tt or tns?

lionelmcc · Mar 20, 2009

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

lionelmcc · Mar 24, 2009

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)

Guest123 · Mar 24, 2009

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.

mrloy99 · Mar 24, 2009

lionelmcc said:
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.

lionelmcc · Mar 24, 2009

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

Spudnik · Mar 24, 2009

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.

lionelmcc · Mar 24, 2009

Are you suggesting a spike as a supplement tot the present arrangement?

Spudnik · Mar 24, 2009

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.

lionelmcc · Mar 24, 2009

this a procedure I'm not familiar with

Spudnik · Mar 24, 2009

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

lionelmcc · Mar 25, 2009

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?

Guest123 · Mar 25, 2009

lionelmcc said:
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.