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

needs to be greater than 3amp, it’s only a small Bluetooth amp, That's your answer then, you need a power supply that falls within that spec.

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!