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Earth Bonding

Posted By: aland

Earth Bonding - 05/30/04 11:00 AM

Gentlemen can I offer you a sinario,A medium sized factory with its own sub-station with a couple of transformers (one stand by one duty). The sub is located some 20 meters from the main factory area. Mains gas is also housed in a brick built gas house another 20 meters or so further away from both the factory and the sub station. Mains water is located within the factory area. Also have a boiler house complex that is reasonably close to the sub-station. All or most areas will be very difficult to access, main factory area does have a steel frame construction.Just for good measure they have a couple of diesel tanks (above ground)with electric pumps. The building was once a hospital site that has been chopped and developed over a good number of years. But it has never had any main earth bonding installed.
Given all the above information does any body have any good practical and compliant solutions as to how to install efficient bonding please.
Posted By: Trumpy

Re: Earth Bonding - 05/31/04 11:32 AM

Aland, what type of building construction is this?.
And also, what type of utilisation?
What type of water mains do you have?, copper?, plastic?.
Also is there a common area where you can place an Earthing Enclosure, where you can run 16-25mm2 earthing conductors in conduit and Bond the whole lot?.
Even if you have to drive stakes at each end of your ECC's, it would have the effect of lowering your Earthing Resistance.
Posted By: pauluk

Re: Earth Bonding - 05/31/04 01:26 PM

I'm not used to dealing with installations of this scale, but it seems strange that bonding was never properly installed in the first place if it started out as a hospital.

Are the spaces between the buildings mostly concreted, making it difficult to run cables underground?
Posted By: aland

Re: Earth Bonding - 05/31/04 05:45 PM

Hi T/PUK,Thanks for your interest. This ones got everything, Its a steel frame building with brick / concreat infill, Water main is metal underground. Making onto plastic through a softener plant then back onto copper.
Paul you are spot on concreate yard and drive between sub and all areas.
My own idea is to run a bonding conductor primarily to the steel structure and use this as a common cage around the facility.
I can then jump off at any point and pick up services. What do you think?
Gas and fuel oils likely to give me the most hassle, they are both across the yard away from the main building. Wondered if I could bond as the pipework enters the boilerhouse area. this is quite adjacent to the electrical sub-station, but some 15 meters from the gas meter rig and the point of storage for the fuels. By the way its a commercial laundry plant now with heaps of pipe-work of all descriptions. Minimum size bond is going to have to be 50mm.
Your quite right Paul it suprised mee to find no bonding especially as there would have been consultants on the original installation.
Mind you the whole thing is turning into a bit of a fiasco the more I look. Got 2 x 600 amp supplies from the sub terminating side by side in the building with then sub mains from this point to all other parts of the factory. Must have cost a fortune in its day.
Posted By: Bjarney

Re: Earth Bonding - 05/31/04 06:04 PM

A generally accepted approach would be to perform “fall-of-potential” or “3-lead” test(s) on the grounding-electrode system(s), with test-rod spacings based on published literature for such tests. Then, [“4-lead”] Kelvin-resistance measurements should be conducted detween various subsurface metallic components {like tanks} and building-electrical gear.

This will give some idea of the magnitude of potential difference that personnel and facilities may be exposed to in fault situations. It would be desirable to have testing conducted {and competently analyzed and upgraded} before some injury/loss incident forced the issue.
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