Workshop - seperate ring?

[Bonce]

Morning all

Have a new extension which increases the size of or kitchen, gives us a utility room and a workshop.

I'm calling it a workshop as it's going to be where I do a bit of woodwork and the wife uses it mainly for her stained glass work and crafty things. It is attached to the main house (if that makes any difference). We are intending to surface mount stuff in here for electrics but just wondered is it necessary for the workshop to be on its own way in the CU. Not sure if a garage has to be and wondered if this would be the same idea? May store stuff like mower's if this also makes any difference regarding regs i.e may have petrol in there etc.

The above may give me a problem as I only have one spare way in my CU and our old kitchen is pretty basic we would be getting a new cooker, which I guess may require larger cabling to it (if eletric oven) and to be on a seperate way. Then there is the cooker hood to consider, how are these usually connected?

If the answers to the above mean I am short of a way or two is it possible to use, dont know what to call it, but something which comes off one way in the CU and gives more ways? Before rewire of old house we had an old CU with wire fuses and there was something that looked like a mini CU that was used for the shower. It had 2 ways in it and this came from the old board and protected the shower with an RCB.

Interested as obviously want to avoid having to get a new CU fitted. I guess in hindsight I should have had more ways in the CU when the house was rewired - but then hindsight is a wonderful thing!

thanks in advance

 

[ericmark]

The regulations state:-

314 DIVISION OF INSTALLATION
314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.
314.3 The number of final circuits required. and the number of points supplied by any final circuit, shall be such as to facilitate compliance with the requirements of Chapter 43 for overcurrent protection, Section 537 for isolation and switching and Chapter 52 as regards current-carrying capacities of conductors.
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated.

As far as you are concerned loading is important if you are using low wattage items less than 2kW and only one at a time then it is unlikely you even need a ring a 13A radial would be enough but if you are drawing more than 3kW then extending the ring looks more likely the answer. Once you start to look at around 5kW as you would in say a kitchen with washing machine, tumble drier, and dishwasher running while you are doing something else then one looks at a dedicated ring.

Step one would be to test the loop impedance and see if there is capacity to extend the ring. We should keep the volt drop within 5% and this give a ring a maximum of 106 meters in a modern house the rules about drilling beams mean it is easy to have cable snaking back and to since you say was re-wired likely you have some paperwork giving the ELI (earth loop impedance) which should tell you if the is capacity to extend. Limit with standard B32 MCB is 1.44 ohms so if under that figure likely you can extend the ring.

One reason for not extending rings is lack of RCD protection. If the consumer unit will not allow RCD's to be fitted then either Ali-tube cable with all RCD sockets or using a RCD FCU (fused connection unit) and spurring from that allows standard twin and earth and sockets. (Ali-tube not needed if cable is surface.)

Since an electrician will have a loop impedance meter he will tend to go for extending a ring. But with DIY with no earth loop impedance meter safe way is to use FCU or a RCD FCU that way unlikely to exceed limits.

With my built in garage the ceiling is a special fire resisting sheet you may need similar if storing petrol also no door direct into house. But that's not my area.

So questions to ask.
What will be the likely loading.
Has the house already got RCD protection.
What is the ELI of the existing ring.

You can get cheap (£50) plug in testers with go/no go ELI check but these don't give a reading only tell you if it is OK which once wired is to me a little late to know if passed or failed. With RCD protection the ELI is not so important it only effect the likely volt drop. With no RCD it is very important and you have not said if RCD protected or not.

 

[Bonce]

Thanks ericmark.

The existing circuits are all RCD protected yes. 2 RCD's on the board, circuits split between. Seperate way for shower and fire alarms. Kitchen on seperate ring.

As for loading will want more than a radial I think. Will be runninng power tools and the like, wife may want a kiln in time (plug in).

Not sure about the ELI of the existing rings but will have a look on my cert, thanks for that info it's interesting.

Re the fire regs of storing petrol etc - I will check that out but yes I do remember reading about fireboard etc or 2 layers of PB or something.

As for the workshop adding a new ring would be easy at present - no floor in place - no plasterboard on walls etc. I guess my worry was that if we did this we would be short of a way for a new cooker unless we went for a gas only oven and hob. In terms of overloaing etc/designing for future I guess a new ring would be good, but then as I say im gonna be short of 1 way I think.

 

[Bonce]

Just checked ELI on the rings.

Downstairs ring 0.44, upstairs 0.49, kitchen 0.48, upstairs lights 0.85, downstairs lights 0.75.

