Cable Calcs

[Steve D]

Hi All,

I'm rewiring a garage. There is SWA into the garage and I intend to fit a new RCD protected garage CU with 16A & 6A breakers.
Would you recommend putting a 25A or 32A breaker in the main CU ?

I haven't inspected site properly yet but I just had a thought with respect to the existing SWA cable sizing which is currently buried. Am I right to assume that the cable needs to be sized in accordance with the size of the CU fuse? Therefore a 32A breaker at the CU demands that the cable is capable of carrying minimum 32A ?

Excuse my ignorance but I'm never really worked with SWA in the real world before, so what is the difference between tables 4D4A 70C armoured thermoplastic and 4E4A 90C armoured thermosetting? I've got a note in my regs to generally use table 4E4A but naively, I don't really know have to identify what type of SWA exists.
Will there be some sort of code on the external of the cable for me to identify ?

Cheers
Steve

 

[Dannyg83]

The breaker size will be decided by the size of cable u are using because ur breaker is used to protect ur cable . Some S.W.A cables have the size written on them i would generally use a 32A breaker for 2.5 and 4 mm cables

 

[Steve D]

Thanks,

With respect to the SWA gland I need for terminating, there are internal & external types. Does this simply mean for indoors use and outdoors use.

When I'm terminating the SWA into my metal CU, and I use a banjo (I think that's the right term anyway!) to link the SWA armour to the CU earth, what size CPC would you normally recommend for this link? Would it be 10mm or would you recommend something smaller.

Apologies for the basic questions, but it's only when you start to do these types of jobs that you see the shortfalls in the college courses - I accept they can't teach absolutely everything, most things will come with experience.

Cheers
Steve

 

[Dannyg83]

Yeah it will just be indoor and outdoor , i tend to use just the external glands

Banjo,s , Frying pans , earth tags , yeah stick one of them on and just use an earth wire the same size as the cores on your S.W.A

 

[Guest123]

i would generally use a 32A breaker for 2.5 and 4 mm cables

2.5mm protected by a 32A breaker, really???

 

[Spudnik]

2.5mm protected by a 32A breaker, really???

Twas what i thinked.

Also, unless the SWA is stamped then its virtually impossible to tell the size.

Even with experience, it doesnt get any better as nearly all the manufacturers cables are different.

 

[electro]

Hi Steve D


Don't worry about the main isolating breaker in the CU you can leave that at 100A if you want, its the overcurrent protection/fuse you are supplying the submain with you want to rate in line with the size of the submain. To get an idea of the size of the submain you need, or to ascertain if the existing is Ok you need to work out the maximum demand. If you are unsure of the size of cable you need, give us more detail of the run and length and the MD and we can give you a indicative cable size.


The way I usually size SWA's

1. By looking (sometimes on side of cable) or taking an educated guess..
2. Disconnecting a core and trying different size lugs to gauge.
3. Use a vernier calliper.

Regards

 

[AMST09]

No you can't call them Banjos anymore...all to do with racism and culture...ridiculous ... I know

 

[hasel5]

banjos reads like we have some cowboys around doing some fishing

 

[Dannyg83]

2.5mm protected by a 32A breaker, really???

Yes

 

[andyb]

No you can't call them Banjos anymore...all to do with racism and culture...ridiculous ... I know

They're called banjos because they are the shape of a banjo, no other reason.

Of course you can call them banjos, whoever told you can't is talking nonsense.

 

[Mac]

No you can't call them Banjos anymore...all to do with racism and culture...ridiculous ... I know

What do you call them then,they will always be called BANJO'S regardless

 

[scotsparky]

I agree Banjoys they are. I have heard them called frying pans though is that more P.C ?

 

[Mr Mark Sparks]

Banjo - Wikipedia, the free encyclopedia

a brief history lesson
maybe this is why someone may not like the term banjo
however a banjo is what it is

 

[Mac]

Too much european intervention as ususal