When do amp ratings matter

[littlespark]

KAre you a Spark? if yes then I WOULD TRY SOMETHING EKSE TO DO AS A LIVING

He's not.... He's a DIYer eager to learn.

 

[DPG]

KAre you a Spark? if yes then I WOULD TRY SOMETHING EKSE TO DO AS A LIVING

He's DIY - hence the DIY tag.

 

[freddo]

When sizing cables and circuit breakers the much simplified rule is:

The cables maximum current carrying capacity must be greater than the current the connected equipment draws.
The fuse/circuit breaker used needs to have a higher current rating than the connected load, (so the fuse/mcb doesn't operate during normal conditions) but lower current rating than the cable used (so under fault conditions the circuit is switched off before the cable is thermally damaged. Remember, fuses and circuit breakers are mostly designed to protect the cables not the equipment connected to the electrical circuit

There are more factors to consider when selecting cable and circuit protection sizes and ratings such as:
The cables length.
How and where the cable is installed.
How many other cables your cable is bunched with.
The external earth loop impedance value.

Under 'fault conditions' a relatively small csa cable will survive a large fault current so long as the over current device disconnects the supply quickly

Even when everything is correctly sized and rated the conductors can still get surprisingly hot during heavy fault currents! Just not hot enough to cause damage to the cable.

JWs experiment is way more scientific than my attempt of just connecting bell wire across the mains: