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Posted (edited)

Am thinking of converting a room in an out house to an ensuite bedroom/ mini annexe for Pop.

Had 2 installers round last year who both said that min cable should be 10mm, requiring new run from consumer unit of about 40 metres.

Just watched this vid and he's saying 7.2 kw shower could run from 6mm cable.

Then i go to Screwfix et al and min shower rating these days is 7.5kw. -- 7.2 kw showers appear to have gone out with the ark. (2004ish)

Then i go to this site and it says if cable run is against plasterboard (which is the majority of the run in the main house), i can do 7.5kw on 6mm over about 40 metres which is likely an over-estimate on distance, but factoring in the scenic route.

https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

 

Could i reasonably have that debate with a bathroom fitter on winging it on 6mm. The MCB currently running supply to this room is 32 amp at the main board, which then runs in to a mini consumer unit in the out room, which currently has a 32A rated RCBO for the sockets. Could i just get a spur off of this board with a 7.5 kw shower? Would we get it past building regs these days?

Trying to save about 800 quid on a sparky really.

 

Cheers.

Edited by Bus Stop Boxer
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No you shouldn't spur a shower off the ring main. It should have its own circuit.

Why worry about 6mm Vs 10 the cost is not significant and as stated above it should have its own circuit 

I did some work for my employer probably 15 years ago now, it was a new circuit for a high power inductive loads, I had done 16th edition regs at the time, I knew what I was doing, fitted a new circui

45 minutes ago, Bus Stop Boxer said:

Could i reasonably have that debate with a bathroom fitter on winging it on 6mm. The MCB currently running supply to this room is 32 amp at the main board, which then runs in to a mini consumer unit in the out room, which currently has a 32A rated RCBO for the sockets. Could i just get a spur off of this board with a 7.5 kw shower? Would we get it past building regs these days?

Trying to save about 800 quid on a sparky really.

 

Cheers.

Have you got a spare way in this mini consumer unit for a separate RCBO? If so don't see why you can't just put a dedicated shower supply off that.  10mm preferred, temptation either now or later is for someone to overload a lower power circuit by putting a larger shower unit in which is one of the reasons your installer not keen on 6mm supply, plus marginal deepening on installation specifics.

You could have an issue with overloading the supply off this mini CU, but if you could argue that rocket usage is minimal whilst shower is in use (i.e. not running electric heating etc off the supply) then think this will be ok and not a case that might cause a lot of nuisance tripping.

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1 hour ago, Bus Stop Boxer said:

Trying to save about 800 quid on a sparky really.

Don't. Or at least, don't skimp on the materials. There are plenty who can fit stuff ok, but don't skimp on the kit.

I am alive today because I smelled the fire in the flat below (back in the UK) caused by an electrical overload.

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Just now, swiss_democracy_for_all said:

Don't. Or at least, don't skimp on the materials. There are plenty who can fit stuff ok, but don't skimp on the kit.

I am alive today because I smelled the fire in the flat below (back in the UK) caused by an electrical overload.

I can fit stuff OK, but for the final testing you will need somebody with a certificate to sign it off for you.

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Posted (edited)
57 minutes ago, onlyme said:

Have you got a spare way in this mini consumer unit for a separate RCBO? If so don't see why you can't just put a dedicated shower supply off that.  10mm preferred, temptation either now or later is for someone to overload a lower power circuit by putting a larger shower unit in which is one of the reasons your installer not keen on 6mm supply, plus marginal deepening on installation specifics.

You could have an issue with overloading the supply off this mini CU, but if you could argue that rocket usage is minimal whilst shower is in use (i.e. not running electric heating etc off the supply) then think this will be ok and not a case that might cause a lot of nuisance tripping.

Yes i have, and i was coming back on to say that i mis-spoke re "spurring orf".

There is a vacant slot on the mini board for another RCBO in the room in question. So they could run 10 cable to that at least i suppose, althought hat would only be a matter of feet.

The existing 6mm cable enters the building in a visible way in a passage way to the mini consumer unit so it would be very apparent, if there was any desire to fit a higher rated shower in future. After all it has already been pointed out twice.

Im just trying to sift through the bullshit really. 7.5 seems border line ok from here and its just the creeping regs that suddenly deem something unsafe.

This would be a bedsit effectively, 6 downlighters, 4 sockets and a shower. And i suppose a mini hand washer hot water heater as there is only a cold supply in the building..

There is an opportunity, post Pop boxer popping off, that i could get all landlordy with this room, so a fridge , mini cooker etc would be in order.

Fuck it im going to have to put a 10mm cable in arent i?:/

Edited by Bus Stop Boxer
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1 hour ago, Long time lurking said:

Why worry about 6mm Vs 10 the cost is not significant and as stated above it should have its own circuit 

Was quoted 5k for a wet room conversion a year ago. From memory £800 of that was running cable.

Though now wont be going for wet room just a very shallow tray.

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1 minute ago, Bus Stop Boxer said:

Was quoted 5k for a wet room conversion a year ago. From memory £800 of that was running cable.

Though now wont be going for wet room just a very shallow tray.

