What size SWA for main 80A supply?

[AndyPRK]

Do we know what supply type has been provided ?
Is there an earth terminal

 

[d000hg]

Do we know what supply type has been provided ?
Is there an earth terminal

I don't offhand. It's a brand new installation from Northern Powergrid and EON. We have overhead cables and someone suggested that means we need to fit an earth rod but I have no idea on that.

 

[JohnW2]

I don't offhand. It's a brand new installation from Northern Powergrid and EON. We have overhead cables and someone suggested that means we need to fit an earth rod but I have no idea on that.

That's not necessarily the case - even with an overhead supply they could well be providing a ("PME") earth. Is there an earth block (with green/yellow wire connected to it) in the vicinity of the cutout and/or are there any stickers around there which say anything about "PME"?

Kind Regards, John

 

[d000hg]

Fairly sure not. When I look at our house - which is the only other property these lines serve - there is a cable that runs down the pole into the ground, and we have an earth in our cellar.

I'll check though.

 

[AndyPRK]

I picture of this new supply and meter would be interesting.

 

[Notch7]

, and partially because, in the event of the outer sheath being penetrated/broken, it's not unknown for the armour to corrode and 'fall apart

I got shouted down last time I mentioned that possibility.
Although it seems logical to me.

 

[flameport]

We have overhead cables and someone suggested that means we need to fit an earth rod but I have no idea on that.

You need to find out.
If the trench is still open, earth tape or some other item could be installed in it. Far easier and more effective than a random rod shoved in somewhere.

Even if it is PME, installing an additional earth yourself may be desirable.

 

[JohnW2]

I got shouted down last time I mentioned that possibility. Although it seems logical to me.

A good few people in the "2-core SWA" and "3-core SWA" camps appear to be pretty strong/passionate in their viewpoint about what is 'correct', so are inclined to 'shout'!

However, for what it's worth, there are no electrical downsides of 3-core - the only ones being a small increase in cost and a small increase in size/stiffness.

Kind Regards, John

 

[Keithmac]

I ran 3 core SWA and used the internal earth wire as well as earthing the armour strands.

Belt and braces, why leave any doubt about longevity on the table when the cost is negligible between the two.

 

[d000hg]

I ran 3 core SWA and used the internal earth wire as well as earthing the armour strands.

Belt and braces, why leave any doubt about longevity on the table when the cost is negligible between the two.

That kind of argument can be taken a long way though... why not wear a crash helmet in your car just in case. IF SWA is designed to work with the sheath as earth, AND the regs are happy with using it that way, WHY be worried? It's not the regs aren't already quite conservative.

As a query, if your SWA earth gets breached underground... isn't it then earthed underground like a ground-rod anyway? If someone damages your cable aren't you going to replace it anyway?

 

[bernardgreen]

isn't it then earthed underground like a ground-rod anyway?

No it is not.

A ground rod has a large area of contact between rod and earth, A small hole in the outer plastic sheath of SWA can allow moisture to reach and corrode the steel armouring to the extent that over time the armouring loses continuity from end to end. The area of contact with earth is via the small hole in the outer sheath and this cannot provide an effective low impedance path to ground from the steel armour

If someone damages your cable

The outer sheath can be damaged when the cable is drawn into the duct.

 

[d000hg]

It doesn't seem like very good armoured cable if you can damage it just pulling it through a pipe! Not exactly the best armour

As said though, 3 core doesn't add much cost.

 

[bernardgreen]

if you can damage it just pulling it through a pipe!

Snagged on the edge of the access chamber before it reached the pipe.

 

[Keithmac]

That kind of argument can be taken a long way though... why not wear a crash helmet in your car just in case. IF SWA is designed to work with the sheath as earth, AND the regs are happy with using it that way, WHY be worried? It's not the regs aren't already quite conservative.

As a query, if your SWA earth gets breached underground... isn't it then earthed underground like a ground-rod anyway? If someone damages your cable aren't you going to replace it anyway?

That's just me and what I thought would be the best scenario, same as two RCD's on same circuit (one in consumer unit and one in plug socket).

For the sake of a few extra ££ it's not worth buying the "better" parts imho.

 

[JohnW2]

That kind of argument can be taken a long way though... why not wear a crash helmet in your car just in case.

It's obvious a matter of a risk assesment and deciding 'where to draw the line'.

Rally and racing drivers do, of course, where crash helmets, in addition to all the other safety factors built into their cars.

In terms of ordinary cars/drivers, you might argue that it is "taking things too far" to have seat belts AND air bags AND crumple zones AND collapsible steering columns/wheels etc etc. - but I don't think many people would argue that! Perhaps more relevant to the context of this discussion, if it were known that there was a significant risk that, under certain circumstances, one of those safety features might 'fail', that would be an argument for having others (as 'belt and braces').

IF SWA is designed to work with the sheath as earth, AND the regs are happy with using it that way, WHY be worried? It's not the regs aren't already quite conservative.

I think your premise may not be totally correct. I would say that the armour of SWA is "designed" to provide mechanical protection and also an earthed sheath that will facilitate operation of a protective device in certain situations of cable 'penetration'. It so happens that the armour is usually (but not always - see our wiki) electrically adequate to be also used as the cable's 'earth' conductor - but I would not personally say that it was "designed" to have that role.

However, as has been said, you are right that the armour alone usually is adequate, and compliant with regs, and that a good few people believe that is the appropriate and 'correct' way to do things. However, as I said earlier, the only advantages of doing it are slight benefits in terms of cost and convenience - there is no electrical reason for not having an 'earth' core.

Kind Regards, John
Regards, John