fault on new sy cable

[ohlins]

First of all hello everyone this is my first post on here.
Working at a church in london today sorting out a few problems on a Niche warm air heater control pannel, The heater is in undercroft and the pannel is remote mounted above (through floor) in church.We were getting loads of weird voltage reading on an old swa 10 core eg 60v/90v on cores we would ecpect to be dead.Went to van to get IR tester and sods law its gone sick on me.No probs we had a 10m lenght of new sy cable on board for another job so we pulled this in (very easy as duct through).Did all reconnections and tested again.Now i know when you read this you will all say must be a jb or something in circuit but its doing it again.Got cores number 1/2/3 disconected both ends (others have 230v) and we are still getting 60v/90v/109v....answers on a postcard.Ive isolated and left safe to return Friday with another tester.

 

[Steve1412]

Never be surprised by electricty. I once had a 48 core swa on a straight run along traywork. Core No.1 which was the centre core was giving me very strange IR readings and low voltages. All other cores spot on!!!! Luckily plenty of spare cores.
I would expect once you stick a megger on it you will have some insulation problems.

 

[ryanryan]

when ables are twisted together you can induce voltage through the insulation.

 

[benji]

how many cores does the sy have ? how many are you using ?and the cable length is only 10mtr?

you can get induction, you can also get capacitance with long runs of multicore best bet is to ground spare cores

 

[ohlins]

ive thought of induction but only a short lenght and no problems to earth or N.Cable is brand new of a drum Monday so would be very surprised if IR readings low.Kept looking at readings thinking i must be missing something .

 

[Des 56]

how many cores does the sy have ? how many are you using ?and the cable length is only 10mtr?

you can get induction, you can also get capacitance with long runs of multicore best bet is to ground spare cores

There lies the most probable reason and solution

 

[ohlins]

Troble is we have no spare cores at present.Ive only come across induction in much longer runs,this is no more than 10m.Must admit does seem the logical answer.