electric shower in outbuilding

[J.C.E]

Been asked to make previsions for elec shower in a future outbuild in garden of house I am starting to rewire tomorrow.

The house itself will be heated by central heating- all lights led etc just 1x induction hob then a fan oven +MW. so no excessive load in the house.

Head is 100a SP in external meter box- and c/u in house is >3m so will need to fit a switch fuse isolator switch in the external meter box then 25mm 3c swa from box to c/u.

My question is for the outbuilding supply- theres no space in the meter box for a 2nd switch fuse isolator for the outbuilding so will have to come off of an upfront mcb in the house c/u. But if there wanting like a 9kw shower plus a handful of sockets/lights/heater down there- thats looking at 25/35mm 3core at a 35meter run- which i think is pretty excessive.

1)Has anyone ever fitting a shower at such a distance in for example an outbuilding
2)does the isolator for the house >3m swa tails need to be fused or can it just be a 100a dp main switch? (i think the answer to my question is yes as I can't rely on the dnos mains head fuse- but space looks tight and I know them wylex fused isolators are quite bulky!)

 

[J.C.E]

suppose 16mm swa could work at 35m on a 50amcb

 

[LankyWill]

I'd fit an rcbo off the existing board, less faff and switchgear. Plus one point of isolation, for the cable size you need to design the final demand for the outbuilding and size from there.

 

[Leesparkykent]

How far is the meter to the board position?

 

[7029 dave]

Just a thought, can you not fit another surface meter box adjacent, split tails at origin, conduit between the 2 boxes and fit your switch fuse etc in box 2.?

 

[J.C.E]

I'd fit an rcbo off the existing board, less faff and switchgear. Plus one point of isolation, for the cable size you need to design the final demand for the outbuilding and size from there.

would do an upfront mcb (as will be running in swa) then have the rcd protection at the local c/u in the outbuild

 

[J.C.E]

How far is the meter to the board position?

around 10m- theres a w/c on the other side of the wall to the meter box so have to go around this to have the c/u on the other side of the hall to the w/c

 

[LankyWill]

Could you fit a small cu in the meter box and use BS88 fuse carriers mcb's instead? One to the house cu and one with the armoured glanded off?

 

[Leesparkykent]

around 10m- theres a w/c on the other side of the wall to the meter box so have to go around this to have the c/u on the other side of the hall to the w/c

can you install another meter box next to the existing?

 

[J.C.E]

Could you fit a small cu in the meter box and use BS88 fuse carriers mcb's instead? One to the house cu and one with the armoured glanded off?

will not get a 25mm into a mcb

 

[J.C.E]

can you install another meter box next to the existing?

for?

the meter box is recessed- so would now probaly struggle to wire between a reccessed and an additional surface one

 

[Leesparkykent]

for?

the meter box is recessed- so would now probaly struggle to wire between a reccessed and an additional surface one

for the switch fuse for the out building/shower. Is a builder involved with the job?

 

[J.C.E]

for the switch fuse for the out building/shower. Is a builder involved with the job?

yes but shells all built now (his sparks broke his foot) so I got the job
(his crap temp supply- on the other side of meter box (see photo)

If I get rid of the old meter at the bottom and get the client to get a new small digital meter in place of the big dial meter I can probaly squeeze a 100a switch fuse iso in there and 25mm to c/u in house

then a upfront 50a mcb in the house c/u- and 16mm out to the outbuilding

 

[Leesparkykent]

yes but shells all built now (his sparks broke his foot) so I got the job
(his crap temp supply- on the other side of meter box (see photo)

If I get rid of the old meter at the bottom and get the client to get a new small digital meter in place of the big dial meter I can probaly squeeze a 100a switch fuse iso in there and 25mm to c/u in house

then a upfront 50a mcb in the house c/u- and 16mm out to the outbuilding

View attachment 36914

would take the builder about half an hour to cut in a recessed box and cost about £30 to buy.with this you could house a switch fuse for the house and another for the outbuilding. In the existing you could install something like a rec 2 for a single point of isolation. Much better than having to run the SWA internal and also having the distribution circuit on a circuit breaker where you will struggle to achieve any discrimination... just my thoughts.

 

[LankyWill]

does the property have a septic tank?

 

[J.C.E]

would take the builder about half an hour to cut in a recessed box and cost about £30 to buy.with this you could house a switch fuse for the house and another for the outbuilding. In the existing you could install something like a rec 2 for a single point of isolation. Much better than having to run the SWA internal and also having the distribution circuit on a circuit breaker where you will struggle to achieve any discrimination... just my thoughts.

like this idea lee thanks!
going to ask the builder to cut a 2nd meter box in and run 2x 32mm pipes between.

then fit a 100a rec switch after the meter- then into a henley (in the 1st meter box)

then 2 sets of 25mm tails through the pipes into the 2nd meter box

hopfully 2x of these will fit side by side:
Wylex 100A Domestic Switch Fuse Unit - http://www.screwfix.com/p/wylex-100a-domestic-switch-fuse-unit/5290J?kpid=5290J&gclid=CM6_4P3cytQCFc2d7QodAP0FJg&gclsrc=aw.ds&dclid=CJHY__3cytQCFWmnUQodOrQIRw

have a 63a isolator with 35meters of 16mm going to the future outbuilding
and a 80a isolator with 10meters of 16mm supply the house c/u

