Published:
16 June 2014
Category:
Q&A
Jean-Pierre asks this question, which concerns cabling from an existing distribution board to an attic distribution board, and whether it needs a separate earth. It has been answered by SELECT (Theme – Distribution Equipment including Cable Management):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I intend to run a 10mm twin & earth cable from the ground floor distribution board using a 40A RCD for protection, 25m up into a new attic distribution board (solely for lights and sockets). This will be achieved via a void being created for a 4inch plastic waste pipe.
Should I run a separate 10mm earth cable as well?
And are there any requirements on how close to the waste pipe that I can run the cable?
Answer: It is not normally necessary to run an additional protective conductor and the circuit protective conductor (CPC) within the 10mm2 cable may be adequate.
You should, however, carry out a design calculation to establish that the reduced size of CPC within the 10mm2 cable is adequate with regard thermal constraints.
Note: I presume that, when you mention a 40A RCD is being provided for overcurrent protection, that you actually mean a 40A RCBO…?
RCD protection only provides earth fault protection and a circuit may also require overload and short circuit protection - this would normally be provided by a suitably rated fuse or circuit breaker.
There is a simple nine step procedure that could be adopted to verify the cable size is adequate - see the attached for information (please go to the link at the bottom of this web page).
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