Submain swa size check

[andyb]

Have you been specifically asked for a 63a supply?

 

[Leesparkykent]

Very rough calculation whilst sat on my sun lounger next to the pool.....If the earth leakage relay was set to o.8xIn then 50V/50A=1 Ohm

Gives you a bit of room to play with if your taking Ze at 0.35 Ohms.

If your calculations are using 63A as Iz then i recon your looking at using around 150mm based on volt drop.

 

[davesparks]

The DNO will be able to tell you the designed Ze for the supply, if it is a completely new supply then they will possibly be working to a maximum value of 0.25 in their calculations.
0.35 is the stated value for existing networks.

Assuming this is a 100A supply coming in that is, if it's bigger than that then the Ze requirements are lower.

 

[davesparks]

Very rough calculation whilst sat on my sun lounger next to the pool.....If the earth leakage relay was set to o.8xIn then 50V/50A=1 Ohm

Gives you a bit of room to play with if your taking Ze at 0.35 Ohms.

If your calculations are using 63A as Iz then i recon your looking at using around 150mm based on volt drop.

Can you get an earth leakage trip with a 50A tripping current? I've never yet seen them go above 10A

What are you basing your VD calculation on?
My rough calculations based on voltage drop come out at 2x50mm in parallel, based on a mobile phone mast not including any lighting requirements and not having any specified voltage limits stricter than 6%

 

[Leesparkykent]

Can you get an earth leakage trip with a 50A tripping current? I've never yet seen them go above 10A

What are you basing your VD calculation on?
My rough calculations based on voltage drop come out at 2x50mm in parallel, based on a mobile phone mast not including any lighting requirements and not having any specified voltage limits stricter than 6%

I got the mV/A/m figure from a manufacturers data sheet. Good point about to 50A setting....I just assumed they did. I've fitted one with a 30A max setting before.

 

[bigspark17]

Thanks for replies.. some good input from respected members.

Its the max disconnection time & VD that are the main influences over this length.

I was looking at putting a kmf or switch fuse between dno and metering with a bs88 gG 63amp fuse in, @ 80% value gives me a max zs of 0.62.

Using 95mm 2c swa & 35mm cpc gives me a max Zs of 0.56 assuming 0.35 @ dno.

Using the 95mm gives me a VD of 9.5v which is less than the 5% (11.5v) i need to be under.

Any thoughts on this method?

@davesparks i like the idea of parallel cables but would you do this using 2 swa or 4c in one swa?

 

[bigspark17]

Bump