Earthing inside a submain panel from main swa incomer

[Guest 004]

OK, going to keep this short.

Supply is 150mm 4 core SWA, with NO supplymentary earth ( calcs done by others, )

QUESTION IS. Do you NEED to run an earth ( is it a regulation) from banjo on inside to earthing terminal inside board. Common sense and a simple ohms continuity test (0.01 ohms) says no. Just want people's thoughts on this.

 

[Darkwood]

Is the gland fitted into a gland plate?
Is the banjo fitted with heavy duty serrated washers to ensure good contact through any paint or the paint has been removed fully from the contact area?
Is the enclosure a 1 piece enclosure or segmented panelling which is screwed together?

If in doubt, tail it out!

 

[davesparks]

Did common sense and simple continuity testing get a value of 0.01 ohms at a test current roughly equivalent to the PFC at the panel? A value of 0.01 measured with a multimeter with a sub-1A test current could be through a tiny spot of good contact which will pretty much melt instantly under the available fault current (which is presumably significant on that size supply)

In short, unless you have ensured a good high current connection to the earth bar by other mans then yes a suitably sized flylead is a damned good idea if not essential.

 

[Leesparkykent]

Reg 543.2.7...where the protective conductor is formed by metal conduit, trunking or ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure.

 

[Guest 004]

Did common sense and simple continuity testing get a value of 0.01 ohms at a test current roughly equivalent to the PFC at the panel? A value of 0.01 measured with a multimeter with a sub-1A test current could be through a tiny spot of good contact which will pretty much melt instantly under the available fault current (which is presumably significant on that size supply)

In short, unless you have ensured a good high current connection to the earth bar by other mans then yes a suitably sized flylead is a damned good idea if not essential.

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?

 

[Leesparkykent]

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?

Adiabatic equation and table 54.7

 

[Guest 004]

Is the gland fitted into a gland plate?
Is the banjo fitted with heavy duty serrated washers to ensure good contact through any paint or the paint has been removed fully from the contact area?
Is the enclosure a 1 piece enclosure or segmented panelling which is screwed together?

If in doubt, tail it out!

Good answer like it.
No gland plate, no serated washers, 1 piece enclosure.

 

[Guest 004]

Adiabatic equation.

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.

 

[Leesparkykent]

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's the PFC and what's the over current protective device?

 

[Guest 004]

No supply into the building yet, but the HV chamber is next door, so we are looking at Zs values of 0.01 by calculation, as we are top of the Tx

 

[Leesparkykent]

No supply into the building yet, but the HV chamber is next door, so we are looking at Zs values of 0.01 by calculation, as we are top of the Tx

Ok so you have calculated the Zs of the distribution circuit based on your assumed Ze of 0.01?

 

[Guest 004]

What's the PFC and what's the over current protective device?

The MCCB is Siemens, the frame and type has escaped me for the moment, think it's a BGG on a 'N' curve.

 

[Guest 004]

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.

 

[Darkwood]

If and when you test it, you may have to introduce a fixed resistive component as the TX is so close that the resolution of your testers won't be able to measure it thus your reading will fluxuate wildly

 

[Guest 004]

Believe you me, I will be testing it.

 

[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.