I'm not sure if the Regs allowed separately bare earths.

sham · Oct 17, 2018

I've been on this job to do an inspection before fitting a new RCD OR RCBO board. In most of my career until now the CPC is inside the T+E cable. This property has a separate CPC all through out the building. Only where there has been modifications, modern wiring has been used. If I can prove the ZS is good, is it ok to connect to this system. It's seems to be mainly the lighting that is wired in single sheathed cable which has been ran in conduit. I am hoping if anyone has any information regarding the regs about separate bare earth running through the property. There is a risk of borrowed neutrals if changing to an rcd or rcbo board. The customer does not want a Rewire but wants spots fitted and sockets moving. I have convinced him to change the board, now I am worried about nuisance tripping. However if you could advice about the earth mainly would be a great help. Personally I feel the wiring was good for it's day.

[ElectriciansForums.net] I'm not sure if the Regs allowed separately bare earths.

MFS Electrical · Oct 17, 2018

sham said:
Do I need to be careful is I was to do live ZS test as the earth is all over the place

Definitely I’d be tempted to do it on no trip to limit the current

westward10 · Oct 17, 2018

Give an inch people take a mile.

davesparks · Oct 17, 2018

MFS Electrical said:
Definitely I’d be tempted to do it on no trip to limit the current

Why do you say that?

MFS Electrical · Oct 17, 2018

davesparks said:
Why do you say that?

The bonding isn’t exactly satisfactory And when doing ELI certain meters can pump up to 26A down the earth that would hurt like hell and might have some bad consequences... I’d be wanting to do a full range of dead tests first before doing a Zs

davesparks · Oct 17, 2018

MFS Electrical said:
The bonding isn’t exactly satisfactory And when doing ELI certain meters can pump up to 260milliamps down the earth that would hurt like hell and might have some bad consequences... I’d be wanting to do a full range of dead tests first before doing a Zs

0.26A? A normal Zs test should be more than that!
This is why we carry out dead tests before live tests and the regulations specify this order.

Anti-trip tests regularly give incorrect readings and are not a good replacement for a standard efli test,

MFS Electrical · Oct 17, 2018

davesparks said:
0.26A? A normal Zs test should be more than that!
This is why we carry out dead tests before live tests and the regulations specify this order.

Anti-trip tests regularly give incorrect readings and are not a good replacement for a standard efli test,

I did at first say 26 amps but i edited it and I don’t know why I changed it to be honest

MFS Electrical · Oct 17, 2018

I do agree that the high current test should be used wherever possible but without the appropriate bonding in place and so much bare earthing conductor around it may give rise to a dangerous situation

MFS Electrical · Oct 17, 2018

MFS Electrical said:
I’d disconnect the bonding and the bare earths from the board and do an R2 on the bare earth from the end at the board to ensure its complete and then again at the bit your going to connect into and to the board itself and then the pipes themselves just to rule out that the bare earth was coming from elsewhere I reckon if you do that you’ve pretty much proved beyond reasonable doubt that the earth is suitable and actually coming from the CU and not the pipes or anywhere else.

I did hint at doing the dead tests first several times throughout the thread as well

sham · Oct 17, 2018

MFS Electrical said:
I did hint at doing the dead tests first several times throughout the thread as well

If I do an ZS through calculation, then I will not really need to do a live test do I ?

MFS Electrical · Oct 17, 2018

sham said:
If I do an ZS through calculation, then I will not really need to do a live test do I ?

Technically yes but I still prefer to do a Zs test

Midwest · Oct 18, 2018

You lot have gone barking again.

Halt, reality check.

Sham don't do it!

Unless your a registered charity, and determined to cocoon this install for historical purposes, tell your customer where to shove it. Even the National Trust rewire their properties.

TRS, aluminium sheathed cables, bear earths. You lot are nuts.

MFS Electrical · Oct 18, 2018

Midwest said:
You lot have gone barking again.

Halt, reality check.

Sham don't do it!

