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

 

[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.

 

[Nigel]

Looks like it was never installed correctly unfortunately.

In this instance I would code it as a C2 and quote to install a 500mA RCD for fault protection for the circuits that do not meet the maximum permitted Zs via the MCB.

Remember the RCD will need to be installed at the supply end of the cable.

No need to TT it and make the earth even worse.

 

[Bobster]

Looks like it was never installed correctly unfortunately.

In this instance I would code it as a C2 and quote to install a 500mA RCD for fault protection for the circuits that do not meet the maximum permitted Zs via the MCB.

Remember the RCD will need to be installed at the supply end of the cable.

No need to TT it and make the earth even worse.

What was it you disagreed with in my posts Essex?

 

[Pete999]

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

UKZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzoff

 

[Nigel]

What was it you disagreed with in my posts Essex?

I think you made assumptions with not enough information and I also do not think it is time to quote to do the job properly.

 

[davesparks]

In this instance I would code it as a C2 and quote to install a 500mA RCD for fault protection for the circuits that do not meet the maximum permitted Zs via the MCB.

This is only viable if the problem is not degradation due to damage to the underground cable.
Proper testing needs to be carried out first rather than the clutching at straws and repeated EFLI tests that appear to be happening.

I wouldnt be entirely surprised if it turns out the op is getting poor results due to using a low current test.

 

[Charlie_]

This might seem a bit unorthodox but I always like to find out what the actual problem is before coming up with a solution

 

[Nigel]

This is only viable if the problem is not degradation due to damage to the underground cable.
Proper testing needs to be carried out first rather than the clutching at straws and repeated EFLI tests that appear to be happening.

I wouldnt be entirely surprised if it turns out the op is getting poor results due to using a low current test.

The op has stated that the EIC was over the max Zs anyway. It was never installed correctly so some sort of change is required to meet max permitted Zs.

 

[Nigel]

I do agree that more testing should be done but what we have been given the advice is sound IMO.

 

[Nigel]

This might seem a bit unorthodox but I always like to find out what the actual problem is before coming up with a solution

The problem is Zs higher than the maximum permitted for the OCPD installed.

 

[Charlie_]

The problem is Zs higher than the maximum permitted for the OCPD installed.

Ok for the more pedantic ones;
I always like to ascertain what is causing the problem first before coming up with a solution