DISONECTION TIMES- Circuit Ratings

[Davetherave]

Stupid question that i need answering. How do what your circuit is rated at? I know that if its above or below 32A there are different disconnection times depending on the type of earthing system

 

[telectrix]

very unclear question.

 

[Pete999]

Dave your question needs a bit more thought, as Tel says it's not very clear.

 

[telectrix]

@OP. if you're asking what the disconnection times are, then, in general, it's 0.4secs for final circuits up to 32A. 5 secs for circuits >32A and for distribution circuits.

 

[Pete999]

Dave look at page 25 in your OSG it expands on what Tel has just posted

 

[Davetherave]

how do you know what your ciruit is rated at tho?

 

[7029 dave]

Those things in the CU called fuses, mcb's. etc

 

[telectrix]

as above. go by the fuse/MCB rating, even though the design current may be less.

 

[Davetherave]

Thats good then, I was made confused when i looked in the regs and saw B40 MCB with a disconnection time of 40ms

 

[trev]

how do you know what your ciruit is rated at tho?

What do you mean by that mate because I think you have a different meaning for it than an electrician would.

 

[Plonker 3]

Thats good then, I was made confused when i looked in the regs and saw B40 MCB with a disconnection time of 40ms

I want some of these monday drugs too

 

[Pete999]

how do you know what your ciruit is rated at tho?

I your circuit is designed for 32 amps or under then the disconnection time is 0.4 seconds example RFC lighting radials under 32 amps

For final circuits over 32 amps and distribution circuits it 5 seconds examples a supply to a smaller DB,

These times relate to TN circuit arrangements

If you are in a rural area for example where the earthing arrangement is TT then the circuits are protected by and RCD where the disconnection time is 0.2 seconds for circuits under 32 amps, circuits above 32 amps and distribution circuits the time is 1 second. To get back to your question "how do you know what your circuit is rated at" then that is governed at the design stage, example, what am I wiring? a RFC then that must disconnect within 0.4 sec , because the OCPD (circuit breaker) will usually be a 32 amp breaker. Hope this helps