Max cable lengths table question

[gpz900jim]

I have been looking at the tables in my onsite guide. I have noticed that when you get to the table for radial circuits (5% drop, page 50, ) when you get to the 45amp ratings, there are maximum cable lengths given for bs1361 and bs3036 fuses, but nothing for any type of mcbs or mcbos. Does anyone know why? cheers

 

[Guest123]

Cos you dont get 45A MCB's!!!

 

[gpz900jim]

Thats funny, they sell them in denmans ???

 

[Amp David]

I've never seen one

 

[Guest123]

Well they're not common.

Dont think I've ever used a 45A MCB as they're always special order.

Either 40A or 50A.

 

[gpz900jim]

are you serious, im looking at one now?

 

[Rappid]

Just found it in their catalogue, MCB & RCBO and it's made by MK.

 

[Amp David]

Deadly serious mate. Never used one, asked for one or seen one.

Always used 40 or 50 amp really.

If they are out there then great

 

[gpz900jim]

Thanks, any way, back to my question, does any one know why the max cable length tables in the onsite guide stop where they do? ie no max lengths for 45a breakers and no info at all for 50a breakers.?

 

[ezzzekiel]

because where do they stop? 60a 80a 100a etc etc, osg is aimed at domestic installs where 40a is typically the max anything above that youre expected to know enough to do the calc yourself.

 

[gpz900jim]

Ok, could someone explain how to calculate the following; Max cable length for an electric shower rated at 10.5kw @ 230v using a 50a mcb, with rcd protection, and 10.mm twin and earth cable, installation method C ?

 

[Bigboy247]

End to End resistance over
ohm resistance/ metre

10mm - 0.01 measured x 1000 = 5.46 m
10mm - 1.83, page 104 OSG

software said, 10.5kw ,230v ,50amp,
10mm clipped direct,
11.4v drop
5% drop
45.7amps current load
65.9 max cabble load
57m max cable length
hope this helps.

 

[gpz900jim]

excellent, thanks very much for that