This discussion is locked.

You cannot post a reply to this discussion. If you have a question start a new discussion

OSG 7.3.2 cables in walls and partitions

In the above,item d states the cables can be protected by earthed steel conduit or,

Item e then states :mechanical protection sufficient to prevent penetration of nails,etc,

but no mention of earthing..

I have a situation with a short 200mm horizontal run outside the zones.

I could slide a lenght of earthed conduit over,but then the earth connection would be plastered

over and could not be inspected.

If I treat the conduit as mechanical protection,it would not need earthing?

Wondered what others would do.

Regards,Hz

0 gkenyon over 4 years ago

AJJewsbury:

For example, from Eland:

Protective devices used for these cables shall be either Type B to BS EN 60898 or Type B RCBO to BS EN 61009-1. The protective devices shall have a maximum let through energy (l2t) of 42000A2s when used with 1.0mm2 or 1.5mm2 cable and 60000 A2s when used with 2.5mm2 or 4.0mm2 cable.

Whereas the k²S² for a 1mm² c.p.c. (as in 1.0mm² and 1.5mm² T&E) would be just 13,225A²s and a a 1.5mm² c.p.c. (as in 2.5mm² and 4mm² T&E) would be just 29,756.25A²s.

- Andy.

Definitely ... scarily, these are far below the maximum energy let-through stated in BS EN 60898 / BS EN 61009 for 6 kA breakers .... leading to a minimum csa of 2.5 mm² ! (see Table 8.4 of the IET's Electrical Installation Design Guide).

Does this mean you can't use 6 kA fault level mcb's to protect most circuits in dwellings??

No ... manufacturers' quoted values need to be used, as these are much less ... see Table 8.5 in EIDG. But it does mean you shouldn't simply assume that any and every 6 kA fault-level breaker to EN 60898, EN 61009 or EN 60947 will be suitable for use with a particular cpc, particularly the 1.0 mm² and 1.5 mm² reduced cpc's in T&E.
Cancel
Vote Up 0 Vote Down

Cancel

OSG 7.3.2 cables in walls and partitions

Join us to get the best from IET EngX.

Community Rules & Guidelines