Unless your a registered charity, and determined to cocoon this install for historical purposes, tell your customer where to shove it. Even the National Trust rewire their properties.

TRS, aluminium sheathed cables, bear earths. You lot are nuts.

Why not with bare earths? I can understand rewiring aluminium cables lead sheathed cables and TRS but as long as the PVC cables that are in use in the installation test ok ie good insulation resistance and the earth is actually from the CU and not a water pipe I don’t really see a problem with the bare earths? Is there some sort of requirement to replace a system that still works and is effective? As I said Regs aren’t retrospective so why would you be saying don’t do it? He is going to upgrade the CU and the bonding so I don’t think it’s any different to connecting to Red and Black PVC? It’s old cable and yeah it’s not to current standards but what is the reason to replace it if it tests out ok and the cable is in generally good condition?

Wilko · Oct 18, 2018

Hi - being open, due to my lack of experience with the installation and maintenance of these older systems, I couldn't say with confidence whether the installation satisfied Reg 132.16 or not. So it'd be some level of re-wiring or re-staffing

.

telectrix · Oct 18, 2018

MFS Electrical said:
I have not a clue what that means imperial is complete gibberish to me

i therefore beg to educate you:
12 inches = 1 foot
3 foot =1 yard
1760 yards (5280 feet) =1 mile
22 yards= 1 chain
5.5 yards = 1 pole/rod/perch
4 rods= 1 chain
6 feet = 1 fathom
10 chains = 1 furlong
8 furlongs = 1 mile
4840 sq. yards= 1 acre.

what's hard about that?

snowhead · Oct 18, 2018

telectrix said:
i therefore beg to educate you:

22 yards= 1 chain = Length of an English Cricket pitch

what's hard about that?

I've added a piece of usefull information to that.

telectrix · Oct 18, 2018

firther info:
2 pints = 1 quart
4 quarts = 1 gallon
2 gallons = 1 peck
9 gallons = 1 firkin.

westward10 · Oct 18, 2018

Unless I am misreading it Regulation 543.3.201 would deem those cpcs as no longer adequate so I would not be considering a board replacement unless they were rewired.

MFS Electrical · Oct 18, 2018

telectrix said:
i therefore beg to educate you:
12 inches = 1 foot
3 foot =1 yard
1760 yards (5280 feet) =1 mile
22 yards= 1 chain
5.5 yards = 1 pole/rod/perch
4 rods= 1 chain
6 feet = 1 fathom
10 chains = 1 furlong
8 furlongs = 1 mile
4840 sq. yards= 1 acre.

what's hard about that?

That’s easy enough but what is 7/0.29? And what does that mean in metric also 7/16ths? 3/32nds and so on.

10foot 7inches and 3 wee bits on the tape measure as one guy I used to work with would say

MFS Electrical · Oct 18, 2018

westward10 said:
Unless I am misreading it Regulation 543.3.201 would deem those cpcs as no longer adequate so I would not be considering a board replacement unless they were rewired.

Ahh I see. But again regs aren’t retrospective so back to the old argument should it be replaced as you wouldn’t replace a Plastic CU with a metal one just because you extended a lighting circuit and you wouldn’t rewire the lighting circuit in the new colours the old colours don’t comply but that doesn’t necessarily mean that they need replacing.

westward10 · Oct 18, 2018

That is for you to decide the level of what you feel is still okay to be left in service, me personally I would be suggesting that should be rewired. You also need to consider was it actually compliant at the time of installation or a later ad hoc addition.

MFS Electrical · Oct 18, 2018

westward10 said:
That is for you to decide the level of what you feel is still okay to be left in service, me personally I would be suggesting that should be rewired. You also need to consider was it actually compliant at the time of installation or a later ad hoc addition.

I couldn’t agree more if you yourself are in any doubt as to whether or not it ever complied then as its you signing the Cert you have to make the decision

westward10 · Oct 18, 2018

For interest it says much the same in the 15th Ed.

