touch voltage help

[Dean Williams]

Hi all
i'm currently testing a very large office complex on nights. in the boiler house, there are some boilers fed with SY flex. As per usual, the SY braid has not been bonded. When i tried to test for continuity to the braid i found 23v ac on the braid, only with that circuit switched on. is this to do with touch voltages.

firstly, what is this voltage i'm finding on the braid (note. its single phase), is it a capacitive effect and would bonding remove this.
Secondly, i always bond the SY flex yet many people don't. the SY manufacturers make specific glands that no one seems to use. is it a requirement that its not bonded, should i put it on the EICR.

any help would be appreciated

 

[malcolmsanford]

I doubt very much it is any form of capacitance by the make of the cable, you have the conductor, surrounded by basic insulation, then you have the outer sheath and then the braid, so highly unlikely it would be that.

As you say if indeed this braid is totally free of earth, then what you have is just a bit of metal floating free, and highly unlikely to be picking up any form of voltage. Sounds like you have a phantom voltage that can often happen with a MFT or electronic voltage tester.

 

[Dean Williams]

i measured it with a voltmeter and it was my fluke MFT that wouldn't test continuity because of the voltage it was finding

 

[telectrix]

Earth it. That'll solve the problem.

 

[Dean Williams]

i just read on another forum about induced phantom voltages in unearthed braided cable after malcolm mentioned it. thats what it must be. oh how i wish so-called sparks would earth SY flex braid. it drives me mad

 

[Silly Sausage]

Have a read of this...

http://support.fluke.com/find-sales/Download/Asset/2514193_6001_ENG_B_W.PDF

 

[Dean Williams]

can this phantom voltage ever be dangerous. for example in an explosive atmosphere.

 

[Deleted member 26818]

can this phantom voltage ever be dangerous. for example in an explosive atmosphere.

Yes it can.

 

[Dean Williams]

so therefore, in this case, if our sparks always bond the braid on SY flex, this problem should never arise. I need to get the message across to them to always earth the braid.

 

[Deleted member 26818]

What you have to do, is decide whether the un-earthed braid is likely to cause a problem.
When you tested for voltage, I assume that it was between the braid and an earth point?
You have to decide whether the braid is exposed to atmosphere, and whether there is a likelyhood of a spark jumping from the braid to an earth point.

 

[Bobster]

Even though sy cable is supplied in mains colours, and it's rated to 600v.

It's designed to be used as a control cable, to which the manufacturer states not for use with mains voltage.

 

[micknew]

Even though sy cable is supplied in mains colours, and it's rated to 600v.

It's designed to be used as a control cable, to which the manufacturer states not for use with mains voltage.

Your wrong it's can be used for mains voltage Rob.

 

[rich.250]

Earth the braid, don't bond it

 

[keniff]

Anybody use sy glands? Iv always seen stuffing glands with the braid twisted and earth sleeved

 

[electric will]

Instead of using the sy glands I wonder if you could use the external swa glands?