Should I install a PEN monitoring device on a problematic outside light?

Question:

The customer wanted an industrial type of installation for outside lights. The metal conduit is low level 2 meters and in reach.

The supply is fused from the kitchen ring RCD protected via a swa to a metal box containing the terminals for the lights and motion detectors.

During testing it was discovered that the lead sheath had a break and the DNO converted the earthing to PME. I've now exported a PME outside, although it is not a sub main and just an extension of the kitchen ring.

My question, how would you resolve this issue, should I install a PEN monitoring device. What guidance does BS7671 offer.

Thanks

Stuart

Answer: 

Hi there.  There is nothing in BS 7671 that stipulates you cannot have metallic conduit outside on a PME system.  There is a risk of a broken PEN, of course, but this is little difference here to an outside light on a house wall.

However, if you feel there is an increased risk then you can, if you wish, install a monitiroing type device, though this would be optional.

Many TN-S systems are hybrids, they have been repaired over the years and have an element of TN-C-S within them.

- Gary Parker, ECA

Gary holds a Bachelor of Engineering Degree in Electrical & Electronic Engineering along with numerous years of experience across many aspects of the electrical industry.