6mm Earth and Main protective bonding conductors

[Michaelwgroves]

Ian1981, sorry read and forgot your first post, got tied up with bedtime.......

I don't get how you get your 2300 amps, my Ze is 0.22, what calculation do I need to do?

 

[Ian1981]

Ian1981, sorry read and forgot your first post, got tied up with bedtime.......

I don't get how you get your 2300 amps, my Ze is 0.22, what calculation do I need to do?

That was just my example of a ze of 0.1 ohms
A ze of 0.22 is by calculation 230/0.22 =1045 amps
So times 1045x 1045=
Then times that by your fuse disconnect time which I'll take your word as 0.03 without me trying to look it up
If it's a bs1361 fuse 60 amp then your disconnection time will be below 0.1 seconds
Square root the answer then divide by either 115 or 143.
If the answer is below 6mm then your 6mm which is already in place is adequate for the earthing conductor.
Tho why not change it anyway if it's not a chew on?

 

[KEV 1 N]

......Could of had those 10mm2 earths pulled in by now!

 

[Michaelwgroves]

Sorry, lots of hand holding required. It's big job to replace so hoping the figures here work out.

my "t" was wrong, I used RCD being 30ms.

Cut out is BS (EN) 1361 IIa, Appendix 3 does not list this?

 

[KEV 1 N]

It's ok, I realise the situation, was just having a joke!

 

[Ian1981]

Sorry, lots of hand holding required. It's big job to replace so hoping the figures here work out.

my "t" was wrong, I used RCD being 30ms.

Cut out is BS (EN) 1361 IIa, Appendix 3 does not list this?

It will have a 60,80 or 100 amp rated fuse inside.
Thought you said it was a 60 amp to be honest

 

[Michaelwgroves]

Yes it's 60A, but how do I calculate fuse disconnect time?

 

[Ian1981]

Bs 1361 fuses are not listed in bs 7671 17 th edition as they've been superseded by bs 88 fuses but the red version of the 17 th has 1361 fuses still listed in appendix 3.
The disconnection time will be below 0.1 seconds on a 60 amp bs1361 fuse so it's extremely likely that your 6mm earthing conductor is satisfactory

 

[Michaelwgroves]

I don't have the red version. Just checked latest version, it says replaced by BS 88-3
So I'm now on the right table, but don't know how to read it?

 

[Ian1981]

At 0.1 seconds a bs 1361 fuse will open at 880 amps so your fault current of 1045 amps will make the fuse operate below 0.1 seconds
If you used 0.1 seconds as t then I get 2.31 mm required size of earthing conductor so 6mm is fine.
Obviously the higher the disconnection time then the larger the CSA of the earthing conductor will need to be.
But with all this said and done if it can be upgraded then I'd do it anyway tho not easy if it's a ball ache of a job such as an external meter with the consumer unit inside