Earthing Arrangements Explained + Photo's

[Engineer54]

I think these overhead earthing systems are being done away with due to copper theives leaving the rural customer without an earth

Not a chance in hell, the cost of taking most of these overhead supplies underground will cost more money than what the banks lost, when the massive fraud scam came to light!! lol!!

 

[Richard Burns]

Think you'll find that for most BS88 fuses it's 80KA, not 50KA....

BS88-2 50kA
BS88-6 80kA
BS88-3 33kA
I think, so with just BS88 and no following number a minimum of 50kA, unless it is a BS1361 that is now BS88-3.

 

[Engineer54]

BS88-2 50kA
BS88-6 80kA
BS88-3 33kA
I think, so with just BS88 and no following number a minimum of 50kA, unless it is a BS1361 that is now BS88-3.

Other way round i'd say!! ...lol!!

 

[mrloy99]

no I meant the dno just leaving the poor consumer with a TT and having to fend for themselves for a local earth rod(consumers responsibility)

 

[mrloy99]

I was under the impression that we were to assume a value of 16ka(but I could be wrong)

 

[Engineer54]

I was under the impression that we were to assume a value of 16ka(but I could be wrong)

That would be with the old BS1361 -3 service fuses...

 

[Richard Burns]

I was under the impression that we were to assume a value of 16ka(but I could be wrong)

According to the OSG the maximum fault current likely to be found in domestic properties in the UK (unless in heavily built up areas) is 16kA.

However this is probably stated because annex Za of BS60439 provides an additional test, for domestic consumer units that are protected by a BS1361 fuse at the supply, to ensure that a BS60439 consumer unit can take a 16kA fault current without danger.
This permits the use of protective devices in the consumer unit that may not have the short circuit rating to cope with the prospective fault current since the assembly as a whole will cope.
This is part of why the manufactures do not permit different makes of breaker in their consumer units, they say they are not tested for those units.

 

[aesmith]

Here's our overhead supply for comparison and comment. Our transformer is served by two high voltage conductors, which in turn come from a string of poles carrying three conductors - ie two of the three branch off to our property. I assumed these were two phases from three phase, but comments here now make me unsure.

One green/yellow sheathed cable comes from the case of the transformer into the ground on the N side of the pole.

On the other side of the pole the two cables out of the transformer join the underground service cable which goes to our meter cabinet. One connects via the isolator or fuse or whatever it is (the grey item), the other is clamped directly. After the join to the service cable, there's another earth that goes underground at the foot of the pole on the S side. The DNO guy who traced and marked the cable routes for us said that this would run some distance horizontally underground while still insulated, then further distance uninsulated.

Our earthing arrangement was described as "CEW" and also "TN-S" by the DNO engineer, after he opened part of the cut-out to check.

Tony S

 

[Silly Sausage]

aesmith, can you go and zoom in and get a picture of the plate on the tranny?

 

[aesmith]

Will do tomorrow, it's dark just now.

 

[baldsparkies]

So does anyone have a picture of a PME system :joker: Seeing as freshman are bound to be seeing that old chestnut.
I know, I know, but the question will be asked, guaranteed.

 

[aesmith]

aesmith, can you go and zoom in and get a picture of the plate on the tranny?

Here you go ...

 

[Knobhead]

Thanks for the picture of the makers plate. Blows yet another hole in the declared voltage debate.

 

[MrLights]

Below is an install done by member Dave85. You can't get any clearer than that. Nice job Dave.

Far too tidy!!!

 

[Admin]

This is another nice thread.

 

[Rockingit]

This is another nice thread.

Sadly most of the contributors can no longer share their wit and wisdom with us, which is very sad.

 

[Admin]

Yeeeeah, some can though.

 

[LastManOnline]

If you have a neutral connected to an installations earth terminal (eg PME/TNC-S) then the incoming supply cables metallic sheath connection must be disconnected. Especially important where a supply cable is suppling both TN-S and TNC-S earthing arrangements!! eg, ....where the DNO cable is in the process of being PME'd....

Well Dan,on your recommendation ,I decided to read this thread (all 12 pages of it). Very interesting.Feels a lot older than 10 years.It also raised a question for me ,based on the comment above from "Engineer54". He suggests that the metallic sheath of a TNS cable must be electrically isolated as soon as the TNS supply is converted to TNCS.Why does this have to be done?