Connection a junction box to a 10mm ring

[crystal ball]

there is also the henly block but i didn't want to mention it

What is a "henly block"

 

[andy]

large junction box, designed for high currents (e.g splittint meter tails to 2 CU's etc

 

[mildmanneredjanitor]

[code:1]
===10mm²====[JB]====10mm²====[CCU]==={HOB}
||
||10mm²
||
[FCU]------1.5mm²-----{Oven}[/code:1]

That would also give you separate isolation

Shouldn't that be 2.5mm² after the FCU?

 

[ban-all-sheds]

What is a "henly block"

Bottom photo shows the inside of a single-pole one. You can also get DP versions (top).

 

[ban-all-sheds]

Shouldn't that be 2.5mm² after the FCU?

It's only got to carry 13A. 1.0mm² would do....

 

[jcdotcom]

Many people must be faced with the same dilemma these days, going from the huge old cooker to separate hob and oven. Although you can usually put the oven on a ring main (if it's a single) it seems you guys think it better not to do this. Taking a (an?) fcu from the existing cooker supply cable sounds like a good idea, if the original cable is big enough.

Starter question is, is this something that is or is not acceptable, or is it something that n electricians will have n+1 opinions over.

and for a bonus - the circuit diagram provided by B-A-S has 10mm2 between the JB and the FCU. If the fcu is fused at 13A, why can't you use 2.5mm2

 

[Diyisfun]

This is what I did..
From cooker switch took cable to the terminal block (that is designed for oven connection), from here I ran 2 cables 1 for the hob another for the oven.

When I was in domestic appliance development many many years ago the practice was to run the wire to the hob unit then link the hob to the oven. That was in the installation leaflet.


ps
My hob unit was supplied fitted with a cable, instruction said not to remove, as it was a few feet short I connected this to a 30amp inline connector.

 

[mildmanneredjanitor]

and for a bonus - the circuit diagram provided by B-A-S has 10mm2 between the JB and the FCU. If the fcu is fused at 13A, why can't you use 2.5mm2

Because you can't mix cables of a different capacity on the same circuit.

Tis the same for say spurring a fused connection unit to a ring, 2.5mm should be used. The (smaller) cable used after the FCU is irrevelent. The fuse/MCB (or whatever) at the consumer unit is there to protect the cable connected to that circuit, the FCU then provides (reduced capacity) load protection for the cable thereafter.

I'm sure one of the experts will correct me if I'm wrong here...

Someday, someone will come up with a small consumer unit (like the sort used for garages/outbuilding) suitable for oven installations - which can be changed as per requirements change, that can cope with large cable sizes easily.

 

[plugwash]

why do you need anything special?

garage CUs are just normal ip rated CUs fitted out with a couple of small breakers theres nothing special about them.

 

[Canny]

Because you can't mix cables of a different capacity on the same circuit.

Does this work both ways? Is it acceptable for example to replace/alter part of a lighting circuit wired in 1.0mm T&E with 1.5mm T&E? I would have thought using cable above that required wouldn't cause problems but am I missing something here?

 

[plugwash]

there is some serious misonformation being spread here

there is nothing wrong with mixing cable sizes in a cuircuit (and with very long runs you often have little choice because of volt drop and terminal size issues)

using cables with ratings below the current rating of the cuircuit is a different matter. Its generally considered best not to but provided the short cuircuit protection upstream is adequte and there is suitable overcurrent protection downstream it is ok.

look at your spurs from rings (protection from the plug fuse for the spur)

or look at your service cable

both examples of where it is considered perfectly normal to have the overcurrent protection at the load end

Lectrician posted a while back that he knew of a spark who failed two hand driers run with seperate runs of 2.5mm from a 32A breaker to individual fcus. niceic OVERRULED and said it was fine

 

[mildmanneredjanitor]

Does this work both ways? Is it acceptable for example to replace/alter part of a lighting circuit wired in 1.0mm T&E with 1.5mm T&E? I would have thought using cable above that required wouldn't cause problems but am I missing something here?

No it isn't.

A chain is only as strong as the weakest link...

What if at a later date, you (or someone else) connected an appliance to that cable assuming that it was of the correct rating??? Which it wouldn't of course, as it is connected to a cable of a lower rating.

I'm sure there are technical reasons against this also... Maybe to do with resistance differences...?

Like I said before, I'm no expert. But the more I learn, the more I realise I don't know...

 

[mildmanneredjanitor]

why do you need anything special?

garage CUs are just normal ip rated CUs fitted out with a couple of small breakers theres nothing special about them.

I'm just saying that there doesn't appear to be anything available to overcome the problem of connecting two seperate cooking devices neatly.

A second set of terminals in cooker connection units would suffice maybe?

 

[plugwash]

Does this work both ways? Is it acceptable for example to replace/alter part of a lighting circuit wired in 1.0mm T&E with 1.5mm T&E? I would have thought using cable above that required wouldn't cause problems but am I missing something here?

No it isn't.

A chain is only as strong as the weakest link...

What if at a later date, you (or someone else) connected an appliance to that cable assuming that it was of the correct rating??? Which it wouldn't of course, as it is connected to a cable of a lower rating.

thats one of the reasons we have overload protection. If people chance the overload protection without proper information on the cuircuits structure thats not the installers problem.

face it you can't reasonablly protect your installation against an idiot with a toolkit.

I'm sure there are technical reasons against this also... Maybe to do with resistance differences...?

from a resistance point of view an oversized cable would be just the same as a shorter run of the normal sized cable.

EDIT: i said longer when i meant shorter correction in bold

 

[mildmanneredjanitor]

I think I might just shut up and go to bed...