Cable size question from a non-electrician

wtf????????????????????

 

Would this just constantly trip the RCD
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It might when the cable melted!

 

4mm cable can take max current of 37A if say clipped direct and even less for other reference methods. A 9.5 KW shower can produce nearly 40A..!!!So your 4mm would get hot and likely to melt,especially on an old fuse type breaker..! People are pushing it with a 6mm2 cable on a 9.5kw, use 10mm2 for a proper job!

 

The melting point of copper is approximately 1064 deg Celsius. It is not likely to melt!

Overloaded cable only ever heats up. Thats all it will do. Too much current just causes heat. Cables are sized to ensure excessive heat does not become an issue.

In laymans terms, if the cable is too small for the load it is carrying AND the mcb or fuse is too high a rating for the cable the PVC sheath and PVC insulation will become affected by the heat generated in the copper due to excessive electrical current causing it to harden, discolour, and ultimately burn off. It will smell awful.

If, howevdr, the fuse or mcb is correctly rated for the cable then it will trip long before sufficient heat can build up and cause damage.

An RCD is not designed to detect overcurrent so it will sit there all day and get damaged like the cable.

 

The copper won't melt but the insulation might, then the rcd will trip when the live or neutral contacts the earth, there now UP is that better?

 

It might do in the right circumsatnces sen. Could well do. But the RCD will probably weld and nowt will 'appen as like

 

jinkes UP are you sure

***

cheers

 

I think so, daft one. Cable sizing is proper complex aint it. I can't do it. All that stuff in the regs. Who reads it?

cheers

wtf

 

I've come across that sized shower run on 4mm twin & E, and it did get quite warm. Main factor probably is how long is the cable run, and where it is sited. In a cool location, it might be OK, but in a hot roof, another matter. You might not get the right disconnection times in the event of a fault though, if the circuit-resistance is too high.

When a conductor gets hot, its resistance rises, so reducing the actual current flow and wattage. Only raising the supply voltage would that be reversed.

If you knew the actual current, the length of run, and the resistance of 4mm per metre, you could work out the total power-loss in watts.That shower I worked out was dissipating a quarter of a Kw. over its entire run. Not so much per metre there. I(current)squared/R(total resistance)= watts is the formula.You would also have to take temperature into consideration too. Best run in a bigger cable!

Js