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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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  • Thread Starter Thread Starter
  • #3
So you've installed the wrong size cable then...
Not installed anything
 
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
Esteemed
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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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
Esteemed
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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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 .
 

Pete999

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To be or not to be TT or TNS is noble in the mind .
Shut up Buzz:tongue::tongue::tongue::tongue::tongue:
 

ChrisElectrical88

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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.
 
N

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.
 
B

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?
 
N

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

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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.
 
N

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.
 
N

Nigel

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

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_

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Arms
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
 

Charlie_

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Arms
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
 

Charlie_

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Arms
No dead testing currently occupied
How did you manage to change glands without switching off the power??
 

davesparks

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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.
 

richy3333

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

PEG

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I'm having an awful holiday,here.....lights and telly keep going off...
 
  • Thread Starter Thread Starter
  • #43
Not changed any glands yet and only going by EICR at the moment, so I’m getting 1.13 ohms on earth loop but if I go to PSC L+N is 0.26 so may get round it that way as will still disconnect in required time, have 63amp 60898 MCB at mains DU then feed the caravan boxes
 
  • Thread Starter Thread Starter
  • #44
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.
Yes sorry
 
B

Bobster

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
Not changed any glands yet and only going by EICR at the moment, so I’m getting 1.13 ohms on earth loop but if I go to PSC L+N is 0.26 so may get round it that way as will still disconnect in required time, have 63amp 60898 MCB at mains DU then feed the caravan boxes
You're contradicting yourself.

PSC L+N is 0.26 so may get round it that way as will still disconnect in required time
What do you mean by this then?
 
  • Thread Starter Thread Starter
  • #46
You're contradicting yourself.



What do you mean by this then?
Sorry meant to put I’ve not tried changing any glands yet

Well calculates the max current flow between L+N same as earth loop between L+E in the event of a fault?
 
B

Bobster

Sorry meant to put I’ve not tried changing any glands yet

Well calculates the max current flow between L+N same as earth loop between L+E in the event of a fault?
Ok, but what has that got to do with Zs requirements?
 

Baddegg

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So you’ve taken pscc at the origin and your testers also give you a Ze reading but that would include any parallel paths as well? I’m so confused.....did you take Ze with main earth disconnected?
I’d go with Petes post a while back and get some R1-R2 readings from the swa....
 
  • Thread Starter Thread Starter
  • #49
Ok, but what has that got to do with Zs requirements?
Well you do a Zs at a panel/consumer so PSCC and PFC and record highest what’s difference but just another sub circuit? As if you measure either of these on my tester you get impedance value and kA so breaking capacity?
 
B

Bobster

Again, what has PSCC and PFC got to do with the Zs requirements?

Either I am misunderstanding the point you are trying to make, or you don't fully understand the difference in tests and what to do with the results.
 

buzzlightyear

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Arms
Esteemed
In order to get the values write in the being at the incoming what was the ohms and the ka.
Ovasly you have sub circuits to diffrant pitches ,the sub circuits are on bs60898 and you are testing each circuit ,but some how you are getting well beyond the max range .
Are the glands in good order or they
Are not earthed correctly.some how we are going round the caravan pictches if you know what i mean.
 
  • Thread Starter Thread Starter
  • #52
In order to get the values write in the being at the incoming what was the ohms and the ka.
Ovasly you have sub circuits to diffrant pitches ,the sub circuits are on bs60898 and you are testing each circuit ,but some how you are getting well beyond the max range .
Are the glands in good order or they
Are not earthed correctly.some how we are going round the caravan pictches if you know what i mean.
Well the panel feeding the sub circuits has Zs of 3.15 and KA of 3.0 but some of the circuits are ok and some are not but there are endless joints underneath the ground so can’t help and glands are ok
 
B

Bobster

So the Zs of the sub circuit is 1.22 ohm, the Zs at the panel feeding these is 3.15 ohm?
 
  • Thread Starter Thread Starter
  • #54
So the Zs of the sub circuit is 1.22 ohm, the Zs at the panel feeding these is 3.15 ohm?
Yes, at a guess paralel paths
 

Charlie_

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Arms
you need to make proper arrangements with the client so you can turn the power off and then carry out all the necessary tests correctly.
You need to isolate each circuit, disconnect them from the MET and then test accordingly
 

buzzlightyear

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FFS ,hit your client over the head with the BBB and tell him either turn the power off for the pitches that dont comply with the reg or some body get else in.simples .
Me i would quote the elec act .
 

davesparks

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Well the panel feeding the sub circuits has Zs of 3.15 and KA of 3.0 but some of the circuits are ok and some are not but there are endless joints underneath the ground so can’t help and glands are ok
Then you've got a serious problem because a Zs of 3.15ohm should give a pfc around 76A at 240V, or a pfc of 3kA would come from a Zs of 0.8ohm.
I'll ask again, what test are you using, high current or anti trip?
 
S type RCD, simples.
 
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