Marcus Ting said:

My guess is that it is a minimum requirement to earth at 1 end for 1C SWA cables, where earthed at both ends are totally fine, Eg. cables for instruments are earthed at both ends due to highly sensitive equipment they have. 

1c SWA for single-core cables for AC circuits is NOT PERMITTED by BS 7671 (Regulation 521.5.2 of BS 7671). 1c AWA may, however, be used. The (very simple) reasoning is given in BS 7671.

Marcus Ting said:

In short, armoured cable earthing is to mitigate stray current induced within the cable, but we were told that rule of thumb practice (compliant to IEC) is that 3C SWA cables shall be earthed at both ends

Which "IEC" are you talking about (or if IEC 60364, which part and Clause?)

I can confirm that this statement is NOT ALWAYS the case for safety.

And for EMC (BS IEC 61000-5-2) whilst it is generally the case that earthing armour at both ends is better for EMC, there are cases where single-end earthing is best (or necessary for safety).

Marcus Ting said:

Why is 1C SWA cables earthed only at 1 end?

They can't be used for AC power circuits (see above); however, if we are talking about AWA power cables, Regulation 523.201 permits single-point (one end only, or one point only) or solid bonding (bonding at both ends)?

To conclude, it doesn't appear your information is 100 % correct? Perhaps you could provide some references to help guide us to the requirements you are looking at?

Marcus Ting said:

My guess is that it is a minimum requirement to earth at 1 end for 1C SWA cables, where earthed at both ends are totally fine, Eg. cables for instruments are earthed at both ends due to highly sensitive equipment they have. 

1c SWA for single-core cables for AC circuits is NOT PERMITTED by BS 7671 (Regulation 521.5.2 of BS 7671). 1c AWA may, however, be used. The (very simple) reasoning is given in BS 7671.

Marcus Ting said:

In short, armoured cable earthing is to mitigate stray current induced within the cable, but we were told that rule of thumb practice (compliant to IEC) is that 3C SWA cables shall be earthed at both ends

Which "IEC" are you talking about (or if IEC 60364, which part and Clause?)

I can confirm that this statement is NOT ALWAYS the case for safety.

And for EMC (BS IEC 61000-5-2) whilst it is generally the case that earthing armour at both ends is better for EMC, there are cases where single-end earthing is best (or necessary for safety).

Marcus Ting said:

Why is 1C SWA cables earthed only at 1 end?

They can't be used for AC power circuits (see above); however, if we are talking about AWA power cables, Regulation 523.201 permits single-point (one end only, or one point only) or solid bonding (bonding at both ends)?

To conclude, it doesn't appear your information is 100 % correct? Perhaps you could provide some references to help guide us to the requirements you are looking at?

Hi gkenyon, 

Appreciate your input, I wasn't precise on the armoured material when posting this thread, however I have changed to the actual armour spec we're using, Tinned Copper Wire Braid (TCWB) for both 1x3C and 3x1C copper cables.

I was referring to a design specification, and couldn't recall which one I've referred to. Now I was skimming through IEC61892-2 for that particular statement just fyi. 

However, I have found in IEC60092-352 that mentions a special precautions on using non-mag material, but it only mentions about earthing the metallic screening at one point, not the amouring.

I don't think that in IEC60364 will be highlighting such requirement. But truly appreciate you highlighting BS 7671, perhaps I would take a look at it to see if AWA does the similar practice, which i think would be unlikely. 

Marcus Ting said:

Tinned Copper Wire Braid (TCWB) for both 1x3C and 3x1C copper cables.

TCWB is more problematic because the braid is not necessarily specified to take full fault current if we are talking about power cables. It is the common approach in the EU and UK (where this is used, called SY cable) to use the braid as EMC screen, and an internal protective conductor.

For EMC purposes, BS IEC 61000-5-2 recommends bonding at both ends where at all possible, and in the general case, with 360 degree terminator gland of the correct type, but under some conditions, one end only is permitted (to prevent circulating currents etc.).

You need to be careful about inductance of single-core cables even if you are not using braid as a protective conductor.

I think IEC 61000-5-2 is what you're looking for in this case ?

Marcus Ting said:

I don't think that in IEC60364 will be highlighting such requirement. But truly appreciate you highlighting BS 7671, perhaps I would take a look at it to see if AWA does the similar practice, which i think would be unlikely. 

IEC 60364-5-52 has the same requirement... see 521.5.2 of IEC 60364-5-52 which is (bar minor wording international English to UK English) identical to Regulation 521.5.2 in BS 7671.

This is no surprise, because BS 7671 is the UK implementation of HD 60364 series, which in turn implements IEC 60364 series in CENELEC countries.