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Discuss High TNS readingssssss in the Electrical Forum area at ElectriciansForums.net

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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
 
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B

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?
 
  • Thread Starter Thread Starter
  • #6
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

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Arms
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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?
 
B

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.
 

davesparks

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Mentor
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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

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Arms
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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 :) .
 

buzzlightyear

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Arms
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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 .
 
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