Quick question regarding fuse ratings...

[peterguk]

Replacing the various old fuse assemblies with a new consumer unit.

I have found 1 lighting circuit, 1 ring main (2.5mm) and 2 radial circuits (2.5mm).

Obviously a 6A MCB for the lighting circuit and a 30A MCB for the ring, but am i right in saying i should be using 16A MCBs for the 2 radial circuits??

 

[plugwash]

what are the radial cuircuits feeding?

you can use either a 16A or a 20A mcb on a 2.5mm radial
if its only one socket you may as well use the 16A for more protection

if its a number of sockets use the 20A for more total load capability

 

[Adam_151]

if its in thermal insulation 16A is the one to use, if not and its less than 25.5m you can use a 20A, if its not a 16A will let you go upto 32m

Adam

 

[peterguk]

Thanks for your help guys!

OK, on closer inspection, one cable is actually cooker cable and only powers the cooker hood and one double socket. The cooker has been replaced with a gas item by the previous owner so from what you say, this should be a 16A MCB.

The other supplies the sockets to several rooms, so i will do this one with a 20A.

Sound OK? BTW, not sure what "thermal" is, but all the cable looks like standard, modern, flat twin and earth cable...

 

[Adam_151]

I did not mean the electrical insulation of the cable, but the way its installed, if it is enclosed in anything which slows down the rate at which the cable can disapate heat, its rating is lowered, there are tables with rough values for different situations, but there are derating calculations to get a more reliable maximum rating for the cable.

In theory you could rate the circuit the run in (6mm ?) higher, becuase of the thicker cable, but

A) you don't know if thinner cable is used at the end where its been modified from a cooker circuit

B) There would be little point as cooker hoods draw little power and double sockets are only rated at 13A total

In light of these, I would also us 16A in your case, but make sure the cooker hood is fused down in a FCU