TNCS or TNS

[kiles1]

Hi All,

Woriking on job today and I saw that the main incomer had the config of a TNCS system with the 16mm earth coming out of the neutral block but it also had an earth clamp around the cable with a 6mm coming out going into the MET with the 16mm, is there a reason for this or what. Cheers everyone

 

[Andy™]

TNCS. if there is a problem with the sheath, they have been known to PME at the head and 'earth' the sheath at the service head - which is the link you see

 

[kiles1]

thought it must of been due to a problem but many thanks for reassuring me. cheers

 

[green-hornet]

Be carefull here!!!

There is a way of testing the earthing to establish which arrangements you have.

The supply cable will often greatly differ for PME and TNS.

Any new cut out changes done by the DNO will almost always connect to the existing earthing unless the suitability to change is ok.

TNS supplies may LOOK like they have been changed to TNC-S but if there is a link from the lead sheathing to the met, I would bet the earthing is still TNS.

You can not have TNS and TNC-S on the same in comming cable.

 

[Evans Electric]

This can be confusing, as the Hornet says . It could be a straight forward TNS . As it is an STA cable it could have been converted to TNCS which includes , I'm sure, a link to the lead sheath. The networks should sticker these things properly.

 

[septiclecky]

Hi All,Woriking on job today and I saw that the main incomer had the config of a TNCS system with the 16mm earth coming out of the neutral block but it also had an earth clamp around the cable with a 6mm coming out going into the MET with the 16mm, is there a reason for this or what. Cheers everyone

How can you see it coming out of the neutral block, the incomer is a sealed unit?

 

[Apache]

How can you see it coming out of the neutral block, the incomer is a sealed unit?

Is this a good time to ask for pictures?

 

[Andy™]

You can not have TNS and TNC-S on the same in comming cable.

you can. its been know to chance a TNS supply to PME if there is a high Ze on TNS, and to correct the high Ze on the sheath, its been connected to neutral at the service head.

also, further to your comment about using existing, if they move a service head etc and join the cable, they may use split con, and give a TNS supply, but it may look like a TNCS supply because its probably the same service head, but without an internal link to neutral/earth