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Posted By Topic: 5.5.2.2.1 Taking earth's from other cables

OctaneOutlaw
Mar 08 2020 12:35

"5.5.2.2.1 Circuits
The protective earthing conductor for a circuit that is incorporated in the
same cable sheath or wiring enclosure as the associated live conductors for
the circuit shall only be used for the earthing of equipment supplied from
the circuit.
Exception: This does not preclude an unenclosed common protective
earthing conductor being used for a number of different circuits."

Just want to get confirmation, I understand you can't take an earth from another circuits PEC but is this saying that provided the items are on the same FSC that the earth may come from any point on that FSC?

Or is it saying that if you use the PEC from another cable that the item your using it for must be downstream of the associated active and neutral conductors in that specific cable you take it from?
   

DougP
Mar 08 2020 14:32

The exception:
"Exception: This does not preclude an unenclosed common protective earthing conductor being used for a number of different circuits."

It is saying that you can have a common earthing conductor for multiple circuits. It would run from the earth bar, to wherever it was needed. So you could loop it around lights that need earthing for example.

The minimum size of that earth conductor is 2.5mm2. 5.3.3.4(a) and table 5.1

You really have to read all parts of 5.5.2 together, including the exceptions, rather than just picking out one sub clause.
   

OctaneOutlaw
Mar 08 2020 15:18

Apologies, I think I've worded this wrong

Let's say for example I have a light that needs an earth, supplied by a 2c cable

I have another light on the same circuit with 2c+e

Can I take an earth from this 2c+e to this light fitting?
   

DougP
Mar 08 2020 15:48

Yes. Minimum 2.5mm2.

   

OctaneOutlaw
Mar 08 2020 19:18

Yeah I always knew the 2.5 minimum size and oh right, I think I got mixed up initially because I thought the wording was a PEC in a cable could only be used to earth equipment supplied by the actives and neutral in that cable but it's actually supplied by actives and neutral from the same circuit isn't it
   

DougP
Mar 08 2020 21:10

Yes it's for the circuit. It's so that if a circuit is removed or modified, you don't inadvertently disconnect an earth for something connected to a different circuit.