unit rewire

[gordy71]

My dad has just started renting a new comercial unit on an estate and asked me to move a light switch and a socket and put a couple of new sockets in. an afternoons work i thought... Got there and done some initial tests, the average zs was around 3.00 ohms which i wasnt too pleased about so i went to look at the origin of the source in the owners property. it had a 300ma rcd and i could not work out the earthing arrangement as the main earth just went down a piece of pipe with the main incomer? Now normally i would just run a mile from a job like this as the existing wiring is shoddy and its an awkward job to change the c/u but as its my dad i cant really say no! I was just wondering what you would do in my situation, I was gonna change the c/u and rewire the sockets circuits and put a local earth spike in. But is the high zs on the armoured feeding the unit an issue for me to carry out any work?

 

[Badger]

what was the ze though, as thats where id have checked if i found a zs like that, it could be that the circuits wiring is ok but the main earth has corroded.

 

[sprocketflup]

Surely if he is renting it you can report your findings to the landlord/company and get them to sort it? The incoming supply is not gonna be your Dads responsibility

 

[spinlondon]

Maximum Zs for a 300mA RCD is 167ohms I believe.

You should be able to contact the DNO to find out the earthing arrangements and what the maximum Ze should be.

If it is TT, then the reading is quite low, however if it isn't then you might want to report it when making your enquiry.

If you don't want to rely on the SWA as the earth, it might be an idea to isolate the armour.

 

[sellers]

Surely if he is renting it you can report your findings to the landlord/company and get them to sort it? The incoming supply is not gonna be your Dads responsibility

Depends on the lease, you can have clauses in leases meaning the tenant has to repair faults, even renovate!

 

[Evans Electric]

As said , you need the Ze for a start. In this area a supply as you describe is usually a TT but not always !! Don't let it worry you , get stuck in and sort it.

 

[gordy71]

Would the ze be taken at my dads end because it is classed as its own installation or where the supply enters the estate? I only tested from the swa in the unit as i thought there is not much i could do about the earthing conditions at the other end and the landlord is a bit old school so is reluctant to get things upgraded. i will try and get a ze at the supply end to ensure the armour hasnt deteriated, And enquire about the earthing arrangement. I have a feeling it might not be tt so how would i stand if it turns out the ze is too high or the swa has a high resistance? Can i just tt my dads installation? Or is it a requirement for the swa earth to be sound as it needs to operate the protective device? Thanks for the replies

---------- AUTO MERGE Post added at 12:50 ---------- Previous post was at 12:41 ----------

If you don't want to rely on the SWA as the earth, it might be an idea to isolate the armour.

What would be the alternative though? It is only a 2 core swa so no other earth. I really need to get this sorted asap so the less work the better.

 

[Larnacaman]

gordy71,

It wouldn't surprise me in the least, that the SWA cable wasn't laid correctly in the first place. You could well have a situation where the cable sheath has been damaged/penetrated and the SWA is now happily rusting away.

Depending on how long the cable has been in the ground and on the type of soil, or even the presence of chemical contamination (as it's on an industrial estate) It could well be there's a section of armouring where there isn't much steel wire left!! ..lol!!!

OK, ....here's a tip i was going to put in the tips forum here. If you ever need to check for sheath damage on an Armoured cable that's in the ground. Disconnect armouring from any ground/earth source at both ends, then check from a sound ground/earth to the cables armouring. ....ANY reading present, will indicate you have a damaged cable sheath!!

I wouldn't mind putting money on this one, that the cable sheathing has been penetrated. ...lol!!!

 

[septiclecky]

gordy71,It wouldn't surprise me in the least, that the SWA cable wasn't laid correctly in the first place. You could well have a situation where the cable sheath has been damaged/penetrated and the SWA is now happily rusting away.

Depending on how long the cable has been in the ground and on the type of soil, or even the presence of chemical contamination (as it's on an industrial estate) It could well be there's a section of armouring where there isn't much steel wire left!! ..lol!!!

OK, ....here's a tip i was going to put in the tips forum here. If you ever need to check for sheath damage on an Armoured cable that's in the ground. Disconnect armouring from any ground/earth source at both ends, then check from a sound ground/earth to the cables armouring. ....ANY reading present, will indicate you have a damaged cable sheath!!

I wouldn't mind putting money on this one, that the cable sheathing has been penetrated. ...lol!!!

You need to give us more info like is it on a industrial estate, a country estate with units in the grounds, are there any electrical poles around etc

 

[Larnacaman]

gordy71

Can i just tt my dads installation? Or is it a requirement for the swa earth to be sound as it needs to operate the protective device?

You can Rod any type of supply into your dad's unit, but 2 bad readings ain't gonna make a good one!! Get all the facts in place first before you make any judgments as to what your going to do as a corrective measure.

As Septic stated, give the forum some more information, ...preferably after you have done your enquires and i'm sure you'll get some good advise as to how best to proceed ....

 

[gordy71]

ok thanks for the replies, im going there to make a start tommorow so will come back with more info:good luck: