with this problem but where volt drop could be an issue then one should used active RCD's.
But returning to bulb blowing fault the extra current produced with C and D type MCB's can cause the contacts on BA22d bulb holders which in the main are only rated at 2A to fuse and so instead of just changing a bulb you need to change the bulb holder as well. So since I find it far easier to just change the bulb I will continue to use B6 MCB's in my house.