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Discuss Ze of 3.39 ohms!!! in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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davino

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hello, done a test today and the ze was 3.49ohms, its throwing my zs well out, can someone comfirm this is a manweb/scottish power problem and how to sort this out.. also can some one tell me how to get PFC need it for the test sheets...
iam using a metrel 2100 easytest.thanks
 
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hi mate that does sound a tad high, not sure if your tester will do pfc (amps) but you can get PSCC - measure between phase and neutral incoming side of isolater, then PEFC - measure between phase and earth. the highest value is your PFC. hope this helps

oh forgot to mention make sure switch is off! you're measuring to find out if the rating is correct to blow fuse or trip etc.
 
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davino

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  • #3
I have a metrel easitest , so if i mesure across phase neutral at the incoming of the isolator on psc on the tester , do i use the 3 prong lead, ? as the only other lead i have is for continuity and isulation resistance.
also how do i find short circuit capacity on the main fuse ?
thanks
 

jeremy

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Mentor
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What sort of earthing system do you have TT TNS TNCS. If it's either of the latter two, it's a supply problem probably a cracked sheath under the pavement. ring the supplier immediately and let them know and they'll come round quick to make amends probably by converting it to a pme by joining the earth into the neutral at the supply.
 
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coxy

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  • #5
I had the same problem recently.Believe it or not the supply company changed the service cut out and did not reconnect the main earth to the db.The ze was 3.1 ohms.The supply was a tns,when eventually got through to the supply company they are going to charge for a pme !!!!! (*******).However as a temp measure i managed to put a earth clamp on sheath of cable untill pme fitted.It got the ze down to 0.23 ohms.If not tt supply,make sure main earth is connected,if it is contact supply company asap.
 
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davino

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  • #6
thanks coxy,
the system is a tncs , i have renewed the main earth to from supply terminal to db (16mm) i have also tried to tighten the connections at the supply terminals, i have called manweb but they just keep me on hold for ever...
 
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coxy

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  • #7
Hi Davino,
I know what you mean.I was on the phone for hours trying to spaek to the correct person.It is unusual on a pme (tncs) supply to have a problem.The supply company should fix this free of charge as in bs7671 the supply on a pme is a maxiumn 0.35 ohms.
One other option is to maybe try next doors to see if they have a problem.
Are you sure the testers are ok ??
Is the property rcd,if it is it is a bit safer.
Coxy
 
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davino

  • Thread Starter Thread Starter
  • #8
yeah the testers fine, use it daily, think i will knock next door and see if i can get a reading there...

What sort of earthing system do you have TT TNS TNCS. If it's either of the latter two, it's a supply problem probably a cracked sheath under the pavement. ring the supplier immediately and let them know and they'll come round quick to make amends probably by converting it to a pme by joining the earth into the neutral at the supply.
thanks mate, gunna call them today
 
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just installed a 17th ed board on a property ... all internal cabling ok the only issue I found was an incomplete ring which i traced and split into two radials ..... biggest problem was the Ze its a TNS system and I have a reading of 8.6 ... i know the max is 0.8 ... I checked the neighbors supplies and both sides were within the max allowed ..... the earth is connected to the sheth via an earth clamp ... and I checked my results by bypassing the clamp direct to the sheath indicating a breakdown in the supply earth .... now I havnt come across this before and would like to know .... is it the duty of the supplier to rectify the problem ... do I rod the system in an effort to bring the readings into line for now or will this not do the job ... I have told the owner of the property to contact the electricity supplier and ask for the matter to be resolved either by repair or by changing to a TNCS system ... is there any thing else I could have done ?
 
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monkeyelectric

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  • #10
Its the dno's problem , i've had it a few times and they come out and sort it. You say above that you traced the problem with the ring and split it to two radials anyway, couldn't the ring be repaired?
 

Gavin A

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Arms
rung the supplier yourself while on site as you can actually explain properly what your readings were so it gets treated as a 4 hour call out instead of being put on a several week long waiting list, then asked the customer to ring you when they'd arrived / finished the work so you could go back and complete your testing.

and isolate it unless the bonding to the water pipe gives a sufficient earth for it to be safe for a short time anyway.

at least that's what we would have done / have done many times.
 
cheers ....... "ring main" at the existing board was infact already two radials bunched into a 30 fuse .... when I say traced the problen I mean confirmed it was two radials and not a broken cable / connection and split them onto their own mcbs

will the Board charge the owner ???? its all about £££££s these days and people worry ..... tho I pointed out that with the RCD protection of the new board they are so much safer than before .... and they have lived for the past 30 years with this problem without knowing .....but if its breaking down it will only get worse

thanks again peeps
 

Gavin A

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Arms
no charge as long as it's an official suppliers earth rather than an unnofficial bodge. The DNO would then be responsible for maintaining the integrity of the earth they'd supplied.
 
