6mm Main Earth

[E.E.I]

TNC-S system
60A BS1361 Fuse
16mm Tails
6mm Main Earth
6mm Bonding

Ze 0.30
PFC 0.9kA

So if the CSA meets the requirements of 543.1.3

s= sq route of I2t/k

Sq route ((900x900)x0.1)/115

I got the 0.1 from table 3A1 pg 319, looking at the graph it looks like its about 750A to blow in 0.1 but to stay safe say 800A.

s = 2.47mm.

does that sound ok?

would you say the 6 mm is adequate?

 

[davesparks]

It's unusual to see a 60A TNCS supply!

If it's an existing installation and there are no signs of thermal stress to either the earthing conductor or main bonds then it is not a problem.
For a new installation it may not be acceptable if it is a PME connection due to the minimum 10mm requirement.

 

[E.E.I]

Would you code it in an EICR? even though it meets 543.1.3.

 

[davesparks]

If it is a PME supply I would record an observation with no code attached of the bonds and EC are in good condition.
If it's not PME then it's fine

 

[E.E.I]

No PME sticker and different results for pefc and pssc, would you say no pme?

 

[davesparks]

No PME sticker and different results for pefc and pssc, would you say no pme?

That suggests that it's not TNCS

 

[E.E.I]

That suggests that it's not TNCS

yes you are correct there. my bad!

and yes it is defiantly tncs

 

[davesparks]

yes you are correct there. my bad!

and yes it is defiantly tncs

How do you know that it's TNCS?

 

[E.E.I]

by looking at the service head, earth cables connect into service head with the neutral

Ze of 0.30 would also suggest

 

[davesparks]

by looking at the service head, earth cables connect into service head with the neutral

Ze of 0.30 would also suggest

That doesn't tally with the differing PEFC and PSCC though.

Have you got a picture?

 

[E.E.I]

sorry no pic

difference was 0.10,

 

[davesparks]

0.10 what? Amps, kiloAmps, elephants?

 

[Simonslimline]

by looking at the service head, earth cables connect into service head with the neutral

Ze of 0.30 would also suggest

Is it definitely connected or does it just go in to an earth block in the side of the cutout?

The earth block may not be connected to the neutral.

What is the supply cable?

 

[E.E.I]

0.10kA

 

[E.E.I]

simon it was a concentric cable supplying the property

 

[Simonslimline]

So a straight concentric. Definitely not a split?

 

[E.E.I]

im certain it was straight concentric, could only see two sleeved cores going into the service head, im sure if it was split they would have separated the earthing conductors and used an MET

 

[Andy78]

Sometimes a TN-S connection is made into the side of the service head and looks just a like a TNC-S. All that differs is that the internal link plate is removed. You could of course only visually confirm this by taking the fuse out and taking the side cover off the live head, which of course you are not going to do.
Lack of PME label and differing PEFC and PSCC would suggest it's a TN-S. Your insistence that it is TNC-S relies on a lot of assumptions.

 

[Simonslimline]

Sometimes a TN-S connection is made into the side of the service head and looks just a like a TNC-S. All that differs is that the internal link plate is removed. You could of course only visually confirm this by taking the fuse out and taking the side cover off the live head, which of course you are not going to do.
Lack of PME label and differing PEFC and PSCC would suggest it's a TN-S. Your insistence that it is TNC-S relies on a lot of assumptions.

Precisely. This is the setup in my flat.

 

[davesparks]

I don't know what it's like around there but around here the two legged breakout boot is common on PME supplies.

Without knowing exactly how and where the tests were carried out it could easily be TNCS with poor testing methods.

If for example the two tests were carried out using three leads and just changing the setting on the tester then one may have been a high current test and one a low current test, which will give different results.

 

[E.E.I]

Ze at fuse board with main earth disconnected

pefc at fuse board with main earth connected

pssc at fuse board

all tests carried out using two lead test on Hi current setting on Meggar MFT

 

[E.E.I]

The difference may down to the meter or my testing method.