PME carport

[marcuswareham]

Hello

Hope everyone if well with this cover-19 stuff going on

Quick question

I would like to put a power supply to a metal framed car port, the metal frame is buried into the ground so definitely introduces earth potential, the ground inside the carport is tarmac laid on top of soil

The power supply is coming from P.M.E house, I think the best option is to make the carport TT and install RCD protection, However I cannot achieve sufficient separation between PME bonded gas pipe and water pipes in the ground and the new earth electrode.

If I export the PME earth and bonding the metal structure then surely this is creating a large shock risk to anyone standing on the wet grass next to the car port and in contact with the metal structure if there was a PEN conductor fault.



Looking at 18th Edition Amendment 1 section on EV charging

722.411.4.1
(iv) Protection against electric shock in a single-phase installation is provided by a device which electrically disconnects the vehicle from the live conductors of supply and from the protective earth in accordance with Regulation 543.3.3.101(ii) within 5 s in the event of the utilisation voltage at the charging point, between the line and neutral conductors being grater than 253 C rms or less than 207 V rms. The device shall provide isolation and be selected in accordance with Table 537.4. Equivalent means of functionality could be included within the charging equipment. Closing or resetting of the device shall be possible only if the voltage between line and neutral conductors is in the range 207 to 253 V rms.



Maybe I could use a device like this but not for EV charging but instead to protect car port from open PEN

Although I cannot find anywhere to buy such a device

Many thanks

Marcus

 

[pc1966]

I guess in the house on a TN-C-S supply if you had such a fault (say from a mouse in the loft chewing some cable (yes the mouse shouldn't be there and the cable should be protected if they are there)) then even if the RCD was not to work as you have such high earth fault currents then the MCB could work as a back up

On a TT system a N-E fault might not be detected by the RCD as you say. For example if the N is only a 2-3V above E and your rod is, say, above 30 ohms then it is going to be doubtful if a 100mA S-type RCD would see enough to trip.

In your case, as you have a MFT and know how to use it, it would be easy to periodically trip the main RCD (as it should be tested anyway) and do an overall insulation test N->E without having to disconnect anything (in effect you would be doing N+L to E as there are bound to be loads L-N even if you do the decent thing and pop each MCB before the main one)

At least with T&E a mouse-nibbled cable is likely to leak L-E and show up quickly to you by the RCD tripping before you get to the high faults currents that L-N would see before the MCB trips. Not as quickly as it will to the mouse though...
[automerge]1587140019[/automerge]
Of course if any electronics are still plugged in (as it might be if you are just doing a RCD check when clocks change or whatever) then testing at 250V would be sensible.

 

[marcuswareham]

On a TT system a N-E fault might not be detected by the RCD as you say. For example if the N is only a 2-3V above E and your rod is, say, above 30 ohms then it is going to be doubtful if a 100mA S-type RCD would see enough to trip.

In your case, as you have a MFT and know how to use it, it would be easy to periodically trip the main RCD (as it should be tested anyway) and do an overall insulation test N->E without having to disconnect anything (in effect you would be doing N+L to E as there are bound to be loads L-N even if you do the decent thing and pop each MCB before the main one)

At least with T&E a mouse-nibbled cable is likely to leak L-E and show up quickly to you by the RCD tripping before you get to the high faults currents that L-N would see before the MCB trips. Not as quickly as it will to the mouse though...
[automerge]1587140019[/automerge]
Of course if any electronics are still plugged in (as it might be if you are just doing a RCD check when clocks change or whatever) then testing at 250V would be sensible.

Exactly as I was thinking. Same the is an RCD to save the mouse :- P

 

[pc1966]

Same the is an RCD to save the mouse :- P

I'm not taking any bets on the mouse!

 

[Lister1987]

It has inbuilt RCD protection and uses the current clamp to monitor overall load on incoming supply and lowers/increases its power consumption during time of high/low demand, if I'm remembering correctly it monitors current instead of voltage and being the only one (apparently) to work on this manner it will isolate correctly in the case of a broken neutral, whereas others won't

Of course rereading your post your just after sockets, not an EV Charger, my bad.

There is a device (Matt-E) by the same company I believe that does what the Zappi does in terms of voltage/current monitoring but is designed to be used inline with a supply, going to for example a hot-tub or in this case; exterior sockets.