problem with service earth

[dean7828]

hello people, just thought id ask a question on todays finding! i have been conducting a pir in a large shop and noticed every circuit had high ZS values which would fail max allowence eithen befor corecting for heat, i then obtained the external earth impedance and its 1.54ohms, the system is TNS 3phase-4,

basically i have called in the energy supply to sort out the unstable earth on the supply side but have no idea how they will over come this? im sure it will be simple for them or maybe not. anyone had experience with this situation?

 

[telectrix]

they should sort it. max. allowed on TN-S is 0.8ohms.

 

[dean7828]

that's right they should! just wondering how they go about it? if i had my way i would shut the shop down untill they arrive, they say 24 hour response.....ow health and safety surely

 

[polo1]

Or....they might just tell you that they can't provide an earth and you'll be knocking rods in!

 

[johnboy6083]

to keep the shop operational, i would install a temp RCD.

 

[i=p/u]

if is unstable earth will they just throw in 300mA powerbreaker????????????

 

[Knobhead]

Have a look at http://www.electriciansforums.net/e...al-forum/36671-dno-earthing-arrangements.html

 

[dean7828]

buildings too built up for any rodds unless a big rod pi is dug out of the concrete, im sure they will find away around paying or doing anything to fix the problem, im sure the use of RCDs is out of the question, they will trip with the high air-con loads

 

[mechelec]

you should have reported it as an unsafe situation ie emergency they would then respond in 4hours or less. If it is a paper lead cable and the sheath is not bonded correctly in the joint giving a high resistance they will have to dig up and renew the service connection on the main. They may just PME it and link the lead sheath to the neutral terminal at the cutout. If the DNO supply an earth terminal they are obloged to maintain it, the only time they will walk away is if one has never been supplied ie TT

 

[dean7828]

you should have reported it as an unsafe situation ie emergency they would then respond in 4hours or less. If it is a paper lead cable and the sheath is not bonded correctly in the joint giving a high resistance they will have to dig up and renew the service connection on the main. They may just PME it and link the lead sheath to the neutral terminal at the cutout. If the DNO supply an earth terminal they are obloged to maintain it, the only time they will walk away is if one has never been supplied ie TT

thanks for your advice, i did tell them its unsafe, they said any earth faliures will go onto 24 h response, seems poor to me as circuits will clearly not disconnect in time of fault, i made my recommendations to the company and its now up to them, i will continue the inspection only after a suitable earth has been supplied.

im sure once the DNO has verified the is an unstable earth they will close down the shop anyway, will see tommorow

 

[Engineer54]

im sure once the DNO has verified the is an unstable earth they will close down the shop anyway, will see tommorow

Don't count on it!!! That would imply that the DNO are at fault and leave them open to any financial claims by this business for loss of trade!!

 

[johnboy6083]

if you ever encounter this situation again, then please install a temp RCD. This will protect the user of the installation from dying because the circuit didnt disconnect within 40ms, and it will protect you from being accused of doing nothing, and leaving a dangerous installation. at the moment its your word aginst theirs, and they could say that you didnt explain the dangers properly. Did you write a small letter, and get them to sign a copy of it, or issue a Danger notice?

 

[dean7828]

if you ever encounter this situation again, then please install a temp RCD. This will protect the user of the installation from dying because the circuit didnt disconnect within 40ms, and it will protect you from being accused of doing nothing, and leaving a dangerous installation. at the moment its your word aginst theirs, and they could say that you didnt explain the dangers properly. Did you write a small letter, and get them to sign a copy of it, or issue a Danger notice?

thanks for reply, i did inform them and the company and my company, the dno arrived today nice chap he did hum and har about the place and he got the exact reading as me, he then told me and the client that it was safe and ther is an earth present and that it would be fine to leave until for time being, he has now passed the job on to the joiners to dig up the concrete for further inspection
the funny thing is the supply transformer is 5 meters away from the premises so somethings not right.

 

[Engineer54]

thanks for reply, i did inform them and the company and my company, the dno arrived today nice chap he did hum and har about the place and he got the exact reading as me, he then told me and the client that it was safe and ther is an earth present and that it would be fine to leave until for time being, he has now passed the job on to the joiners to dig up the concrete for further inspection
the funny thing is the supply transformer is 5 meters away from the premises so somethings not right.

Told Ya didn't i ...lol!!!

Doesn't mean that transformer is supplying your premises, although it could well be doing so. Even if it was, your supplying cable is a T off of a network distribution cable that will be serving many other installation loads along the street or even an area...

 

[dean7828]

well im just glad i managed to get on site to meet the guy, i have herd they can rectify a fault and then turn round and say there is no problem and pass the call out cost on to the customer or worse..me!