why does the RCD trip the moment I plug something in?

[humptydumpty]

We laid a 10 mm cable to the fusebox which was connected by the electricial using a 45 A fuse for an induction hob. the cable goes to the kitchen to the cooker socket which also has a normal socket. The moment anything is plugged in (eg induction hob or anything is plugged in the socked, such as a small light) the RCD trips. Any idea what might cause this? I have replaced the cooker switch with socket but this has not solved the problem. Where the cable is easily accessible it looks absolutely fine. Help urgently needed! do I have to lay a new cable?

 

[holmslaw]

,,

 

[humptydumpty]

The connections to the fusebox were carried out by a qualified electrician, I should be able to locate the neutral from the cooker cable (which is the only 10mm cable entering the fusebox) but what do I do next?

 

[Lectrician]

All too common an error!

There are two neutral bars in the consumer unit, one associated with the main switch, and one associated with the RCD. Which ever side you have placed the MCB/fuse is where the neutral should go.