Mains distribution upgrade work, 3 phase,old isolators, steel conduit & trunking providing CPC

[Delectrician]

Hello everyone

I'm picking up some remedial works from an EICR fail in a commercial property.

Its a 3 phase supply with old steel conduits , trunking & coupled metal equipment, that provides the earth to the various locations.

At present the earthing is insufficient, every earth in the building comes via the continuous metal structure of the installation.

The supply looks very old, the incomer is wrapped in a cloth like material & it looks to be a TN-S system, the earth looks to be the armour of the cable, connected into a chalk block terminal, then there is a old & uninsulated 10mm cable connected to the main earth boss on the metal trunking, from there the 3 main isolators are coupled to the trunking & feed various areas & DBs, each isolator has a exterior earth connection & at present they are all linked together with uninsulated 6mm2 cable!

The values back to earth are pretty good from even the furthest off DB, 0.21 ohms.

I was planning to upgrade the main earth link, from the main earth to the trunking to 16mm2 & renew the external earthing of the metal enclosures to 6mm2.

Is this correct?

Thanks

 

[Pete999]

Hello everyone

I'm picking up some remedial works from an EICR fail in a commercial property.

Its a 3 phase supply with old steel conduits , trunking & coupled metal equipment, that provides the earth to the various locations.

At present the earthing is insufficient, every earth in the building comes via the continuous metal structure of the installation.

The supply looks very old, the incomer is wrapped in a cloth like material & it looks to be a TN-S system, the earth looks to be the armour of the cable, connected into a chalk block terminal, then there is a old & uninsulated 10mm cable connected to the main earth boss on the metal trunking, from there the 3 main isolators are coupled to the trunking & feed various areas & DBs, each isolator has a exterior earth connection & at present they are all linked together with uninsulated 6mm2 cable!

The values back to earth are pretty good from even the furthest off DB, 0.21 ohms.

I was planning to upgrade the main earth link, from the main earth to the trunking to 16mm2 & renew the external earthing of the metal enclosures to 6mm2.

Is this correct?

Thanks

Is the main bonding OK? What type of supply is it? have you tested Ze?

 

[PEG]

What you describe,sounds like a lot of older installations,from the 50's onwards,in fact,i have a pal works out of an old dairy,with this set-up,and the containment would have provided earthing.
Over time,modifications to this containment,degrade the original intention,and you will find "ad hoc" attempts to reinstate continuity.

You may have to do further testing and inspecting,and then calculations,to determine,whether these "links",are capable of providing sufficient integrity. Mere long-leading,with a MFT,will not provide a conclusive answer.

 

[Lucien Nunes]

The supply looks very old, the incomer is wrapped in a cloth like material & it looks to be a TN-S system, the earth looks to be the armour of the cable

That is probably the serving (waterproofing layer) of a PILC STA or SWA cable. If so, the lead sheath, rather than the armour, would normally provide the earth, and it is usually a very good one provided the tail has been sweated on or correctly terminated (i.e, not a BS951 clamp or other nonsense).

Whilst a new bit of G/Y 16mm² would add a splash of colour, you will probably find using the adiabatic equation that the existing connections are perfectly large enough. But look for corroded or loose fasteners and conduit joints especially on modified sections - earthing is more likely to suffer from poor workmanship than small conductors.

 

[Deleted member 9648]

You don't state the rating of the incomer....if it's 400a a bit of 16mm is not going to cut it.

 

[PEG]

You don't state the rating of the incomer....if it's 400a a bit of 16mm is not going to cut it.

Which is exactly the issue,with my pals aforementioned premises.
The likely and possible loads drawn across such venerable systems,can find out,the weaknesses in alterations carried out over the years,which do not meet the original installation standards.

One particular favourite,of the larger,older factories,where over time,building alterations are carried out,to make separate units,or vehicle/plant access,is the "Through-way".

Most distribution circuits,will radial out,from the incomer,at a height,that does not allow vehicles through,when new openings are formed. This means that wherever an opening is made,the circuit and containment,has to be sectioned and bridged,over the thing.

