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Posted By Topic: Earthing 20ft container

bakinthegame
Nov 01 2018 11:54

Hi just after some clarification on earthing requirements for semi-permanent container as My experience dealing with such things is limited.

Will just be tapping off an existing rcd protected powerpoint to provide 1 x socket & 2 x led lights to the container.

I will run everything in conduit wich will technically make everything triple insulated so any requirement to actually earth the container?

I was hoping at the very minimum I could just run a bond the container with a 6mm earth back to the earth terminal of the powerpoint.
   

DougP
Nov 01 2018 15:35

You shouldn\'t need to earth it. 5.4.6

But as it\'s possibly sitting on the ground, it is an extraneous conductive part and should probably be bonded.
   

OctaneOutlaw
Nov 01 2018 21:01

\"I was hoping at the very minimum I could just run a bond the container with a 6mm earth back to the earth terminal of the powerpoint.\"

I was under the impression this wasn\'t allowed unless I\'m misreading it

5.6.3.1 The selection and installation requirements for equipotential bonding
conductors shall be in accordance with this Standard for protective earthing
conductors.

That leads me to 5.5.2.1 which details the permissible locations in which earthing conductors may be connected

Also doesn\'t 5.5.2.2.1 directly relate to this?
   

medistat
Nov 01 2018 23:56

If the feed is done via a plug then surely the container is technically the same as a caravan which doesn\'t require an earth peg.... I have a few containers and all have Electrical WOFs and are fed via a 32A 3-pin plug but the Inspector has never suggested earth pegs at all...
   

AlecK
Nov 02 2018 08:45

Octane Outlaw is correct, both those clauses comply.

No electrode required; unless using the PEN-to-outbuilding provision of 5.5.3.1(b).

If double insulation not maintained, then earthing required. If using subcircuits for this (eg earthing at open-backed fitting) then earthing must be done for each subcircuit and should be done at each place where the loss of DI occurs.

Generally better to install a separate earth wire, sized for largest active; and take it back to a point compliant with 5.5.2.1. See also Fig 5.3
   

DougP
Nov 02 2018 09:43

This seems to have gone off on a tangent. Maybe if we stick to addressing the original post?

There was never any mention of an earth stake, or of it being a plug in transportable.

bakinthegame said the wiring system would be enclosed satisfying 5.4.6.1, and that it would be an RCD protected final subcircuit.

Even if it was determined that the metalwork required earthing, there is no requirement for a separate earth wire. It can be earthed by the earth conductor of the circuit the same as conductive building materials or any other equipment.

If it is determined that the requirement is \"bonding\", then there is still no requirement for a separate bonding conductor or for the bond to be connected directly to the earth bar or MEC - the same as a bathroom slab bond, or pool bond connection point.
   

OctaneOutlaw
Nov 02 2018 12:45

Just trying to understand a few things you are both saying, I was always told you couldn\'t take it back to the terminals of an item

Could either of you elaborate on this?

\"If double insulation not maintained, then earthing required. If using subcircuits for this (eg earthing at open-backed fitting) then earthing must be done for each subcircuit and should be done at each place where the loss of DI occurs.\"

And

\"Even if it was determined that the metalwork required earthing, there is no requirement for a separate earth wire. It can be earthed by the earth conductor of the circuit the same as conductive building materials or any other equipment.\"

Are you both basically saying it\'s ok to take a protective earth conductor back to the terminals of a plug for example provided that those active conductors are the ones posing the risk of single insulation to the conductive part? And when there is more than one item, it must be done for each item with the appropriate sized earth depending on the size of the actives in question?

Otherwise you can just use one sized to the largest but if this is done it must go back to one of the appropriate locations in the clause mentioned above?

   

bakinthegame
Nov 02 2018 18:35

After reading 5.5.2.1 it doesn’t say it’s compliant to run a protective earthing conductor back to a PowerPoint terminal so outlaw is correct on that one.

However after reading 5.4.6.1 which deals with structural metalwork - doug & aleck are right - container doesn’t need to be earthed at all as everything will be double insulated.

Sorry I had a poor choice of words with ‘bonding’ which probably didn’t help, meant to be ‘earthing’

People standing inside conductive metal containers which have electricity to them just freak me out - so just wanted to be sure I hadn’t missed anything!
   

DougP
Nov 02 2018 19:40

5.5.2.1 relates to where a submain or subcircuit PEC can be connected. It doesn\'t directly apply to earthing or bonding of extraneous conductive parts or conductive building materials.

5.4.1.2, 5.4.1.3 and 5.4.6 etc all simply say \"shall be earthed\" - and 5.4.6.3 for structural metalwork is headed \"connection to protective earthing conductor\" but is silent on where that earthing conductor originates.

Items on any particular final subcircuit that require earthing, are allowed to be earthed from the subcircuit earth. So it follows that any conductive building material related to wiring of that circuit can also be earthed from that circuits earth to satisfy 5.4.6.1 requirements - and that is a common occurrence with metal framed buildings which are earthed at each power point or light switch.
   

bakinthegame
Nov 02 2018 20:57

Cheers Doug, regardless we’ve established it doesn’t necessarily need earthing.