 

[Leesparkykent]

like this idea lee thanks!
going to ask the builder to cut a 2nd meter box in and run 2x 32mm pipes between.

then fit a 100a rec switch after the meter- then into a henley (in the 1st meter box)

then 2 sets of 25mm tails through the pipes into the 2nd meter box

hopfully 2x of these will fit side by side:
Wylex 100A Domestic Switch Fuse Unit - http://www.screwfix.com/p/wylex-100a-domestic-switch-fuse-unit/5290J?kpid=5290J&gclid=CM6_4P3cytQCFc2d7QodAP0FJg&gclsrc=aw.ds&dclid=CJHY__3cytQCFWmnUQodOrQIRw

have a 63a isolator with 35meters of 16mm going to the future outbuilding
and a 80a isolator with 10meters of 16mm supply the house c/u

sounds good to me.

 

[freddo]

Why is the off peak supply connected to the normal supply like that? Seems a waste of a cable!

 

[Taylortwocities]

Personally, I would consider not putting one of them 'instant' heat shower in the outbuilding.
Instead, have a look at one of the smaller unvented direct hot water tanks (Megaflo, etc) with an immersion heater. A 70litre or 125litre tank should be plenty big enough.
Your electrical current requirement for the shower then plummets to 3KW. Its also easy then to add other hot water items, like a wash-basin.

 

[davesparks]

Why not use a smaller switchfuse like a KMF unit, if the meter gets changed for a digital one you might get two in the same meter box.


I'm curious as to what people would think about having only one distribution circuit which feeds both the house and the outbuilding?

 

[Toneyz]

What about a 80A 3 phase switch-fuse in another meter box next to one with meter/cut out or if you think that after diversity the demand will be no more than 50A from house consumer unit.

 

[davesparks]

What about a 80A 3 phase switch-fuse

I can kind of see where you're going with this, but I'm not sure you'll get one small enough to fit in a meter box sensibly.
Plus I don't like the idea of a metal switchfuse in a meter box which doesn't really provide much in the way of waterproofing

 

[Taylortwocities]

Where's the over current protection for that bit of white T&E cable. I can only see the service fuse..

 

[Toneyz]

I can kind of see where you're going with this, but I'm not sure you'll get one small enough to fit in a meter box sensibly.
Plus I don't like the idea of a metal switchfuse in a meter box which doesn't really provide much in the way of waterproofing

100A Eaton Glasgow (reduced fuse size) but all depends on if after diversity the outbuilding can come off house consumer unit on 50A mcb

 

[davesparks]

100A Eaton Glasgow (reduced fuse size) but all depends on if after diversity the outbuilding can come off house consumer unit on 50A mcb

In my xperience they go rusty rather quickly in damp environments like this.

I thought when you said TP switchfuse you were suggesting using the L1 fuse for the house and the L2 fuse for the outbuilding, I can't see why you'd want a TP one otherwise on a single phase supply.

 

[Toneyz]

In my xperience they go rusty rather quickly in damp environments like this.

I thought when you said TP switchfuse you were suggesting using the L1 fuse for the house and the L2 fuse for the outbuilding, I can't see why you'd want a TP one otherwise on a single phase supply.

TP and switched N and yes fuse for L1 and L2 I take the point of if in a damp environment .I think Legand do a IP enclosure with din rail and have DP switches and fuse holders could be an idea

 

[davesparks]

TP and switched N and yes fuse for L1 and L2 I take the point of if in a damp environment .I think Legand do a IP enclosure with din rail and have DP switches and fuse holders could be an idea

Personally I wouldn't be trying to reinvent the wheel, KMF switchfuses fit nicely in a meter box alongside the meter etc, so will be fine with two in an empty meter box.

 

[J.C.E]

the wylex amd 3 switch fuse isolators litterally just fit side by side!!!
enough room at the top to have a tails gland and make the swa off at the bottom

 

[davesparks]

the wylex amd 3 switch fuse isolators litterally just fit side by side!!!
enough room at the top to have a tails gland and make the swa off at the bottom

Again they are going to be painted metal which is not suitable for the environment of a meter cabinet, it will rust.

 

[Toneyz]

Again they are going to be painted metal which is not suitable for the environment of a meter cabinet, it will rust.

Sorry I thought that I replied to your concerns regarding rust I thought I posted back perhaps Legrand IP enclosure with main switch and fuses

 

[J.C.E]

Sorry I thought that I replied to your concerns regarding rust I thought I posted back perhaps Legrand IP enclosure with main switch and fuses

wouldnt comply with amd 3

 

[Toneyz]

wouldnt comply with amd 3

in a external meter box

 

[davesparks]

in a external meter box

Strictly speaking that is irrelevant to Amd3 compliance, the requirement for non-combustible CU specifies domestic premises. By definition the premises includes everything within the boundaries of the property whether internal or external.

 

[Toneyz]

wouldnt comply with amd 3

have you worked out what the load is after diversity that could be put on the 50A mcb

 

[J.C.E]

have you worked out what the load is after diversity that could be put on the 50A mcb

its 'future plans'- so they dont really know yet
I have allowed for a 63a switch fuse isolator with 35m of 16mm swa