Industrial Building Earthing?

[SparkSmog]

Ive been enquiring about our earthing system at work, a chemical plant, and the electrician wasnt too sure what we had so we investigated

From the onsite transformer we have a combined earth & neutral, with a earth plate underground

We have 3 main buildings, which are either Zone 1 or Zone 2 areas, one of the 3 buildings has approximatly 12 Earth Rods and multiple Earth Bars (The newest building)

The other two buildings are earthed mainly through SWA & Earth Bars but each building only has one Earth Rod (One of them also has a I.S. earth point though) - Is one earth rod per building sufficient? We always ensure all vessels & framework are adequatly earthed so i know it will be bonded, I was just wondering if there are certain requirements or legislations that require a certain amount of Earth Rods per Sq. Meters etc. Also with it mostly being Zoned areas will this require extra protection?

Can anyone reccomend a good book on earthing legislation?

What earth system would this mean I have? It seems a combination of TT & TN-C (I think, dont have my Big Red Book at the moment) Or do these systems not apply as such with the transformer being on site - As opposed to housing etc.

Also can anyone tell me the required resistance of the ground from earth rod to earth rod? (I assume it will differ dependant upon distance etc. And with TT Systems its usually 200ohm IIRC?)

Sorry for all the questions, just out of my time and im starting to get quite curious as i read the Big Red Book

Thanks for any help

 

[scotsparky]

Spargsmog As the main ditribution pannel How is the earth attatched? or is a seperate Earth run into the building from the transformer

 

[Guest123]

Hi.

Surely a combined earth and neutral conductor from the supply transformer to your main switchgear would give you a TN-C-S system??

Or do you mean combined at the star point of the transformer and the two seperate conductors to your main switchgear?? which would then give you a TN-S.

It would also appear though that the buildings have been converted into TT systems (safer in my opinion) with all that steel framework about.

The only way to be sure of sufficient earth electrode resistance is to measure it, chances 1 rod is enough as no doubt on a site like that it will have been measured.

As for legislation and guidance maybe this link to the IEE views will be of use to you.

Cheers.

http://www.electriciansforums.net/redirector.php?url=http%3A%2F%2Fwww2.------.org%2FPublish%2FWireRegs%2FWiringMatters%2FDocuments%2FIssue16%2F2005_16_autumn_wiring_matters_earthing_your_questions_answered.pdf

 

[SparkSmog]

Sorry yeah i meant TN-C-S, a combined earth & neutral in the main switchgear

Cheers for the rreply, we have already measured it and it seems fine, i was just curious as to why we had approximately 12 earth rods for one building and 1 earth rod for another building of a similar size

Cheers

 

[uksel]

i think in the envirnoment you are in, you are outside of the scope for BS7671

 

[scotsparky]

Uksel he is very much in scope for the oly areas out of scope are listed at the front of the BRB.

 

[uksel]

industrial sites don't have to conform to bs7671 as far as I was aware, though it is good practice to do so

 

[scotsparky]

uksel have a look at the front of the brb it tells you any areaas that are not covered by BS7671. you will find trains,oil rigs,ships, planes are not covered but Industrial sites are its even more important as there is a higher risk factor.

I wouldn't like to useo the "didn't think 7671 applied* line to the Judge. probbable get a few months at leaset to think about it in a reoom with NO view and big BUBBA to keep me warm at nights.

 

[sparks1234]

The electricity at work act applies

 

[hollywoodsparky]

Hi Guys
Yes the eawa applys but if it is installed to the regs it will meet these req.
If you have an on site tanny your neutral and earth will be linked at the lv side of the tranny.
Your rod req are based upon your earth loop test at the db's in each building these have meet discon times for your protective device.
steelwork gas water to be earthed etc earth rod resistance also.