Are there any consumer units that have 3 bus bars?

[ericmark]

I seem to remember the telemecanique distribution boards had a central neutral and the sandwich of MCB and the converter module which made them into RCBO's did take the neutral from the central point.

However the number of units taken for each device were twice that taken in a consumer unit and it was not type tested like the consumer unit so not suitable for use in a domestic premises.

I would not really want a box that size in my house think it was called Vigi or something like that. Also rather expensive.

 

[JohnW2]

I seem to remember the telemecanique distribution boards had a central neutral and the sandwich of MCB and the converter module which made them into RCBO's did take the neutral from the central point. ... However the number of units taken for each device were twice that taken in a consumer unit and it was not type tested like the consumer unit so not suitable for use in a domestic premises.

BS7671 does define a Consumer Unit as a 'type-tested' distribution board (for use "principally in domestic premises"), but I am not aware of any requirement that domestic installations have to have them (i.e. that non-type-testsed DBs are 'not suitable for use in domestic premises'). Am I missing some regulation(s)?

Kind Regards, John

 

[ban-all-sheds]

AIUI there's an exemption for "official" consumer units from the requirement for the MCBs to have an Icn > PFC when used downstream of a BS1361 fuse of not more than 100A.

 

[JohnW2]

AIUI there's an exemption for "official" consumer units from the requirement for the MCBs to have an Icn > PFC when used downstream of a BS1361 fuse of not more than 100A.

That rings a vague bell. However, as far as I can make out, particularly outside of London, it's going to be pretty (very?) rare for a domestic PFC to be anything like as high as the Icn of even the most modest of MCBs, anyway, so I suspect that it's an 'exemption' that will very rarely be of any relevance.

Kind Regards, John

 

[ldoodle]

Can somebody describe what this means in aesthetics terms.

I am considering a CU change and was planning to go all RCBO. I don't have the luxury of having my CU in a garage so aesthetics is quite important.

I had in mind keeping the 6 current circuits as is and adding 2 more if that makes a difference:

1x 32 radial (cooker)
3x 32 ring finals
3x 6 lighting radials (one new going to shed)
1x new 20 radial for shed sockets

But I would consider splitting 2 of the 32 ring finals to 4 20 radials; one of the 32 rings supplies sockets and fcus in the kitchen so I could split sockets and fcus. Another 32 ring supplies upstairs and the loft so could split them too.

Thanks

 

[JohnW2]

Can somebody describe what this means in aesthetics terms. ... I am considering a CU change and was planning to go all RCBO. I don't have the luxury of having my CU in a garage so aesthetics is quite important.

What are you asking - which CU is the 'prettiest' (which is obviously somewhat subjective)? It would seem that what you propose would require a DB with between 8 and 11 available 'ways' for RCBOs, which is certainly do-able.

Kind Regards, John

 

[ban-all-sheds]

I don't have the luxury of having my CU in a garage so aesthetics is quite important.

Would the wall it's going on be suitable for a flush unit?

 

[AndyPRK]

Normally a shed would only take up one circuit.

In the shed you would either have a 2 way cu with rcd
Or a 3a fused switch spur for the lights.

 

[ban-all-sheds]

Normally a shed would only take up one circuit.

Missed that.



Ideally a shed should not be supplied from the house CU at all.

 

[ldoodle]

I don't have the luxury of having my CU in a garage so aesthetics is quite important.

Would the wall it's going on be suitable for a flush unit?

It's the inner leaf of an external wall. So would depend on the cut out required to make it flush.

 

[ldoodle]

Normally a shed would only take up one circuit.

In the shed you would either have a 2 way cu with rcd
Or a 3a fused switch spur for the lights.

I'm not a fan of the latter option (fcu). I think lights should be on a 'lighting' circuit.

But I take your point about having a dedicated CU in the shed, which I am assuming is what b-a-s is referring to.

That would, overall, require 1 more RCBO ( for the house CU ) plus another CU?

The 2 other RCBOs originally going in the house CU would go in the shed CU?

 

[ldoodle]

Ideally a shed should not be supplied from the house CU at all.

Actually, I don't think that's what you meant.

What is the best way then?

 

[JohnW2]

Normally a shed would only take up one circuit. ... In the shed you would either have a 2 way cu with rcd ... Or a 3a fused switch spur for the lights.

I'm not a fan of the latter option (fcu). I think lights should be on a 'lighting' circuit. ... But I take your point about having a dedicated CU in the shed, which I am assuming is what b-a-s is referring to. ... That would, overall, require 1 more RCBO ( for the house CU ) plus another CU? ... The 2 other RCBOs originally going in the house CU would go in the shed CU?

If you transferred the two RCBOs (one for lighting, one for sockets) into a garage CU, the feed from the house CU could (would better be) protected by just an MCB (i.e. not an RCBO or RCD), so that faults on the garage lighting circuit or sockets circuit would not take bothe circuits out. However, that's only possible if the nature and routing of all cable from house CU to garage CU was suitable for not having RCD protection (e.g. SWA all the way, or surface T+E connected to SWA).

However, with that system an overload or L-E fault on either of the garage circuits could well take out the house MCB (hence both garage circuits), unless you were able to achieve reasonable discrimination between house MCB and garage RCBOs (which may not be easy).

Kind Regards, John

 

[JohnW2]

Ideally a shed should not be supplied from the house CU at all.

Actually, I don't think that's what you meant. What is the best way then?

I think it probably was what he meant. The 'ideal' is for a CU in the outbuilding to be fed independently from the house installation (i.e. split the house supply prior to house CU), protected by a switch-fuse at the supply end. That makes the outhouse installation totally independent of the house one - but it is probably a bit OTT for the very modest supply requirements of the average garage or shed.

Kind Regards, John

 

[ldoodle]

However, that's only possible if the nature and routing of all cable from house CU to garage CU was suitable for not having RCD protection (e.g. SWA all the way, or surface T+E connected to SWA).

My shed 'backs' on to the wall where the CU is (with a gap of about 1.5m), so I had in mind to go straight out the back of the CU with T+E, then transition to SWA in a conduit box (http://www.tlc-direct.co.uk/Images/Products/size_3/CO20BX1.JPG), go down the wall, under the patio (can lift slabs and make a trench), then in through the bottom of the shed.

If SWA could bend 90 degrees could do away with the transition from T+E altogether!

Can a CU take SWA directly or would you need to transition back to T+E.

PS: Not doing any of this myself (well I may route the SWA).