Twin and Earth CPC

[Cookie]

IEC 60364-5-54 states that phase conductors 16mm2 and smaller require a CPC of the same size, over 16 to 35mm2 a 16mm2 CPC and over 35mm2 a half size CPC is required.

My questions is why am I seeing catalogs with harmonized twin and earth with reduced size CPCs over 2.5mm2? And why doesn't the half size rule kick in when wire is over 4mm2 instead of 16mm2?

 

[Ian1981]

A cpc can be either sized to table 54.7 in bs7671 or calculated using the adiabatic equation. An equal sized cpc to the line conductors is rarely required, especially when current limiting ocpd’s such circuit breakers and fuses are used.
I believe in Ireland, the twin and cpc cables have equal sized conductors as is now required by their regulations.
Only 1mm2 twin and earth has the same sized cpc, 1.5 has a 1mm cpc, 2.5 a 1.5 mm cpc, 4mm a 1.5mm cpc, 6mm a 2.5mm cpc ,10mm a 4mm cpc and 16mm a 6mm cpc.

 

[Cookie]

Interesting way of doing it. Why do some countries use a full size CPC others go one or two sizes smaller?

 

[telectrix]

Interesting way of doing it. Why do some countries use a full size CPC others go one or two sizes smaller?

simpless , ,saves money.

 

[GBDamo]

Interesting way of doing it. Why do some countries use a full size CPC others go one or two sizes smaller?

Different electricity, I think.

As soon as all our Chinese nukes are online we will have to revisit our CPC requirements and bring them in line with Chinese regs, I think.

 

[Ian1981]

Interesting way of doing it. Why do some countries use a full size CPC others go one or two sizes smaller?

The only reason I can think is cost to manufacture the cable, as the regulations don’t bound you to use a cpc the same size, it’s not required to produce twin and cpc cables that have conductors all the same size.

 

[freddo]

I do like the Ireland cable as their CPCs are also insulated.

 

[Risteard]

I believe in Ireland, the twin and cpc cables have equal sized conductors as is now required by their regulations.

5th September 2017 was the cut-off date for the old-style T&E. (It should be noted that there weren't identical cpc sizes to British Standard cable before that, however. As an example 16mm^2 T&E had to have a 10mm^2 (rather than 6mm^2) cpc; 10mm^2 had a 6mm^2 (not 4mm^2) cpc etc.)

 

[davesparks]

Interesting way of doing it. Why do some countries use a full size CPC others go one or two sizes smaller?

Because some countries like to waste the rapidly dwindling natural resources of this planet.
Or maybe they just don't trust the people installing the cables to understand the relatively simple calculations required.

 

[Lucien Nunes]

I think the only types of general light duty installation cable that have a bare CPC are UK T+E and USA NM and their derivatives, of which the NM has equal CPC but T+E CPC is reduced above 1.0mm². I think I have seen a couple of types of reduced, bare CPC T+E of indeterminate origin in North Africa with an approximation to US colours, but it might have been equal.

Australian TPS, Russian ВВГ-Пнг and its derivatives, and all the common European circular cables like NYM-J and KH05-VV, and other kinds of flat cable such as NYIF share with the Irish cable the equal-sized, insulated CPC.

There are probably many historical factors that led to the present-day choice of round vs. flat, bare vs. insulated, equal vs. reduced CPC; just as there are with choices of voltage, frequency, plug designs etc. So I don't think it's as clearcut as one country having a 'better' cable specification than another through engineering design alone.

 

[Cookie]

US NM-B has a full size CPC for 2.08mm2, 3.31mm2 and 5.26mm2 live and neutral.

https://www.mysouthwire.com/medias/Romex-Brand-SIMpull-Type-NM-B-Cable.pdf?context=bWFzdGVyfHByb2R1Y3Qtc3BlY2lmaWNhdGlvbnN8MjAxMDc2fGFwcGxpY2F0aW9uL3BkZnxwcm9kdWN0LXNwZWNpZmljYXRpb25zL2g3Ny9oZmMvODg1NDA4MzY5ODcxOC5wZGZ8MDYyMjJiYjAyZWRiZDM2MWEyNGI2YjUyNmFjYzEyNDIyMzIzZmI2ZTZjYWE1N2VmNTFiZWYzNWNjNTJjY2FiOA

Here is the Canadian version, reduced size CPC for 12 and 10 gauge live and neutral:

https://www.mysouthwire.com/medias/...2JiNDI0NDZkYTc0MzM1MDUwNzc4Y2M2ZjgwOGQ3M2JkNg

The thing is the IEC-60364 seems to be most conservative in that they advocate for a full size CPC all the way up to 16mm2... something that I don't think any country does except those that use 60364 without amending it.

 

[Mark Wright]

We choose cost over safety we then have to waste time doing doing direct Zs tests etc to make sure the CPC is satisfactory.

There is a youtube video about adiabatic equation, think it's Italian.

 

[Cookie]

The adiabatic equation is scary to be honest... I thought 2.08mm2 on a 40 amp breaker wad bad The IEC seems to insinuate its better for TT earthing. And I could understand that, especially since TT earthing tends to be used in developing countries where cost is critical.

I'm trying to find the k factor for AWG wire sizes just so I can compare our CPCs.

 

[davesparks]

We choose cost over safety we then have to waste time doing doing direct Zs tests etc to make sure the CPC is satisfactory.

There is a youtube video about adiabatic equation, think it's Italian.

Why do you think Zs testing is a waste of time?
Whatever size CPC you install it is still an essential test to confirm the requirements of ADS have been met.

 

[Mark Wright]

Why do you think Zs testing is a waste of time?
Whatever size CPC you install it is still an essential test to confirm the requirements of ADS have been met.

Waste time was a bit harsh but the money we save will eventually be lost to testing, where as if we used the same size CPC we would only need to test PEFC/Ze at origin like we do PSCC.