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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
Arms
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!
 
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