Can the shield of a cable be used as a protective bonding conductor?

[JamesB87]

I'm working on a test equipment design that needs to comply with IEC 61010-1 and IEC 60950-1 among others. It needs to have protective earthing.

This product is powered by an external class I AC/DC converter, providing nominal 12 volts at 1 amp max. We would like to use the shield of the power supply output cable as the protective earth conductor. The shield combined with our chosen connector easily meets the 0.1 ohm requirement, and our tests have shown they can also survive the 40a for 2 minutes required by 60950.

However, 61010-1, 6.5.2.2 f) states that "The exterior metal braid of cables shall not be regarded as PROTECTIVE BONDING...".

I at first took this to mean/include the braided shield of any cable, e.g. the braided shield of RG58 coax. But I'm now wondering about the word "external". I'm thinking that what they are referring to here is something like the metal braid sometimes used for physical protection of cables in industrial environments (attached photo). Technically, since the shield of our power supply cable has a layer of PVC around it, it would seem to be internal rather than external.

Has anyone come across this issue during compliance testing?

 

[JamesB87]

Does anyone have any experience or opinion about this?

 

[Marc]

I don't have experience in that area with those standards, so I can't help. It may be that no one visiting here knows. Sorry, but unfortunately some questions can't be answered here.

I have seen cables with a braided cord, but not for a long time other than in some residential/industrial wiring, but even there typically there is some sort of "plastic" (or vinyl of such) coating.