16A MCB for a Ring Main

[MHK]

Howdy

I've come accross a situation where 16A MCB have been specified for ring circuits. The rings serve socket outlets having looked through the regulations I have been unable to locate any specific requirement stating that they can not be used, however, I would be grateful for some alternative views!

Many thanks in advance

 

[Octopus]

Why can't you use 16A MCB's? What size of cable has been specified? Sounds to me like a typing error.

 

[MHK]

The query wasn't necessarily as to whether you can or can't use 16A rings. There are approximately 200 ring circuits specified on 4.0 XLPE/LSF singles protected by 16A MCB breakers. I could understand if the intention was to reduce cable sizes by reducing the breaking capacity, however, this is not the case. I can really understand the benefit of wiring in this way?

 

[not clever]

Nothing wrong with using 16A ocpd for a ring final & you'll not find anything in the regs that says otherwise.
How big/long are the rings & what is the customer use.

 

[MarkieSparkie]

The most likely reasons for the specification of 4mm[SUP]2[/SUP] XLPE (90 degree C operating temperature) and 16A MCB is this cable and it's protective device has been downrated because the cable is run through significant amounts of thermal insulation and/or areas of high ambient temperature and/or large number of cables grouped together.