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L

lionelmcc

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Hi
I was looking at a job the other day which had a recent minor works cert which had the arrangement down as TT.
On further invesigation I discovered that the 16mm earth cable did indeed leave the building but went up the wall outside and was connected into a 3 wire overhead supply.
I am presuming this is TNS or am I barking up the wrong wall?

L
 
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J

jimcallear

  • Thread Starter Thread Starter
  • #2
I'd say that without checking how its connected up there you cant be sure as to if it's a tns or tnc-s.
 
S

Spudnik

  • Thread Starter Thread Starter
  • #3
I would contact the DNO.

Sounds a bit odd to me.
 
G

Guest123

  • Thread Starter Thread Starter
  • #4
Agreed. I aint never seen one of our earthing cables going up the wall and connecting into the OHL. Very weird:confused:
 
J

johnnyb

  • Thread Starter Thread Starter
  • #5
I have never seen that done either, something not quite right there, the DNO don,t run earth wires to there overheads, they usually are pme at the cut out, they are around here anyway.
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #6
Ok, I'll investigate further and keep you all posted

I have never seen that done either, something not quite right there, the DNO don,t run earth wires to there overheads, they usually are pme at the cut out, they are around here anyway.
I will contact the suppliers on Monday, however I have just been back to the site and followed the poles back a few hundred yards, until it disappeared into wood.
The house is an old gate lodge for to a larger house, which I am also looking at doing some work on.
The big house would appear to be supplied by the same method and, on looking inside would at first glance, seem to have a PME arrangement although there is no PME label at the main fuse or meter.
also , when driving home I did notice lots of poles ( all over the place) with three wires

I feel Like I am on a different planet
 
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Des 56

-
Arms
Esteemed
It may be a third wire earth This would probably be a overhead TT supply Not seen much nowadays
 
J

johnnyb

  • Thread Starter Thread Starter
  • #8
Hia mate, the only time i have seen anything of the like is when the DNO has brought there own earth off the pole to an earth rod or plate near their pole, but never back into a dwelling or such like, interesting though what u have said.
 
G

Guest123

  • Thread Starter Thread Starter
  • #9
Hey.

Des seems to have the most logical opinion. But then that 3rd wire could also form part of a TN-S system, depends where and how the other end is connected

Very difficult to tell really.:confused:
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #10
i followed the poles back for about 400 yds until they crossed a stream and on into the woods
then walked on to the house which has the same arrangement with the wires coming back accross from a different part of the woods
it's difficult walking country
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #11
Ok the plot thickens

I took a reading fo Ze; 0.46. Would suggest PME?

when I phoned he DNO (Scottish Power) I was told that they did not have that information.
I was then condescendingly told by some jumped up receptionist, that, "Any electrician worth his salt would be able to tell"
At this point I am glad that I am not the only person on this forum who is confused

Comments please

L
 
Hi
I was looking at a job the other day which had a recent minor works cert which had the arrangement down as TT.
On further invesigation I discovered that the 16mm earth cable did indeed leave the building but went up the wall outside and was connected into a 3 wire overhead supply.
I am presuming this is TNS or am I barking up the wrong wall?


L
sounds pretty obviously a TN-S.Separate earth throughout.Your ZE reading is also too high for TN-cs.
The suppliers have moved away from using these systems nowadays due to economical reasons and safety(cost of extra cable,and possibility of gypos stealing it for scrap) But as it is a pretty old installation by the sound of it TN-S sounds favourate.
 
S

Spudnik

  • Thread Starter Thread Starter
  • #13
Agree with the above.

PME max Ze 0.35 and TNS is 0.8, so there must be a path somewhere!

How did you test the Ze?
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #14
Hi jason

I disconnected the bonding and tested between the incoming earth and the henly from the L tail

What about the attitude of the DNO?
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #15
Hi jason

I disconnected the bonding and tested between the incoming earth and the henly from the L tail

What about the attitude of the DNO?
Im afraid its the luck of the draw who you get when phoning them.

You could try phoning back and asking to speak to someone more in the know. They are there.

Remember, when you call them, the people that answer the phone do not have a lot of technical knowledge.

I struggle when i phone to book a PME enquiry.

Is there any way you can get us some pics?
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #16
I am presuming this is TNS or am I barking up the wrong wall?
It looked at first glance like TNS

Big house also has 3 overheads but is connected inside like PME
(one incoming armoured with attached henly for earth)

this "girl" was talking as thou she had a 2391 ( very snooty in her attitude as well)
 
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G

Guest123

  • Thread Starter Thread Starter
  • #17
Hey Li.

If this is a TN-C-S, then there is an external problem somewhere as the max is 0.35ohms.

The reading you have suggests a TN-S and with the third wire is a possibility.

If you ring them again, ask for technical dept.
 
It looked at first glance like TNS

Big house also has 3 overheads but is connected inside like PME
(one incoming armoured with attached henly for earth)
Maybe I'm missing something here--but from your above description-your armour straight to your henly block--that again sounds like TNS....PME would have a link from neutral to MET surely?
I think it has to be remembered here that aTT supply doesn't have to be overhead and likewise a TNS supply doesn't have to be underground--it is to do with the system earth--The earth will be linked to the neutral back at the supply transformer star point with a local electrode.
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #19
Ok guys the lodge looks like TNS and the house looks like PME bu they both have three overheads outside.
Recently came across an installation in his area that that looked like PME and the houses either side were PME .It was ( to my surprise) TT.
However, I feel that my reading is too low for TT

I think I will try the DNO again
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #20
I wouldnt say it was too low for TT, however, it is very rare.

Another DNO phone call is the way to go i think, given the uncertainty of the install.

At the end of the day, if they do not want to assist, maybe TT the install anyway.
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #21
Are you suggesting a spike as a supplement tot the present arrangement?
 
S

Spudnik

  • Thread Starter Thread Starter
  • #22
If it was me then yes, even though the reading is low.

Peace of mind as a temporary measure while you establish what you have.
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #23
this a procedure I'm not familiar with
 
S

Spudnik

  • Thread Starter Thread Starter
  • #24
The earth that is currently in place COULD be unstable, especially when you consider that you are not able to confirm its connection point.
 
L

lionelmcc

  • Thread Starter Thread Starter
  • #25
are you suggesting I leave the current arrangement but connect it to a spike via 16mm cable to the henly block?

If so, what do I put on the cert?

I think I may have sussed this out

I managed to follow the poles back to th trannie; Two wires,,, and then to the pole where the supply splits between the house and the lodge three wires but the third not connected ????
on to the house,,,scrambled down a banking (next to 50ft waterfall) to get a butchers at the connection
EUREKA!!! SWA into the house is fed from the three wires L,,,N,,, E but E & N connected together at the top of a pole that cannot be seen from anywhere without descending into the ravine.TNS methinks
Question is; why does the earth cable go go back into the wilderness for 200yards and not teminate into anything when it is connected to th Neutral 10 FT from the house?
 
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G

Guest123

  • Thread Starter Thread Starter
  • #26
E & N connected together at the top of a pole that cannot be seen from anywhere without descending into the ravine.TNS methinks

it is connected to the Neutral 10 FT from the house?
Have to say that screams TN-C-S to me mate, as the supply neutral is grounded to earth at various points along it 's course to maintain earth potential.

TN-S is completely seperate all the way back to the the star point of the transformer.
 
S

Spudnik

  • Thread Starter Thread Starter
  • #27
PME to me too.

However, your Ze is a little high for PME to leave as is, so i would, dare i suggest, RCD the whole install.
 
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