Cable leaving house to underground.

[sparkwright]

I'm beginning to wonder how much of this job has actually been done.

 

[winston1]

You are under the mistaken impression that 20MCB will not trip at 19.9A and will at 20.1A. That is not the case. With your setup a problem in the garage will almost certainly trip both the garage 16A MCB and the house 20A one. In fact if there happens to be a significant load on the house radial already, say a kettle, only that one will go.

 

[Deleted member 18243]

Is there a prize for the right answer?

 

[matlob]

Best you read the thread from the beginning before you mouth off.

I did, and you still come across as being hard work

 

[hard-work]

Are you well?

Amazing, from someone who follows me around forums.

 

[hard-work]

I think you got the answer(s) you needed to get.

In the end, but boy was it hard work for something so simple and common.

 

[hard-work]

If you spur from a ring in the house to the garage and then installed a small CU in the garage, any problems in the garage can still trip the RCD in the house CU. You'd lose some or all of the electrics in the house as well as the garage so that's very inconvenient and certainly doesn't provide 'garage protection self contained within the garage'.

The 13A fuse on the ring can blow for sure, but unlikely as lower trip values are inside the garage. As the garage piggybacks the ring if the ring drops out so does the garage of course, which is far from ideal.

 

[hard-work]

Is there a prize for the right answer?

There should be. It was a marathon.

 

[hard-work]

I'm beginning to wonder how much of this job has actually been done.

None. And will not be in 4mm.

 

[EFLImpudence]

I never thought the 4mm cable was right.

Wrong again.

No wonder you didn't understand my first reply.

 

[hard-work]

You are under the mistaken impression that 20MCB will not trip at 19.9A and will at 20.1A.

I am? new to me.

That is not the case. With your setup a problem in the garage will almost certainly trip both the garage 16A MCB and the house 20A one. In fact if there happens to be a significant load on the house radial already, say a kettle, only that one will go.

House ring did not have heavy appliances. TV, computer, etc. splitting the ring into two radials gave a much better setup than what was there for sure.

 

[hard-work]

Wrong again.

No wonder you didn't understand my first reply.

Electrically there was nothing wrong with what he sort of proposed. Give us your take on the 4mm.

 

[winston1]

I am? new to me.

OK. I suggest you look up the curves for MCB tripping. They certainly don't suddenly trip at their exact rating current.

 

[hard-work]

OK. I suggest you look up the curves for MCB tripping. They certainly don't suddenly trip at their exact rating current.

You wrote: "With your setup a problem in the garage will almost certainly trip both the garage 16A MCB and the house 20A one".
If there is a load on the garage radial of 18A the 20A mcb in the main CU will not trip (unless it is faulty). The 16A mcb in the garage will.

 

[winston1]

You wrote: "With your setup a problem in the garage will almost certainly trip both the garage 16A MCB and the house 20A one".
If there is a load on the garage radial of 18A the 20A mcb in the main CU will not trip (unless it is faulty). The 16A mcb in the garage will.

Probably neither will trip. As I said a MCB will not trip at just above its rated current, 16.1A in this case. A short circuit type fault WILL trip both MCBs. As I said you need to look up the curves.