Diconnection times

[lionelmcc]

I just got some new certs. Asks for disconnection times in circuit info
can someone tell me where 5s disconnection applies under the 17th edition
as it does not seem to be just hard wiring or sockets anymore (Big red is making me Dizzy)

 

[Smugley]

In a TN 230V system, maximum disconnection time for final circuits up to 32A is 0.4 seconds. Final circuits exceeding 32A are permitted up to 5 seconds. BS7671 411.3.2

 

[Graeme Harrold]

In a TN 230V system, maximum disconnection time for final circuits up to 32A is 0.4 seconds. Final circuits exceeding 32A are permitted up to 5 seconds. BS7671 411.3.2

Dont forget distribution circuits e.g. main CU to garage CU, this sub main is also permitted 5sec

 

[Sintra]

TT system 0.2 seconds

 

[lister]

Is lighting classed as a final circuit?

 

[Sintra]

Is lighting classed as a final circuit?

Yes lighting circuits are final circuits.

 

[Graeme Harrold]

Cooker circuit WITHOUT a 13A socket can have a 5sec disconnection

 

[ronturner]

I think the proective device must be greater than 32 amp to allow 5 secs rather than 0.4. Most cooker circuits are 40 or 45 amp so 5 secs is allowed.

Page 282 of the regs indicates that if the cable was 4mm then depending on the ref. method the CB would be unlikely to be greater than 32 amps therefore min. cable size must be 6 or 10mm.

 

[slocm3105]

Cooker circuit WITHOUT a 13A socket can have a 5sec disconnection

Only if its OVER 32A. If its on a 32A mcb then its 0.4 seconds.

 

[ronturner]

I thought if a cooker switch incorporates a socket outlet then the disconnection time is ALWAYS 0.4 sec regardless of the size of the MCB but I can't find it in the regs.

 

[shagg]

I thought if a cooker switch incorporates a socket outlet then the disconnection time is ALWAYS 0.4 sec regardless of the size of the MCB but I can't find it in the regs.

Thats right Ron, Well that's what i got told on my 2391 anyway

 

[slocm3105]

I thought if a cooker switch incorporates a socket outlet then the disconnection time is ALWAYS 0.4 sec regardless of the size of the MCB but I can't find it in the regs.

Your bang on mate. But he said without a socket outlet it can be 5 seconds disconnection time. But if its only 32A then its still 0.4seconds.

Cheers

 

[sixfingers]

TT system 0.2 seconds

0.2 seconds? Does that apply on all circuits on TT system?

 

[Mac]

Disconnection Times


230v final circuits in a TN system not rated greater than 32A must disconnect within 0.4 seconds under fault conditions. 411.3.2.2
230v final circuits in a TT system not rated greater than 32A must disconnect within 0.2 seconds under fault conditions. If disconnection is made by a fuse or mcb and all extraneous conductive parts are connected to the main equipotential bonding then a disconnection time of 0.4 seconds is permitted. 411.3.2.2
Under fault conditions in a TN system, circuits over 32A including distribution circuits must disconnect within 5 seconds. 411.3.2.3 Under fault conditions in a TT system, circuits over 32A including distribution circuits must disconnect within 1 second. 411.3.2.
All this can be found in the sticky Brightspark posted.
BS7671 : Reference

 

[calv68]

page 46 in the red book table 41.1

 

[malcolmchisholm]

Table 41.1 in 17th Ed book refers to this.

I have been told that if a final cct is off a sub-main board then the disconnection time is 5 sec. Is this true? I cannot find any reference to this.

 

[brucelee]

no mate only if its a distribution circuit 5 secs for tn and 1 sec for tt
final circuits are 0.4 for 32a and under and 5secs for over 32a in tn systems
and final in tt are 0.2secs under 32a and are 1 sec for over 32a in tt sytems like mac said
this is what we was taught in 2391