garage conversion supply cable.

[perfo]

Sorry if this topic is covered elsewhere I couldn't find something quite the same.

My question if you don't mind is :-
I'm converting part of my attached garage to living accommodation for my parents. They will in effect have a two bedroom flat attached to my house. I'm hoping to supply their flat from my supply and put a separate consumer unit in their flat somewhere to provide the normal discrimination.
My questions are:-
1, Should I take this feed from my consumer unit with a spare way ?
if so what size MCB etc should it be?
Or should I connect it to a separate isolator and have the rcd / elcb in their consumer unit.

2, What size cable would I need. It is about 20 m and will be in the roof space but free from insulation clipped to the rafters.

thanks for reading and any advice you can provide.

 

[plugwash]

This requires a bit more care than your average garage supply both because the load is likely to be larger and because elderly and infirm people will likely be living in it.

I would suggest using a seperate switchfuse in the house feeding a SWA cable. The reasons for using a switchfuse are that MCBs don't discriminate very well and it keeps things seperate from the house's electrics. The reason for using SWA is so you don't have to have RCD protection at the source. I'd suggest a 60A fuse and 10mm cable. The 60A fuse is large enough that it's unlikely to blow when a breaker trips in the granny flat and large enough that an electric cooker can be installed in the granny flat.

This would then feed a consumer unit in the "granny flat" with RCBOs for sockets, lighting and any other circuits that are required. The CU should be located so elderly/infirm people can easilly access it.

The size of the switchfuse and cable will depend on the expected demand.

The above assumes a TN supply, with a TT supply some kind of time delay RCD will be needed at the origin.

 

[JohnW2]

Given that this is essentially 'separate accommodation', which might possibly involve, for example, an additional electric cooker and/or shower, I wonder if this is a situation in which one ought to inform/ask the DNO about the adequacy of the present supply?

Kind Regards, John

 

[Taylortwocities]

When folk post on here it is quite possible to make a guess as to thier ability to do the job they have in mind.

Now, do not take this the wrong way, but a few things in your OP make me think that you do not have the level of knowledge or skill to carry this out yourself.

For example

what size RCD etc should it be?

It would be a 30mA RCD. But perhaps you didn't mean RCD. Did you mean MCB? Do you know the difference?

2, What size cable would I need.

You should be able to do cable size calculations for a job like this rather than ask on a DIY internet forum.
You will need to notify the electrical works, as there will be new circuits and there will be electrical works in areas like bathrooms.
You'll need a detailed knowledge of Wiring Regulations and a set of calibrated test equipment so you can present your test results to the Local Authority.
Are you really able to do this.?

 

[JohnW2]

When folk post on here it is quite possible to make a guess as to thier ability to do the job they have in mind. ... Now, do not take this the wrong way, but a few things in your OP make me think that you do not have the level of knowledge or skill to carry this out yourself.
For example .... You should be able to ... You will need to ... You'll need a detailed knowledge of ... Are you really able to do this.?

I share those sentiments, and would like to suggest that TTCs post is an excellent example of how such a post should be written - in a perfectly resonable, pleasant and helpful fashion. Others who frequently wish to convey similar messages/sentiments could well learn a lot from this example.

Kind Regards, John

 

[plugwash]

I woudl also suggest though that getting an idea of what is required for a "good job" is important even if you don't plan to do the work yourself. Especially for those who are not lucky enough to have a tradesman they trust available.

 

[JohnW2]

I woudl also suggest though that getting an idea of what is required for a "good job" is important even if you don't plan to do the work yourself. Especially for those who are not lucky enough to have a tradesman they trust available.

I certainly agree with that. Whenevr I employ the services of a professional or tradesman, in any field, I do attempt to first gain at least a little knowledge about what I will be asking them to do.

However, as I need not tell you, the problem in forums like this is that many people who actually intend to do work themselves (often with clearly inadequate knowledge or 'competence') so often hide behind the pretence that they are trying to gain knowledge before involving an electrician (who may or may not be on an extended holiday ).

Kind Regards, John

 

[perfo]

Sorry to be misleading I did mean MCB I do know the difference between an MCB, RCD and RCBO etc. As I had made a mistake I don't blame you for your scepticism.
I can and have looked up the cable size in the regs and looked up if I should have and RCD at my end and in the consumer unit at the other end. I'm an electrical engineer not an electrician so I value people’s ideas whom have done the job probably many times over.
Thanks for the helpful comments especially about the SWA that’s the sort of input I wanted I wouldn’t have necessarily thought about that seeing as the run will be totally indoors and in an attic space.
I have contacted the DNO as my supply only has a 60A fuse, they are willing to put it up to 80A FOC but need me to fill in a few forms and pass their hand with silver to get it up to 100A the cable to the house is fairly new so they should have the size and length etc on their records.
I will need to get all this work signed off so it will need to be inspected. I’m at present hoping to produce some diagrams and run it past the inspector/certifier and see if I’m on the right tracks and thus this is why I asked you learned folk

 

[RF Lighting]

What's the proposed load of the new flat?

How will you be heating the rooms?

