Earth loop impedance testing

[ians]

A question for all the bright sparks, It you are busy doing an inspection report and find the earth loop impedance reading higher than it should be, what do you do?

I was told by the technical division of the Durban electricity department 2 very interesting points:

1/ That i am suppose to do an earth loop impedance test at each and every plug socket or power outlet, interesting because according to page 276...8.7.5 Earht loop impedance test should be done at the the main switch.

2/ If the reading is higher than it is suppose to be, for example 10 ohms at a 60 amp breaker, it is my responsibility to isolate the power imediately, report it to the electricity department and they will sort out the issue within the same day, funny they should say that because if i have switched off the power in the most recent test (15/11/2012) the power would still be off, i still havent had a reply from them todate. If i dont switch off the power i will be held responsible for any injuries caused by bad earth, surely the responsibilty would become theirs, if they dont attend to the problem within a 24 hour period?

[AndyD]

What earthing arrangement did the premises have? TNCS?

We perform an external earth fault loop impedance test (Ze) on the incoming supply with the earth disconnected and the installation isolated plus we do earth fault loop impedance testing (Zs) from the farthest end of any circuits we install to ensure MCB protection times are met.

[ians]

Durban has a TN-S earthing system.

I use a fluke 1653, so i can and do tests at every single point,

voltage : L-N, L-E, N-E and include the phases if it is a 3 phase system.
polarity.
E/L (RCD as Andy refers to them) trip time which should be done in both in 0 and 180 degree (not a requirement in South africa) you can just use a normal plug in e/l tester.
E/L tripping current.
loop/line impedance and at the same time the prospective earth fault current.

It gets a little more complicated when we test points in other applications like hospital theatres for example.

The tests above are normally only done if the power is already on, for example in exsisiting installation inspection reports when properties are sold.


What does the law(SANS) say about it, at what point should the loop impedance be carried out.

What would be the ruling in court if someone was injured if you didnt switch off the installation?

Just like elevated voltage rule, which happened a couple of weeks ago, i was called out on a Sunday morning to find the that the voltage was way about recommended value, so i didnt even think twice, I isolated the entire installation and boy did i collect for that. Customers where complaining threatning me win court cases etc, i eventually found the neutral bussbar between the transformer and the main frame had been stolen, i only reset the breakers at 4 pm. Lucky for me non of shop owners went through with the threats to sue me.

[ericlowry]

SANS 0142 section 8.7.5.2 tells you to install an ELU
Eric

[Sparks]

Looking at the COC as a whole you will see it is split into sections. The Loop,PSC, Supply Voltage,Elevated voltage,erath resistance are all tests done at the DB with the installation isolated. This is to determine whether the supplier is providing withing spec. Once these specs have been met the installation can be connected provided the installation complies. There are specs regarding bonding conductors, earth continuity which are tested for at each point of consumption will determine if the installation conforms to minimum requirements.

[GrahamF]

Did you ever resolve this with the municipality. I've just done an inspection and test on a very old property and it has an Earth loop impedance (at the main switch) of 16 Ohms! Way too high to allow 2 times the current to trip the 60A mains breaker. Most houses I've tested in the suburb have Earth loop impedances of less than 0.2 Ohms. All are TN-C-S by the way. One interesting thing is that the house has a Zellweger Uster ZE-22 ripple meter installed. I've tried to find a contact at Tswane Metro to see if they are still using these and if it could be introducing extra impedance into the circuit but to no avail. Also can I disconnect the thing? I'm probably going to be doing a complete rewire of the property as it dates to 1937 but the Earth loop problem is really a supplier problem. Early days though!

[Sparks]

I see my previous response has the spelling of a new SA graduate, my apologies. I however reiterate what I said. Do the test at the main switch with it off. The ripple relay will not influence the reading at all. What must be tested at all the points of consumption for the COC is the earth continuity to the DB. This must comply with the regs according to the CB rating of the particular circuit. The local supplier is obligated to rectify a non-compliant loop impedance reading immediately. If you cannot get hold of a local supply employee willing to lift his backside you can resort to threats of claims for damages and the possible charges of culpable homicide being laid against said authority as well as public denounciation in the interest of consumer safety as well as fraudulent abuse of monopoly.

[ians]

Some feedback...it is 2019 ...still havent heard from the electricity department.

I now have another 16 ohm reading...reported it and logged the fault report number on the COC...what more can we do?

[Dave A]

reported it and logged the fault report number on the COC...what more can we do?

We don't issue the COC until the earth loop impedance fault is fixed.
And we nag.

[ians]

We don't issue the COC until the earth loop impedance fault is fixed.
And we nag.

it is 2019 and we have to sit and listen to everything being repeated in 10 official languages then press 1 or 2 or 3 etc etc etc

is there not an email or whattsapp message service ...where you can report a fault and they can get back to you at some stage?

[ians]

So another service gone down the tube...tried to contact the fault number again today...9.53 am ...they still havent answered the phone...almost 20 min and still waiting...what a joke.

What is the chance anyone will even notice the 16 ohm reading and the note in bold letters ...on the COC?

What is the chance the electricity department will get around to sorting it out this year?

Maybe when the new owner has some changes done to the property he might use a registered electrician who might do a loop impedance test and waste his time trying to get through to the faults number.

[ians]

40 minutes later...sent an email to CustoCare@elec.durban.gov.za.

Cant do much more than that...the info is on the COC ...let someone else bother this crap.

[ians]

There you go...it cant be THAT dangerous...i have received a response.

custocare@elec.durban.gov.za
11:28 AM (25 minutes ago)
to me


Dear Customer.

Thank you for contacting eThekwini Electricity.

We acknowledge receipt of your email and we will respond within 24 hours.

Regards

eThekwini Electricity Contact Centre

[SeanM]

Greetings all

My understanding of the loop impedance test is that we are testing the earth resistance from the DB to the TRFR, Then surely doing a earth resistance test from the DB to the rest of the installation i.e: sockets, light fittings and so on this should suffice.

[skatingsparks]

I am yet to meet a municipality worker who understands earth fault loop impedance test or even has a loop tester (usually just a multi meter from cash converters).

In Jo'burg Sooo many properties don't have in coming earth.

The earth cable is there but it isn't connected or its broken or been stolen. Over half the domestics we get involved in have no earth - half the job is getting municipality to sort it.

I have been trying to buy a house since June and the hold up is, ironically, the COC. I know the wiring is not great (won't pass) but I said I'd disconnect everything and do a COC on a temp board for the purpose of transfer and so we can renovate and rewire.

Home owner says wiring is fine (). Home owners gets quote to get COC - 2 electricians quote in the region of R37000 to rewire - smug face

Home owner come back to me.....

I find no incoming earth on a TN-S earthing sytems (well its was something like 4 ohms of 60 amp main switch so probably picking up reading from bonding or something).

I said to the home owner I'll do the COC for free, just contact municipality and get the earth sorted.

They called (many times) and finally went to the guy who is the manager of the area - his solution - whack an earth spike in and put E/L.

I said its TN-S and would like TN-S but this has been dragging on for months.

I have been to the municipality. The over head cables were upgraded but the earth.... wasn't. They will not be doing anything so they say whack a spike in.

I tested the neighbours house - same - TN-S around 4 ohms. 4 other houses come of this pole - guess no one has earth

I think I'm going to have to accept a TT earthing system but I will be charging the home owner for 100mA earth leakage at the mains and everything in the new temp board - 30ma E/L, breakers, earth rods, my time (x2 for pissing me off).