TT System questions

[Engineer54]

i got the local electric compant to convert it to pme for nothing that must be better !!!!!!!!!!!!!!!!!!!!!

Please explain how a PME supply would be better for this industrial site?? You have a ''True Earth'' with a Ra value of .03 ohms. You can throw out all special tripping times imposed on a typical UK TT system!!!

Mind, i would be a little doubtful myself at that .03 ohm reading, but i could well believe a .30 ohm value, that is very much achievable in a good resistivity soil area...

 

[kev123]

Yeah there is a lot of planning gone into the setup of the site, there is tape, mats and rods with some interconnected via each other.

My question remains though does it still require a time delayed main switch back at the point of origin? even though values are met?

I personally think that yes the requirement is still needed, but would it be beneficial to start fitting RCBO to every final circuit?an industrial special location it is something i have never seen before.

In a domestic scenario not a problem, or in an agricultural scenario too. But the fact that this is an industrial site i am not 100% sure

the joys of TT

ha ha

 

[Engineer54]

With Ra levels that low (and i do still doubt .03 ohms) that is proven stable, why would you be making special considerations that are based on Ra's of around 200 ohms??


I hope when you tested this extensive TT system you used a dedicated earth tester, and not relied on your MFT. and that your test spikes were placed outside any Zone of influence?? Otherwise your test results would be considered to be unreliable and be probably incorrect....

 

[UKMeterman]

Lots of tapes and mats? Is this radio transmitter, they do tend to have a very extensive functional earth system. These USA DOD documents may be of interest http://www.tscm.com/MIL-HDBK-419A.PDF http://www.wbdg.org/ccb/FEDMIL/hdbk419a_vol2.pdf
UK Meterman

 

[kev123]

Hi it is not a Radio Transmitter, it is renewable energy.

cheers

 

[kev123]

tell you what though, that does look like an intersting read!

Saved!

 

[UKMeterman]

Do remember that they are documents from the US DoD and so are for information only, if BS7671 or other documents differ then the UK standards must be followed.

 

[kev123]

I do realise that

Thank you

 

[Engineer54]

UK Meterman,


That was a very interesting 2 hour read!! ...Thnks!!

 

[UKMeterman]

Another good site regarding grounding, shielding, bonding and EMC issues is EMC Information Centre - The EMC Journal (Free in the UK) and have a look at the EMC information section.
UK Meterman.