Pme & Tt Earthing

[marky1]

Hi

Went to property today to do EICR that has x3 DB's,

DB1 with x7 mcb's, 80a 100mA Earth leakage circuit breaker on a TT system with 6mm earthing conductor, 6mm water bonding.

DB2 with x2 mcb's 100a 30mA RCD MS feeding shower & electric heater on TNCS system with 16mm earthing conductor.

DB3 with x6 mcb's 100a MS feeding night storage heaters on TNCS system with 16mm earthing conductor.

I am aware that you should not have 2 different types of earthing system within domestic property, so i have asked her to contact electricty supplier to check if PME system available. She has done this but dont know how long we will have to wait! I done some tests whilst on site. DB1 Ze 83.5 ohms DB2 Ze 0.36 DB3 Ze 0.38. Although DB2 & 3 Ze slightly high (have seen higher readings accepted by supplier in the past) all 3 boards have fairly good earth paths.

If PME available, then easy to convert DB1, but would need to upgrade main earth & water bonding. customer wants house made safe so is willing for me to carry out any required work.

Prob i have is that i contacted Part P scheme help line with no real help regards EICR code! whilst i wait to hear back from supplier. 

What do you guys think??

Thanks

All 3 DB's are side by side

 

[ProDave]

So DB1 is the original DB

DB2 sounds like an addition either because there was no spare capacity, or someone wanted a 30mA rcd on the new circuits.

DB3 is the off peak CU.

All from the same supply.

So the SUPPLY is TNCS already.

It's just that for some odd reason DB1 is not connected to the TNCS earth and connected to a rod instead.

So as the TNCS earth is there, why not just connect DB1 to it?  I don;t see where DNO involvement is required.

Or am I missing something?

 

[marky1]

Thanks for your response, 

Connecting straight to the TNCS supply was my first thought, but i've had in the past a similar situation but with only one DB, although the Ze was good reading both TT & TNCS the DNO said that there was no facility to convert to TNCS their end. Hence why i've covered my back & am checking all is good their end first this time. Best to be safe than sorry.

However in case customer decides not to go ahead with work, (despite what they have said already) what do you think code should be? Im struggling because the property is earthed, but not correctly. No immeadiate danger or potential in my mind unless it is not a true TNCS supply from DNO

 

[Doc Hudson]

So is there more than one supply coming into the property, i.e. two or more supply cables and two or more supplier cut out fuses?

Doc H.

 

[Sharpend]

Perhaps a few snaps may give us a better indication of what you're up against?

 

[apprentice87]

Hate to tell you, if you mean there is more than a single supply to the place then you cannot have 2 TNCS supplies either....

john...

 

[marky1]

No, there is only one supply & one cut out fuse. The TT DB & TNCS DB2 are fed from meter via henley block, the TNCS night storage DB3 is fed from meter & neutral from henley block.

 

[ProDave]

So 2 of the three DB's get their earth from the supply head.

Why do you not just connect the third one there as well?

 

[ProDave]

Dave - Do you charge for your advice ?

Funny question. this is a forum isn't it?  (or did the question go over my head?)

 

[batty]

If they are all side by side why is there not just one main earth point?

 

[marky1]

Batty - i don't know? i personally think that previous electrician converted system into TNCS himself.

however if DNO confirm TNCS supply available from their end then i will upgrade main earth to 16mm & connect to MET and remove rod & 6mm earth. Advise that water bonding needs upgrading to 10mm at same time.

thanks for your help & advice, appreciated

 

[batty]

I have seen a few DIY TNCS. personally these days with the theft of DNO property I  rather TT much safer.

 

[Evans Electric]

What makes you think the previous sparks has created his own PME firstly?

As said ...any pics?

Otherwise it shouldn't be a big deal for DNO to confirm the earthing system.  

Electricians should not be creating their own PME systems without the knowledge of the DNO TBH .     Theres a large area local to us where the TN-S system  is failing and PME is not avaliable , presumably because there are no earth spikes on the system. 

What Part Pees me off is that all the sparks who have carried out work at these properties prior to us , have conveniently ignored the high or none existing Ze,s when they were there and we seem to be picking them up on a weekly basis . 

We just rodded three properties  in the area which have been ignored by previous sparks .   One took 7 rods   

I mentioned it to two or three  local sparks who generally chat in the wholesalers and realised they didn't give a sheet .     

 

[Manator]

Speaking of which a Ze test on a rodded supply showed a result of 0.49, I think I need to borrow Steps tester for a proper Ra

 

[apprentice87]

If the TNS system is failing, why not just go and see the HSE armed with a copy of the ESQCR.....

They have a legal requirement to maintain the system..

john...

 

[steptoe]

I can lend you a Megger DET4TCR2 next time your local ish if you want, It does stateless testing up to 200Ohms with 2 clamps 

Priceless - Last EICR i did had 30 earth rods - did the lot in a morning and that included breakfast and hot chocolates

Needless to say, but I'll bet that cost quite a bit more than my humble tester, :|

Manator, anytime, you're not that far from me, I don't think,

Yes, it does take a little more setting up,

But, VFM, it does what it says it does at a price I can afford for the Times I require it.

 

[Evans Electric]

If the TNS system is failing, why not just go and see the HSE armed with a copy of the ESQCR.....

They have a legal requirement to maintain the system..

john...

I'm considering writing to the MP for that area  TBH   .   Obviously the scores of different firms who work the area aren't bovvered.  

One reason I don't stick my nose in , is I've been told to butt out in the past , basically .

I once asked the NIC why do we have to put up with the new (then) crappy solid core cables , 2.5 specially and X grade although that died a death .

         Was told " No one is interested in what you have to say,  you're way down in the pecking order".

I asked the ECA once about the (then)  new thing with plumbers using plastic couplers & pipework and neegating all the earth bonds we were fitting on a 16 house job.

             Was told "Whats it to you ...why are you so bothered ...just get your cable to the stop valve and if its plastic don't connect it"

I advised a design engineer that he's spec'd the wrong floor trunking to a hospital scanner ,  (the lid should be the concave version to take the floor covering )   He told me to mind my own business .  We got a letter from him confirming it was correct and when the brown stuff hit the fan he tried to blame us  until we produced the letter .     The trunking ended up with a raised cover that everyone tripped on   and it stayed that way because of the old school tie brigade stick together and they couldn't blame the contractor. 

 

[marky1]

What makes you think the previous sparks has created his own PME firstly?

Because if he had looked at the main DB1 he would have realised it was a TT supply, plus you cant miss the rod by back door (main entrance into property.

As said ...any pics?

will attach pics

Otherwise it shouldn't be a big deal for DNO to confirm the earthing system.  

LOl, customer has since informed me that the DNO came round and checked, said it was not a PME supply. They even informed her that they made this assumption as they drove down her steet

Electricians should not be creating their own PME systems without the knowledge of the DNO TBH .     Theres a large area local to us where the TN-S system  is failing and PME is not avaliable , presumably because there are no earth spikes on the system. 

What Part Pees me off is that all the sparks who have carried out work at these properties prior to us , have conveniently ignored the high or none existing Ze,s when they were there and we seem to be picking them up on a weekly basis . 

We just rodded three properties  in the area which have been ignored by previous sparks .   One took 7 rods 

I mentioned it to two or three  local sparks who generally chat in the wholesalers and realised they didn't give a sheet .     

 

[marky1]

 Anyone please advise how to upload pic's?? 

thanks

 

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