Earthing for an EV Charging Point

[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...

 

[uksparks]

Im is the max neutral current, so having just worked it out,i think its worked out at 91A, does this figure sound like a realistic figure? I don't really know what to expect here...

 

[spark 68]

Don't forget to add your new charger load

 

[Simonslimline]

Im is the max neutral current, so having just worked it out,i think its worked out at 91A, does this figure sound like a realistic figure? I don't really know what to expect here...

How have you calculated the neutral current out of interest?

 

[uksparks]

How have you calculated the neutral current out of interest?

Well thats based on what I measured at the cutout with a clamp meter round the tails. See photos below. I did sit for around 5 mins to see if it fluctuated etc... The neutral was reading 8A.

 

[spark 68]

Your max IM I calculated at about 53 to 54 A taking into account adding a proposed further 60A load to one of the low loaded phases assuming say L1=8A,L2 =25A, L3=68A

That is just from the information you have given, your PME rod/s in this case would need to be about 3 ohms

This is only a quick and rough calc with using assumed values

 

[telectrix]

maybe what's needed is a 3 phase charger. :49:

 

[uksparks]

Your max IM I calculated at about 53 to 54 A taking into account adding a proposed further 60A load to one of the low loaded phases assuming say L1=8A,L2 =25A, L3=68A

That is just from the information you have given, your PME rod/s in this case would need to be about 3 ohms

This is only a quick and rough calc with using assumed values

How did you come to that? can you show me the calculation how you did it please, my one came out different...?

 

[Simonslimline]

How did you come to that? can you show me the calculation how you did it please, my one came out different...?

Im=√((IL1-0.5(IL2+IL3))²+(0.866(IL2-IL3))²

I got 53.57 Amps.

 

[spark 68]

How did you come to that? can you show me the calculation how you did it please, my one came out different...?

I cheated lol I used Tony's XL spreadsheet to calc the N current

Simon above did it long hand

 

[Simonslimline]

I cheated lol I used Tony's XL spreadsheet to calc the N current

Simon above did it long hand

I have an Excel spreadsheet as well. Wanted to show the way to calculate it though. Either way its the same answer