Earth Melting

[MCB]

Hello all
Please help I have been doing a rewire on a house for my NAPPIT assement tt system I have installed 2 lighting circuits all ok still got an old wylex con unit at the mo
I disconectted the water heater and run a 2.5mm cable on a 15amp fuse straight to the c/u to the fused spur connected to a honeywell junction box ( hope this sounds ok so far)
Now the problem
the sockets trip when the water heater asks for power or you turn on the hot water advance button the 3 amp fuse spur also blows god confused noe!!!
on top of this I connect a new fuse wire in to the box and the earth sleeving melts from the 2.5mm 15amp water heater cable
I cant work it out as you can see I am new
I think that I should install a new eart rod with 10mm cable back to cu dual 30ma rcd disscinected every circuit and install new one by one would this be the easiest way Please
sorry spell check dont seem to work
any help be great why is the earth heating is it pfc??

 

[calv68]

was the water heater origionally on the ring circuit

 

[MCB]

yeah just cant work out why it was ok before

 

[Darkwood]

Athough you dont give enough info' i would assume you have a high resistance earth and a possible earth fault on the water heater or even a wiring problem its common for two fuses of different sizes to blow its just that discrimination cant be met between the 15 amp fuse and the 3 amp fuse what worries me is why the earth is getting so hot for long enough to melt the sleeving?
1. Check you have a good installation earth.
2. Check your equipotential bonding
3. Make sure your piping around the cylinder has supplementary bonding
4. D

 

[baldsparkies]

If its TT and your rcd is functioning then this should not be happening, even with a suspected earth fault. I reckon you need to check that the systems rcd is working correctly. What Ze are you getting and what are your rcd operating times ??

 

[Darkwood]

You give me concern about this fault because it sounds worrying, you say the earth sleeving melted to the earth wire so with respect it got hot enough which it shouldn't have even under a fault condition.
It could be a number of reasons but you need to confirm the mains has a sufficient earth for a tt system
Check equipotential bonding is ok
Check supplementary bonding is done where required
I would do an insulation resistance test to confirm if water heater is ok too and if you still unsure post results so we can try help further.

 

[MCB]

sorry rcd not working yellow push to test not working but going to rip out tomorrow and install new board and start again

 

[calv68]

have you got a tester m8

 

[MCB]

yeah metrel/alpha teck multi tester

will test each circuit one by one and let you know

 

[old dog]

hi it sound like earth neutral fault ie you have lost the neutral and its returning through the cpc.
test for voltage line and neutral

 

[baldsparkies]

sorry rcd not working yellow push to test not working but going to rip out tomorrow and install new board and start again

Thats probably your answer. You have an earth fault on the heater and due to the rcd not working along with a Ze to high to take out the overcurrent device the excess current to earth would continue to flow uncontrolled causing the heat build up you describe. Glad your ripping out tomorrow needs to be sorted ASAP.

 

[rodney12]

i'm really hoping it's an unoccupied rewire.......