Strange looking fuse!

[ryanj]

What happens when the element casing ruptures and the water shorts the element?

Then the 16amp MCB, would surely trip?

 

[Damocles]

If there is now a path to earth via the casing, water and element, but not complete short? Seen some posts where the result of such a fault seemed to be that the immersion was still operating after a fashion, but current was also runing to earth.

 

[ryanj]

Hmm, theres a reason to support RCD's for Immersion Heater Circuits.

 

[Lectrician]

1.5 flex will handle 16amp in either case.

 

[plugwash]

If there is now a path to earth via the casing, water and element, but not complete short? Seen some posts where the result of such a fault seemed to be that the immersion was still operating after a fashion, but current was also runing to earth.

which is why i have seen some of the more paranoid types advising 10mm bonding to the immersion heater cupboard run back to the CU

 

[Damocles]

umm, yes, we are arguing round in circles. My point was that it is possible for a faulty heating device to draw more than its rated current on a semi-permanent basis.

 

[plugwash]

so a bit of current escapes from an immersion heater and heats the water directly

SO WHAT?

as long as the tank is properly earthed no dangerous potential will appear on it

heaters already have thermostats to prevent them heating the water to dangerous tempreatures a slight increase in output won't change that behaviour

the cabling has enough design slack to cope with the extra current

so just whats the problem?

 

[ryanj]

which is why i have seen some of the more paranoid types advising 10mm bonding to the immersion heater cupboard run back to the CU

How would that actually help?

I mean, if it's a partial short, and the cylinder is earthed properly, adding more parallel paths to earth, won't help at all?

 

[plugwash]

the point of putting in the 10mm is to keep any voltage on the cylinder resulting from the earth current to a minimum

 

[kai]

Your's quite right plugwash.

 

[ryanj]

Wouldn't a RCBO on that circuit, or it moved to the RCD side of a split-load board, be a better safer more practical soloution?