OP
hightower
Thanks for your help everyone. On phone at minute so will respond properly when i get on a computer.
Discuss Bit quick advice please in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
no if another metal is used for bonding then it needs to offer at least equivilant conductance. The carbon content of steel varies so you have to use the guidance in GN8 which I believe is in the region of 8.5. So if 10mm copper is deemed adequate then the steel armour would need to have a cross sectional area of at least 85mm. It would be better to use 5core SWA or run in a seperate bonding conductor. Remember if the seperate bonding conductor is to be buried you would have to use 16mm.According to this table:
http://www.askthetrades.co.uk/hosted_images/Armour CSA.pdf
6mm 4-core has a copper equiv. CSA of 16.8mm so my thoughts are I can take a 10mm cable straight from the feed terminated in the isolator and bolt it on to the metal frame, and use the armour as my bonding return to the MET?
They are for earthing not bonding.So what are the copper equivalent columns in that link referring to then? Reason we've used 4-core is because it's what the factory owner had lying around and he's on a cost saving exercise. Will have to have a look at pulling in a separate conductor.
Why should they be different though?They are for earthing not bonding.
Because for a cpc the Adiabatic equation can also be used.Thanks but why are they different. Why is a steel to copper equivalency that's good for a CPC not good enough for bonding?
544.1.1 and the * under table 54.8 both say about the bonding conductor being copper or a cross-sectional area affording equivilant conductance in other metals. GN8 has a section on it but I don't have it around me ATM. Probably to do with limiting touch voltages under fault conditions etc.Why should they be different though?
Man did I struggle with this one ... The SWA table gives k numbers suitable for use in the adiabatic equation. I haven't got it open, but I recall the factor is about 2.2. For bonding it's about voltage rise so it's the resistivity that's important and as LSK has said the factor is about 8.5. So armour is normally ok for CPC but rarely enough for bonding.Why should they be different though?
So what are the copper equivalent columns in that link referring to then? Reason we've used 4-core is because it's what the factory owner had lying around and he's on a cost saving exercise. Will have to have a look at pulling in a separate conductor.
Reply to Bit quick advice please in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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