Install/re-furb chicken hatchery

[just add water sparks]

Just have a temporary assignment at a chicken hatchery for a few months rubbish money but home by 3-30pm not much about anyway.Came across an installation that was fairly old and cable sizing is not right.A 3phase supply comes from a 32amp type 4 merlin gerin mcb wired in what looks like 10mm2 to a isolator 10metres away.From the isolator it goes to a contactor then to a din rail with connecter blocks.From the connector block it serves 12 6amp mcb's " in 1.5mm each radially fed i.e one 1.5 for each mcb and has not fused down also feeds a few other mcb;s relays heliwell temp guages not any high loading but obviously.So basically the 1.5 is only a short length of about 8" or so.Normally this would have been fed from the 10mm2 by a correctly rated bus bar.I know its not right but just wondered as the 1.5mm2 was such a short distance would this be o.k Thinking of similar examples unfused radial 2.5 spurs on ring mains which are 32amp mcb's ,I know effectivley the main loading is on a ring but it does eventually spur off and reduce to a radial 2.5 sized cable???? YOUR THOUGHTS would be grately appreciated

 

[Sintra]

If i am reading your post correctly this would be fine according to reg 433.3.1 p74.

 

[Guest123]

Agreed.

 

[Adam W]

Knew it was around there somewhere - 434.2.1; basically you can reduce the csa of the cable if it doesn't exceed 3m in length.

 

[just add water sparks]

Many thanks sintra you are right mate and quoted regs no. but i must be missing something as i still cant get my head around it effectively the 1.5mm2 albeit short length is protected by a 32amp fuse and generally 1.5mm2 takes around 15.5amps what am i missing????

 

[Sintra]

You are missing the bit that the 1.5mm is supplying a 6A mcb so the cable can not overload as it is limited to the 6A of the mcb.

 

[just add water sparks]

nice one too! Novus have seen this done before with 6mm feeding a hob then a radial from leg of hob into 2.5 feeding oven never seemed right but always wondered how they got away with it Thanks.Wondering how common practice this is really

 

[Adam W]

I was sold the idea as being like using a thin bit of flex on a lighting pendant.

 

[mechelec]

I was sold the idea as being like using a thin bit of flex on a lighting pendant.

yes that is a reduction in the current carrying capacity but i cannot see how how it is protected against overload as in the op's example, you could overload the flex in the event of a fault with the lamp or holder.

 

[Adam W]

... you could overload the flex in the event of a fault with the lamp or holder.

Really?

 

[mechelec]

theoretically yes although not very likely i admit