TT to TNC-S

[markymark2406]

My property is fed by a SWA into the service cut out Line and Neutral (I have a TT system) im thinking of having it converted to TNCS system, I just want to know what the earth loop should be at the board with a TT system before i change if i need to.

 

[Spark123]

The max Ze for a TT system with 100mA or 30mA RCD protected circuits for reliability is 200 ohms, unless you are with the NICEIC who deem 100 ohms to be the max.

 

[markymark2406]

I have a MK sentry Dis Board (4 way) with a double pole 80mA main switch (can't remember the amps)

I know i have an earth electrode i think its buried beneaf some concreate as an 6mm earth wire goes into the concrete.

 

[ericmark]

There must be an access pit for testing. Also not sure a TN-S at 0.8 ohm will help much is that all the supply authority offered? It is a little odd as you as the user has no say as to what earth system must be used that is decided by the supply authority as all houses in same area must have same system. TN-C-S would be more common at 0.35 ohm and as to the ohms of a TT system measured where and how? The supply authority is allowed 11 ohms and any rod will normally be tested to be less than 200 ohms but if in respect of supply then that may vary 11 ohms from that measured using an earth rod test meter.
Eric

 

[markymark2406]

I suppose the closer the transformmer you live the lower the Earth loop will be and the PSC will be higher.

 

[Steve]

all houses in same area must have same system.

Really?

 

[Click-Sure]

decided by the supply authority as all houses in same area must have same system.

So that why my house gets a TN-C-S supply from the same pole as 2 close neighbors (one of which on the same phase) who have a TT supply.


OP:

Give phoning your supplier (not DNO) and asking for a conversion, failing that, write a letter to them. You can expect a charge for this service of around £60-£100.