Low Voltages in unused cores in a multicore cable

Carlow52

Some cores in a 20 core cable used to supply power, via 4 time clocks to pumps/boilers etc in a garage.

There are 6 unused cores at the garage end and when one time clock, [and just a particular time clock, not any one] is 'on' the 6 unused cores in the garage have voltages varying from 40 to 70v AC

Had a look at the board/time clock end and can find 4 unused at that end, dont know yet if the 'board 4' are in the 'garage 6' as the lengths are too short to read the writing

Without having to strip out the board to see, [there are 30 MCBs...] would welcome some ideas on how to kill the voltage in the garage 6 as I want to use few of them.
Thanks

Bruthal

Its likely the unconnected cores are showing induced voltages from being beside the other live AC cores.

The 4 free ends in the board could be put into a connector and then see if you can find the 4 now shorted out at the garage end with a continuity tester. Turn main switch for the board off first. If you find the 4 at garage end, mark them, then remove connector at board end and see do they now show as clear at garage end with continuity tester. If so, thats 4 identified and they can be used as 4 extra cores.

M cebee

ya i think the induced voltage reading may vary depending on the type of meter used

http://support.fluke.com/find-sales/Download/Asset/3392489_6003_ENG_B_W.PDF
-assuming cable isn't damaged

prob not an issue if it's all mains voltage

can't recall rules on different ccts in a multicore if that's what you plan

Carlow52

robbie7730 wrote: »

Its likely the unconnected cores are showing induced voltages from being beside the other live AC cores.

The 4 free ends in the board could be put into a connector and then see if you can find the 4 now shorted out at the garage end with a continuity tester. Turn main switch for the board off first. If you find the 4 at garage end, mark them, then remove connector at board end and see do they now show as clear at garage end with continuity tester. If so, thats 4 identified and they can be used as 4 extra cores.

Many thanks for this

Bruthal

M cebee wrote: »

ya i think the induced voltage reading may vary depending on the type of meter used

The main problem measuring induced voltages with digital meters is that old problem again (for certain scenarios), very high impedence, the same as measuring from a live to an earth wire connected to nothing, the impedence is so high, it will measure a high percentage of the mains voltage, as it is in series with a very high impedence (open) circuit, but the meters impedence is just as high or close anyway, so has a good voltage across it. A lower inpedence coil meter wont and would likely show a much lower, if any, reading.

M cebee

yes

Carlow52

Am using the Fluke T5-600.

The old fashioned 'finger on the end phase tester' also 'glows'

M cebee

Have one
they're classified as high impedance tester afaik

make sure cores are ok anyhkw

Carlow52

Thanks for the replies.

Spent a few hours on it this morning

[16,17, 18,19] at the board are not the same as [16,17, 18,19 ] in the garage.:mad:

16 in the garage is a neutral which is needed to keep gargae lights on,
and 17, 18,19 which are visible at both ends have no continuity

My conclusion is that the multi core is joined under the floor somewhere and they only joined what they wanted.

In addition 1 at the board is into a mcb which does not end up as a live in the garage.

M cebee

this link shows dual impedance testers

http://www.fluke.com/fluke/usen/community/fluke-news-plus/articlecategories/dmms/dual+impedance.htm

deandean

I've had the same issues with a 7-core to my garage (if ONLY I'd put in a 20-core...) and with nothing connected at either end of the unused cores, I can get tiny sparks by touching the ends of the unused cores together...230V in t'other cores for various things. Induced voltage.

M cebee

the unused ends should at least be taped up

it seems to be common practice to earth unused cores in other countries-must look up the rules on this