Steel Container/cabin with PME supply

[Aaron b]

Hello, Where I work there's a steel cabin that other employees have installed and powered up without certification. Am I correct in thinking it's covered under part 717.411.4 that it can not be connected to a PME supply? I've been asked to test it and I'm concerned with the design and installation of the supply. With how easy it would be to TT I don't feel the risk is worth it even if it wasn't covered by 717.

 

[timhoward]

Do either of the exceptions in 717.414.4 apply - is it under continuously supervised by skilled or instructed person(s), and was the earthing checked before it was connected. (You said it wasn't certificated; was it tested?)

 

[buzzlightyear]

Hello, Where I work there's a steel cabin that other employees have installed and powered up without certification. Am I correct in thinking it's covered under part 717.411.4 that it can not be connected to a PME supply? I've been asked to test it and I'm concerned with the design and installation of the supply. With how easy it would be to TT I don't feel the risk is worth it even if it wasn't covered by 717

what where they thinking faraday cage .

 

[cliffed]

TT the sensible thing to do, especially with the MBPC sizing issues

 

[brianmoooore]

what where they thinking faraday cage .

It is a Faraday cage, and they are absolutely safe inside of it, whatever condition the supplier's combined N & E is in. The potential problem occurs when they enter or leave it.

 

[Aaron b]

As far as I'm aware no testing has been completed. There is no management system detailing supervision or instruction, it's just a cabin used as storage with heating and lighting and I think it is reasonable to think any employee could use it.

Would these exceptions be for exceptional circumstances such as where the task would make a TT system impractical and testing would be conducted before each use? I struggle to see how an instruction would make the loss of a neutral less hazardous unless it was switched off before touching the true earth.

It's also appears to fed from a 32a socket that doesn't appear to be RCD protected. I think it's reasonable for me to refuse to test it.

 

[brianmoooore]

Why would you refuse to test it? Test and condemn.

 

[snowhead]

If you don't test it you can't document the faults with it (if any exist) and it will continue to be used in a potentially unsafe condition.

(Beaten to it byBrian)

 

[Aaron b]

Thanks, I suppose that's true. Should I conduct live testing though as surely it would fail on inspection? The main building has a couple of extraneous conductive parts not earthed, steel braces from the building that has recently had conductive parts installed near it and a new gas main. Would it be a bad idea to live test without that being sorted first?

 

[brianmoooore]

If you believe that it's unsafe to live test, then don't live test. You're the expert on site.

 

[pc1966]

I think these days a 230V/400V outdoor plug/socket without 30mA RCD protection would be a C2 on any EICR inspection. Not sure how that would apply to your site though.

From my own limited experience of these sort of cabins they usually have a 30mA incomer, so TT'ing is easy. But you would need an acceptable rod or similar for earth, and you also have the risk of a fault L-E before the RCD which might be worse than the PME risk depending on how the cable is routed into the cabin and the quality of the electrics there.

 

[Aaron b]

Thanks for everyone's input. Hopefully I can get them to make it safer by fitting a RCBO to the socket and TT'ing the cabin.

 

[buzzlightyear]

Thanks for everyone's input. Hopefully I can get them to make it safer by fitting a RCBO to the socket and TT'ing the cabin.

Just think about it a lost neutral on the DNO side the metal would become live the first thing any body would do is to open the bloody metel handle so they would become live straight. way.

 

[timhoward]

It’s slightly grey in my mind whether a 32A outside socket would attract a C2, as before 18th edition I think anything over 20A wasn’t required to have RCD protection. I’d like it to be a C2!
In this case it’s effectively an extension to the installation as the thing will never get unplugged, so the circuit supplying it should be up to current regs.
I’d insist on the RCD protection.

The risks of likelihood and consequences of pen fault versus TT and RCD failure are interesting.
With no data, if forced to place a bet, I’d go with the RCd never being tested and getting stuck one day as more likely to happen. But losing fault protection only matters in a fault, going open pen in this situation is always going to be serious. I’m not a “just TT it” person but I think it’s justified in this situation.

I’d like to see more affordable pen protection devices (as per car charger market) so the benefits of low impedence earthing can be retained in these situations.

 

[Aaron b]

It’s slightly grey in my mind whether a 32A outside socket would attract a C2, as before 18th edition I think anything over 20A wasn’t required to have RCD protection. I’d like it to be a C2!
In this case it’s effectively an extension to the installation as the thing will never get unplugged, so the circuit supplying it should be up to current regs.
I’d insist on the RCD protection.

The risks of likelihood and consequences of pen fault versus TT and RCD failure are interesting.
With no data, if forced to place a bet, I’d go with the RCd never being tested and getting stuck one day as more likely to happen. But losing fault protection only matters in a fault, going open pen in this situation is always going to be serious. I’m not a “just TT it” person but I think it’s justified in this situation.

I’d like to see more affordable pen protection devices (as per car charger market) so the benefits of low impedence earthing can be retained in these situations.

It's not just a C2 though as although the electrical install in the cabin is existing the supply is new so as far as I'm aware can't have any non conformities unless declared by the designer. I've brought in my big hammer and my mft so I'll see how it goes.

 

[Aaron b]

I'd agree with relying on one RCD though and think having a type s upstream is good practice. In this case if I get the socket on a RCBO too both would need to fail

 

[brianmoooore]

I’d like to see more affordable pen protection devices (as per car charger market) so the benefits of low impedence earthing can be retained in these situations.

Had these years ago - voltage operated earth leakage breakers. Modern version would have to be three pole rather than two, though, to break the earth as well.

 

[timhoward]

Had these years ago - voltage operated earth leakage breakers. Modern version would have to be three pole rather than two, though, to break the earth as well.

Ah yes, but those things had a number of flaws including needed a working earth to work at all didn’t they, as it was a coil between the energised earth conductor and real earth that triggered the trip?

I think there's now an £80 ish solution from CityVolt that looks interesting, as it's getting towards the price point where customers could be convinced into having one....

CityEV Safevolt® 50 EV PME Automatic Fault Detector Single Phase Version - CityEV

The New CityEV Safevolt® 50 model – no 6mA DC block Install single phase charge points compliant with 18th Edition recommendations and IET Code of Practice for Electric Vehicle Charging Equipment. Simple indoor installation of the CityEV Safevolt® PEN fault detector, 7Kw, 32A. No need to convert...

cityev.net

 

[Rockingit]

Answer is found in GN8 10.5.6 (717.411.4) - "Regulation 9(4) of the ESQCR prohibits a distributor's combined neutral and protective (PEN) conductor (from a PME network) being directly connected to any metalwork of a caravan. For safety reasons, the same requirement also applies to mobile and transportable units, with certain exceptions, as stated in Regulation 717.411.4 of BS7671..... [Another] precaution that can be taken is the connection of earth electrodes to the main earthing terminal (MET)....."