Cable calculation

[Deleted member 26818]

Are you using 70 degree or 90 degree armour?

 

[Spoon]

I dont know the design current so im taking it as 80amps, as thats is the fuse rating on the head.

Fare enough mate. Hard to do cable calcs without it though.
If this is an actual job then don't you need to have a fused insolator fitted? Won't the insolator fuse be lower than 80A?
Please correct me if I'm wrong in this.

 

[Nigel]

I dont know the design current so im taking it as 80amps, as thats is the fuse rating on the head.

If you do not know the design current then you are looking at worst case so that will push costs up. Are you not installing the final circuits?

 

[Simon Burton]

Are you using 70 degree or 90 degree armour?

70 degree mate,

 

[Simon Burton]

If you do not know the design current then you are looking at worst case so that will push costs up. Are you not installing the final circuits?

Yeah however he may be adding at later dates i know all the lighgs will be led tho and its literally gonna be 13 amp sockets, so in terms of circuits, 4 lighying and 2 or 3 radials maybe, the circuits again will be a good run in armoured so il also be cable calculating these but this wont be a problem as i will have design current as and when the cistomer knows what hes having in. Just this main cable with the run like

 

[Simon Burton]

If you do not know the design current then you are looking at worst case so that will push costs up. Are you not installing the final circuits?

Yeah however he may be adding at later dates i know all the lighgs will be led tho and its literally gonna be 13 amp sockets, so in terms of circuits, 4 lighying and 2 or 3 radials maybe, the circuits again will be a good run in armoured so il also be cable calculating these but this wont be a problem as i will have design current as and when the cistomer knows what hes having in. Just this main cable with the run like

 

[Simon Burton]

Fare enough mate. Hard to do cable calcs without it though.
If this is an actual job then don't you need to have a fused insolator fitted? Won't the insolator fuse be lower than 80A?
Please correct me if I'm wrong in this.

Yeah im now thinking degrade the fuse rating in my isolator, going off topic how do this work in domestic when the heas is a 60amp but the mainswitch on a db is 100amp

 

[Nigel]

Yeah im now thinking degrade the fuse rating in my isolator, going off topic how do this work in domestic when the heas is a 60amp but the mainswitch on a db is 100amp

The main switch is not a fuse. Are you a qualified electrician?

 

[Simon Burton]

What’s you design load and max demand? Earthing arrangement? Any utilities that require bonding?

I dont have one as the customer doesnt exactly know what he is having, i was going with the worst case being the fuse rating on the main head. No utilities as its pvc water main. And main earth will be tt as its in a field, western power have put a tncs in but we will be putting a earth rod in along with rcd ect ect

 

[Nigel]

Yeah however he may be adding at later dates i know all the lighgs will be led tho and its literally gonna be 13 amp sockets, so in terms of circuits, 4 lighying and 2 or 3 radials maybe, the circuits again will be a good run in armoured so il also be cable calculating these but this wont be a problem as i will have design current as and when the cistomer knows what hes having in. Just this main cable with the run like

I would design to 63A if this was me.

 

[Nigel]

I dont have one as the customer doesnt exactly know what he is having, i was going with the worst case being the fuse rating on the main head. No utilities as its pvc water main. And main earth will be tt as its in a field, western power have put a tncs in but we will be putting a earth rod in along with rcd ect ect

How comes you are not using the TN-C-S?

 

[Simon Burton]

The main switch is not a fuse. Are you a qualified electrician?

No but in terms of over current in a domestic dwelling ive seen a db have 100amp main switchbwith and the main head bein 60amp fuse, the fuse in the main head would blow before rhe main switch would trip. Which is incorrect but why is this done.

 

[Nigel]

No but in terms of over current in a domestic dwelling ive seen a db have 100amp main switchbwith and the main head bein 60amp fuse, the fuse in the main head would blow before rhe main switch would trip. Which is incorrect but why is this done.

So you are a DIYer?

 

[Simon Burton]

How comes you are not using the TN-C-S?

Not allowed to export the earth. Think about it, if you loose your neutral on the main, youve also lost your earth, so anybout building ect will not be earthed

 

[Baddegg]

The main switch wouldn’t trip mate......