Why cover earth wire?

[Ziggie]

for T@E cable, we cover the bare earth wire with a sleeve of green / yellow. Why?
The basic idea is that if there is a fault then the live wire meets with the earth and covering the wire with insulation potentially stops this action in some cases. Is it not better to have the bare wire to increase the chance of making contact with a live?

I realise that it makes it easy to identify, but all other cables have coloured sleeves.

 

[pc1966]

In a typical installation there will be screws and similar that are live but only just shrouded as nobody is supposed to be poking at the back of accessories with the power on. A kinked CPC could poke in to such a hole causing a short.

Now you might say "well that is its job" which is true, it has allowed automatic disconnection, but the result of such a direct arc on to the CPC might blow a hole in it, and then after someone resets the MCB they might have the appliance-end of the failed wire still in contact with the live, making anything attached live and dangerous.

 

[pc1966]

This post might give you an idea of why it is serious:

Wiring External lights > Page 3 > on Free Electrical Advice - Electricians Forums

Find Wiring External lights Advice and Help. How-to Wiring External lights in the UK Electrical Forum advice boards on Electricians Forums. Wiring External lights on ElectriciansForums.net Electrical Advice Forum.

www.electriciansforums.net

 

[7029 dave]

Keeps cable costs down having the CPC naked, we are just used to sleeving this type of cable.

 

[telectrix]

because you don't want a L -E fault to occur except when and if there's a fault with the accessory/equipment. or wiring.

 

[loz2754]

The wiring regulations require it to be sleeved. That's all you need to know.

 

[pc1966]

Keeps cable costs down having the CPC naked, we are just used to sleeving this type of cable.

It probably has a small impact on cost, not as much as the reduced-size based on adiabatic limit (e.g. 1.5mm CPC on 2.5mm cable).

Where the unsleeved CPC also helps is the overall cable size and ease of getting it in to places.

 

[SJD]

Eire use seem to use twin & earth with an insulated earth, you can see examples if you visit screwfix.ie etc. Not sure of the advantages, compared to a bare earth, but I guess it is required by their regs.

 

[pc1966]

Yes, ROI has gone towards three equal cores in CSA and insulation, so significantly larger and more expensive. I guess it is more in line with EU practice.

 

[stevethesparks]

Never mind a L-E fault, what about creating a N-E fault when replacing a socket and introducing a possible unknown fault

 

[Dustydazzler]

americans and canadians leave the ground wire (cpc) completey bare throughout entire installation. With one caveat to this they have single core wire insulated with green to act as pigtail between un sleeved grounds usually shoved at the back on the enclosure and accessories front plate

I personally would prefer our T&e cable to be sold with pre sleeved cpc

no more faffing with hanks of green sleeve

 

[Lucien Nunes]

Is it not better to have the bare wire to increase the chance of making contact with a live?

That's an odd way of looking at it - like fire extinguishers that randomly set your building on fire to justify their own existence!

Round sheathed installation cables (such as NYM-J used in many countries) normally, perhaps exclusively, have an insulated CPC of equal size to the live conductors. Flat cables vary in construction with different approaches to the CPC under different sets of standards. Some top-of-head examples:

Equal insulated: Aus, ROI, Russia
Equal bare: USA
Unequal insulated: Japan
Unequal bare: UK.

Although not all circuits in all the above are required to have a CPC. Japan, for example, is not big on earthing for domestic wiring (they use a US-derived system at only 100-0-100V) and Aus I believe does not require a CPC in a TPS switch cable.

Looking at sleeving though, the paradox is that the country that uses binding-screw terminals with exposed heads on many of their accessories (USA) does not normally sleeve the grounds, whereas the country with partially shrouded screws and terminals that are less likely to contact any bare metal (UK) requires sleeving.
In Russia, CPC sleeves you!

 

[pc1966]

In Russia, CPC sleeves you!

Well played sir!

 

[pc1966]

I personally would prefer our T&e cable to be sold with pre sleeved cpc

But how would you get 3 CPCs in to the same sleeve then?

 

[pc1966]

I personally would prefer our T&e cable to be sold with pre sleeved cpc

no more faffing with hanks of green sleeve

Being serious again, it would save a bit of effort, though maybe not so much as stripping the CPC is only a bit quicker than cutting some sleeving. What you would get though is an easier sleeved conductor to terminate as the sleeving would be exactly the required size.

I guess the issue is cost and any issues of new cable size not fitting existing glands or junction boxes, etc. Without a change in regulations to require it I suspect most would still choose a cheaper cable, as it is not just the extra PVC for the whole cable length, it is also the greater size and weight to store and transport.

No idea how much, probably a small percent given how much cable cost is dominated by raw copper prices, but there is an argument in favour of least use of the Earth's resources which the RFC and T&E construction were originally driven by.

 

[Ziggie]

The wiring regulations require it to be sleeved. That's all you need to know.

Then there isn’t any errors in the wiring regs and you trust everything Boris is saying . Knowledge comes from asking questions. I found the replies below quite interesting. ?

 

[loz2754]

Then there isn’t any errors in the wiring regs and you trust everything Boris is saying . Knowledge comes from asking questions. I found the replies below quite interesting. ?

Whether we agree with a particular reg or not, or trust the wisdom of those who compile the regulations, we still have to follow what they say. Otherwise what's the point of having regulations in the first place? ?

 

[loz2754]

Then there isn’t any errors in the wiring regs and you trust everything Boris is saying . Knowledge comes from asking questions. I found the replies below quite interesting. ?

