Borowed / Shared Neutrals

[electek]

Hi , Can someone tell me how to test for borrowed neutrals prior to fitting a new Consumer Unit (To avoid any problems when fitting RCD's)

I am aware that a lot of the time borrowed neutrals are evident on the lighting circuits (especially two way stair circuits).

Exactly how would you test the circuits to find this and what readings would you expect in a correct / incorrect (borrowed neutral circuit) ?

Thanks
Chris.

 

[Spudnik]

http://www.electriciansforums.net/e...ctrical-regulations/12971-cu-changes-you.html

 

[electek]

BRILLIANT , Thanks Jason s

 

[boon1986]

put a load on the circuits put a clamp meter round the neutral, pull one fuse at time and check when the load clears

 

[electek]

BOON 1986 Hi mate , can you explain to me ?

 

[NickJPalmer]

Been thinking about this myself. Wondered if you for example isolated say the upstairs and downstairs circuits, removed line and neutral conductors from each, connected line and neutral for each circuit, then tesed IR between both - any borrowed/shared neutral show as a low reading? Since I have only about 2years experience would appreciate any comments fron the "more" experienced!

 

[davelerave]

off the top of my head if you connect a load to each final circuit

ielug in heater or switch on lamp
switch off power
turn off all mcbs take a resistance reading at each mcb to the N bar
check resistance readings between all mcbs
you'll get the combined reading at the final circuits which which are sharing neutrals(ie load 1 + load 2)

 

[nickblake]

do a continuity test between all the neutrals ,

 

[Des 56]

Switch on a couple of lights on both circuts ( especially the landing)
Remove fuses
Disconnect neutrals
Insert one fuse
Check voltage between each neutral and earth
Remove fuse
Put the other fuse in
Check voltages again

If you have a shared neutral,the supply voltage will be evident on both neutrals when only one fuse is inserted

You can also use an insulation tester between the neutrals to check for continuity

 

[davelerave]

getting the idea now i think it may be easier to test at the mcbs rather than neutrals

because if they are 'sharing' a single neutral- you will get a reading with any load on each mcb

if one is 'borrowing' from another-you'll get a reading with the 'borrowing load' on and any load on the other mcb


assuming all neutrals disconnected and all mcbs off


as already said the voltage tester will do it as well