High TNS readingssssss

[Bradley6969]

TNS system
60947-2 main switch
60898 double pole 63amp MCBs that feed some caravan boxes now some circuits I can get below the disconnection times of 0.56 ohms but some are 1.22 ohms now I’ve tried changing glands anything else I can do apart from TT the hook up unit? Or do you need upfront RCD

If not change the distribution unit feeding boxes with RCD and Rod it

 

[Bobster]

So you've installed the wrong size cable then...

 

[Bradley6969]

So you've installed the wrong size cable then...

Not installed anything

 

[westward10]

This is the third thread you have started on this theme.

 

[Bobster]

So what is it your doing? Remedial work?

What are the values on the original EIC?

Is the cable running to the DB SWA?

 

[Bradley6969]

Yes, some values are ok then some are not all SWA some original values are 0.79 ohms need to be below 0.56 ohms

 

[Pete999]

TNS system
60947-2 main switch
60898 double pole 63amp MCBs that feed some caravan boxes now some circuits I can get below the disconnection times of 0.56 ohms but some are 1.22 ohms now I’ve tried changing glands anything else I can do apart from TT the hook up unit? Or do you need upfront RCD

If not change the distribution unit feeding boxes with RCD and Rod it

What R1+R2 readings?

 

[Bradley6969]

What R1+R2 readings?

No dead testing currently occupied

 

[Bobster]

Yes, some values are ok then some are not all SWA some original values are 0.79 ohms need to be below 0.56 ohms

So there's a good chance the SWA is damaged and the Armour is rotting.

Original install wasn't designed correctly.

Time to quote to do the job properly.

 

[Charlie_]

I would arrange a convenient time to turn the power off.
This will then allow you to do the necessary tests

 

[Yozza19]

TT the installation

 

[davesparks]

No dead testing currently occupied

You can't expect to solve the problem without doing all of the testing needed to find the source of the problem.

As Rob has suggested the SWA may be damaged and the armour rusting, you should test the integrity of the cable sheath to confirm whether this has happened, if it has then the only answer is to replace the cables.

 

[Wilko]

Hi - is there any visible reason for the different Zs readings? (Run length?) If not, then full testing required and interim derating to say B25 for the 1.22 Zs. Also make sure the Zs result is not from using the RCD test, if that makes any sense .

 

[davesparks]

Wilko makes a good point, what type of test are you carrying out?

 

[buzzlightyear]

Is this carry on caravaning ,start in the being so we are reading the same newspaper .either you have got incoming TNS or TT.
Agree with Wilco .

 

[westward10]

Is this carry on caravaning ,start in the being so we are reading the same newspaper .either you have got incoming TNS or TT.
Agree with Wilco .

Caravan site readings on TT system - https://www.electriciansforums.co.uk/threads/caravan-site-readings-on-tt-system.172970/

 

[buzzlightyear]

To be or not to be TT or TNS is noble in the mind .

 

[Pete999]

To be or not to be TT or TNS is noble in the mind .

Shut up Buzz

 

[ipf]

Shut up Buzz

Pete's off Buzz?...……..so buzz off Pete!

 

[ChrisElectrical88]

Surely this needs finding Via R1+R2? Test between each caravan on the line and calculate the reading you thing you shold be getting by the table in GN3?

Depending on how many caravans coukd you not install a 100mA or 500mA RCBO to bring the disconnection tines up, although this coukd cause all sorts of issues with multiple vans switching off for one fault.

Having worked on quite a few caravan parks they are poorly maintained, armoured go rusty over time, glands arnt great, boxes are swapped often. There a $hit show.