falling foul of 'maintenance free' derating

The assumption is that the maintainence free location needs to run cooler, as it may well be buried deeper in the building fabric, and also that degradation or smell of hot insulation is less likely to be spotted early. Hence the calculation in effect looks at all the heat sources in the box - which is why we have the aggregate current thing.

I also think the MF ratings are quite conservative.

I spoke to an engineer (who apparently has something to do with the design of the connectors, etc) about this last year, and he said aggregate thing is really simple, once you know how to apply it (re Wago connectors, that is). Basically, count the load in each L and N conductor in the MF box, and add them together, and ensure they don't exceed 50amps. For example, for a 32amp RFC, if the box had the leg in and the leg out (i.e. you've cut into a leg), assume 16A in each L and N conductor that you're joining together (the other leg would that you've not touched would carry the other half 16/32A), so the total would be 32A in the box; which is below the allowable 50A maximum. That's why you can have one leg through the box (equalling 32A) but not two legs in the box, which would equal 64A.  


I've attached some documents which detail what you can do with ring and radial ccts, and some other stuff.


Hope this helps


F

I think that you also need to put Wago connectors in a Wago box, etc.

They aren’t actually made by the same company, are they?

Thank you everybody !


@Farmboy - thanks for the attached info as well.


@Mapj - do you mean that its the BS std that 'forces' the derating or is it a manufacturer thing - because and do correct if needed, the Ashley-Hager j803 read as if they are better rated than the Wago/Ideal type approach (though I may be wrong again).  Moreover, imagine an MF approach of this type under a bare wood floor that leaves a screwed down 'hatch' (not quite but you get the idea). This would be reasonably 'accessible' and therefore can run at the full up current carrying capacity the manufacturer specs.  Later on (or as an alternative scenario from the outset), down goes some laminate or glued flooring making the setup reasonably considered 'inaccessible' but that's ok, 'you' used an MF approach...but oh wait, its maybe now 'not compliant' (bit severe assessment I know), in that suddenly one has to think about the [daft?] implication derating from the BS Std. and the manufacturer instructions for use !   To me its the same install situation considering environment factors and electrical stuff, same components etc. Hence my question, is the derating there just in case of worst scenario/leaving margins etc and to not allow judgement for scenarios as described (if my scenario holds water hehe )?


edit: missed a bit....  Or maybe it is because there is nervousness from whoever, about it being inaccessible so better have a safety margin just in case; it can run full up so long as you can get to it, but if you cant get to it, just in case, it has to be derated, (even though electrically it is fine).

brief update - following some protracted discussion via email and trying to confirm the situation with Ideal Induestries In-sure  box and pushfit/lever connectors (similar to Wago - and I suppose the Ashley-Hager box), it would appear that there are some limitations on use when in an inaccessible location...to the point that they dont advise using their connectors in their box to join for example, a broken leg of a ring final circuit. The deratings they detail on their products in relation to BS5733 seem much more severe than others'  (but correct me if I'm wrong).