Industrial unit-2 incoming supplies both TNCS

[LewisS]

Hi

Just in the process of completing some remedial works on an industrial unit with two tncs supplies, one is 100a the other 200a and on opposite sides of the building! The main issue picked up from the testing was the lack of bonding to all the site services. This is where im after some help, not a problem to bond incoming gas water building fabric air lines etc but will this need to be linked to the 100a main earthing terminal? I was planning to run my bonding from a new met at the 200a supply as this is bigger and should more then protect the smaller supply.

Any help would be appreciated.

Lewis

 

[guest119]

Do you know if they come from the same hv transformer?

Boydy

 

[LewisS]

Im hoping so mate but will have a good look tomorrow when back on site. Failing that the supplier should be able to tell me?

 

[LewisS]

Not to sure but im hoping they are. Will have a proper look into it tomorrow when back on site. Would the supplier be able to tell me if they are?

Thanks

Lewis

 

[Darkwood]

Same building i would assume its same source although having said that are you using both supplies?

If not just Met for the 200amp..

Does the site need both supplies?... a standing charge will be x2 to start with but as goes equip' bonding i assume the building was segregated at some point as 2 separate buildings?

If it was was the gas/water etc common supply or independently fed ?

Need more info'

 

[Engineer54]

Further to what's already been suggested and after ascertaining if the two supplies come from the same DNO source....

You don't say if these two supplies are 3 phase or not?? If they are both single phase, it'll be a good bet that they are on different phases so test just to make sure one way or the other!!
Earthing wise make the 200A supply you're MET and link the other supply (EMT) to that MET and connect all the main bonding cables to the MET. If the building is a steel framed structure, don't forget to bond the steelwork to the MET.

 

[LewisS]

Excellent thats the way I had planned on doing it. Both supplies are 3 phase and both currently being used. Single gas meter and water meter so maybe was one building the whole time.

Thanks for your replys

 

[Engineer54]

Excellent thats the way I had planned on doing it. Both supplies are 3 phase and both currently being used. Single gas meter and water meter so maybe was one building the whole time.

Thanks for your replys

That's all fine, but make ''SURE'' first, that these two supplies do indeed originate from the same DNO source, or you may be in trouble with the set-up described above...

 

[Knobhead]

Just to follow on from E54. The reason for ensuring the supplies are from the same source is the possibility of circulating currents in any bonding including the building steel work.
Is there any defined areas for the two independent supplies or are they overlapping? It’s not a great problem so long as the origin is known. A simple way is label all sub-boards Supply “A” or “B”.

I’ve had some experience of overlapped supplies renovating a plant switch room. One 433V 600A supply from one substation, four 550V 400A supplies from two other subs. To add to the fun all the 550V supplies could be paralleled. When I started the project I was stood in the middle shaking my head trying to make sense of it all, it's also why I became an AP. It took me near three years on and off to sort out. We ended up with one common MET for all supplies. But this was a private network where everything was cross bonded as a matter of course.