Earthing question - three phase into main building, then single phase to EV charger

Peter55 · Jul 12, 2022

Hi there, new to the forum and in final stages of completing C&G level 3; need to complete design project to complete. Am struggling to get my head around how to draw up correct circuit diagram showing EF Loop path for EV charger where initial supply is described as 'three phase TNCS' feeding to seperate dist board for single phase and TT earthing arrangement for EV charger. I can draw up the three phase supply, three phase dist board with 3 seperate busbars for each of the phase subcircuits. I can draw the connection to a seperate sub dist board for the EV charger. It's the earthing arrangement that I'm confused about; I understand I have to use an earth electrode for the EV charger so that it is isolated from anything else, I'll attach a sketch of what I've done so far. Has anyone tackled anything similar?

[ElectriciansForums.net] Earthing question - three phase into main building, then single phase to EV charger

timhoward · Jul 13, 2022

Welcome. I think you are very close!
I agree with your earth fault path arrows.

To me, what is missing from the diagram is showing where the supplier earthing stops.
As each cable needs a CPC, you'll typically end up with the CPC/Armour connected one end to the supplier earthing, and the far end terminated in a plastic enclosure with the CPC not connected to anything. TT earthing starts from that point onwards.

Does that answer your question?

Peter55 · Jul 13, 2022

Hi Tim thanks for taking time to reply...yes I agree. I did a bit more research and head scratching and came up with a second version of my diagram (attached) which I think has just about everything on it ...apart from a CPC connection for the second dist board to earth..which I forgot to draw in. This assumes the second single phase board is not dedicated to serving the EV charger alone but might offer power for lighting circuits etc as well. The other item I guess I could have included would be some kind of surge protection to allow for the variable charge rate of the EV charger but I was assuming I had dealt with that risk with a type B RCD or RCBO.
on reflection I think I was getting confused in my first diagram with the idea of a common neutral bar and a MET. My courses so far have mainly focused on single phase with limited 3 phase testing so the layouts look unfamiliar...but hopefully with practice things will get easier. cheers

marconi · Jul 14, 2022

Peter55 said:
Hi Tim thanks for taking time to reply...yes I agree. I did a bit more research and head scratching and came up with a second version of my diagram (attached) which I think has just about everything on it ...apart from a CPC connection for the second dist board to earth..which I forgot to draw in. This assumes the second single phase board is not dedicated to serving the EV charger alone but might offer power for lighting circuits etc as well. The other item I guess I could have included would be some kind of surge protection to allow for the variable charge rate of the EV charger but I was assuming I had dealt with that risk with a type B RCD or RCBO.
on reflection I think I was getting confused in my first diagram with the idea of a common neutral bar and a MET. My courses so far have mainly focused on single phase with limited 3 phase testing so the layouts look unfamiliar...but hopefully with practice things will get easier. cheers

I liked very much the clarity, detail and labeling of your electrical diagram.

Peter55 · Jul 15, 2022

marconi said:
I liked very much the clarity, detail and labeling of your electrical diagram.

thanks ! - I find it easier to understand if I can draw something that approximates what I would actually see in real life in terms of component parts. I still have to be careful with terminology though, especially around earthing. MET, CPC, equipotential bonding, PEN etc. I have to think carefully what each means / is referring to. I'm looking forward to being in a position to put this into practice because I know from other studies that then things will become more familiar and easier to comprehend.

GBDamo · Jul 15, 2022

Peter55 said:
thanks ! - I find it easier to understand if I can draw something that approximates what I would actually see in real life in terms of component parts. I still have to be careful with terminology though, especially around earthing. MET, CPC, equipotential bonding, PEN etc. I have to think carefully what each means / is referring to. I'm looking forward to being in a position to put this into practice because I know from other studies that then things will become more familiar and easier to comprehend.

I'm very similar mentally.

When faced with a tricky fault I usually break out the crayons, it helps to visualise problems.