Main fuse and rcd issue

[eyeball]

I over looked a job today and I saw a situation that had me thinking...
Basically it was a 6 way consumer unit that was about 15 years old and has a BS 4293 100A RCD fitted. Now the main service fuse was rated at 60A i think. Now what can be done in this situation...
The consumer unit needs to stay but what can be done with the main service fuse, can this be changed for a 100A by the supplier or should the RCD be changed as these large RCD's are obsolete now??

 

[ezzzekiel]

why does anything need to be done?
60a fuse is quite normal and if max demand is ok then no need to upgrade, all of which is dno responsibility anyway.
why must the db stay?

 

[sparks1234]

Cant see any problems there

 

[eyeball]

It was because the chap doing the work commented on divesrity and that 100 Amp RCD should have a smaller max current rating to the main service fuse. Is this not required? the reason why the unit needed to stay was purely down the the size and location. The final circuits had no leeway on length and changing it could mean extending all the end's of the cicuits. The maximum demand checked out fine.

 

[Darkwood]

I think this chap needs to refine his knowledge as the rcd 100a rating is what it can operate up to and not a overload tripping rating, rcd gives earth leakage protection only and as long as its ampage ratinge is greater or equal to the fuse upstream then its ok.
This chap is probably getting confused with a rcbo where in this case the 100amp would be the overload rating and thus a comparison for the rcbo and hrc fuse tripping/current curves will show which device would open first, in a short circuit situe the smaller device downstream usually gives discrimination against the incomming fuse and only a short in the tails should effect this fuse unless the demand of the installation exceeds 60amps for a long period of time due to the accumulative loads on each mcb.

 

[eyeball]

Yes, it was something that had me thinking as I'd not come aross this before and like you say it would only be a short very close to the main that would create any real issue. Thankyou for setting me staright on this.