MDJ · Oct 18, 2018

sham said:
I've been on this job to do an inspection before fitting a new RCD OR RCBO board. In most of my career until now the CPC is inside the T+E cable. This property has a separate CPC all through out the building. Only where there has been modifications, modern wiring has been used. If I can prove the ZS is good, is it ok to connect to this system. It's seems to be mainly the lighting that is wired in single sheathed cable which has been ran in conduit. I am hoping if anyone has any information regarding the regs about separate bare earth running through the property. There is a risk of borrowed neutrals if changing to an rcd or rcbo board. The customer does not want a Rewire but wants spots fitted and sockets moving. I have convinced him to change the board, now I am worried about nuisance tripping. However if you could advice about the earth mainly would be a great help. Personally I feel the wiring was good for it's day.

View attachment 44940

I would be giving the customer a quote for a full rewire as well, what a mess, buckle clips, bare earths and double insulated singles, 1950s -60s wiring, must be 60-70 years old now

Lucien Nunes · Oct 18, 2018

Common cable types explained...

VIR: Vulcanised India Rubber. Single-core unsheathed cables used in conduit. Rubber insulation has an outer fabric layer impregnated with a preservative compound. Tinned copper conductors, stranded in all but the smallest size. Conduit was normally black-enamelled. Domestic installations often used 5/8" or 3/4" slip conduit that was not threaded at joints but clamped by the fittings, a.k.a slip conduit. Continuity required enamel coating to be scraped off and was considered unreliable with cheaper fittings.

TRS: Tough Rubber Sheathed. Construction generally similar to modern T+E, rubber insulated cores with or without a bare CPC, inside a rubber sheath. Usually black, occasionally white. Tinned copper conductors, stranded in all but the smallest size.

Lead sheathed twin: Rubber insulated cores with or without a bare CPC, inside a grey lead metallic sheath that serves as CPC unless a copper CPC is included. Tinned copper conductors, stranded in all but the smallest size. Original work will be jointed in metal junction boxes with continuity clamps that connect the lead sheaths together, rather than bakelite ones.

Imperial sized PVC and PE insulated twin / twin + earth: Construction generally similar to modern T+E but with imperial sized conductors, either tinned or plain copper, stranded in all but the smallest size. Some early plastic-insulated cables used polyethylene insulation which has a smooth, waxy appearance and may be semi-transparent.

Aluminium conductor: Construction generally similar to modern T+E. Conductor soft and brittle regardless of whether copper-clad. Cladding was to improve contact at terminations, plain Al makes poor terminations that tend to go high resistance unless special precautions are taken.

Imperial sizes:
Example: 7/.029 (note position of decimal point carefully)
7 strands of 0.029 inches diameter.
CSA (0.029/2 x 25.4)² x pi x 7 = 3.0mm²

Normal strand diameters: .029, .036, .044, .064, .083
Normal strand counts: 1, 3, 7, 19, 37

Common domestic applications:
Lighting circuits: 1/.044 or 3/.029
Power radials: 3/.036 or 7/.029
Ring finals: 7/.029
Cookers and submains: 7/.044
Tails: 7/.044 or 7/.064

There were other / older systems for specifying cable size, e.g. 3/18 meaning 3 strands of 18SWG. These were not normally used after WW2.

Midwest · Oct 18, 2018

MFS Electrical said:
Why not with bare earths? I can understand rewiring aluminium cables lead sheathed cables and TRS but as long as the PVC cables that are in use in the installation test ok ie good insulation resistance and the earth is actually from the CU and not a water pipe I don’t really see a problem with the bare earths? Is there some sort of requirement to replace a system that still works and is effective? As I said Regs aren’t retrospective so why would you be saying don’t do it? He is going to upgrade the CU and the bonding so I don’t think it’s any different to connecting to Red and Black PVC? It’s old cable and yeah it’s not to current standards but what is the reason to replace it if it tests out ok and the cable is in generally good condition?

It'll be ok when the house burns down; the new metal CU will be holding up the only remaining wall.

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