S
Silly Sausage
What should a certain member do?
- Thread starter Silly Sausage
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- charging earthing ev charging point
As far as I know. If EV fitted on an actual building that has PME, it can be connected to PME. However if fitted remotely, has to be TT. Others may differ though
Also, if TT Ra reading to be as low as possible. Best below 100 ohms. If around 150 ohms vehicle may not charge.
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UK, have you not understood anything we have being saying to you ?
You have a few options,
1) ensure the three Phase supply is balanced according to the formula in the associated annexe with exemption I), and then it doesn't really matter how good the building is earthed to true earth, the load balancing alone will prevent the N/PME Earth from rising above 70V in the case of a broken suppliers N, you just use the existing earthing system for this method, as per the Niccys advice, if the building and services happens to be in fortuitous contact with true earth so much the better, but you are relying on a balanced system as the main method of compliance via exemption I)
2) add additional rods to the PME MET to achieve the same ends, you need an extremely low Ra for this method at about circa 1 or 2 ohms, this is nothing to do with TT
3) supply it from a 1:1 isolation transformer, meaning a fully floating supply
You cannot TT it due to the proximity of the PME bonded metal building
You have a few options,
1) ensure the three Phase supply is balanced according to the formula in the associated annexe with exemption I), and then it doesn't really matter how good the building is earthed to true earth, the load balancing alone will prevent the N/PME Earth from rising above 70V in the case of a broken suppliers N, you just use the existing earthing system for this method, as per the Niccys advice, if the building and services happens to be in fortuitous contact with true earth so much the better, but you are relying on a balanced system as the main method of compliance via exemption I)
2) add additional rods to the PME MET to achieve the same ends, you need an extremely low Ra for this method at about circa 1 or 2 ohms, this is nothing to do with TT
3) supply it from a 1:1 isolation transformer, meaning a fully floating supply
You cannot TT it due to the proximity of the PME bonded metal building
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E
Engineer54
uksparks
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1. I am just waiting for Amazon to deliver my book to day so will look at (i) then and calculate it.
2. I could put rods in, but what is it actually going to achieve on the basis the steel of the building is already doing the same job? I am not against the idea, but want a rock solid explanation as to how its any better than the steel work?
3. Where am I to buy one of them from? I do not know enough about transformers to even know if what I am buying is suitable in that respect, yes I know how they work, but have very little experience in using them and certainly not in this area.
uksparks
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Ok thats fine, same question goes to you, if the steel of the building is suitable, why can this not be used?
Hi E54,
I don't make the rules lol
Option 2, using this method the additional rods need a low enough Ra as a standalone solution, you cannot rely or really take into account of any bonding connections as this could change and is outside of our control, in other words they have to be low enough Ra on their own to satisfy that exemption.
Option 3) Is valid according to the regs, whether that is a better solution is open to debate lol
I don't make the rules lol
Option 2, using this method the additional rods need a low enough Ra as a standalone solution, you cannot rely or really take into account of any bonding connections as this could change and is outside of our control, in other words they have to be low enough Ra on their own to satisfy that exemption.
Option 3) Is valid according to the regs, whether that is a better solution is open to debate lol
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Engineer54
I didn't say it couldn't, but you have no idea of it's standing value at the moment do you??
See my answer to E54 above, this is akin to relying on parallel paths to achieve a low enough Zs, it cannot be relied upon
tell me roughly where and ill look in mine and post a pic, just got mine 10mins ago
uksparks
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No I don't, there is a brand new building going in next door to theirs which is identical so may take a look at it to see what the footings are like and how its anchored, might give me an insight.
uksparks
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Section 722.411 I think it was, then it refers to the an annex so you can calculate it something.
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Engineer54
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....
uksparks
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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.
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.
He is the man signing the paperwork to say it complies and which exemption he is using.
uksparks
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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
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I would like to think I have at least tried to comply with one of the options available.
E
Engineer54
That's the problem, we don't have any hard data on anything as yet....
wrong.
look at the bottom of the page, its quite straightforward.
its explained in A722.4
uksparks
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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....
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
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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.
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
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
uksparks
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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 currentSimon above did it long hand
I cheated
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
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