# TT Earth Loop Impeadance, stangley odd

#### julioarca

I am currently carrying out a new installation in a new kitchen extension, the whole house was tested last year, the customer gave me the results so I could compare against mine to determine any detrioration.

MMMmmmmmmm, its a TT supply, they test value of the ELI done in 2008 was 4.7 ohms, my measurement is 42.3 ohms, I have checked the earth stake and the continuity to it, all is ok, undisturbed.

100mA RCD, just kind of wonder why the huge difference, would it be advisable to bang some more stakes in to lower this reading?

I bet Zdb is around 4.7 oms....

#### ericmark

I will guess the last guy did not test rod but tested the whole installation.

Reading you have is fine that is what you would expect.

4.7 ohms with earth rod would be very hard to get. I fitted 100's of rods around a gas terminal and we wanted 8 ohms per rod. To get that needed 4 to 8 rods and only way one can drive them in is with a paddies motorcycle.

I would not think anyone on a normal building site would ever be able to drive in 8 rods even 4 rods would be hard going so I would think he has measured it with water, gas etc still connected to get readings that low.

#### julioarca

Thnx guys, Zdb was tested and gave .47 ohms, the pscc then is 5A, its just a high reading as compared before, this was from a NICEIC contractor, so made me stand up and think, also measurements were made with no bonding in place by me..

#### Spark123

50p says PSCC isn't 5A!
He may have tested Ze (Ra) when it was raining so results differ.
As long as Ze is below 200 ohms it isn't a problem.

#### julioarca

thought pscc was supply V divided by external earth loop

#### GaryMo

thought pscc was supply V divided by external earth loop

That's PEFC, not PSCC.

PEFC is the external Line to Earth loop.
PSCC is the external Line to Neutral loop.
PFC is the higher of the two.

#### Spark123

PSCC in a single phase is P-N, if you have a 3 phase system it is the greatest of the P-N and the P-P readings.

#### julioarca

thnx chaps, was having a blonde moment