2.5mm swa from 4mm radial?

[eveares]

I need to run a power supply up to a shed/decking area at the top of the garden from a 4mm radial circuit.

While i know i can use 3 core 4mm swa, it is really expensive and hard to work with.

3 core 2.5mm swa is rate at 31 Amps, 1 amp under the rating of the 4mm twin/earth what i will be spurning from!

The run will be about 20 meters; and as the cable will not be buried underground.

Any better ideas other than 3 core 4mm swa?

Regards.

 

[PrenticeBoyofDerry]

I don't think the difference in price between 20m of 4.00mm and 2.5mm is going to be extortionate! Maybe £10-£12.

 

[eveares]

2.5mm - £1.28 per meter, 4mm - £1.78 per meter.

Guess I am left with no option but 3 core 4mm swa!?

 

[ban-all-sheds]

I see that 2.5mm swa is rated at 36 Amps

That will be for XLPE insulated cable, not PVC. XLPE can be run at 90° vs 70° for PVC, hence a higher CCC. But of no use unless the accessories you're terminating it in are also rated at 90°.

over the normal 24 Amps for 2.5mm Twin/Earth.

1) There's no such thing as a "normal" rating for any cable - it always depends on how it's installed.

2) 24A is not one of the published CCCs for installation methods for 2.5mm² T/E in Table 4D5.

Does this mean, accounting for voltage drop and de-rating factors I can use 2.5mm swa from the 4mm radial circuit or do i need to use 4mm swa?

You need to use the size of cable which will safely carry the current you require over the distance you require and which is rated no lower than the device protecting it.

Ib ≤ In ≤ Iz

The run will be about 20 meters; and as the cable will not be buried underground, is hituf cable also suitable in replacement for swa?

Probably not. Where do you intend to run it, and how do you propose to protect it from damage?

 

[JohnW2]

<all sorts of things>

I'm a bit confused - none of the four quotes you include in your post appear in the OP. Do I take it that you grabbed those quotes and then spend at least 22 minutes completing your reply (the OP was not edited after 5:21, yours posted at 5:43), during the early part of which period the OP was extensively edited?

Kind Regards, John

 

[ban-all-sheds]

You may take it that every single quote was in the OP's original post, and that at some point I left my reply, and them returned to it, by which time he'd changed his post completely.

 

[ban-all-sheds]

While i know i can use 3 core 4mm swa, it is really expensive and hard to work with.

It's neither.

If you can't afford the right materials you can't do the job.

If you are unable to work with SWA you can't do the job.

3 core 2.5mm swa is rate at 31 Amps,

Installed how?

Any better ideas other than 3 core 4mm swa?

Have you actually designed the circuit properly?

 

[EFLImpudence]

I don't think outdoor installation is a DIY job.

 

[ban-all-sheds]

It's fine as long as it is done properly.

 

[EFLImpudence]

Yes, that is obviously true but usually entails telling the DIYer EVERYTHING.

 

[JohnW2]

I don't think outdoor installation is a DIY job.

I understand what you mean, but I don't really like 'tarring with a single brush' - it obviously depends upon the DIYer concerned. After all, outdoor installation is probably not a job for some so-called 'electricians', either!

Kind Regards, John

 

[EFLImpudence]

Yes, I knew what I meant, too.

It obviously depends on the definition of DIYer.
I suppose, strictly speaking, it is just someone who does it themselves - period.

Is asking others how doing it yourself?

 

[JohnW2]

Yes, I knew what I meant, too. It obviously depends on the definition of DIYer. I suppose, strictly speaking, it is just someone who does it themselves - period.

Well, yes, but in context I think it's fairly clear that you are referring to someone who is not a 'trained' electrician (albeit the maning of that may be debated!).

Is asking others how doing it yourself?

Hmm, philosophy time, is it? I suppose that no-one knows how to do anything until they are 'told' - by a teacher, a book/video/whatever, by 'observation' or by a person responding to their questions! I don't think that asking questions about 'how to do something' is fundamentally different from discovering how to do it by looking in a book, searching on-line, going on a course or whatever, is it?

Kind Regards, John

 

[EFLImpudence]

Quite but, as I said, with such installations the person has to be told everything step by step.

I think perhaps in my mind DIYer has evolved to mean someone who does not know rather than its literal meaning.

 

[JohnW2]

Quite but, as I said, with such installations the person has to be told everything step by step.

Fair enough - but do I not also often see that very same thing happening here in relation to (indoor) light switches?

I think perhaps in my mind DIYer has evolved to mean someone who does not know rather than its literal meaning.

I agree that it's difficult to get the terminology (and way of thinking) right - particularly when we are usually thinking about various different considerations. One might think that 'formally trained' and 'not formally trained' would be a good classification - but that can go all wrong. As we know, 'formally trained' can cover multitude of things, some not very satisfactory. On the other hand 'not formally trained' will also cover a wide spectrum of knowledge, skills and experience.

What we need to try to avoid is an assumption that anyone who needs to ask questions on a DIY website is 'by definition' not competent to undertake electrical work!

Kind Regards, John