Seperate Earthing circuits

[robmark1976]

Hi hope you can help, we have just carried out a survey of an office floor that we are due to fit out and the floor boxes and VAV units don't have separate Earth cables to them, even though there are numerous circuits the earth relies on 1 earth cable bolted onto the metal trunking by the distribution board and then linked to all the different circuits and not separate earths, I know this does not comply with BS7671 but the consultants wants me to be detailed and quote the regulation from the REGs to show this does not conform, Thanks Rob

 

[davesparks]

What makes you think that it doesn't comply?

 

[robmark1976]

I thought all individual circuits had to have there own cpc and not share an earth with other circuits or am I wrong?

 

[telectrix]

the metal containment can be a common cpc for all circuits contained within it.

 

[Engineer54]

I thought all individual circuits had to have there own PC and not share an earth with other circuits or am I wrong?

Not when a full metal containment system (eg, trunking and conduit) is being used to distribute several circuits within....

I'll put money on that metal containment providing a far better Zs value than your 1mm and 1.5mm separate CPC's.

 

[Deleted member 9648]

Hi hope you can help, we have just carried out a survey of an office floor that we are due to fit out and the floor boxes and VAV units don't have separate Earth cables to them, even though there are numerous circuits the earth relies on 1 earth cable bolted onto the metal trunking by the distribution board and then linked to all the different circuits and not separate earths, I know this does not comply with BS7671 but the consultants wants me to be detailed and quote the regulation from the REGs to show this does not conform, Thanks Rob

A very good illustration of the dangers of being self appointed electrical police without knowing the regulations or even where to find the appropriate regulations. Humble pie beckons.

 

[davesparks]

I thought all individual circuits had to have there own cpc and not share an earth with other circuits or am I wrong?

No they don't, a single cpc can be common to multiple circuits provided that it meets the requirements for the most severe fault possible in that group of circuits.

 

[Engineer54]

Hi hope you can help, we have just carried out a survey of an office floor that we are due to fit out and the floor boxes and VAV units don't have separate Earth cables to them, even though there are numerous circuits the earth relies on 1 earth cable bolted onto the metal trunking by the distribution board and then linked to all the different circuits and not separate earths, I know this does not comply with BS7671 but the consultants wants me to be detailed and quote the regulation from the REGs to show this does not conform, Thanks Rob

Now i wonder WHY the project consultants want you quote the regulation from BS 7671?? Because they already KNOW there isn't one, and that there own site survey has already confirmed compliance maybe??

 

[telectrix]

Hi hope you can help, we have just carried out a survey of an office floor that we are due to fit out and the floor boxes and VAV units don't have separate Earth cables to them, even though there are numerous circuits the earth relies on 1 earth cable bolted onto the metal trunking by the distribution board and then linked to all the different circuits and not separate earths, I know this complies with BS7671 but the muppets in suits wants me to be detailed and quote the non-existant regulation from the REGs to justify their existence, Thanks Rob

correction applied for you