I’m struggling to find the following anywhere though, that says you can earth from a PowerPoint (where previously I thought this was possible)

“Items on any particular final subcircuit that require earthing, are allowed to be earthed from the subcircuit earth. So it follows that any conductive building material related to wiring of that circuit can also be earthed from that circuits earth to satisfy 5.4.6.1 requirements - and that is a common occurrence with metal framed buildings which are earthed at each power point or light switch”

Do you have a reference for this? I can’t see anything like that in 5.5.2.1.


   

DougP
Nov 02 2018 21:52

If there was a requirement for a specific method of earthing or bonding, it would be stated.

Bonding a water pipe for example, 5.6.2.2 states exactly where the connection must be and where it must be connected (MEC or bar).
5.6.2.5 for shower concrete reinforcing - states \"bonded to the earthing system of the electrical installation\" so that allows any point, on any circuit. And even thought the actual bonding conductor is required to be 4mm2, the earth it connects to can be smaller.
Swimming pools are the same. The bonding conductor is 4mm2, but it just gets connected to the circuit supplying the pool equipment.
   

DougP
Nov 02 2018 21:54

5.6.3.1 that OctaneOutlaw previously highlighted, states that The selection and installation requirements for equipotential bonding conductors shall be in accordance with this Standard for protective earthing conductors. except for size (5.6.3.2).

To me selection and installation is 5.3.3.1.2 and all of 5.5.5

Whereas 5.5.2.1 is part of 5.5.2, which is only related to the connection of submain and final subcircuit PECs.

It relates to where a circuit earth can be connected to - rather than what can be connect to and earthed via the circuit earth.
   

AlecK
Nov 03 2018 10:20

Travelling today, so don\'t have ready access to the references. But my feeling / recollection is that the rule for where a PEC can be terminated applies to all PECs, not just to submain / subcircuit PECs.
And since terminating is part of installation, it carries over to apply to equipotential bonding as well.

The bit about using a subcircuit PEC to earth associated metal sn;t specifically stated; it just follows from the other rules that if tyhe only bit ofg c abling that doesn\'t have DI is at eg a switch on an open-backed mtgh block, or at a batten holder / ceiling rose, or similar, then since the relevnt active is that subcircuit you can earth using that sunbcircuit\'s PEC. There may be several such points along the subcircuit, but you only have to do it at one point. Which of course should be the first point, closest to supply; so that it doersn\'t get disconnected when the subcircuit is altered later. And of vourse best practice would be earth at every such point.

But since we can\'t use one subcircuit to earth items associated with another subcircuit, we have to do this for each subcircuit that has such points - even if they are the same metal items and in fact even if the points on 2 subcircuits are co-located.
OR we can use an independent earth, in which case because it\'s separate from any of the subcircuits can be used to earth any items associated with any / multiple subcircuits.

It\'s mot just about ensuring it\'s earthed now, it\'s also about ensuring that alterations to one subcircuit don\'t remove an earth that\'s still required for another subcircuit.

Time was when the container would have been requited to be earthed regardless, but not any more - unless it\'s domestic.
And for bonding, it\'s not specifically required any more either. Though since a container sitting on the ground presents the same risk of touch voltage between it and the earthing system of the installation as a water pipe does; I believe it should be required and I\'d certainly bond it. In fact I\'d probably earth it by independent PEC run back to supplying DB; thus ticking both boxes (protective earthing and equipotential bonding.

   

bakinthegame
Nov 03 2018 14:26

Thanks & all makes sense.

Unfortunately running a PEC back to the DB board is not possible.
It’s a school & the container is located next to a garage which only has one rcd protected powerpoint in it, which in turn is fed from a classroom.
So my only real option is to feed the container off this exisiting garage powerpoint.

Even though it doesn’t need to be earthed I think I’d feel better about the situation if I at least bond the structure back to the PowerPoint.

   

OctaneOutlaw
Nov 03 2018 16:08

Right, awesome that makes sense, thank you

So it\'s more a procedure of earth or bonding to a location that\'s not going to be accidentally disconnected?

And the reason it\'s ok when it\'s the relevant actives is because if that circuit is disconnected then that earth connection was for them anyway and without them is redundant so doesn\'t matter

So basically for bonding it should always go back to one of the specific locations in 5.5.2.1 to ensure that it can\'t accidentally be disconnected? Same for a common PEC? Because if the one circuit it was connected to was disconnected it wouldn\'t risk losing that protection when it\'s still needed elsewhere?

Am I on the right page now?
   

AlecK
Nov 04 2018 09:19

That\'s pretty much on the button.

When i was an apprentice, we used to be required to \"bond\" s/s sink benches; and commonly used the nearest socket\'s PEC to do it. That sort of thing is no longer allowed.
But also bonding things like sink benches, shower trays, and urinals that have no independent continuity to mass of earth is no longer required. Of course there never was a good reason to do it in the first place, \'cos there was never any real chance of touch voltage appearing on such items.

If you can find a copy of the 1976 Regs handbook, there\'s an explanation after R 151 of some of the ways touch voltage can appear.
It even talks about the different resistance of hot water as compared to cold water, so that hot taps had to be bonded to cold. But when you look at it, that one is really about earthing rather than bonding, as it\'s about leakage currents being higher.
   

OctaneOutlaw
Nov 04 2018 10:28

Makes complete sense, apologies to everyone for sometimes drawing out some of these posts/straying sometimes from the original point but I hope these questions will benefit some of you as it does me, only way to learn is to ask!