Hi Ze Reading

[westward10]

Do some continuity tests to establish where continuity is amiss.
R1+R2, R1+Rn, R2+Rn.

 

[DefyG]

Its quite concerning that the reading is so different.

What IR readings are you getting now?

 

[Julie.]

Ze o

Connections look all clean and tight with origin reading 0.16
Ins res L-E 3.37, N-E 4.27
and N-L 2.36 so not great

You don't appear to be clear with the problems here.

You talk about insulation resistance of 2.36 to 4.27 - is this Mohm?

This is irrelevant to the Zs

You don't appear to know the differences between insulation resistance, Ze and Zs.

If you do have Ze of 0.16 ohm at the feed end of the cable and ~2.5 ohm at the load end, there is absolutely something wrong with the cable or terminations.

I would expect a r1 + r2 of 0.5 ohms or thereabouts.

You need to find this fault, not cover it up by adding rods or anything else.

You need to measure the r1 + r2, the r1 + rn etc. This will show if you have a cable fault. And will identify which conductor is the problem, if they all read 0.5 ohms (less for r1 + rn) then the fault is between the cable feed end and the header. - most likely a bad connection in the earth path.

 

[westward10]

Thank you DefyG
Ze at origin 0.16, zs at annex csu 2.42, total zs on socket circuit 2.67

The Zs for the socket circuit is not relevant your problem is the submain.

 

[sidekick]

What IR readings are you getting now?

Ins res L-E 3.37, N-E 4.27
and N-L 2.36

 

[sidekick]

Ze o


You don't appear to be clear with the problems here.

You talk about insulation resistance of 2.36 to 4.27 - is this Mohm?

This is irrelevant to the Zs

You don't appear to know the differences between insulation resistance, Ze and Zs.

If you do have Ze of 0.16 ohm at the feed end of the cable and ~2.5 ohm at the load end, there is absolutely something wrong with the cable or terminations.

I would expect a r1 + r2 of 0.5 ohms or thereabouts.

You need to find this fault, not cover it up by adding rods or anything else.

You need to measure the r1 + r2, the r1 + rn etc. This will show if you have a cable fault. And will identify which conductor is the problem, if they all read 0.5 ohms (less for r1 + rn) then the fault is between the cable feed end and the header. - most likely a bad connection in the earth path.

Thank you for the advice..
yes - Clearly stated
Insulation resistance
N-L 2.36 Mohm
N-E 4.27 Mohm
L-E 3.37 Mohm
Ze at origin 0.16
Load end of swa 2.42
Connections at feed end sound
Will double check load end next visit as earth clamp used on armour and not accessible yet (cupboard base being removed to access)
Will do continuity tests same time.

 

[newfutile]

earth clamp on armoured? i would hope we are not talking about a BS951 earth clamp . as everyone says you have either a bad cable or bad connections .sometimes a thermal camera can help if you load the cable with an electric heater .
I squared R losses would make for some heat under load.
check for thermal damage ,could the cable be joined somewhere else?

 

[davesparks]

You talk about insulation resistance of 2.36 to 4.27 - is this Mohm?

This is irrelevant to the Zs

It may be linked though, based on the information in this and the other thread about this cable. It sounds to me.like the cable is damaged underground and water is getting in, hence the variable IR results which would possibly link to the poor Zs as the armour will be rotting away nicely.

 

[davesparks]

Connections look all clean and tight with origin reading 0.16
Ins res L-E 3.37, N-E 4.27
and N-L 2.36 so not great

I did. Have since gone back withnewly calibrated tester and done a new clean test. Its quite concerning that the reading is so different. The 63a mcb at origin has tripped out several times but not recently.

cable in ground approx 25 years

All this, and your previous thread, point towards the submain cable being damaged underground and deteriorating.

No amount of checking connections at each end or other faffing about will make it any better.

You could fully isolate that cable and test it to confirm.

If it is damaged underground then no amount of earth rods or workarounds will fix it. It needs to be either repaired or replaced.
If it has been damaged for a while then water will have got quite a long way along the cable and rotted away a lot of the armour so it's unlikely you'd be able to do simply cut out the damaged section and joint a short piece of cable in, you'd end up digging up many, many metres of it to find an unaffected but of the armour.

 

[Julie.]

It may be linked though, based on the information in this and the other thread about this cable. It sounds to me.like the cable is damaged underground and water is getting in, hence the variable IR results which would possibly link to the poor Zs as the armour will be rotting away nicely.

Agree, overall the cable may be FUBARed, however in diagnosing the high Zs the IR results don't help.

I would have spent the time finding the high resistance fault as the priority.

Once that's found, it may mean the cable needs repair/replacing anyway.

 

[sidekick]

The Zs for the socket circuit is not relevant your

All this, and your previous thread, point towards the submain cable being damaged underground and deteriorating.

No amount of checking connections at each end or other faffing about will make it any better.

You could fully isolate that cable and test it to confirm.

If it is damaged underground then no amount of earth rods or workarounds will fix it. It needs to be either repaired or replaced.
If it has been damaged for a while then water will have got quite a long way along the cable and rotted away a lot of the armour so it's unlikely you'd be able to do simply cut out the damaged section and joint a short piece of cable in, you'd end up digging up many, many metres of it to find an unaffected but of the armour.

Thank you for that.
Time to bite the bullet I think.

 

[westward10]

Do some continuity tests if you don't know how to do this find some assistance.

 

[sidekick]

Do some continuity tests if you don't know how to do this find some assistance.

Thank you. I do know and that is my plan as soon as I can gain access to the load end earth clamp.

 

[westward10]

You test from the main earth terminal to eliminate problems between that and the cable armour if this gives problems then test to the armour. If this is an adjustable earth clamp that needs addressing anyway.

 

[davesparks]

Thank you. I do know and that is my plan as soon as I can gain access to the load end earth clamp.

What earth clamp? I thought this was an SWA cable, why is an earth clamp involved in this?