adiabatic on earth bonding

[malcolmsanford]

you cant selecvt bonding conductors as 50% as a min telectrix????

Why can't you on a non TNC-S system ??

 

[Deleted member 26818]

Thanks Malcolm! Ok, so I should be using Ze. I think I sort of realised this when typing my post but thanks for confirming it.

Actually, I am feeling slightly embarrassed now - I was using the adiabatic to check final cct cable ratings last night so why I decided this morning to use the fuse trip current instead of the PEFC I don't know.

Ref 544.1.1. Again, I don't know why I missed that. I think the lesson is to not do sums with a hangover

In a way, you do use the fuse trip current.
If you had a PEFC of 500A, with a BS1361 fuse, you would either have to use the values in the table (460A and 5s), or determine from the graph at what the actual disconnection time would be (about 1.5s).
Where people often go wrong, is they use the time value from the table, along with the measured value of PEFC. This results in a larger CSA than is necessary.

 

[brman]

Ok, still a little confused then.
Table 54.3 "...incorporated in a cable or bunched with cables..."
table 54.2 "...not incorporated in a cable and not bunched with cables"

So isn't a single cable taped to another single cable (tail) counted as "bunched with cables"? and so table 54.3 applies?

There again, on 54.2 it also says "or for a separate bare protective conductor in contact with cable covering but not bunched with cables"
I am struggling to see how it can be in contact with a cable covering but not bunched with a cable.

I assumed it must be 54.3 with the logic that it is affected by the heating of the tail.

Or is my hangover still stopping me thinking straight......

 

[i=p/u]

i cant swnser that with out stuttering and starting again, so i dont know, but i would be greatfull if you teach me a lesson

Why can't you on a non TNC-S system ??

 

[malcolmsanford]

As Tel said by using the 115 value your not going wrong as your erring on the side of caution, all your going to do is get a higher CSA value which in anything under 16mm is not going to be that expensive. Once your starting to go over that and it's running 60-70 metres then it can become an expensive mistake

In your scenario I would not consider a single earth conductor taped to a single SWA as "bunched". if there were 6/7 SWA and 6/7 Earth conductors all taped together and run together, then to me that would be "bunched", and I would use start to use table 54.3 and the lower value for safety.

 

[telectrix]

min size for bonding conductors on TNC-S is 10mm.

 

[malcolmsanford]

i=p/u read regulation 544.1.1 it will reveal the lesson

 

[Engineer54]

Shut up you lol ....................All this talk of Sunday Roasts, I have a chicken Swarma for my tea

And very nice they are and cheap too!! lol!!

I see your saving the pennies up for your next trip home then...lol!!

 

[brman]

As Tel said by using the 115 value your not going wrong as your erring on the side of caution, all your going to do is get a higher CSA value which in anything under 16mm is not going to be that expensive. Once your starting to go over that and it's running 60-70 metres then it can become an expensive mistake

In your scenario I would not consider a single earth conductor taped to a single SWA as "bunched". if there were 6/7 SWA and 6/7 Earth conductors all taped together and run together, then to me that would be "bunched", and I would use start to use table 54.3 and the lower value for safety.

Ok. thanks, makes sense.
Actually I started all this to decide whether an installation I've looked at is ok. 10mm2 main earth and 4mm2 main bonding.
I think I can now safely say (pending a proper check of the Ze and fuse type) the 10mm2 main earth is fine but the main bonding could do with replacing, particularly as it magically turns from 4mm2 at the MET to 10mm2 at the water pipe! :-O

Thanks to all the other comments too, I am struggling to keep up with you all but I think it makes sense to me now.

 

[i=p/u]

so 6mm for TN-S and TT as minimum and 10mm for TN-C-S.. thats me lesson.. i know this , think i need a holiday, info overload

 

[telectrix]

TT can be as low as 2.5mm if protected. i need a holiday as well. was thinking of ireland this year, never been.

 

[i=p/u]

just uproot and move here, im sure my scottish lady would take your house/home, swap

 

[i=p/u]

and see when you say a TT can be as low as 2.5mm (protected against mechanical damage)

is on the surface then going under the floorboards of a house covering mechanical damage in your mind..

the only tt instalation ive seen this is how it goes and i reckon is in 2.5mm

 

[pencilpusher]

In a way, you do use the fuse trip current.
If you had a PEFC of 500A, with a BS1361 fuse, you would either have to use the values in the table (460A and 5s), or determine from the graph at what the actual disconnection time would be (about 1.5s).
Where people often go wrong, is they use the time value from the table, along with the measured value of PEFC. This results in a larger CSA than is necessary.

Spin - I was thinking about this myself but cannot find a graph in Appx 3 for a BS 1361 fuse. Am I going nuts?

For example, on my TNCS I have a Ze of 0.22 ohms. 230/0.22 = 1045 amps. Where am I checking my fault current against in the tables?

PP

 

[Guest123]

Spin - I was thinking about this myself but cannot find a graph in Appx 3 for a BS 1361 fuse. Am I going nuts?

PP

You wont find any reference to BS 1361 in the new amendment as it no longer exists. It has been replaced by BS 88-3.:stooge_curly: