16mm or 25mm from consumer unit to consumer unit.

[chets42]

First of all I will get an electrician to fit the new consumer unit. This post is about running a cable while I can still get to it easily.

The current setup:

Consumer unit downstairs feeds an 80amp fuse ( right next to downstairs cu) which feeds an upstairs consumer unit about 15meters away using 16mm twin and earth cable. Its definitley 16mm on the live and neutral, I have used a micrometer on the individual strands and checked, however the earth seems thinner.

If I need to change the cable, I need to run it now because of the stage I am at during a renovation. I don't intend to connect it yet just have it in place ready.

The upstairs cu will have 2 electric showers, an electric oven, hob, dishwasher, a couple of electric hand washes, 2 ring circuits, and lighting. (no gas).

My question (or questions) is:
Do I need to upgrade the cable from 16mm to 25mm or is 16mm fine?

Will an 80amp fuse be sufficient for the said load?

Does there need to be a separate earth running with whichever cable I use or is the current set up of twin and earth correct?

For obvious reasons, I have not touched the cable that on the side of the first consumer unit/meter side of the fuse, but at a glance that looks to be 16mm too. I am asuming that would need to be upgraded too if I were to change the other to 25mm?

Thanks in advance for anyone that can give me a definite answer to one or even all of the questions and I'll just re-iterate I will not be making the final connections, I just want to run the cable (if I have to) before I reach a point where I cant get under the part of floor where I intend to run it.

The cable runs under floor boards and then in a hollow stud wall vertically up to the current consumer unit so its in the safe zone.

 

[ericmark]

The big question is where is the cable run that you can't after reach it? If the cable is hidden less than 50mm deep then likely using twin and earth will not comply. Likely cable complying with BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 will be required as clearly that cable will not be RCD protected.

I would suspect this means using SWA cable although one may be able to use the steel as an earth I would really want to also use a core. As to if core and steel armour or just the steel armour is something for the guy signing the paperwork to decide.

As said so many times on here get the electrician on board first and get him to decide what he wants. It is all well and good for us to give advice but we are not signing the installation certificate or issuing the completion certificate it is the guy doing that to who you should ask the question.

 

[Chri5]

First of all I will get an electrician to fit the new consumer unit. This post is about running a cable while I can still get to it easily.

The upstairs cu will have 2 electric showers, an electric oven, hob, dishwasher, a couple of electric hand washes, 2 ring circuits, and lighting. (no gas).

My question (or questions) is:
Do I need to upgrade the cable from 16mm to 25mm or is 16mm fine?

Will an 80amp fuse be sufficient for the said load?

Is this a sub main via an 80 amp fused switch?

What is the main rated at?

Loading will be something like

2 x 10.5 kw
1 x 4 kw
1 x 4 kw
1 x 3 kw
2 x 3 kw
2 x 6 kw
1 x 2 kw

So at full tilt circa 33 kw divided by 230v is 143 amps

No diversity considered and very rough counting, so how do you intend to deal with real overload issues?

Overload issues will be muchly increased If the property is domestic and the whole property is a 100 amp main with two cu's. We haven't even begun with the loading on the ground floor

 

[ban-all-sheds]

First of all I will get an electrician to fit the new consumer unit.

Then I'm not even going to read the rest of your post, because the only person who can answer whatever questions it contains is that electrician.

She will have to sign this:


FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING
I being the person responsible for the design, construction, inspection & testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design, construction, inspection & testing hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to ............. (date) except for the departures, if any, detailed as follows:


So if she doesn't do the design and the construction she won't be able to, and therefore you won't get an Electrical Installation Certificate, and depending on what you tell your council will be the way the work will comply with Part P you may not get a Building Regulations completion certificate either.

 

[chets42]

First of all I will get an electrician to fit the new consumer unit. This post is about running a cable while I can still get to it easily.

The upstairs cu will have 2 electric showers, an electric oven, hob, dishwasher, a couple of electric hand washes, 2 ring circuits, and lighting. (no gas).

My question (or questions) is:
Do I need to upgrade the cable from 16mm to 25mm or is 16mm fine?

Will an 80amp fuse be sufficient for the said load?

Is this a sub main via an 80 amp fused switch?

What is the main rated at?

Loading will be something like

2 x 10.5 kw
1 x 4 kw
1 x 4 kw
1 x 3 kw
2 x 3 kw
2 x 6 kw
1 x 2 kw

So at full tilt circa 33 kw divided by 230v is 143 amps

No diversity considered and very rough counting, so how do you intend to deal with real overload issues?

Overload issues will be muchly increased If the property is domestic and the whole property is a 100 amp main with two cu's. We haven't even begun with the loading on the ground floor

Thanks for your reply, ( and thank you for reading the post.)

It is a domestic property and is , like you said on a 100amp main switch. The ground floor on the first consumer unit has only 1 ring and lighting so I think the loading from that is minimal.

I understand your calculations (the showers will be more like 8.5kw however but that does not make too much difference) . I am sure it is usual to have a domestic property running those type of loads on a single CU with a 100amp? I thought 100amp was pretty standard. I don't understand fully, and this is where I perhaps need the advice, because like you I have added it all up and come to over 80amps, but from what I have read the diversity comes in to play . Am I right in thinking that as long as not everything is on for over an hour or more its ok? So unless I'm cooking with all for rings of the hob on and the oven, two people washing their hands, another two in the showers, and someone doing the ironing and boiling the kettle for over an hour all together, its not going to get anywhere near 140 amps.

The current upstairs cu already runs these except for 1 shower, and I am getting it replaced as it is a 100ma protection and needs to be 30ma.

