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.

 

[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

 

[Nigel]

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

It was never installed right in the first place.

 

[ipf]

It'd be useful to know how old the installation is.

 

[Charlie_]

It was never installed right in the first place.

How do you know that?
Op said he has high Zs readings but has done nothing else testing wise

 

[Nigel]

How do you know that?
Op said he has high Zs readings but has done nothing else testing wise

Because I read all the posts.

 

[Charlie_]

Because I read all the posts.

Yes me too

 

[Charlie_]

No dead testing currently occupied

How did you manage to change glands without switching off the power??

 

[davesparks]

It was never installed right in the first place.

It would be good if the OP could clarify the test results and what they mean by original values. Their other threads recently about this same job make me think these original values refer to the EICR conducted before they started the remedials rather than referring to an EIC.

 

[ipf]

Because I read all the posts.

Come on, my mate. The OP's only posted 4 times, with not a great deal of info......and his last one was at 10am.
We know SFA about it, really.

 

[richy3333]

op- HELLO?????????????? (echo, echo) empty room!

 

[buzzlightyear]

op- HELLO?????????????? (echo, echo) empty room!

padded cell.