Hi all!!
Here is a good one!!
Now, i am sorting out the electrics on a house i inherited [so i know its history] Earthing by the way, is TNS.
Anyway, back in 1988 the then electricity board [sWEB??] came along and fitted a new cutout and meter. All very good, apart from their provision for earthing... Cable to the house is 70 odd year old PILCSWA. Sooooo, what they do?? Cut back the armour to expose the lead sheath, wrap black insulating tape around the sheath and top of the wire armour ends [the tar and stringy stuff having long since fallen off] and fit the new cutout complete with molten pitch.
All very nice, apart from that they decided that they would provide for earthing, by fitting a BS 951 to the armoured bit of the cable. [instead of re-fitting the little tag thing that was fitted to the cable sheath before]
Fitting BS 951 clamps to cables is very much frowned upon now, but it was quite the thing in them days apparently. Anyway, turns out that Ze is 2.2 ohms when measured from phase to armour, but 0.29 when measured from phase to lead sheath.
I asked a WPD cable jointer about this once, well, after explaining my figures, what i actually asked him, was why the huge discrepancy in the readings and do they not link the armour of the service to the armour of the main when they fitted service cables. I was told; "some jointers do, some do not"
Now, i know that earthing to the armour is not going to give you such a good earth as connecting to the sheath, [As an asides, the armour in the cable itself is insulated from the sheath] but i thought it would be better than that, as the conductivity of lead and iron is about the same.
Anyway, If i get hold of WPD i expect they will deny they fitted the BS951 and tell me to TT the lot. What is to stop me though, just fitting an earth cable to the neutral block and having "home made" PME ???
I know that if you ask the DNO in most areas they will "convert" your system to "PME" for several hundred quid, but, and this is a HUGE MASSIVE but, I cannot see how this is possible without digging up the street, as, i always thought that one of the things with "PME", was that they had to rod the joint between service and main when they made the connection????
Happily for me, i KNOW that the lead sheath and neutral are linked only about 3 feet further along the main, i saw it with my own eyes. This i think, is the reason for the very good Ze when i test to the sheath, it would be, it is tied to the neutral 30 feet away
Could I not just earth to the neutral block and off i go, as this is all the DNO's do with their "conversions" only i got a rodded service joint with mine!!!! or should i just get one of them "constant force spring" earthing gizmos and leave it as TNS...
I know i am not meant to do this, and should leave it to the DNO, but they will just tell me that "we never fitted the BS951, and so we have not provided an earth up to now, and so best you go and provide your own..
What you all think???
john....
Here is a good one!!
Now, i am sorting out the electrics on a house i inherited [so i know its history] Earthing by the way, is TNS.
Anyway, back in 1988 the then electricity board [sWEB??] came along and fitted a new cutout and meter. All very good, apart from their provision for earthing... Cable to the house is 70 odd year old PILCSWA. Sooooo, what they do?? Cut back the armour to expose the lead sheath, wrap black insulating tape around the sheath and top of the wire armour ends [the tar and stringy stuff having long since fallen off] and fit the new cutout complete with molten pitch.
All very nice, apart from that they decided that they would provide for earthing, by fitting a BS 951 to the armoured bit of the cable. [instead of re-fitting the little tag thing that was fitted to the cable sheath before]
Fitting BS 951 clamps to cables is very much frowned upon now, but it was quite the thing in them days apparently. Anyway, turns out that Ze is 2.2 ohms when measured from phase to armour, but 0.29 when measured from phase to lead sheath.
I asked a WPD cable jointer about this once, well, after explaining my figures, what i actually asked him, was why the huge discrepancy in the readings and do they not link the armour of the service to the armour of the main when they fitted service cables. I was told; "some jointers do, some do not"
Now, i know that earthing to the armour is not going to give you such a good earth as connecting to the sheath, [As an asides, the armour in the cable itself is insulated from the sheath] but i thought it would be better than that, as the conductivity of lead and iron is about the same.
Anyway, If i get hold of WPD i expect they will deny they fitted the BS951 and tell me to TT the lot. What is to stop me though, just fitting an earth cable to the neutral block and having "home made" PME ???
I know that if you ask the DNO in most areas they will "convert" your system to "PME" for several hundred quid, but, and this is a HUGE MASSIVE but, I cannot see how this is possible without digging up the street, as, i always thought that one of the things with "PME", was that they had to rod the joint between service and main when they made the connection????
Happily for me, i KNOW that the lead sheath and neutral are linked only about 3 feet further along the main, i saw it with my own eyes. This i think, is the reason for the very good Ze when i test to the sheath, it would be, it is tied to the neutral 30 feet away
Could I not just earth to the neutral block and off i go, as this is all the DNO's do with their "conversions" only i got a rodded service joint with mine!!!! or should i just get one of them "constant force spring" earthing gizmos and leave it as TNS...
I know i am not meant to do this, and should leave it to the DNO, but they will just tell me that "we never fitted the BS951, and so we have not provided an earth up to now, and so best you go and provide your own..
What you all think???
john....