So I guess then this means I have the choice. Just thinking would it be better to isolate the workshop (and it doesn't have an adjoining door - have to go outside to get in, if you see what I mean). Really I wouldn't think I will be loading it excessively, just run of the mill power tools etc.

So basically in terms of regs - no real requirement to seperate, and perhaps therefore makes sense to keep the way for a cooker if we have a combined gas and electric.

 

[PrenticeBoyofDerry]

It would really depend on the loading of the equipment that would be used for craft/workshop. It could be that extending the existing circuit could well lead to potential overloads and nuisance trips.
As you only have one spare way and you still require power for a cooker/oven, which is always advisable to have a separate circuit for, even if the appliance you buy, is suitable for 13A plug connection, you may want to upgrade to higher output cooking appliance in the future.
So I personally would recommend that you fit a second unit external to the existing one, to power the workshop. A two way garage CU should be fine, ideally having a way for 32A circuit for sockets and 6A circuit for lighting, if no lighting is present.
As machinery/power tools are to be used, I would recommend having the sockets and lighting protected by two separate RCD units or avoid having any RCD protection on the lighting circuit at all (requirement permitting). or use of RCBOs. This would help prevent loss of light. whilst power tools are still operating, if a fault or trip should occur.
As it is being used as a craft/workshop and storage, it would be wise to install sockets, switches, isolator and cable, that are protected against mechanical damage.
The extraction for cooking can be taken from the lighting circuit or from a fused spur via a socket circuit (again requirements permitting)

 

[Bonce]

Thanks PrenticeBoyofDerry.

I will look into the seperate garage CU - sounds like a sensible idea, and yes understand regarding the lighting being on a seperate RCB to the sockets for safety reasons.

I was looking at mechanical protection in the workshop 20mm galvanized but trying to think what would other people want of this room (if we moved). I guess you can never accommodate everything though! At the least I would want strong metal face plates.

On talking of future proofing - we may go for a loft conversion in time, which will have an en-suite at a guess, so this would likely be another shower (electric) unless I run off my water supply, and another ring unless I can accommodate into the upstairs ring.

Essentially I am thinking would it be a good idea to somehow get some extra ways onto the board in the main house now! and how do you experts do this, do you generally fit a newer bigger CU replacing whats there or go for something like your suggestion of another smaller CU.

Interested in knowing the options and thanks for the post much appreciated.

 

[ericmark]

If I give an example it may help.
In my mothers house she wanted a new kitchen with many new items so the original supply to cooker was removed and replaced with a larger supply to a mini consumer unit which in turn supplied new cooker and all the other items.

So in your case taking the cooker ear marked supply to a mini consumer unit then feeding cooker from that would allow you extra rings, lights etc the only disadvantage is there is a limit to the size of MCB in main consumer unit with my mum 50A so if that was to trip she would lose whole kitchen. In her case 10mm² SWA cable feeds the consumer unit clipped to outside of house.

Having a local consumer unit with RCBO's in her case means in the main she can reset breakers with easy even though in a wheel chair.

There will be a way it's just working out best way for you.

We tend to read label "Power Tools" and think they need loads of power but in real terms very little without a heating element uses more than 3 amp. Even where there is a heating element often it is thermostatically controlled and although protected with 13A fuse uses on average a lot less and although on the odd time two elements or more may come on together it is rare and as long as the cable can carry the current allowed by the trip there is no real problem the trip comes out we let things cool reset and start again. It fails safe.

My cooker can draw 50 amp but manufacturer recommends a 32A supply it's called diversity.

Clearly you need to look at the tools you want to use but I would from what you have said so far extend the existing ring to include new room.

 

[PrenticeBoyofDerry]

With regards to what other potential buyers of the property are concerned, at the moment you want it meet your requirements, alterations can alwats be made later on. You could sink backboxes and still fit metal clad face plates, which can be replaced easy enough. Or fit surface mounted metal clad backboxes, with metal clad face plates, with surface mounted metal conduit for cables. This can be easily removed and altered in the future.
If you still have plans for future circuits it would be wise now to plan for those provisions. Maybe sensible option would be to replace existing CU for one with more ways, then running a distribution circuit to the workshop, with a garage CU installed there.

 

[flameport]

I was looking at mechanical protection in the workshop 20mm galvanized but trying to think what would other people want of this room (if we moved)

It's irrelevant what other people may or may not want in the future - install what YOU need.

As for the CU - options are either install another, or replace the existing for a larger one.