Cable size

[uksparks]

Hi,

I am going to be connecting an out door power supply, away from the building, its all metal casing.

The supply is 10mm, I am using a 3 core SWA for part of the run, the inside part was going to be in twin and earth, but then I was just thinking, going on table 54.8 section 544.1, am I looking into this too much or does it need to have a 10mm earth as its extraneous metal which is fixed into the ground?

In which case I was just thinking of running 3x 10mm inside the building so the earth is 10mm too to them comply with min size of bonding conductor.

I am right to make it 10mm throughout the entire run aren't i?

 

[Guest125]

My BYB will arrive on Wednesday too so will look then. I think it will probably end up just being a rod(s) at the end of the circuit.

Would be more cost effective for the client too. I get grief for being 'a rip off merchant' in other threads so hopefully this suggestion wins me some brownie points back.

 

[davesparks]

My BYB will arrive on Wednesday too so will look then. I think it will probably end up just being a rod(s) at the end of the circuit.

What are you installing the earth electrodes for? to comply with item (ii) of that list that allows you to connect to the PME earth it specifies that they be connected to the MET doesn't it?

 

[uksparks]

What are you installing the earth electrodes for? to comply with item (ii) of that list that allows you to connect to the PME earth it specifies that they be connected to the MET doesn't it?

It is connected back to the MET via the CPC, play on words... i'd say it open to interpretation.

 

[uksparks]

What are you installing the earth electrodes for? to comply with item (ii) of that list that allows you to connect to the PME earth it specifies that they be connected to the MET doesn't it?

Hmm "An installation earth electrode is an additional earth electrode connected to the main earthing terminal."

I won't win with this one will I, I need to run one back to the MET really don't I. Ill call the NICEIC in the morning and ask them their opinion on it, im sure they will put some other spin on it that doesn't exist.

 

[spark 68]

trying to steal dave's thunder lol

No I would disagree slightly with Dave in that I would use at least 16mm (> 1/2 the tail/N size @ 25mm^), my reasoning is because if we are going with bonding back to the MET as a backup for a broken suppliers Neutral and going with very low Ra readings we could end up with substantial diverted current flow from the 3 phase supply for the entire building, albeit the normal Main Bonding conductors will share some of this burden but for the relatively small run I would prefer the larger size if the worst case was to happen.

 

[Guest125]

Oh no. You mentioned the N word! Brace yourselves.

 

[davesparks]

Hmm "An installation earth electrode is an additional earth electrode connected to the main earthing terminal."

I won't win with this one will I, I need to run one back to the MET really don't I. Ill call the NICEIC in the morning and ask them their opinion on it, im sure they will put some other spin on it that doesn't exist.

I dread to think what that bunch of crooks will have to say about it!

I thought you'd done the vehicle charging point installation course? Did they not cover all of this on that course? if not then what exactly was the point of the course?

 

[Guest125]

No I would disagree slightly with Dave in that I would use at least 16mm (> 1/2 the tail/N size @ 25mm^), my reasoning is because if we are going with bonding back to the MET as a backup for a broken suppliers Neutral and going with very low Ra readings we could end up with substantial diverted current flow from the 3 phase supply for the entire building, albeit the normal Main Bonding conductors will share some of this burden but for the relatively small run I would prefer the larger size if the worst case was to happen.

Now ow that is just showing off now isn't it?

 

[Guest125]

Popcorn

 

[davesparks]

No I would disagree slightly with Dave in that I would use at least 16mm (> 1/2 the tail/N size @ 25mm^), my reasoning is because if we are going with bonding back to the MET as a backup for a broken suppliers Neutral and going with very low Ra readings we could end up with substantial diverted current flow from the 3 phase supply for the entire building, albeit the normal Main Bonding conductors will share some of this burden but for the relatively small run I would prefer the larger size if the worst case was to happen.

I can see your point with this, but what are the chances that the building is going to be so far out of balance that the neutral current is going to be that great?

plus I would suggest that it depends on how you connect the rods, I have assumed (possibly incorrectly) that each rod will be connected individually and that there will be multiple rods sharing the current (as this is the way I do it)

 

[uksparks]

It does feel like I'm doing more than I should if you know what I mean, think about it, why am I bothered about the installation and esrthing that when that's already got a perfectly good earth.

I I feel if I put a charger in, with an additional rod, I've done my bit, then in the event of a fault where you loose the neutral, it's there as a fail safe / backup.

 

[Guest125]

It does feel like I'm doing more than I should if you know what I mean, think about it, why am I bothered about the installation and esrthing that when that's already got a perfectly good earth.

I I feel if I put a charger in, with an additional rod, I've done my bit, then in the event of a fault where you loose the neutral, it's there as a fail safe / backup.

Yeah the rod.

 

[telectrix]

10ft scaffold pole hammered in with a JCB.

 

[uksparks]

That's what I'm saying, it will be connected to the met via the armouring and the 10mm cpc which is going to be better than a standalone conductor.

Ill wait it until my book arrives to see whT it says about the figure it's expecting for Ra

 

[Leesparkykent]

It does feel like I'm doing more than I should if you know what I mean, think about it, why am I bothered about the installation and esrthing that when that's already got a perfectly good earth.

I I feel if I put a charger in, with an additional rod, I've done my bit, then in the event of a fault where you loose the neutral, it's there as a fail safe / backup.

i could understand just putting a spike in just for the EV charging point if the building wasn't metalic, its the fact the building is metalic and the EV charging point being so close to the building that you could poss touch both at the same time, if the building wasnt metalic then i wouldnt have a prob with just spiking the EV charging point