Electrics RCD Question

[JohnD]

About 6 weeks ago my cooker tripped the RCD. When the electrician came, the plug socket was partially melted,

What sort of cooker is this, that has a 13Amp plug and socket?

 

[JohnD]

The OP's RCD is rated at 80A, it is significantly lower than the max of the MCBs (114A).

It doesn't work like that.

It is highly unlikely, and in an ordinary domestic house pretty well impossible, that all the circuits would be carrying their maximum rated load at the same time.

An electric shower, and an immersion heater, may run at nearly their rated circuit load. Pretty well nothing else comes close.

 

[SinsSinatti]

What sort of cooker is this, that has a 13Amp plug and socket?

Sorry I meant the switch rather than plug.

 

[Ragnar_AT]

So basically two accessories (cooker switch and dryer socket) melted within a fairly short period of time?

That seems to suggest poor connections (that lead to overheating) or poor quality accessories. Get an EICR done and specifically ask the electrician to look for loose connections.

 

[opps]

It doesn't work like that.

It is highly unlikely, and in an ordinary domestic house pretty well impossible, that all the circuits would be carrying their maximum rated load at the same time.

An electric shower, and an immersion heater, may run at nearly their rated circuit load. Pretty well nothing else comes close.

I appreciate that (tnx), and yeah, I am also familiar with the concept of diversity.

I did however think it odd that the lower rated RCD has a higher (relative potential) load than the higher rated one. In no way am I maligning the electrician that fitted the CU. I was asking because I was uncertain.

 

[ericmark]

At one point we would consider a consumer unit with two RCD's neither would take the whole house load so they could be smaller, however I am sure one of the addendums or issues of BS7671 clarified that, and the RCD should be rated at the total of the MCB's or the DNO fuse, which ever was the lower, I do hate it when it clarifies, as it means work one has done now is shown to not comply.

The whole idea of one RCD covering many circuits is now in question, I felt when 17th came out, "Every installation shall be divided into circuits, as necessary, to: (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation." showed that the RCD formed a circuit, but my peers said no, "Circuit. An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)." so a RCD did not form a circuit as it does not protect from overcurrent, that did not make sense to me, 30 mA is current, so it protects against 30 mA to earth, it would have needed to say "overcurrent in the conductors" or some other way to define overcurrent, but I was told I was completely wrong at the time. My wife, an English student would say yes that's what it says, but she would say "you don't want a cup of coffee" and all to easy to answer "yes" so not get one. But to read the regulations one really do need to become an English student.

 

[SinsSinatti]

So basically two accessories (cooker switch and dryer socket) melted within a fairly short period of time?

That seems to suggest poor connections (that lead to overheating) or poor quality accessories. Get an EICR done and specifically ask the electrician to look for loose connections.

Yes two seperate accessories (three if you count the previous dryer socket). Thank you for your reply! Very helpful.

 

[JohnD]

You might also want to see which scheme your qualified electrician is a member of (if any).