Discuss Enclosure used as earth in the Industrial Electrician Talk area at ElectriciansForums.net

Trig

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Hi all, question regarding earthing in hazardous areas distribution panels. The issue is that on most equipment in hazardous areas they use the metal of the enclosure as the earth so if a threaded entry and metal enclosure no need for internal earth cable, like wise if going through a clearance hole they would put serrated washers on the inside given the earth through the enclosure. Now have came across this in a distribution board where the entry is threaded, the enclosure is metal but the issue I’m having it’s a removal gland plate that the gland is threaded into then is bolted inside the enclosure but there is a gasket between the gland plate and dist board. It’s getting metal to metal contact with six 10mm bolts holding it in place but on this dist board there is earth terminals to terminate but the cable feeding the dist board is 70mm going into main isolated and the din rail earth terminals are 16mm. So they have taking a 16mm earth from the gland plate to this earth terminal. Now this is only 300mm if that, of 16mm earth to the gland plate. My question is will 300mm if 16mm earth cable carry fault current for that short run for a 70mm cable as a 35mm earth cable won’t fit into terminals without going to manufacture to get permission to replace with 35mm earth terminals as this is a EXe. Mostly inside the dist board they are using the enclosure as the earth with earth din rails terminals onto din rail then out going cables but nothing at the other end. Sorry for the long winded story. Thanks in advance.
 

M4SSO

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Are there any external earth bosses on the enclosure, do you have a suitable camera to take a picture?
 

TJ Anderson

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As you already recognise, as your line conductor is 70mm then 35 mm would automatically satisfy the protective conductor sizing requirement of Table 54.7

16mm may well be adequate but this will need to be confirmed by using the adiabatic equation. Will need some more info for this though.

What is the PEFC at this enclosure and what is the details of the OCPD that is protecting it?
 

davesparks

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. My question is will 300mm if 16mm earth cable carry fault current for that short run for a 70mm cable as a 35mm earth cable won’t fit into terminals
Have you calculated the size of cpc required? Unless there are special rules affecting this 35mm would usually be bigger than actually needed.
 

TJ Anderson

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Have you calculated the size of cpc required? Unless there are special rules affecting this 35mm would usually be bigger than actually needed.
He knows he can use 35mm, he wants to know if he can use 16mm. It needs to be calculated.
 

westward10

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The OP hasn't been seen since he posted this in May.
 

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