PIR

[rob196]

Have just done a PIR and now looking for some help if possible guys.... house with a TT system put no access to the Earthing rod, earth cable just dissapeares under the front of the house, no garden just a public pavement so all concrete and tarmac.......

Ze reading is 157ohms .....

Zs reading range from 19.4-20 ohms

all other readings are fine R1+R2 etc, etc

6 circuits, four 5A, 32A & a 45A.........With a 80A main switch/30ma ELCB ( please see pics) not sure if ELCB'S are even in the regs?.....can anyone tell me what the breakers are? bs 3871 perhaps? or even the type of cut out fuses used? And any ideas for coding this PIR?

 

[PBC_1966]

house with a TT system put no access to the Earthing rod, earth cable just dissapeares under the front of the house, no garden just a public pavement so all concrete and tarmac.......

Probably lost under resurfacing at some point in time. Personally, I'd be considering whether to install a new rod. The resistance is within the specified limits, although sounds a little on the high side compared with your Zs readings, so I would be inclined to start wondering if it's begun deteriorating significantly.

With a 80A main switch/30ma ELCB ( please see pics) not sure if ELCB'S are even in the regs?

Fine, so long as it tests O.K. It's a 30mA RCD, which is just a current-operated ELCB by another name. You're probably thinking of the older voltage-operated ELCB's, which have not been recognized by the regs. since the 15th edition.

.....can anyone tell me what the breakers are? bs 3871 perhaps?

Yes, MEM QB/QEB are BS3871. Replacements available, e.g:

http://www.thefusecompany.com/fuse.php?***th=68&products_id=460

or even the type of cut out fuses used?

Looks like an old double-pole fused service head. One has probably been replaced with a solid link by now, judging by the different color carrier.

 

[Andy™]

Have just done a PIR and now looking for some help if possible guys.... house with a TT system put no access to the Earthing rod, earth cable just dissapeares under the front of the house, no garden just a public pavement so all concrete and tarmac.......Ze reading is 157ohms .....

Zs reading range from 19.4-20 ohms

all other readings are fine R1+R2 etc, etc

6 circuits, four 5A, 32A & a 45A.........With a 80A main switch/30ma ELCB ( please see pics) not sure if ELCB'S are even in the regs?.....can anyone tell me what the breakers are? bs 3871 perhaps? or even the type of cut out fuses used? And any ideas for coding this PIR?

id be tempted to leave the rod as is, just mark lack of access. unless you have reason to believe it has a corroded connection which may fail?

thats not an ELCB - its an RCD (which are still used today). ELCB's are usually external to the DB, large and with a test button. BS number is in pic 3. MCB's are 3871's

cutout looks like it may have fused neutral. maybe a call to DNO to get them to either check, or confirm that its been changed to solid link in the past

got to ask - are you competent to be doing a PIR?

 

[rob196]

[quote name='Andy

 

[Andy™]

HAHA I knew someone would ask if i was competent lol...yes i'm competent :| have all the quals but quals don't make up for experience which is why i'm here asking guys who have the experience........

dont take this the wrong way, but qualifications doesnt mean competent - im guessing you havent had much experience with older wiring methods & equipment, which you have found at this job?

obviously though, once youve worked with stuff like this a few times, then you will get to know what your looking at

 

[Andy™]

ESC PIR guide

 

[PBC_1966]

[quote name='Andy

 

[rob196]

An RCD is a current-operated ELCB, even if "officially" it's not called that anymore.

Your right Andy, i haven't had much experience with older wiring and when I did my 2391 it was all new installation so it does get the old grey cells going when i come across fittings i haven't seen before.... When i saw ELCB my mind instantlly started thinking about the older version which as I know are not in the new regs so wasn't sure how to code it O)

 

[Andy™]

Your right Andy, i haven't had much experience with older wiring and when I did my 2391 it was all new installation so it does get the old grey cells going when i come across fittings i haven't seen before.... When i saw ELCB my mind instantlly started thinking about the older version which as I know are not in the new regs so wasn't sure how to code it O)

no need to code it unless it doesnt work, as you now know what it is ( the BS number is a giveaway - 4293 has never been ELCBs (that i know of?))

 

[rob196]

[quote name='Andy

 

[PBC_1966]

It's important to differentiate between a voltage-operated ELCB and a current-operated ELCB. It's only the former which ceased to be recognized by the Wiring Regs. with the 15th edition.

 

[rob196]

It's important to differentiate between a voltage-operated ELCB and a current-operated ELCB. It's only the former which ceased to be recognized by the Wiring Regs. with the 15th edition.

Totally agree..........I learn something new with every job I do, last week i did a PIR at a house with a TT system and it had a 300mA rcd at it,s main switch........

 

[Andy™]

Totally agree..........I learn something new with every job I do, last week i did a PIR at a house with a TT system and it had a 300mA rcd at it,s main switch........

normally would have been 100mA TD to 16th

 

[PBC_1966]

a house with a TT system and it had a 300mA rcd at it,s main switch........

Pretty common at one time. And before that, 500mA was the general standard, assuming a voltage ELCB wasn't used.

If in doubt about the ELCB type, remember that the voltage-operated type will have two terminals for earth connections: One for connection to the installation's earthing system, and one for connection to the earth electrode.

 

[ProDave]

can anyone tell me what the breakers are? bs 3871 perhaps?

Yes, MEM QB/QEB are BS3871. Replacements available, e.g:http://www.thefusecompany.com/fuse.php?***th=68&products_id=460

They are also the same pattern as Wylex NB series, half the price http://www.thefusecompany.com/fuse.php?products_id=398 or available new from CEF as Proteous

 

[rob196]

[quote name='Andy

 

[revjames]

Ze reading is 157ohms .....

Zs reading range from 19.4-20 ohms

all other readings are fine R1+R2 etc, etc

just noticed you have Ze as 157 ohms and Zs 20 ohms?

don't see how thats possible unless R1+R2 is 137 ohms

or am I missing something here?

 

[Andy™]

just noticed you have Ze as 157 ohms and Zs 20 ohms? don't see how thats possible unless R1+R2 is 137 ohms

or am I missing something here?

your missing something

Ze is rod only

Zs is Zdb + R1R2. Zs is taken with parallel paths. i.e your Zs route may be earth to MET, to water pipe, through water pipe to next house, through their bonding to their TNCS MET, to neutral back to star. you could get a Zs of values well within TNS/TNCS range

 

[Lurch]

or am I missing something here?

Parallel paths.

 

[revjames]

Thanks Andy, thats a lot clearer. Dont come across TT much up here.