20A Fused Switch or DIN mounted 20A RCBO

[iclegg]

Hi,

My central heating wiring centre (Honeywell S Plan) is hanging off a 13a plug in the garage which is plugged into a double gang socket with integrated RCD at waist height close to where I would to fit a sink.

I'd like to move the wiring centre much higher up the wall so it is out of the way and free up the socket, perhaps having it wired into a 20A Fused DP Switch. But, while I am at it I was planning on having two new 3kw immersion heaters wired up as well. I have a spare 32A MCB in the CU about 4 metres way. I would like the immersion heaters to be switched on/off from another control system which can supply a 240V ac signal (obviously not suitable to drive the heaters though).

I would end up with quite a few fused switches and I'd need to house some relays.

Would a DIN enclosure with 3 x 20A RCBO's for the two heaters and wiring centre, and 2 x DIN mounted DPDT 20A relays to switch them on and off be suitable.

My late father was an electrician and i'm lucky to know a very good one, but I'm loathed to drag him over to discuss this if its not a good idea. I guess I don't see a lot of DIN boxes in domestic settings or know whether we could use a DIN mounted 20A RCBO in place of a 20A fused switch - or maybe there is a more applicable DIN mounted module which could be used

 

[Ian1981]

Fit a fused spur with a 3 amp fuse in it for your central heating system.

Does your immersion tank have a thermostat on the top and bottom of the cylinder?
If so you don't want the both of them to be on at the same time as the top thermostat usually is just for a boost to top the hot water up when the cylinder is out of hot water.

Next question does your boiler not heat your water anyway you said it was an s plan ?
Immersion heaters are expensive to run and are usually just a back up incase your boiler breaks down for hot water or they are found In economy 7 systems along with electric heaters or storage type.
Confused as to why you require 2 immersions.

 

[Leesparkykent]

Depending on existing loads off the house you could feed another consumer unit off your existing or split the tails. This consumer unit Could house 4 circuit breakers...2 for the immersions, 1 for the heating controls and 1 for the relay control circuit. In this consumer unit you could also house both relays/contactors. Obviously this is notifiable work so best to get your electrician involved right from the start.

 

[LankyWill]

Whats the need for 2x immersion heaters? you converting to HMO?

 

[iclegg]

Its an 250 litre indirect unvented cylinder, the dual safely thermostat is at the bottom, they are wired in series (as normal), the temp of dual safety is set to 60. I also have a 3rd thermostat which is wired into a digital control system I put together based on opentherm, this is what determines the final HW temp.

The two immersion heaters will be used as a backup. I figure if I'm going to have some re-wiring done I might as well connect them up.

 

[iclegg]

@Leesparkykent - I hadn't thought of that, I guess I could also move the whole garage and outdoor sockets onto their own circuits too. I just dug out a trench and had UKPN run a new conductor with an upgraded 100A fuse (was 60A) so lots of capacity in the CU

 

[iclegg]

@LankyWill - no just an over-engineered backup

 

[iclegg]

Is what I proposed using a DIN enclosure with a 20A RCBO in place of a 20A fused switch crazy, are they functionally the same?

 

[Leesparkykent]

The RCBO wont isolate the neutral as 99 out of 100 are solid neutral, where as a double pole switch would.

 

[Ian1981]

Is what I proposed using a DIN enclosure with a 20A RCBO in place of a 20A fused switch crazy, are they functionally the same?

The 2 immersions are 13amps each so I'd fit 2x 16 amp mcbs or if needed by the regulations 2x Rcbos
I'd go into a 20 amp double pole switch for isolation as a double pole switch is required for each immersion then flex out with heat resistant flex to each immersion heater stat.

 

[iclegg]

@Leesparkykent - thats the answer I was looking for
@Ian1981 - cool

Many thanks! I'll start thinking about fitting a mini CU for the garage which will also house the relays.

 

[Ian1981]

@Leesparkykent - thats the answer I was looking for
@Ian1981 - cool

Many thanks! I'll start thinking about fitting a mini CU for the garage which will also house the relays.

Just make sure it's a steel cu/enclosure

 

[iclegg]

Absolutely, I was thinking of a IP rated unit with some level and dust and water ingress protection! Thanks @Ian1981

 

[iclegg]

Absolutely, I was thinking of a IP rated unit that meets regs on CU's with some level and dust and water ingress protection! Thanks @Ian1981

 

[LankyWill]

Keep us posted @iclegg a finished photo would be cool aswell

 

[davesparks]

Absolutely, I was thinking of a IP rated unit with some level and dust and water ingress protection! Thanks @Ian1981

All consumer units are IP rated, presumably you mean one with a higher IP rating than a standard CU?
I don't think you will find a steel one to comply with the current regulations.