How will you be heating the water?

Will there be an electric shower?

Will there be an electric cooker?

 

[JohnW2]

What's the proposed load of the new flat? How will you be heating the rooms? How will you be heating the water? Will there be an electric shower? Will there be an electric cooker?

Indeed.

Given that this is essentially 'separate accommodation', which might possibly involve, for example, an additional electric cooker and/or shower, I wonder if this is a situation in which one ought to inform/ask the DNO about the adequacy of the present supply?

Kind Regards, John

 

[ban-all-sheds]

I'm converting part of my attached garage to living accommodation for my parents.

When you apply for Building Regulations approval, what do you plan to say will be the way you'll ensure compliance with Part P?

I will need to get all this work signed off so it will need to be inspected.

It doesn't work like that.

 

[perfo]

Gas cooker
Oil fired central heating so no shower load.

This is one of the things I’m thinking about when asking the questions.
Forgetting building regs for a minute. I could design for two sockets and one light but anyone with any sense would say that’s not practical, as soon as someone moved in to that accommodation (maybe in the future) they would add lights and sockets and thus the designed load is wrong.
I was maybe foolishly thinking there would be a standard way of thinking and a common approach to it. For example when they put in the cable to my house as the main supply they didn’t ask any questions about what I was plugging in or how I was doing this or that. They just plopped the cable in and stuck a fuse / meter on the end of it. How I use that supply is then up to me (again keeping within the regs). So a standard answer like the gent gave above like I would expect a 60 amp supply to the accommodation is quite helpful. If you are telling me there isn’t a standard approach to this and I will need to do a complete load analysis before thinking of a supply (even though they use standard installs for new builds). Then that is also helpful information.
According to my local building regs dept it does work like that. You put in a design and they agree it you do the work and they inspect it and certify it. There are of course many different ways of doing it but this is one of them. My intention (as stated above) at this stage is to get a very good idea of what will be a likely set up I will do detailed drawings and send it to a qualified electrician (a mate of mine that unfortunately lives too far away) If and when he is happy with the design I will then enter it for building regs approval along with all the other bits of paper concerning the construction. That way when I get the fellows in to do the work I’ll already know what I want them to do and there shouldn’t be any delays.
I’m searching for knowledge here gents and I’m very appreciative of any helpful comments, I’m not however asking for approval or permission.
Thanks again.

 

[EFLImpudence]

This is one of the things I’m thinking about when asking the questions.
Forgetting building regs for a minute. I could design for two sockets and one light but anyone with any sense would say that’s not practical, as soon as someone moved in to that accommodation (maybe in the future) they would add lights and sockets and thus the designed load is wrong.

That's not your problem.
If all you wanted was one light you would not have to design for a future buyer's welder.

I was maybe foolishly thinking there would be a standard way of thinking and a common approach to it. For example when they put in the cable to my house as the main supply they didn’t ask any questions about what I was plugging in or how I was doing this or that. They just plopped the cable in and stuck a fuse / meter on the end of it. How I use that supply is then up to me (again keeping within the regs).

Yes, but they know that is adequate.

According to my local building regs dept it does work like that. You put in a design and they agree it you do the work and they inspect it and certify it.

Not if they don't consider you or the installer competent.

There are of course many different ways of doing it but this is one of them. My intention (as stated above) at this stage is to get a very good idea of what will be a likely set up I will do detailed drawings and send it to a qualified electrician (a mate of mine that unfortunately lives too far away)

Does he have the internet ?
You seem to expect us to do it for you.

If and when he is happy with the design I will then enter it for building regs approval along with all the other bits of paper concerning the construction. That way when I get the fellows in to do the work I’ll already know what I want them to do and there shouldn’t be any delays.
I’m searching for knowledge here gents and I’m very appreciative of any helpful comments,

That's what you have had whether you so consider it or not.
You cannot expect full design specifications on a DIY forum.

I’m not however asking for approval or permission.

It would make no difference either way.

 

[JohnW2]

For example when they put in the cable to my house as the main supply they didn’t ask any questions about what I was plugging in or how I was doing this or that. They just plopped the cable in and stuck a fuse / meter on the end of it. How I use that supply is then up to me ...

If you read the small print of your T&C/contract, you'll probably find that you are required to inform them if you intend/propose to install/use various things - e.g. more than one electric shower, welders, equipment with large motors etc.

Rules, contracts and regulations aside, if (as you say) your extension is not going to involve any electric cooking or electric showers, then the additional load should be relatively minor, such that I would have thought that the DNO are very unlikely to have any interest.

Kind Regards, John

 

[perfo]

I wont be using a non competent installer so that's not an issue.

He has the internet and may even be willing to assist with the work if it fits in with his leave etc. I think some of you gents are looking at this too deep I don't want a full design. Just suggestion like its normally done like this ....or as a rule of thumb you put a switched fuse on your incomer and an RCD at the end consumer etc etc.
However I don't want this thread (or any other for that matter) to spiral in to unpleasantness so as it seems to be going that way. I'll thank those that actually tried to answer the question and bid you all a good day.