terminating seperate earths

[johnboy6083]

Hi ladies and gentlemen.

Ive just finished working on a power station, and whilst there, i found myself making off the main supplies to the dist boards.

Along with the SWA, they had run seperate earths. all the other boards had been terminated by taking the earth to the banjo, and then on the inside of the board, from the banjo to the earth bar.

Now ive always taken the earth through a metal stuffing gland straight to the bar, and bonded the armour also, as i beleive that when dead testing you get a more accurate r1 + r2.

If doing it the other method, you have to unbolt the bolt on the banjo, or else you will be measuring all the paralell paths of the installation.

Which method do you lads use and why?

 

[Darkwood]

The swa would be earthed down to some extent whether or not the banjo has a tight bolt through it as the gland will cut through the paint to the steel case if its tightened up right to start with so unless you were to drop the swa gland off the board you wont really achieve much removing the banjo bolt,removing the gland at the dist board supply end to test can be negleted as its only within a meter of the actual earth bar anyway, the best way to avoid parallel paths it to drop the swa away if onto a metal enclosure at the load end isolating it from possible parallel paths.

 

[johnboy6083]

what i was getting at mate, is thatb when testing R1+R2 in thisa instance, i would only want to consider the seperate earth, not the arour, as that would be considered with the Zs. So in order to consider the seperate earth,. you would have to unbolt the earth from the banjo, if using the method i first described to terminate the seperate earth. so.rry for not being clear mate

 

[Sparky Ninja]

I would take the single earth to the bar, then another earth from the bar to the gland. It would help maintain the integrity of the earthing. The only thing that could affect that is the size of the earthing as there may be too few terminals within the bar to accommodate the additional earths. As long as everything is correctly and easily identified.

 

[johnboy6083]

when ive had a board with not enough terminlas, i use the bolt on the side of th DB,and link that to the bar.

 

[Steve1412]

I could be wrong ( and am on many occasions!!!) but the SWA only needs earthing at the supply end anyway so I would take the earth straight through to the earth bar ensuring all the SWAs at the supply end where earthed.

 

[nick611]

i think you could include the seperate earth as part of the r1+r2 as it is specific to that circuit.it has a permenant and deliberate effect on the zs value of the final circuit so is not really a parallel earth and should not be treated as one for test purposes

 

[johnboy6083]

I could be wrong ( and am on many occasions!!!) but the SWA only needs earthing at the supply end anyway so I would take the earth straight through to the earth bar ensuring all the SWAs at the supply end where earthed.

you are right mate, it does only need bonding down at the supply end, howver it seems to be common practice to bond it at both ends. It will at least, bring the disconnection times down, but with higher fault current.

On the same installation, we were installing 415 sockets with rotary isolators. they were fed from 63Atype d's and the hada 63A rccb inside the socket (no discrimination?). The cabkle was 10mm2 5c SWa. when the tester tested them, over 3/4 failed due to high Zs. we ended up bonding the armour down at the socket end (plastic sockets, with threaded entry,was a pain to do), and a lot of them still failed. We then had to bond the armour down to the traywork or ladder, which was also mounted upon building steelwork. Somebody messed up on that one. I think its very bad practice if you have to rely on paralell paths for your disconnection times.

 

[ian.settle1]

Don't forget a seperate earth may have been run as the size of the armour does not have the minimum CSA.

There is a chart that shows that certain size SWA cables the armour can not be used a the CPC and a seperate CPC must be run.

 

[johnboy6083]

wasnt disputing that ian, was merely discussing whoch method of terminating the seerate earth makes the most sense. How would you do it mate?

 

[ian.settle1]

wasnt disputing that ian, was merely discussing whoch method of terminating the seerate earth makes the most sense. How would you do it mate?

As you said it had been done in your first post "terminated by taking the earth to the banjo, and then on the inside of the board, from the banjo to the earth bar." Would have used a brass nut and bolt to bolt the banjo.

 

[Darkwood]

what i was getting at mate, is thatb when testing R1+R2 in thisa instance, i would only want to consider the seperate earth, not the arour, as that would be considered with the Zs. So in order to consider the seperate earth,. you would have to unbolt the earth from the banjo, if using the method i first described to terminate the seperate earth. so.rry for not being clear mate

Sorry i went on a different tangent to your intended question, i understand you now and i always send earth through seperate gland and link banjo with a earth tail to earth bar, id only ever consider strapping it to banjo if there were a shortage of earth terminals as my method requires 2 and the latter just 1.

 

[nick611]

why would you not consider the armour, it is part of the final circuit,its not a parallel earth.you don,t need to exclude it from the r1+r2 because it is part of the r1+r2.stop wasting you,r time