SWA cable calculations!!

[Pud]

Ive been asked to confirm the maxium possible supply for an existing SWA sub main and I know im doing something wrong with my cable calculations.
Its a 10mm 3 core SWA currently on a b40 on a split load boad but its about 120m run ( direct burial) and they want to run an airsource heat pump.
each time I work it out I either get 23a or 60a !!!
Any help would be much appreciated

 

[buzzlightyear]

WHAT KW IS IT ?

 

[Pud]

They have 2 options they are considering at the mo requiring either a 42 or 30 a supply. But I was just trying to work out wot I can run on that 10mm SWA before considering everything they would like on the end of it.

 

[buzzlightyear]

They have 2 options they are considering at the mo requiring either a 42 or 30 a supply. But I was just trying to work out wot I can run on that 10mm SWA before considering everything they would like on the end of it.

WELL TELL YOUR CLIENT WHEN THEY MAKE UP THE MIND THEN ,YOU CAN CALCLATE THE LOADING FOR THE JOB .

 

[westward10]

30A or 42A the volt drop will exceed 5% over 120m.
20A is about the maximum to comply.

 

[Pud]

30A or 42A the volt drop will exceed 5% over 120m.
20A is about the maximum to comply.

And that's how I ended up at 23A
but in the real world that dosent seem right to me

 

[westward10]

What is the loading of the pump.

 

[Pud]

What is the loading of the pump.

At the moment I have very limited information and after a look last night I was concerned about the existing cable size and proposed set up.
It will be a pool house supply so air source heat pump to heat water circulation pump power lighting ect
Proposed is The circulation pump requires 0.56kw and the heat pump model has a recommended supply capacity of 31A with a recommended supply fuse of 42A.) or a smaller version at a 30 a supply.
and to make matters worse its a TT supply

 

[westward10]

Lighting and power will mean this is a distribution circuit so volt drop needs reducing as lighting is involved. 2% is often a rule of thumb to allow an additional 1% for the lighting drop. On this basis I would say the cable should be at least 35mm.

 

[davesparks]

And that's how I ended up at 23A
but in the real world that dosent seem right to me

Why not? That's quite a long cable so volt drop will be quite big

 

[Pud]

Thanks Guys guess I was kind of hoping that I didn't have to tell the customer that the "40a" supply the previous electrician installed last year was not sutible

 

[StephenRowley]

Just as long as the pervious sparkie wasn't you I wouldn't worry too much about it.

But best to come up with some. Option for the customer and prices before you break the news.