 

[iclegg]

yes, being in an outdoor garage, higher than standard - ip65

 

[telectrix]

i must ask.why the need for RCBOs? as it's in a garage, i assume the wiring would be surface.

 

[davesparks]

yes, being in an outdoor garage, higher than standard - ip65

It would be better to relocate the consumer unit to a less harsh environment.

 

[iclegg]

Well, its not that harsh, its modern brick construction on concrete slab with a good solid roof - i'm just over spec'ing

 

[davesparks]

Well, its not that harsh, its modern brick construction on concrete slab with a good solid roof - i'm just over spec'ing

Why? A steel IP65 unit, if it exists, is going to be incredibly expensive!

 

[iclegg]

yer, I probably wasn't clear, either steel or IP65 if I overspec it. I wasn't planning a steel + Ip65

 

[telectrix]

Titanic was over specced.

 

[davesparks]

yer, I probably wasn't clear, either steel or IP65 if I overspec it. I wasn't planning a steel + Ip65

so you're not planning on complying with the wiring regulations?

 

[iclegg]

@davesparks We're off topic here, I asked for some opinions on avoiding 20A DP switches and housing relays... sounded like a small CU is good idea. I had seen some MK IP65 Garage CU's on the CEF website and 'assumed' they could be used?

 

[iclegg]

I'm sure my electrician will put me on the straight an narrow - I'm very grateful for the advice!

 

[davesparks]

@davesparks We're off topic here, I asked for some opinions on avoiding 20A DP switches and housing relays... sounded like a small CU is good idea. I had seen some MK IP65 Garage CU's on the CEF website and 'assumed' they could be used?

it could be used, but you'll have to put it inside a non-combustible enclosure.

 

[Deleted member 26818]

Isthe garage detached from the house?
If it is, then there's no requirement (as far as I am aware) for a non-combustible CU.

 

[davesparks]

Isthe garage detached from the house?
If it is, then there's no requirement (as far as I am aware) for a non-combustible CU.

I don't think the regulations make that distinction, they only say domestic premises.
Premises implies everything within the boundaries of the property, which would include all outbuildings

 

[Ian1981]

Isthe garage detached from the house?
If it is, then there's no requirement (as far as I am aware) for a non-combustible CU.

If it's in close proximity it does.

 

[davesparks]

If it's in close proximity it does.

Where do you get the bit about proximity from, and how do you quantify it?

As far as I can see the regulations say domestic premises, with no mention of distance.

 

[telectrix]

i suppose you could argue that a detached garage is not part of the dwelling.

 

[davesparks]

Premises: A house or building together with its land and outbuildings.

 

[Ian1981]

Premises: A house or building together with its land and outbuildings.

On site guide and using your common sense.
It suggests that a risk assessment will need attaching to eic if metal unit is not used
I'd use metal every time to eliminate any doubt

 

[Ian1981]

Argue the point if you like but it's from the on site guide which as name does suggest is a guide only.
Just make sure you tilt your head to read it

 

[Deleted member 26818]

From wiring matters:
Consumer units in outbuildings or on the outside of a building
Regulation 421.1.201 uses the term ‘premises’. The question could therefore arise: do the requirements of the regulation apply to a consumer unit or similar switchgear assembly within an outbuilding such as a garages or shed, or mounted on the outside or a building?

Some dictionary definitions of ‘premises’ are ‘a house or building, together with its land and outbuildings’ and ‘the land and buildings owned by someone’.

However, Regulation 421.1.201 was principally introduced to cover the interior of a household building and any garage or other outbuildings integral, attached, or in close proximity to that building.

Doubt could exist about whether or not a particular outbuilding could reasonably be considered to be in ‘close proximity’ to the household building. A way of resolving this might be to make a judgement of the likelihood that fire originating inside the enclosure of a consumer unit or similar switchgear in the outbuilding might lead to the outbreak of fire in the household building or in any outbuilding integral or attached to it. Relevant factors to consider about such an outbuilding might include whether or not that building or its expected contents are highly combustible.

Regulation 421.1.201 is not intended to apply to a consumer unit or similar switchgear assembly that is not within a building, such as a consumer unit mounted outdoors on the outside of a building.

 

[Ian1981]

A garage is a building is it not?
Then non combustible it should be in my eyes