Earthing inside a submain panel from main swa incomer

[Leesparkykent]

I repeat the HV chamber is next door, so from thr Tx the run is about 6 metres fed by 630mm parallel supply, so we can safely say that the impedance will be on 0.01. Again I repeat all this has been calculated and all protective devices have been designed to take fault current of 0.01 x root 3.

Why haven't they specified the size of the protective conductor?

 

[davesparks]

The safety devices will open mate, the sheath will carry any fault currents that are generated, and the protective devices are 80kA. Don't want to go that route really, just want people's thoughts in the real world.

OK, so I m okay with with a 'fly lead' from banjo, so now what size?

Not your mate!

The sheath won't carry any fault current at all if it is SWA as the sheath is made of PVC, the armour will carry the fault current.
I was not saying anything about the cable's ability to handle the fault current, but that of the connection between gland and enclosure. The connection to the connection to the gland will have to carry that exact same fault current, if it is only making contact on a tiny area like the rough edge of the hole then it may well break down when that fault current flows before the protection operates.

Personally I prefer to use earthing nuts (yes they do make them that big) or else fit a brass gland plate with holes tapped to take the glands of the the SWAs terminated to the board.

 

[davesparks]

OK, that will equate to about a 6mm

Didn't want to go the abiabatic route, because an earth was not being taken back to source, as the the calcs state no supplymentary.

What do you mean you don't want to go the adiabatic route? How did you calculate that the armour is adequate without using the adiabatic?
Supplementary what?

 

[Martin Kerr]

I dont think he is doubting you are not going to test,I believe what he is saying ,is the test equipment may max out at possibly 20 KA and you may not get an accurate reading

 

[Guest 004]

Not your mate!

The sheath won't carry any fault current at all if it is SWA as the sheath is made of PVC, the armour will carry the fault current.
I was not saying anything about the cable's ability to handle the fault current, but that of the connection between gland and enclosure. The connection to the connection to the gland will have to carry that exact same fault current, if it is only making contact on a tiny area like the rough edge of the hole then it may well break down when that fault current flows before the protection operates.

Personally I prefer to use earthing nuts (yes they do make them that big) or else fit a brass gland plate with holes tapped to take the glands of the the SWAs terminated to the board.

Oh I stand corrected, sorry I thought the sheath was the armour.

 

[Guest 004]

Already stated that calcs have been done by 'others' and I'm struggling to see why I need to a adiabatic on a fly lead.

 

[davesparks]

 

[davesparks]

Already stated that calcs have been done by 'others' and I'm struggling to see why I need to a adiabatic on a fly lead.

How else are you going to work out what size it needs to be? It is forming part of the cpc of the circuit so should be calculated the same way.
Your other option is to use the selection table which would have you fitting a 95mm copper flylead.

 

[Leesparkykent]

Already stated that calcs have been done by 'others' and I'm struggling to see why I need to a adiabatic on a fly lead.

So what size are you going to install?

 

[davesparks]

Why has the designer of the installation not specified the method of termination and the size of any flylead required? Or why don't you just enquire as to what it should be? Unless you are accepting liability for this part of the design?

 

[Darkwood]

I dont think he is doubting you are not going to test,I believe what he is saying ,is the test equipment may max out at possibly 20 KA and you may not get an accurate reading

The opposite is what I meant, the resolution of most meters will be to 2 decimal places 0.01, because he is so close to the TX the meter will struggle to verify such a low reading as it will need a minimum level of resistance to settle the reading, as the expected reading is probably going to be at the meters threshhold then it will not find its reading correctly and will generate false readings which will confuse anyone taking them. There are a few options to counter this, buy a nice expensive meter with a higher resolution, or introduce a known resistance into the reading. A simple way would be a local radial socket/spur etc where you can measure the cables R1+R2 giving you a known resistance then you can measure the external impedance from that socket minus the circuits impedance this will then bring your meter back to an accurate reading within its resolution. A simple resistor with high accuracy will also do the trick but not many carry these about as a rule.

 

[Skimpy Wan]

Sorry haven't read the whole post as just walked in the door and the Misses is moaning! Lol

Doesn't GN8 cover what SWA armour can be used as a CPC and which need additional bonding (therfore in parallel).

I'm not sure if I'm allowed to post a link to the page I'm referring to, so please let me know if this is permitted - Mods not us minions! Lol

 

[Skimpy Wan]

If not, maybe I'll see if I can transpose it in a document that is legible for people over the next few days?!

 

[davesparks]

Sorry haven't read the whole post as just walked in the door and the Misses is moaning! Lol

Doesn't GN8 cover what SWA armour can be used as a CPC and which need additional bonding (therfore in parallel).

I'm not sure if I'm allowed to post a link to the page I'm referring to, so please let me know if this is permitted - Mods not us minions! Lol

GN8 does effectively cover it, but it is all there in bs7671 too.
The subject of running bonding conductors alongside an SWA is a completely different matter, and it has presumably already been established that the armour meets any bonding requirements of that there are no bonding requirements

 

[Skimpy Wan]

If not, maybe I'll see if I can transpose it in a document that is legible for people over the next few days as I don't want any repocusions!