earth needed in workshop (metal container)

[peterdennison99]

Hi everyone, new to the forum and have 2 questions.
I have been given a metal shipping container which is to be used as a workshop at the botttom of my garden. it has a relatively new consumer unit and electrics in already.
As it's an all metal body shouldn't the container walls be earth bonded (I assume by a bolt and 10mm earth wire attached to the metal walls and the other end to the earth strip in the cu). The container cu is fed by an armoured cable and the cu is earth bonded to the armouring of that cable and therefore earthed at the house.
Also the 240v sockets (metal mounting boxes and metal face plates - they are all correctly earthed inside each one) are attached directly to the container walls by metal screws. although I appreciate this indirectly creates an earth to the container is this ok or should they be mounted on small wood back plates to insulate them from the metal walls?
Thanks Peter

 

[securespark]

What is your type of supply?

Do you have a water supply to this structure?

 

[peterdennison99]

supply is 10mm twin cable armoured cable 240v. no water (except condensation)

 

[securespark]

Sorry. What is your supply type at the origin?

If you're not sure, post a photo of the cable coming into your house & the associated stuff attached to it.

 

[ban-all-sheds]

It doesn't sound as though there needs to be a water supply to create an extraneous-conductive-part.....

 

[OilLecky]

Someone's got to tell him to earth it! The Container needs "earthing" as opposed to "bonding". Earthing is where a high fault current can be dealt with by the protective devices (fuses / circuit breakers) and "bonding" is where conducting objects are electrically connected to keep them at the same electrical potential.
A 10mm earth cable as you said with a bolt and washers at the Container end and the other end into the earthing terminal in the CU sounds good to me. MAKE SURE THAT THE CONNECTION TO THE STRUCTURE IS LOW IMPEDANCE! To do that, clean off any paint or rust and get a good clean, metal to metal connection with the bolt and structure. After you have made the earth connection protect it from corrosion with silicone or similar. Make sure that you are using a RCD?
Once the container structure is properly earthed, the screws in the accessories will be OK. What about all the sides and doors? Are they electrically bonded to the main container structure?
You must get all this inspected and tested as you MUST ensure that the impedances are correct to operate the protective devices within the correct times.

 

[Spark123]

Think it would be a good idea to know what the supply type is first - if it is TN-CS then a TT conversion might be the way forwards.

 

[peterdennison99]

Thanks v much for replies. Oilecky - very useful and sensible, I think having read one or two forum threads it's common that people forget most of us aren't professionals in that field and thats why we ask advice. I'l earth using a bolt and 10mm cable and protect it (cleaning off metal 1st) and also get the installation checked by a sparky. doors on metal hinges so 'bonded' across too. Thanks again to all.

 

[securespark]

Think it would be a good idea to know what the supply type is first - if it is TN-CS then a TT conversion might be the way forwards.

Thank you!

What is your type of supply?

 

[peterdennison99]

oops, having re read my reply and the following one it sounded as though I was having a dig which wasn't the case. V v grateful for all help. Thanks again.

 

[OilLecky]

Peter,

Yes the others are trying to help. All this TT business will mean nothing to most people but a photo of the incoming supply to your house showing the Live, Neutral and Earth means that we can give you more info. (P.S. Don't rely on the metal hinges to give a good bond, you'll probably need a flexible bonding cable connecting across the door / wall hinge.) You need a tame Electrician with the correct test kit. Working inside and going in and out of a conductive box is extremely dangerous if the power supply and earthing are not top notch!!!!

 

[tim west]

Another thing depending on location and being an all metal structure of fair size does it warrant attention to lightning strikes and need appropriate protection?

Worked on an installation in a metal clad factory in gillingham that wasnt particularly tall but was always getting hit by lightning taking out the main RCD each time, so much for the saying "lightning never strikes the same place twice" in this case its true it must have been half a dozen times in the short time i was working there and didnt half make a bang when it hit the roof .

 

[Adam_151]

so much for the saying "lightning never strikes the same place twice"

I'm sure I remember being told that our local cathedral gets hit many times a year...the saying might hold true for smaller things, but for anything taller/ or metalic and reasonably sized...

Did your factory not have a lightening protection system?

...Though for something the size of a shipping container, I'm not sure you have to worry ... well at least not until you add wheels and tow it to and plonk it in the middle of, a large open field...

 

[Spark123]

Peter,

(P.S. Don't rely on the metal hinges to give a good bond, you'll probably need a flexible bonding cable connecting across the door / wall hinge.)

¿Que?

 

[tim west]

Did your factory not have a lightening protection system?

Yes There was a rod and tape down the side but I'm not sure if itworked or not as the bang seemed to echo from all over the roof perhaps the rod and tape caused a shockwave when it dealt with the strike?