Radial socket circuit - duplicate protective conductors

[jase31]

On a radial circuit, do all sockets require duplicate protective conductors back to the cu.

 

[D Skelton]

Not quite sure what you're asking there? If you're asking whether or not each socket outlet would require it's own individual CPC back to the CU then the answer is no.

 

[MarkieSparkie]

A radial final circuit only requires a duplicate CPC when supplying socket-outlets where the productive conductor current in normal service is likely to exceed 10mA 543.7.2.1 and OSG 7.6 for further details.

 

[Luke238]

ok so how would you correctly calculate the likelihood of there being in excess 10ma being carried by the CPC in a domestic setting ?

 

[telectrix]

ok so how would you correctly calculate the likelihood of there being in excess 10ma being carried by the CPC in a domestic setting ?

this thread is 8 years old. to answer your question, you assume it to be so if you have several computers or other iT gear on the circuit. it's what is known as hi-integrity earthing. if 1 conductor breaks in te socket, you stoill have the other.

 

[Pete999]

ok so how would you correctly calculate the likelihood of there being in excess 10ma being carried by the CPC in a domestic setting ?

Hardly a likely scenario Luke, this sort of circuit is more Commercial or industrial rather than domes tic, not saying it couldn't happen, just unlikely.
Look a 7.5 in the OSG Page 86 this should give you the explanation you are looking for, along with all the relevant regulations appertaining to this subject, enjoy the read on this wet Sunday morning, now back to the World Cup Rugby.
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[Luke238]

Thanks

this thread is 8 years old. to answer your question, you assume it to be so if you have several computers or other iT gear on the circuit. it's what is known as hi-integrity earthing. if 1 conductor breaks in te socket, you stoill have the other.

Thanks telec, yes I understand the reason for it but just curious about how you would go about considering if there is likely to be leakage of 10ma along the cpc ? How would you establish (without clamping it) if there would likely be leakage when designing say a 4mm radial socket circuit

 

[telectrix]

a pc will usually have earth leakage of about 3mA. so you design your circuit so as to have well below 30mA in total. i.e no more than 7 pc's per circuit. assuming that the circuit/s is/are RCD protected.

 

[Lucien Nunes]

how you would go about considering if there is likely to be leakage of 10ma along the cpc

By enquiry as to what the circuit is to be used for. It is very unlikely in a domestic setting, unless the customer indicates that the circuit is to be used to power a roomful of computers or racks of studio gear etc. In a commercial or industrial environment the intended application of the circuit will be known at the design stage.

 

[Luke238]

Thanks all. All understood. Enjoy the rugby ! Another consideration for a domestic setting but will normally be highly unlikely

 

[loz2754]

Also we need to take into account regulation 531.3.2(ii) which states: "in order to avoid unwanted tripping by protective conductor currents and or earth leakage currents, the accumulation of such currents downstream of the RCD shall be not more than 30% of the rated residual operating current".

30% of 30mA is 9mA. This does seem to slightly undermine the the regulation concerning high integrity earthing, and would mean a maximum number of 3 items of IT equipment if each produced a leakage current of 3 mA.

 

[Lucien Nunes]

3 items of IT equipment if each produced a leakage current of 3 mA.

3mA is a rather pessimistic figure. Most individual devices will be <1mA, Class II items <0.25mA. A desktop installation with computer, monitor, printer and a few other peripherals will often fall in the range 1-2mA total.