Disconnection Times

[Traineeboy]

I understand that for a TN system it is 0.4 max disconnection time. 
 

If for a distribution circuit you are allowed 5s max disconnection time, does that mean if you have a garage consumer unit on a MCB of the house consumer unit does that make the circuit a distribution circuit serving the garage and therefore the disconnection time is 5s ? Or have I got that wrong ? 

 

[Andy™]

does that mean if you have a garage consumer unit on a MCB of the house consumer unit does that make the circuit a distribution circuit serving the garage

well that would meet the definition of distribution circuit in part 2

 

[Phoenix]

Yes, and you should state that as the maximum discon. time on the cirucit schedule.

Of course, makes little difference in practice, with 60898 B or C, if you are within the tabulated Zs then it'll be going out in less than 0.1s anyway, now a 400A feeder to the far end of a factory on BS88 fuses, that may well take the full 5s

 

[SPECIAL LOCATION]

I understand that for a TN system it is 0.4 max disconnection time. 
 

If for a distribution circuit you are allowed 5s max disconnection time, does that mean if you have a garage consumer unit on a MCB of the house consumer unit does that make the circuit a distribution circuit serving the garage and therefore the disconnection time is 5s ? Or have I got that wrong ? 

You are thinking along the right lines...

(And once again its another good question, where you put your understanding and thoughts as to what & why you think the answer is how you explained)

But if you re-read section 411 especially 411.3.2.3  and 411.3.2.2,

What conclusions do you come to about final circuits, on a TN system,  supplying fixed equipment,  that have no socket outlets and exceed 32A?

It doesn't actually state ALL TN circuits require a 0.4s disconnection time.

Guinness