high loop impedance reading

[ians]

I am sure there are many of you who have experienced this problem.

I have an interesting problem.

At the main meter room the loop impedance reading is 1.1 ohms.

At the second metering room fed via the main meter the loop impedance reading is more than 20 ohms.

So there are a few ways to determine what exactly is the problem, unlike what we would normally do if it was a council fed meter, just send a complaint to the council indicating there is a high reading and sign off the COC.

Unfortunately the problem is in a complex and must be sorted out. The amazing part is that 3 COC have been issued in this complex recently and none have indicated this problem. I have been called in to give a second opinion.

The first problem I noticed, a lead cable from feeding the main meter room from the council. This is generally where your problems begin. The cable between the meter rooms is an ECC cable. The tinned copper wires are used as an earth

It could also be joint somewhere between the 2 meter rooms.

I did check the earth terminations and found them all loose. I will suggest they are removed one by one, cleaned and reconnected, however i dont believe this would solve the problem.

Time to sit down and get head around this issue.

[AndyD]

I assume this is earth fault loop impedence (Ze).

Even the 1.1 ohms at the main incomer is a bit on the high side and depending on the circuits and the curve of the OCPD's it might not make disconnect times. If required disconnect times on the final circuits of the installation can't be met then I don't see how you can sign the installation off until the remedial work is done.

What is the earthing arrangement? Is the PEFC the same or very nearly the same as the PSCC at the main incomer? If so it's probably TN-C S.

They used a variety of earth clamps on lead sheathed cables over the years and my advice would be not to touch them whilst the cable is live. Depending on the condition of the sheath they can be dangerous.

[ians]

A previous post with regards to loop impedance readings, there was mention of disconnecting if over 10 ohms.

[ians]

Seems there could be a bad connection in a joint or where the ECC cable was terminated.

Lucky the lead cable is not the issue in this case.

100 m of 10 mil was used to link the earth terminals in the meter rooms and a reading taken at the main switch of a DB indicated 0.6 ohms.

It looks like the easiest solution will be to install a new separate earth cable from meter room to meter room.

The joke is the all the COCs which have been issued. I suppose you could turn around and say at the time of test the reading was any number you make up within the standard. It would be your word against whoever challenges you.

Another reason why ever COC should be recorded using a gps.

Until this happens or some policing and some real punishment is imposed, COCs will continue to be a money making for anyone willing to take a chance. Maybe i should start issuing COC as Jack Sparrow again. To think i got away with it for years because i was a pirate contractor. It is a f$&@ joke 😏