Neutral Earth Voltage Readings strange

[s1ms]

Hi,

Some ideas where to look please!

Here goes. I am changing 3 light fittings in a bungalow. Above one light, in the loft there was a junction box, the cpc wires were cut back and not used. (both from feed wire and to switch).

Before connecting up the feed to the light, I terminated it in a separate junction box to test the supply. Using my Metrel 3215, I measured the supply at that point.... The readings were:

(From memory)

L-E 104V

L-N 232V

N-E 128V

I was expecting the N-E voltage to be close to 0V.

I suspect that there is a lose connection for the cpc or the neutral in the circuit somewhere.

The circut is difficult to trace in the loft, if i cannot find a poor connection, I am considering running a new feed to the 5A MCB for that light.

Any ideas welcome! Not too harsh please.

 

[sparkytim]

You have no Earth connection to the CPC by the sound of it.

Try doing a dead continuity test between L - E with short on at C Unit and see what you get

 

[gram1980]

Sounds like a lack of cpc continuity, you need to confirm R2 at each each point on the circuit, you may find that all the cpcs hqve been cut back throughout so itll be a lot of tracing cables in the attic. Or rewire as you suggest if access is difficult.

Good luck

Gram

 

[ProDave]

Easier and safer to test for continuity between N and E.

If it's a TNCS supply, N and E are joined at the head so you can test without making any wiring changes at the CU.

I am sure you will find the neutral is floating, so need to start looking at the rest of the lighting circuit to see if the earth is floating everywhere, or just at that one point. Then fix the faults as you find them.

 

[Steve3948]

Have you taken all the lamps out and tested again.

I suspect you still have incomplete earthing also.

 

[sparkytim]

If you have 230 volts between L-N then the N and L seem ok.

As said most likely CPC not connected to Earth

 

[s1ms]

Thank you guys for responding so quickly.

I suspect you are right, the cpc s have probably been cut back at every junction.

Looks like I could be checking all junction boxes for floating neutrals and cut cpc s. Lots of crawling about in loft finding junction boxes! Great.

 

[sellers]

Before you go running about, do an r2 test on the circuit you may find if localised to one area. To save you looking around for jb's

 

[park1]

What's the earthing arrangement of the supply? What Circuit Protection is there(RCD,MCB)?

 

[Evans Electric]

As the guys have said , I'd be looking at the earth not being connected , it then picks up an induced voltage and gives lots of strange readings .

I've come across earths not connected so often , it really pithes me off , some stupid twonk has snipped off the earths at each JB or ceiling rose , then usually evidence of previous sparks having been there but did nothing about it until Muggins comes along.

 

[steptoe]

question,

how are you measuring this 'voltage' ?

and what current is on it?

personally Im not sure you have a voltage there at all, like has been said, I think its simply induced phantom readings you are getting by using the wrong kit.

 

[batty]

Well if they have cut them of in the loft there's a good chance the CPC is not even connected in the consumer unit. I would start there and work my way round the circuit.

 

[s1ms]

Thank you again everyone.

I solved the problem with a replacement wire to the fuse board. I strongly suggested that the customer got the rest of the house checked, and upgraded his CSU

To answer a few questions, The supply was a TNCS. There was an old style fuse board with no RCDs. The fuse wires had been replaced with push in type MCBs.

Zs 1.09 ohms when I had finished (Metrel 1325)

 

[batty]

You can only advise some people prefer extra safety some don't.

 

[springcrocus]

question,how are you measuring this 'voltage' ?

and what current is on it?

personally Im not sure you have a voltage there at all, like has been said, I think its simply induced phantom readings you are getting by using the wrong kit.

One of the disadvantages of modern digital testers is their high ohms-per-volt sensitivity. A good old fashioned analogue meter at, e.g. 1000 ohms/volt, draws enough current to kill any induced voltages. If I ever get unexplained readings such as yours, I root around in the van for the AVO and take a new set of readings. If the readings return to what I expect, then I know that there is no problem to address.

 

[s1ms]

Thank you for explaining this I suspectected that steptoe was hinting at this, but was not sure. So to invest in another meter. In addition, I have heard some say that using another meter for routine readings is a good idea to preserve my expensive MFT (clambering up ladders into loft spaces, dropping the MFT would be costly). So a lower impedance meter needed... any suggestions?

regards, s1ms.

 

[kerching]

I use a Fluke 113 True RMS....known as a Utilities Meter

Dial has 3 positions off.....Volts/or ohms if no voltage present......ohms/capacitance

also Max min hold beep. with a bit of knob twiddling you can even get it to pick up and hold a momentary hi or Lo.

back in the day as an apprentice, I used a core out of a twin as we had no singles. The unused core was just left floating. Sparked touched unconnected core with neon and it lit up. thought we had nailed a cable and took all landing carpet up...induced voltage, doh! lesson learned... :coat

 

[steptoe]

finger flick,

still a very reliable if illegal an un-recommended test!

 

[springcrocus]

Thank you for explaining this I suspectected that steptoe was hinting at this, but was not sure. So to invest in another meter. In addition, I have heard some say that using another meter for routine readings is a good idea to preserve my expensive MFT (clambering up ladders into loft spaces, dropping the MFT would be costly). So a lower impedance meter needed... any suggestions?regards, s1ms.

I can't help with a recommendation, I'm afraid. My analogue meter is about forty years old and still going strong. I used the term "AVO" because most people have heard of them.

 

[kerching]

I can't help with a recommendation, I'm afraid. My analogue meter is about forty years old and still going strong. I used the term "AVO" because most people have heard of them.

I had one of them about forty years ago as well!!!! Wasn't / isn't it made by Eagle? I think mine was............ :coat