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monkeyelectric

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  • #14
Oh i see! No they won't charge for it as they should legally provide the earth to be less than 0.8 for the tns beings as its there already
 
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rattlehead85

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  • #15
Last time i encountered this problem on a TN-S and rang the DLO i got told it wasn't down to them to provide an earth and i should proceed with installing a T.T rod. Lazy bunch of no goods!
 
did mention to the owner that an old earth clamp to the sheath isnt "proper" ..... but there is no sign of a soldered on earh wire from the lead sheathing .... must have fell off over the years
 
thanks for the input chaps
 
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Engineer54

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  • #19
did mention to the owner that an old earth clamp to the sheath isnt "proper" ..... but there is no sign of a soldered on earh wire from the lead sheathing .... must have fell off over the years

Lead wipe/soldered earth connections to the cables lead sheath don't just fall off over the years, and their will always be signs/evidence of an original earthing connection!!


Still waiting for the answer to MDJ's question too!! lol!!
 
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monkeyelectric

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  • #20
Well what did you do about it? I know what I would do, you first!!!!
I think you'll be waiting a while for that reply Mike, Davino started this thread in 2008 :freak:
 
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SPARTYKUS

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  • #21
Thats only 4 years thats nothing. What can happen in 4 years?

abbi

the complete RCD protection you have installed covers your 'too high' Zs figures. but with this earthing system the RCDs are only an extra layer of protection, the earthing needs repairing as they are obliged to do.

They can and will. i have watched them dig
up the road/pavement/ huge trench just to fit a new head to an old TNS in central Wolverhampton. It was a lovely job. Best earth you'll get. None of this silly " the laws of physics changed in the 50's" TNCS nonsense!!!
 
high ze

Hi pal,
Any chance I can pick ur brains
I have recently installed a dual rcd consumer unit and when it came to the testing the ze was 0.70 ohms on a tncs system overhead supply I know this is double the required reading of 0.35 ohms should I contact the DNO and how dangerous is it.would welcome your advice.
 

telectrix

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Mentor
Arms
Esteemed
0.7 should give you acceptable Zs readings, but it's, as you say, twice the max. allowed on a TNC-S, so get DNO to fix it. it's their problem.
 
Update ............. after some buck passing one of the organisations involved have agreed to change the tns to a PME supply to the property at no cost to anyone .... ..... thanks for the input peeps
 
It does woory me somewhat that practicing electricians are taking readings for their forms without really knowing what it is they are reading along with which leads to use....
 
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SPARTYKUS

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  • #26
Update ............. after some buck passing one of the organisations involved have agreed to change the tns to a PME supply to the property at no cost to anyone .... ..... thanks for the input peeps
changing a beautiful TNS to TNCS...... Arrrrghhhhhhh
 
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Rampantchilli

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  • #27
It does woory me somewhat that practicing electricians are taking readings for their forms without really knowing what it is they are reading along with which leads to use....

and me
i checked some DEIC today done by some subbys working for my employer, at the time of doing the work they also did an DEIRC for the rest of the property, which when i looked had a C1 on it for too high TNS Ze reading, yet they still installed 2 circuits without correcting the issue, and both certs were counter signed too
needless to say they will be going back,
 
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supertoad

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  • #28
make shure main switch is off before test!

use 3 prong lead -connect all leads on the metrel
the other lead has a plug top on it,
 
and me
i checked some DEIC today done by some subbys working for my employer, at the time of doing the work they also did an DEIRC for the rest of the property, which when i looked had a C1 on it for too high TNS Ze reading, yet they still installed 2 circuits without correcting the issue, and both certs were counter signed too
needless to say they will be going back,
And I bet their reply would be.... "Not my problem"
 
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Rampantchilli

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  • #30
And I bet their reply would be.... "Not my problem"
well its up to me if they get paid, so unless its sorted that aint gonna happen
 

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