TN-S or TN-C-S From this photo

[TonyJohnson]

Hi,
I undertsand this to be a TN-S system as the earthing arrangement comes along the SWA metal sheath surround but the Ze i got is 0.19 which falls out side the regs of 0.8.
Chameleon Electrical - https://www.facebook.com/Chameleonelectrical/photos/a.162578514404078/251251892203406/?type=3&theater

I have also read on here that if the earth is then connected to an earthing block as shown on picture, it then becomes a TN-C-S! which doesnt make sense as the earth is outside the sheath not inside on the neutral!

Which is it?

 

[Simonslimline]

0.19 falls outside what value? Are you a trainee? These are worrying questions if you are an electrician!

According to the FB profile, hes a napit verified electrician whatever that means.

 

[Deleted member 26818]

Hi,
I undertsand this to be a TN-S system as the earthing arrangement comes along the SWA metal sheath surround but the Ze i got is 0.19 which falls out side the regs of 0.8.
Chameleon Electrical - https://www.facebook.com/Chameleonelectrical/photos/a.162578514404078/251251892203406/?type=3&theater

I have also read on here that if the earth is then connected to an earthing block as shown on picture, it then becomes a TN-C-S! which doesnt make sense as the earth is outside the sheath not inside on the neutral!

Which is it?

0.8 ohms is the typical value for TN-S, though some would say the ‘typical maximum’.
Anything below 0.8 ohms is acceptable, above would be a concern.

That earthing block does not look connected to the neutral.
If it is, then it is likely that the DNO have converted it to TN-C-S.

Not sure if that’s two supply cables, or a looped supply.
100A main fuse suggests a looped supply.

Although the supply may be TN-S, network upgrades may mean PME conditions may apply.

 

[Midwest]

According to the FB profile, hes a napit verified electrician whatever that means.

Don't start all that old nonsense

 

[telectrix]

NAPIT...

Not
A
Pi$$ing
Idea
Technically.

 

[Deleted account]

Do a pfc and a pscc . If they are the same result it's probablY be TNCS . However as others have said it's probably not.

 

[TonyJohnson]

Do a pfc and a pscc . If they are the same result it's probablY be TNCS . However as others have said it's probably not.

Thank you.

0.8 ohms is the typical value for TN-S, though some would say the ‘typical maximum’.
Anything below 0.8 ohms is acceptable, above would be a concern.

That earthing block does not look connected to the neutral.
If it is, then it is likely that the DNO have converted it to TN-C-S.

Not sure if that’s two supply cables, or a looped supply.
100A main fuse suggests a looped supply.

Although the supply may be TN-S, network upgrades may mean PME conditions may apply.

Thank you, great advice.

 

[Lucien Nunes]

Agree it's pretty clearly TN-S as there's no visible connection from the neutral to the MET. What makes things a little indistinct here, is that the MET is a terminal block of a style often used for a neutral, butted up against the head.

You could do a simple continuity test between the neutral & earth at the mains switch to confirm this.

As per Davesparks, the two are connected somewhere, so there will always be continuity. Of course, if they are connected inside the head, the resistance between them will be vanishingly small, while if they are connected only at the substation there will be measurable resistance. The problem with trying to measure it, is that in a TN-S supply there will be a small voltage present due to the voltage drop along the neutral back to the substation. Therefore, some instruments will refuse to take a measurement and the reading you get on others could be nonsense. In either case it suggests TN-S but relying on a tester displaying an error is not a good method.

The difference between the L-E and L-N impedances gives the resistance indirectly, but without any N-E voltage interfering with the test.

 

[telectrix]

Agree it's pretty clearly TN-S as there's no visible connection from the neutral to the MET. What makes things a little indistinct here, is that the MET is a terminal block of a style often used for a neutral, butted up against the head.

that henleyblock with the earthing conductors is on the wrong side of the cut-out to be TNC-S.

 

[Lucien Nunes]

Indeed it is, but the OP may have considered the possibility of there being an alternative way for the DNO to break out the neutral from the head to provide the MET. I have seen something similar where a 3-core service cable was used to provide two phases, with two cutouts on a standard single-phase head, so they had to cheat the neutral out of the side.

 

[ChrisElectrical88]

Whats the PFC between L&E and L&N?

 

[stevels4]

TNS but why is the centre earth cable insulation from the Henley burnt or is it my eyes?