Who's this Boris??

 

[Mike Johnson]

Who's this Boris??

Isn't he the guy that changed the name of the Ring Main and brought in Part P?

 

[DPG]

Then there isn’t any errors in the wiring regs and you trust everything Boris is saying . Knowledge comes from asking questions. I found the replies below quite interesting. ?

Tell me this thread isn't going to go down this route!

 

[Ziggie]

Whether we agree with a particular reg or not, or trust the wisdom of those who compile the regulations, we still have to follow what they say. Otherwise what's the point of having regulations in the first place? ?

I agree . No one said don’t obey the regs. But that does not and should not stop questioning them. Free speech

 

[stevethesparks]

I agree . No one said don’t obey the regs. But that does not and should not stop questioning them. Free speech

I'd still like a proper answer to 411.5.1 as in the Electrical Wiring, Theories and Regulations section

 

[nicebutdim]

I agree . No one said don’t obey the regs. But that does not and should not stop questioning them. Free speech

This is a moderated forum, not an open platform. Probably best to keep politcs in dedicated threads.

 

[static zap]

Keeps cable costs down having the CPC naked, we are just used to sleeving this type of cable.

I like to think a bare cpc makes detection of cable damage quicker with a bit of water about ... We are in the UK - Not France / Spain.

( I don't have any plumbing tendencies ... applies ldf )

 

[7029 dave]

I like to think a bare cpc makes detection of cable damage quicker with a bit of water about ... We are in the UK - Not France / Spain.

( I don't have any plumbing tendencies ... applies ldf )

And wait for the bubbles to appear eh.lol

 

[Ziggie]

because you don't want a L -E fault to occur except when and if there's a fault with the accessory/equipment. or wiring.

Let’s take a case where the insulation of the live conductor is damaged. If the CPC is insulated then no action occurs. Is it better to do the best one can by having a bare CPC which would in some cases cause the protection to fail and continue to do so until the fault is fixed.
More interesting is if there was a fault in the N where the connection of earth to neutral might exist unnoticed for some time.

of course, insulation testing would reveal the problem

sounds like I am discussing wrapping the conductors ( both L and N ) and turning them into SWA like cables?
Is the question “ why isn’t the earth in SWA cable covered in yellow / green insulation” ??

 

[loz2754]

The purpose of a CPC, as I understand it, has nothing to do with protecting the cable in the case of damage, eg by nail penetration etc.
But rather to provide connected equipment with a means of connection to the main earth terminal to facilitate ADS in the event of a fault in the equipment.
Please correct me if this is an incorrect correction...

 

[Lucien Nunes]

It doesn't protect the cable per se but it can protect the numpty who drives a nail into it. The closer the CPC is to an energised conductor, the more likely that a nail that contacts the energised conductor will contact the CPC too, and hence trip the protection instead of just making the nail live. If you want full protection against that then the CPC needs to surround the other cores with enough CSA to take the hit e.g. Flexishield or SWA. But a fair percentage of T+E 'penetration incidents' probably benefit from the presence of the CPC.

 

[Ziggie]

It doesn't protect the cable per se but it can protect the numpty who drives a nail into it. The closer the CPC is to an energised conductor, the more likely that a nail that contacts the energised conductor will contact the CPC too, and hence trip the protection instead of just making the nail live. If you want full protection against that then the CPC needs to surround the other cores with enough CSA to take the hit e.g. Flexishield or SWA. But a fair percentage of T+E 'penetration incidents' probably benefit from the presence of the CPC.

I was beginning to think that the L and N cores should be wrapped in foil and hence protect from cable damage.This would act as a significant cross sectional area for a CPC.
If the main purpose is to provide an earth to the equipment, then putting on yellow /green cladding doesn’t add anything as it doesn’t cover the screw or clip attachment.
This borders on if you have a cable running to equipment that doesn’t use an earth (eg nest controller) , should one run a CPC to it. The normal answer is yes in case the next job is to replace the kit with something that needs an earth but I always thought that it was to give a little protection against the nail

 

[pc1966]

I was beginning to think that the L and N cores should be wrapped in foil and hence protect from cable damage.This would act as a significant cross sectional area for a CPC.

For cables that absolutely need such protection (e.g. non-RCD with risk of nail penetration, etc) you can get Flexishield cable as an intermediate between normal cables (T&E or 3-core, etc) and SWA with its physical protection as well.

Flexishield also seems to last well on farms, etc, according to a spark we have used who does a lot of industrial and agricultural work. Also they do a cat urine flavoured version specifically for that:

Flexishield R How It Works

Flexishield R How It Works

www.flexcables.co.uk

 

[jay sean]

when I was a apprentice in the late 90s, im sure there was a twin and earth were the earth was sleaved,

 

[Ziggie]

when I was a apprentice in the late 90s, im sure there was a twin and earth were the earth was sleaved,

This is common in Ireland.

 

[westward10]

when I was a apprentice in the late 90s, im sure there was a twin and earth were the earth was sleaved,

I remember working a site in the UK in the late 80s early 90s can't remember exactly but we installed a load of 1.5 with sleeved cpc, didn't take much notice at the time but all other sizes had bare cpcs.

 

[nicebutdim]

This is common in Ireland.

It wasn't in the 90s.

 

[LastManOnline]

but there is an argument in favour of least use of the Earth's resources which the RFC and T&E construction were originally driven by.

If so, then that is very noble.