Mostly labour. Anyone can run the cable. Just takes time.

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Just now, Bus Stop Boxer said:

Head room wise, bearing in mind potential future, use mini cooker etc, there must be a strong case for going straight to 16mm i'd have thought?

A cooker installation would need a separate circuit. A toaster or mini-hob could be plugged into a socket.

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1 minute ago, Option5 said:

Normal ovens are plugged in, it's the hob that's the big load.u

Mine's gas. The socket only works the spark plugs. I still had a 40 Amp circuit put in though.

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2 hours ago, Bus Stop Boxer said:

Was quoted 5k for a wet room conversion a year ago. From memory £800 of that was running cable.

Though now wont be going for wet room just a very shallow tray.

Kinnel I bought 50m of thick 3 core cable last year for 50€....in fact I think it was on special offer for 30€ at one stage!

my whole house runs off 6kw......mind you I try to be modern and 'planet friendly' xD

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3 hours ago, Bus Stop Boxer said:

Am thinking of converting a room in an out house to an ensuite bedroom/ mini annexe for Pop.

Had 2 installers round last year who both said that min cable should be 10mm, requiring new run from consumer unit of about 40 metres.

Just watched this vid and he's saying 7.2 kw shower could run from 6mm cable.

Then i go to Screwfix et al and min shower rating these days is 7.5kw. -- 7.2 kw showers appear to have gone out with the ark. (2004ish)

Then i go to this site and it says if cable run is against plasterboard (which is the majority of the run in the main house), i can do 7.5kw on 6mm over about 40 metres which is likely an over-estimate on distance, but factoring in the scenic route.

https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

 

Could i reasonably have that debate with a bathroom fitter on winging it on 6mm. The MCB currently running supply to this room is 32 amp at the main board, which then runs in to a mini consumer unit in the out room, which currently has a 32A rated RCBO for the sockets. Could i just get a spur off of this board with a 7.5 kw shower? Would we get it past building regs these days?

Trying to save about 800 quid on a sparky really.

 

Cheers.

First 7.5Kw equates to 32.6 Amps so whilst putting it on a 32A MCB probably wouldnt trip, unless the shower was run for hours, its not best practice to have it so close to its design max current.

Second 6mm T&E is good for 51A depending on how its run, if it runs through insulated walls or ceilings that can drop to very significantly.

Third, 40m run is long the volt drop on that circuit, for that load would be about 4% so not an issue for a non lighting circuit.

So...

I would say a 6mm cable is probably ok so long as it is either burried in solid wall and clipped directly to joists and walls but not insulated.

I'd put the circuit on a 40A MCB, needs RCD protection so if not pressent it needs one. The circuit, being a fixed load, does not need overload protection.

So having am MCB rated higher than the rating of the cable is not an issue. The MCB is there solely for fault protection.

I dont have my 18th edition on me so the figures are a bit rough.

 

Can you describe the cable route in detail?

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Posted (edited)
1 hour ago, GBDamo said:

First 7.5Kw equates to 32.6 Amps so whilst putting it on a 32A MCB probably wouldnt trip, unless the shower was run for hours, its not best practice to have it so close to its design max current.

Second 6mm T&E is good for 51A depending on how its run, if it runs through insulated walls or ceilings that can drop to very significantly.

Third, 40m run is long the volt drop on that circuit, for that load would be about 4% so not an issue for a non lighting circuit.

So...

I would say a 6mm cable is probably ok so long as it is either burried in solid wall and clipped directly to joists and walls but not insulated.

I'd put the circuit on a 40A MCB, needs RCD protection so if not pressent it needs one. The circuit, being a fixed load, does not need overload protection.

So having am MCB rated higher than the rating of the cable is not an issue. The MCB is there solely for fault protection.

I dont have my 18th edition on me so the figures are a bit rough.

 

Can you describe the cable route in detail?

Thats great info thanks.

The main consumer unit is at one end of building, above the front door.

Shower would be the entire width of the building away. But then also taking in a passage way then a run back along the passage way then in to the proposed granny flat.

Building is stone. No cavities. Former chapel. Or part of one.

So would have to follow apparent existing course, which is up from front door in to sub floor of upstairs for a run of the length of the living room and a kitchen, then passing out of kitchen wall in to some (shonky) timber doorway framing then in through a brick wall to the mini consumer unit in granny flat.

At this point i dont know what the insultaion sitaution is in the floor cavity. It could be clipped to timbers or now, after 16 years,knowing plenty about the standard of work that was done here prior to me buying the place, its probably just slung on the rafters.:/

Basically though a long straight line with a U shaped hook on the end.

OR it could be run down in to a 3/4 foot high cellar running the same distance/ route.

OR could it be run outside in armoured trunking? Wouldn't look good that though. Would ruin the facade.:Old:

So a run of about 50 - 60 foot tops in fact, to the smaller CU, not 40 metres. Way off there.

Having decided on future proofing this for a bit of possible rental action down the line, it seems there is little point in scrimping on this cable given that its so borderline already, and more day to day appliances may find their way in there.

Cheers.

Edited by Bus Stop Boxer
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