High Zs readings on ring main

[Innominata]

Hi Guys,
I have recently changed the CU in my home in order to have a Napit inspection (not yet a member).I have done a Zs check on all the sockets. Most of the readings are ok but a couple are reading in the region of 1.30 to 1.39 ohms.The MCB is a 32 amp B type.The max allowed from 7671 is 1.44 but do I have to use the 80% rule which would bring the max down to 1.15.The new board is a split load with dual RCD.
many thanks

 

[acat]

Yes mate 0.8 rule applies sockets giving a high reading check for loose connections if you have not got any would recommend changing the sockets as they are probably at fault.


Hope that helps


Chris

 

[Richard Andrews]

Hi Guys,
I have recently changed the CU in my home in order to have a Napit inspection (not yet a member).I have done a Zs check on all the sockets. Most of the readings are ok but a couple are reading in the region of 1.30 to 1.39 ohms.The MCB is a 32 amp B type.The max allowed from 7671 is 1.44 but do I have to use the 80% rule which would bring the max down to 1.15.The new board is a split load with dual RCD.
many thanks

Try putting new sockets on - this has normally sorted out such issues when I've experienced similiar.

One socket where I have recently moved into is within BS on one side and twice the amount on the other side - it's a radial circuit too, hence the sockets at fault.

 

[Sintra]

Are you sure sockets with higher readings aren't spurs.

 

[cashnotakite]

Are you sure sockets with higher readings aren't spurs.

this ^^

 

[confused-fuse]

100% sure its a spur as for the high reading .. i would open the socket to see

 

[roukel01]

Those Zs results only apply to circuits not protected by RCD, otherwise max Zs for 30mA RCD protected circuit is 1667. Obviously if you've done a Ze and thats fine but find your socket circuit Zs is still high I'd look into it further. instead of testing Zs using a plug in type lead, try taking the socket front off and testing at the connections.

 

[cashnotakite]

Those Zs results only apply to circuits not protected by RCD, otherwise max Zs for 30mA RCD protected circuit is 1667. Obviously if you've done a Ze and thats fine but find your socket circuit Zs is still high I'd look into it further. instead of testing Zs using a plug in type lead, try taking the socket front off and testing at the connections.

is this just for TT system

this is table 41.5 in the regs if anyones interested.

i think with the increased use of rcd protected boards in domestic properties it's important that this particular comparison value isn't overlooked