Discuss Metal steps secured to concrete (bonding) in the Electrical Forum area at ElectriciansForums.net

newfutile

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We have had 2 metal steps installed to cover main supply cables (out to flats) from a Ryefield .
when measured IR from MET to steps i got 0.091 MegOhms.

The usual calculations are for when a 30 ma RCD is protecting (which is not the case here)

91 Kohm is above the usual value of 23 Kohm I usually use (10ma).

Should these be bonded to earth?
 

Aaron b

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I wouldn't earth it. As you say using the equations the maximum current that flows through the body is < than 10mA.

Using the formula from GN8:

Metal steps secured to concrete (bonding) 1637827866097 - EletriciansForums.net
rearranged to:
Metal steps secured to concrete (bonding) 1637829024815 - EletriciansForums.net

I get 2.5mA when taking ZT as 1000ohms as suggested in the guidance.

Are there any other earthed parts within touching distance? GN 8 states "Consequently, for a conductive part to be able to introduce a potential to a person (or livestock) in contact with the potential of any of the conductive parts, that part should be accessible to such a person (or livestock)." I assume this would also apply to your situation.

(I am referencing the 17th ed amd 2 of guidance note 8)
 

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