Junction box

[daveparker10]

Hi,

Is it ok to have 5 cables coming out of a domestic 20 amp 4 terminal junction box? They will be powering lights and a bathroom fan, via the correct isolators and switches.

Thanks

 

[OwainDIYer]

if there's enough room in the cover slots and the cables aren't getting chafed.

 

[JohnW2]

I'm sure it's been done (I've probably done it!), but it will certainly get pretty crowded. The greatest problem would probably be in getting the required number of conductors satisfactorily terminated in some of the terminals - particularly the CPCs/earths (of which you will presumably have five) - it may be difficult to get them satisfactorily into a terminal, and you would probably be exceeding the manufacturer's specified (if they did specify!) 'maximum capacity' of the terminals. A bit of connector block, or Wago connectors, within a suitable enclosure might be a better approach.

Kind Regards, John

 

[leeco]

I have spent all day ripping out junction boxes some with 8 wires in this guys loft.

 

[sparkwright]

8 cables in a 20 amp junction box is the most I've ever done (successfully I should add), and ever will.

 

[leeco]

When I go in a loft and see junction boxes I love it because all the wire been wasted.

I'll just wire up the lights without them and take all your wire.

 

[JohnW2]

8 cables in a 20 amp junction box is the most I've ever done (successfully I should add), and ever will.

How many 1.0/1.5mm² conductors do you reckon you can get into one terminal of a 20A JB? Presumably there would (should!) be eight 1mm² CPCs if there were 8 cables - do you reckon you could get all of them into one '20A' terminal (satisfactorily, or at all)?

Kind Regards, John

 

[daveparker10]

Ok thanks for the replies. I was thinking of that myself john buying a box and using some terminal strips. As like u say will give me more room and it does say on the jb about only taking 4 cables.

 

[JohnW2]

Ok thanks for the replies. I was thinking of that myself john buying a box and using some terminal strips. As like u say will give me more room and it does say on the jb about only taking 4 cables.

FWIW, that's probably what I would do - certainly if there were more than 5 cables, and quite possible with 5 (which I reckon is pretty marginal). The '4 cables max' on the JB probably relates primarily to the number of cable entries - but, as I've said, I'm also at little uneasy about trying to get more than four conductors into one "20A" terminal.

Kind Regards, John

 

[sparkwright]

8 cables in a 20 amp junction box is the most I've ever done (successfully I should add), and ever will.

How many 1.0/1.5mm² conductors do you reckon you can get into one terminal of a 20A JB? Presumably there would (should!) be eight 1mm² CPCs if there were 8 cables - do you reckon you could get all of them into one '20A' terminal (satisfactorily, or at all)?

Kind Regards, John

8.

This was eight 1.0 mm2 twin and earth cables going into a large round 20 amp 4 terminal Ashley junction box.

Only three terminals used - just L, N, E.

Seem to recall this was a rare instance where I put two bare earths in one earth sleeve, to save room.

There was a lot of putting some wires in the terminal, tightening it down a bit, then undo it a bit, then put more wires in.

Helps if all the conductors are the same length, which is what I always do. Can't understand why some electricians cut the wires to different lengths, also can't work out why they do some wires to 'dead length', which makes re-terminating impossible.

Don't know if more than eight would fit. Would anticipate problems trying to cram more in. I think any more than eight would be really ridiculous.

 

[JohnW2]

How many 1.0/1.5mm² conductors do you reckon you can get into one terminal of a 20A JB? Presumably there would (should!) be eight 1mm² CPCs if there were 8 cables - do you reckon you could get all of them into one '20A' terminal (satisfactorily, or at all)?

8. This was eight 1.0 mm2 twin and earth cables going into a large round 20 amp 4 terminal Ashley junction box. ... There was a lot of putting some wires in the terminal, tightening it down a bit, then undo it a bit, then put more wires in.

Interesting. I'm not sure I would dare try I've certainly done five in my time, and possibly six, but I really don't think I'd be inclined to try any further than that!

As a matter of interest, how many 2.5mm² conductors do you reckon you can get into the terminal of a standard round 30A JB?

Kind Regards, John

 

[sparkwright]

Never tried it, but I wouldn't do more than four.

Somehow any more just doesn't feel right.

I think a lot of junction boxes do have some cable capacities printed on them, but it never seems relevent to the cables I'm using.

 

[JohnW2]

Never tried it, but I wouldn't do more than four. Somehow any more just doesn't feel right. I think a lot of junction boxes do have some cable capacities printed on them, but it never seems relevent to the cables I'm using.

The only 30A ones I can find which have explicit capacities on them say "4 x 4mm²" (others just say "4mm²") - which might imply that one could probably get away with appreciably more than four 2.5mm² ones. However, I imagine it would be pretty rare to want/need more than four in a JB. Mind you, in terms of terminal capacity, one ought to be able to get plenty of 1mm² conductors into one of them (albeit they're nearly all only 3-terminal, which often won't be enough on lighting circuits), provided they all kept still whilst one was tightening the screw!!

Kind Regards, John

 

[OwainDIYer]

I take the screw out of the slotted terminal type, lay the wires in the slot, then put the screw back in. The wires seem easier to hold in place that way and not pop out unexpectedly.

 

[JohnW2]

I take the screw out of the slotted terminal type, lay the wires in the slot, then put the screw back in. The wires seem easier to hold in place that way and not pop out unexpectedly.

That's what I usually do - but that doesn't always stop some 'popping' out for me, if there are lots of them! Another issue, eluded to by sparkwright, is that, if there are a lot of conductors, one usually has to leave a significant amount of bare copper showing, since umpteen conductors complete with insulation right up to the terminal can be a 'crowding' problem.

Kind Regards, John