This is rarely done to the same standard as the original,in older examples,and i have seen it done many times,to hardly any standard at all.

Add 60+ years of change in ownership and use,and you may well find,what the OP has.

 

[ipf]

Which is exactly the issue,with my pals aforementioned premises.
The likely and possible loads drawn across such venerable systems,can find out,the weaknesses in alterations carried out over the years,which do not meet the original installation standards.

One particular favourite,of the larger,older factories,where over time,building alterations are carried out,to make separate units,or vehicle/plant access,is the "Through-way".

Most distribution circuits,will radial out,from the incomer,at a height,that does not allow vehicles through,when new openings are formed. This means that wherever an opening is made,the circuit and containment,has to be sectioned and bridged,over the thing.

This is rarely done to the same standard as the original,in older examples,and i have seen it done many times,to hardly any standard at al
Add 60+ years of change in ownership and use,and you may well find,what the OP has.

I'll go along with that... an example of altered trunking system to facilitate the installation of a car ramp....

 

[Squid]

Whats the reading between the SWA and the block and the reading from the block onwards?

 

[PEG]

I'll go along with that... an example of altered trunking system to facilitate the installation of a car ramp....

View attachment 40189 View attachment 40190 View attachment 40191 View attachment 40192

Yep,excellent pictures,of what some of us have encountered,a hundred times. No saying that the test readings would not be acceptable,but an EICR is about more than mere readings,an estimation of function,under conditions not present,or that cannot be simulated,is also required.

An old school way of demonstrating the importance of a physical inspection,of such installations,which was shown to me,would be to allow the student to test the integrity of any containment,right to the end,and note the reading.
The student is then given a 1/2" piece of 30A fuse wire,and the same final test is done,with this between the probe and containment.

The result is appreciably the same. The student is then asked how much the result would differ,if the fuse wire was anywhere else in the continuity of the containment,and,most importantly,how it would affect it's ability to carry a fault current,on the circuit supplied.

A lot of lads will have had containment continuity readings alter,due to temperature,or whether the ladder is resting on it

I have seen an incredibly ingenious 'mod',years ago,in a tyre bay,added to one of Manchester's long vanished industrial buildings,at White City,Old Trafford.

Some very careful and dedicated pilgrim,had needed to move a galvanised conduit,containing the supply to a tyre machine,as it crossed where a standard door was being cut-in.

To enable the conduit to be routed up and across,two 90's were needed...but no,some dude had hacksawed,ever so carefully,through the conduit,in two places,without touching the singles,and moved the machine isolator nearer the door.

All clipped back up,with the singles poking out of the two invisible elbows ....and that was one of the buildings better features

 

[ipf]

Yep,excellent pictures,of what some of us have encountered,a hundred times. No saying that the test readings would not be acceptable,but an EICR is about more than mere readings,an estimation of function,under conditions not present,or that cannot be simulated,is also required.

An old school way of demonstrating the importance of a physical inspection,of such installations,which was shown to me,would be to allow the student to test the integrity of any containment,right to the end,and note the reading.
The student is then given a 1/2" piece of 30A fuse wire,and the same final test is done,with this between the probe and containment.

The result is appreciably the same. The student is then asked how much the result would differ,if the fuse wire was anywhere else in the continuity of the containment,and,most importantly,how it would affect it's ability to carry a fault current,on the circuit supplied.

A lot of lads will have had containment continuity readings alter,due to temperature,or whether the ladder is resting on it

I have seen an incredibly ingenious 'mod',years ago,in a tyre bay,added to one of Manchester's long vanished industrial buildings,at White City,Old Trafford.

Some very careful and dedicated pilgrim,had needed to move a galvanised conduit,containing the supply to a tyre machine,as it crossed where a standard door was being cut-in.

To enable the conduit to be routed up and across,two 90's were needed...but no,some dude had hacksawed,ever so carefully,through the conduit,in two places,without touching the singles,and moved the machine isolator nearer the door.

All clipped back up,with the singles poking out of the two invisible elbows ....and that was one of the buildings better features

Les imbeciles....