electrical seperation

[gamblor6]

part of the 2391 20 project req a number of circuits to be protected by separation. i only really have domestic experience. these circuits supply sockets to a repair area of a audio repair garage. ive to explain methods for distribution
, control and protection but im at a loss, cant find any real info in any of my books,ive got a few lol. any info regards fuse rating and wiring method would help me loads. thanks.

 

[pushrod]

You need to look at 413 (page 98) of BS7671

 

[gamblor6]

section 413 doesnt really give guidence on fusing. if these are radial circuits would it still be 20a?

 

[IQ Electrical]

The circuit should PREFERABLY supply only one item of equipment.

It's important to make sure that the separated circuit is not accidentally earthed, thereby becoming a TN system.

A separated circuit can be run with other circuits within the same enclosure provided the sheath and the enclosure are not metallic.

A warning notice must be fixed at every point of access into the location to warn against importing an earth.

Overcurrent detection must be present in EACH POLE of the separated circuit, this is to provide not only overload and/or short circuit protection but also automatic disconnection of any circuit that supplies 2 or more items of equipment, if 2 faults to exposed conductive parts occur and these are fed by conductors of different polarity.
This would in effect, be a short circuit via the equipotential bonding conductor connecting together the 2 relevant exposed conductive parts.
If this bonding were missing, then the 2 fault occurence could lead to the full supply voltage appearing between the exposed conductive parts!

 

[pushrod]

section 413 doesnt really give guidence on fusing. if these are radial circuits would it still be 20a?

AFAIK the fusing of circuits should be unaffected as all you are doing is removing the earth from the circuit by the use of a transformer . So it depends on the usual things involved in circuit design.

 

[IQ Electrical]

AFAIK the fusing of circuits should be unaffected as all you are doing is removing the earth from the circuit by the use of a transformer . So it depends on the usual things involved in circuit design.

Exactly, current carrying capacity of cables and protective device ratings are all as per usual.

 

[gamblor6]

excelent thanks guys, as i posted, its only really domestic i do. never really came across this.

 

[gamblor6]

could i run a separated circuit to supply say 6 sockets or should i run radials to them all?

 

[pushrod]

again this is AFAIK it is best practice to supply just one accessory per circuit and to keep the run after the transformer as short as possible so i would think more likely six transformers but not necessary to be 6 radials to get to them - all depends on loads, usage and lengths of circuits etc, etc

 

[IQ Electrical]

Radials are the preferred method, feeding individual outlets but you can in theory feed multiple outlets-I think the 'preferred' bit is because as a circuit increases in length/size, so does the risk of accidental earthing.

 

[gamblor6]

thanks for your help guys, this project is buggin my happyness lol