I'm not an electrician, I am renovating a house that I live in and I need to do as much work as I can to keep the cost down. Hence wanting to pick, source and physical lay the cable before getting an electrician out. I also wanted a bit of advice so I don't get the wool pulled over my eyes and have to swap a cable that may already be suitable for the job anyway.

 

[chets42]

The big question is where is the cable run that you can't after reach it? If the cable is hidden less than 50mm deep then likely using twin and earth will not comply. Likely cable complying with BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 will be required as clearly that cable will not be RCD protected.

I would suspect this means using SWA cable although one may be able to use the steel as an earth I would really want to also use a core. As to if core and steel armour or just the steel armour is something for the guy signing the paperwork to decide.

As said so many times on here get the electrician on board first and get him to decide what he wants. It is all well and good for us to give advice but we are not signing the installation certificate or issuing the completion certificate it is the guy doing that to who you should ask the question.

Thanks for your reply,

The cable will be over 50mm deep under floor boards ( the current cable is) and in the stud wall it will be vertically straight up to the CU. my undertanding of this is that this is in the safe zone.

There will be part of the run of the cable that will be visible. Does this need to be armoured (its twin and earth currently) or is that only when it is hidden and less than 50mm?

When I do get an electrician, I would like to be armed with as much knowledge as possible, and this is why I am using this form.

 

[ban-all-sheds]

I'm not an electrician, I am renovating a house that I live in and I need to do as much work as I can to keep the cost down. Hence wanting to pick, source and physical lay the cable before getting an electrician out.

THAT WON'T WORK.

Choosing cables is Design.

Physically laying cables is Construction.

If you think that you can present an electrician with something you've designed and constructed and expect him to lie on official forms to say that he did it then you are going to be bitterly and possibly expensively disappointed.

If you want to do some of it yourself to save money then first find an electrician who is prepared to work that way as long as he is telling you what to do and supervising you.

 

[Chri5]

Showers and hw boilers (hand washers) have no diversity. In any house running two showers tends to lean towards overload.

In your house it would very, very likely to hit overload situations. Add in the split nature of the house. By that I mean you haven't mentioned the ground floor area and by having a cooker and two showers on the first floor it seems likely tha you are doing beds sit's, HMO or share. So how will anyone know what is in use on say the ground floor that means using something on the first could overload?

Contactors can be used on the showers to give a one or other, but not both at the same time use.

I think you best bet is getting a spark in for a design brief and to discuss DIY elements of the work.

You could detail the full objectives of your project here and I will help. What I can't do is see the site, and have full knowledge of your intentions. So anything via web it really just "knowledge" rather than firm and correct instruction applicable to you and the property you have.

 

[xr4x4]

Is there no other option for showers than electric?

 

[kai]

Why can't you run an empty plastic conduit to the intended location instead?? - use something like a 32mm plastic conduit, which is big enough for your electrician to slide an armoured cable into.

 

[chets42]

Showers and hw boilers (hand washers) have no diversity. In any house running two showers tends to lean towards overload.

In your house it would very, very likely to hit overload situations. Add in the split nature of the house. By that I mean you haven't mentioned the ground floor area and by having a cooker and two showers on the first floor it seems likely tha you are doing beds sit's, HMO or share. So how will anyone know what is in use on say the ground floor that means using something on the first could overload?

Contactors can be used on the showers to give a one or other, but not both at the same time use.

I think you best bet is getting a spark in for a design brief and to discuss DIY elements of the work.

You could detail the full objectives of your project here and I will help. What I can't do is see the site, and have full knowledge of your intentions. So anything via web it really just "knowledge" rather than firm and correct instruction applicable to you and the property you have.

We do Have a ground floor flat but that is on a totally different supply/meter/cu so it is not relevant to this project. It is fully certified and passed off.

The rest of the ground floor to which this project involves is an extension, there is a lounge and a toilet. It is not a bed sit and I have no intention of making it one. It is the lounge to the part of the house I live in. The first CU just has a ring circuit, 1 hand wash, and lights to the lounge, toilet and two sets of stairs. The sub main feeds the second floor where I have my kitchen (ring,cooker,lights,handwash) and kids bedroom (shower) and also the third floor of the house which has my bedroom (ring,lights) and I am planning an ensuite (another shower + handwash).

There are already two cu's so I feel it will be easier to replace these in their current positions than to extend everything connected to the sub main ( probably over 15 meters) all the way back to the first consumer unit.

Ideally I would not have two CU's but that is what I have inherited. Many years ago It was checked and deemed ok, But I don't know how things have changed since then and I would like it to be ok with the second shower.

I will get a spark in, but only when I feel I have a grasp of what is involved.I have had some good work done by tradespeople but I have also had a couple of bad experiences with tradespeople, so I like to be fully armed with knowledge beforehand so I know what they are talking about. It makes it much easier to spot the bad apples.

 

[chets42]

Is there no other option for showers than electric?

No, there is only an electric supply.

 

[chets42]

Why can't you run an empty plastic conduit to the intended location instead?? - use something like a 32mm plastic conduit, which is big enough for your electrician to slide an armoured cable into.

I had not thought of that, it could be possible, but there are a couple of corners to get around. I will have a think/look/think/look about that.

 

[xr4x4]

Is there no other option for showers than electric?

No, there is only an electric supply.

Wouldn't it be more efficient to heat a tank of water with 3kw, or even 6 and run showers off that?

 

[chets42]

Is there no other option for showers than electric?

No, there is only an electric supply.

Wouldn't it be more efficient to heat a tank of water with 3kw, or even 6 and run showers off that?

An interesting Idea. Its not something I had considered, Thank you. I'll look into this some more. What sort of heater would I be looking for to supply a shower? I'm assuming it would require some sort of pump? Could you point me in the direction of any makes/models that are suitable for this sort of use.