Earthing for an EV Charging Point

[uksparks]

Were talking about a steel structure with maybe piled steelwork and a foundation slab that has steel reinforcement, (which could also be tapped and connected to the buildings MET) what would you honestly expect to change?? The DNO's TN-S, TNC-S, PME earthing provisions are out of our control too. The only earthing system that would be under local control is a made electrode TT system....

I accept that, but my argument is that the steel work is probably going to provide a better resistance than I will achieve with a load of rods.

 

[spark 68]

Well at the moment we don't have any idea as to values, construction method or any other hard data, secondly the services could change (not likely on a new build I agree), there is a formula that needs to be calculated to see what value the Ra is required to meet that particular exemption, it takes no account of existing steelwork or services that may or may not be present.

He is the man signing the paperwork to say it complies and which exemption he is using.

 

[uksparks]

yeah section 722 is "Electrix vehicle charging installations"

If you look there on that page at the bottom of point (i) it referrs to Annex 722 item A722.3, this is the bit we need to see I think.

 

[uksparks]

He is the man signing the paperwork to say it complies and which exemption he is using.

I would like to think I have at least tried to comply with one of the options available.

 

[shanky887614]

If you look there on that page at the bottom of point (i) it referrs to Annex 722 item A722.3, this is the bit we need to see I think.

true

 

[uksparks]

i have just turned it for you

 

[uksparks]

Let me just try to get my head around that for a min.

Thanks for posting up by the way.

 

[Engineer54]

Well at the moment we don't have any idea as to values, construction method or any other hard data, secondly the services could change (not likely on a new build I agree), there is a formula that needs to be calculated to see what value the Ra is required to meet that particular exemption, it takes no account of existing steelwork or services that may or may not be present.

He is the man signing the paperwork to say it complies and which exemption he is using.

That's the problem, we don't have any hard data on anything as yet....

 

[uksparks]

my BY has just arrived

 

[uksparks]

Ok, so...

RA ev less than or equal to 70 divided by (what is Im?)

Im -(70/230) x (8 x 25 x 8)

I being current, I don't understand what m is?

 

[shanky887614]

Ok, so...

RA ev less than or equal to 70 divided by (what is Im?)

Im -(70/230) x (8 x 25 x 8)

I being current, I don't understand what m is?

wrong.

look at the bottom of the page, its quite straightforward.

its explained in A722.4

 

[uksparks]

Ooops I didn't read that far down.

 

[uksparks]

Im, if I am correct, I did put my clamp round the Neutral and it measured approx 8A.

 

[uksparks]

So am I correct in my working of:

Im = 8A (Clamped round Neutral at cutout)
Uo = 230
IL1 = 8A
IL2 = 25A
IL3 = 8A

So, I am typing this in my calculator:

70 / (8 - (70/230) x (8 + 25 + 8))

Answer is: -3.72

So, going on the Note, it says unless it exceeds zero, you do not need an earth rod....

 

[uksparks]

at the top of page 282 of the BYB, it says how to work the neutral current out, ill just try that...