cpc for shower?

[Shootbolt]

Need someone to put me at ease. Working out minimum csa of cpc for a shower using adiabatic equation. I'm using 10mm T&E with 6mm cpc, 17 meter run, no factors to take in to place. I keep coming up with 6mm cpc not big enough or is it just me. TN-S system. All help welcome.

 

[Shootbolt]

Sorry using BS EN 60898 50 amp type b.

 

[telectrix]

without knowing Zs and/or PEFC, impossible to call. a TN-S can have a Ze anywhere up to 0.8.

 

[telectrix]

a quick calc, assuming Ze of 0.2 would give a min cpc size of 2.5mm, so your 6mm is fine.

 

[Doomed]

I'm getting rusty - I approximated just under 2mm (I need to stop using automatic cable calculators!) - anyway, 6mm will be fine

 

[telectrix]

i got 2.2mm so rounded up. used 0.1 for t and 115 for k

 

[Shootbolt]

thought 0.1s was for circuits not exceeding 32 amps. I used 115 for K though. Haven't bought the cable yet. I was just going off 0.8 for Ze and an R1 + R2 resistance of 4.91 mOhms per meter, giving me a Zs of 0.88, Am I wrong in doing this?

 

[AP Electrical]

thought 0.1s was for circuits not exceeding 32 amps. I used 115 for K though. Haven't bought the cable yet. I was just going off 0.8 for Ze and an R1 + R2 resistance of 4.91 mOhms per meter, giving me a Zs of 0.88, Am I wrong in doing this?

With them figs and putting 5s instead of 0.1 cpc would be around 5mm according to my calc.

 

[johnboy6083]

i got 0.71, so 1mm2. your Zs, if the Ze is 0.8, is going to be very close to the max Zs of the 50A MCB. (50x5=250. 230/250= 0.92) bear in mind the 0,8 rule too, which will bring that down to .736!!
i would downrate your MCB.

the tripping currentys of MCB's can easily be worked out. A B type MCB will trip instataneously(0.1 secs) at 5x In. so your 50 will trip in 0.1secs

 

[telectrix]

that's where OP went wrong. value of t should be taken from time/current graph using calculated value of PEFC.

 

[PC Electrics]

I'd be interested to know where you're buying 10mm t&e with a 6mm cpc!

 

[flukey]

I'd be interested to know where you're buying 10mm t&e with a 6mm cpc!

me too

 

[Shootbolt]

I'd be interested to know where you're buying 10mm t&e with a 6mm cpc!

Good shout, looks like 4mm then.

 

[Shootbolt]

Think I've sorted it Ia= 800 t=0.1 came up with 2.1mm cpc needed. Cheers guys.

 

[johnboy6083]

whats your Zs then? i got 1mm, by using the 0.8 maxXe for TNS, and the mohm/m figure you gave during your OP.