Volt reading across N and cpc

[Dicky Woollard]

I'm in a vineyard. There is a 300m buried SWA from the ccu direct to a 2 gang socket.
I'm getting 247V across N and L at the ccu.... But at the socket I'm getting 100V across E and N and 147 across L and N.
Continuity as a radial tested ok
IR All over 500 M
Please list possible issues here. Thank you.

 

[Bobster]

Are there any loads attached at the time of measuring?

What were the continuity results and how did you measure them?

300m is a long way, for what I presume if connecting directly into a socket, is going to be <= 2.5mm SWA.

 

[Pete999]

I'm in a vineyard. There is a 300m buried SWA from the ccu direct to a 2 gang socket.
I'm getting 247V across N and L at the ccu.... But at the socket I'm getting 100V across E and N and 147 across L and N.
Continuity as a radial tested ok
IR All over 500 M
Please list possible issues here. Thank you.

What size SWA?

 

[Bobster]

Also, what were the N->E measurement at the CU?

 

[Silly Sausage]

Also, what were the N->E measurement at the CU?

Smacks of an exam question to me

 

[marconi]

How did you check end-to-end continuity? Is the SWA two core or three core?

First thought is a broken neutral or SWA/CPC somewhere along the length of the cable so am surprised your radial continuity checks are ok.

 

[snowhead]

I'm in a vineyard

Is there a clue above?

 

[static zap]

I'm in a vineyard

Is there a clue above?

I'm sure some of "us" post in a relaxed state
-after a stressful day.
( A cider apple a day keeps the Dr away)

 

[Dicky Woollard]

Are there any loads attached at the time of measuring?

What were the continuity results and how did you measure them?

300m is a long way, for what I presume if connecting directly into a socket, is going to be <= 2.5mm SWA.

It's 6mm SWA
WAS GETTING 2 ohm continuity r1+r2
Measured with L and N cables removed from socket.

 

[Dicky Woollard]

How did you check end-to-end continuity? Is the SWA two core or three core?

First thought is a broken neutral or SWA/CPC somewhere along the length of the cable so am surprised your radial continuity checks are ok.

It's 2core, using armour as cpc
6mm

 

[Dicky Woollard]

Smacks of an exam question to me

I wish it wasn't such a hike from ccu to the sockets

 

[Dicky Woollard]

What size SWA?

6mm 2 core, using armour to carry earth

 

[Dicky Woollard]

Also, what were the N->E measurement at the CU?

I think I have cracked it. Wrong wiring N bus bars. Seems to be root cause.

 

[marconi]

Did you measure 2Ohms for Rn + R2? ie: the same as R1 + R2?

Assuming 2.9mV/A/m volt drop for 2 core 6mm2 core SWA, R1 + Rn is circa 0.0029 x 300 x 2 = 1.74 Ohms.

Please could you describe more the wrong N bus bar wiring?

 

[richy3333]

2 ohms. What’s the protective device?

 

[westward10]

4A is the max you can draw on that cable for vd requirements.

 

[Marvo]

As above, if you put any load above a few Amps on that length and size of of cable you're going to get an unacceptably high N-E voltage....

 

[HappyHippyDad]

As above, if you put any load above a few Amps on that length and size of of cable you're going to get an unacceptably high N-E voltage....

Could you explain that a little please Marvo? I understand why approx 4A is the most you should draw due to VD, but how would increasing the load cause there to be voltage between N-E?

 

[westward10]

In a TN system the potential difference at source should be 0v in an ideal world. A circuit designed to have no volt drop should register 0v between the conductors at its point of utilisation. Once you start getting volt drop you must remember in normal circumstances there is no drop in the cpc but there is in the neutral and this drop will measure a potential difference between the conductors, the higher the drop the higher the pd between neutral and earth.

 

[marconi]

For ease of reference for those who do not carry the Zs figures around in their head:

https://www.niceic.com/Niceic.com/media/Pocket-Guides/Pocket-Guide-18.pdf