Power next to a container.

It sounds like it's a tricky position. The current situation is clearly very poor with vehicles driving over unprotected cables. The ideal permanent soloution would be to bury a cable from the lockup to the container but that is likely to be expensive and disruptive.

Sadly the danger is if you do something that is better than what is happening now but still less than ideal and it goes wrong then you could be held responsible for it.

One concern I have with the idea of running a cable accross the road inside a speed bump (as you mentioned in your other thread) is what happens to the cable after it leaves the speedbump? how will it be protected?

As regards circuit arrangements I'd say the best thing would be to take a SWA cable from the lockup to a consumer unit in the container. Then go from there to lights and sockets inside and outside the container.

Earthing wise you have two choices, you can either export the earth from the lockup or use a new earth rod to make an indpendent TT supply with suitable RCD protection. Both have their pros and cons and which is better will depend on the details of the supply to the lockup. Either way you would almost certainly want to bond the container to the supply being used in it's vicinity.

plugwash said:

One concern I have with the idea of running a cable accross the road inside a speed bump (as you mentioned in your other thread) is what happens to the cable after it leaves the speedbump? how will it be protected?

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I would propose the 'speed bump' was run from the front of the garage, up to the container

Earthing wise you have two choices, you can either export the earth from the lockup or use a new earth rod to make an indpendent TT supply with suitable RCD protection. Both have their pros and cons and which is better will depend on the details of the supply to the lockup. Either way you would almost certainly want to bond the container to the supply being used in it's vicinity.

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stillp said:

We dont know what the earthing or supply details are

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That's the first question you'll need to answer.

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I have asked on of the guys to take photos of the consumer unit, and which of the garages we now have access to, as if it includes the one at the end where I think the cable comes in, that might shed some light. Otherwise clearly, we can only talk about the options.

If the container was not there, playing devils advocate slightly, where would you stand then in terms of having a number of outdoor sockets and or floodlights on poles?


Daniel

Probably the best idea is to take to the meeting a workable system and then let the group modify. A suggestion would be SWA from garages to container under the protector. The steel protective being connected to earth in the garages and the internal earth wire being connected to this at the cabin. The cabin now uses a rod (TT system). You'll need to bond all parts of the metal container, including the doors. Probably easiest to use a "garage" CU in the container with suitable MCBs. RCD protection could be at either end. Suggest in garage because less chance of condensation problems, also if people have to walk across road they will think of problems rather than just flicking back on. All power tools will need PAT testing (who will own what?). Waterproof light switch outside container rather than IR detector to avoid nuisances from wind debris, cats etc.
Not part of the electrical queries, but you will need to show governance to the meeting e.g. you won't be able to store petrol or gas bottles in the container so in your "statement" make it clear that you've thought of these things and have rules of use written down ready to present.

viewer said:

Probably the best idea is to take to the meeting a workable system and then let the group modify.

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Fully agree.
- But obviously that requires drawing up a workable system, and ideally, having a basic understand of what and why the modifications are coming in, as there is proberbly only one hit to determine whats going to be done and hence how much its going to cost!

A suggestion would be SWA from garages to container under the protector. The steel protective [armor/outer] being connected to earth in the garages and the internal earth wire being connected to this at the cabin.
The cabin now uses a rod (TT system). You'll need to bond all parts of the metal container, including the doors.

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Slightly surprised that you seem to be suggesting bonding the 3rd 'internal earth' to the steel armor and the container/cabin end. Although I can see that if your using 3 core (because its whats in the van) you have to fix the third cable to something somewhere.
Valid point about attaching the doors as well, I have seen this done before, with a short piece of cable at the top of the hinge looping them back to the main structure, and I guess things like welding a zinc plated bolt, head first, to the container, and to the door, and both hinges, is something the club could do in advance of the spark installing the cable, and probably the neatest and most robust way of doing the job.

Probably easiest to use a "garage" CU in the container with suitable MCBs. RCD protection could be at either end. Suggest in garage because less chance of condensation problems, also if people have to walk across road they will think of problems rather than just flicking back on.

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Can you TT the earth and then have the RCD at supply? Sounds find to me if it works, and I presume there is an RCD in the garages already although its long enough ago I cant recall.
In terms of damp, the garages are damp enough there is going to be very little if anything in it. The container might even be better ventilated.

All power tools will need PAT testing (who will own what?).

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Powertools are PAT'ed annually by the university for the club.

Waterproof light switch outside container [for the flood lights] rather than IR detector to avoid nuisances from wind debris, cats etc.

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Yes. You also dont want them to go of when your working on a car, just because you the otherside of it than the PIR. And for me it makes sense to use metal halides rather than halogens to boot.

Not part of the electrical queries, but you will need to show governance to the meeting e.g. you won't be able to store petrol or gas bottles in the container so in your "statement" make it clear that you've thought of these things and have rules of use written down ready to present.

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I agree.
- We don't store petrol on site, other than in the cars, which are always outside.
- We dont have any gas onsite, except a handheld butane blowtorch, and maybe at max one spare cylinder for that. And a cylinder of argosheild, which the Uni are aware of, and we have the required 'pressurised gas' sticker on the door of the garage.
- We also don't allow battery charging inside the garage.
- There is a written statement of what can and cant be done in the garage or in the work area, but this may need updating, and printing out a copy to take with may will also be a good shout. Along with checking the condition of the compressed gas sticker, etc.

The yellow/orange square on the plan is a LPG tank used be the balloon club for re-filling there tanks, but sadly we don't get to use that!



Daniel

dhutch said:

viewer said:

A suggestion would be SWA from garages to container under the protector. The steel protective [armor/outer] being connected to earth in the garages and the internal earth wire being connected to this at the cabin. The cabin now uses a rod (TT system). You'll need to bond all parts of the metal container, including the doors.

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Slightly surprised that you seem to be suggesting bonding the 3rd 'internal earth' to the steel armor and the container/cabin end. Although I can see that if your using 3 core (because its whats in the van) you have to fix the third cable to something somewhere.

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It's a bit confusing. Viewer seems to be talking about separately TTing the container, with the SWA armour earthed only at the garage end (fair enough), but also connecting the third core ('internal earth'?) of the SWA to the armour at the container end. In as much as one would probably want to connect that 'spare' core to something, that's fair enough, but I'm not sure why he talks about connecting it to the armour at (or only at) the container end. If one were separately TTing the container etc., the important point would be that nothing connected to the garage's earth (SWA armour and/or core) should be connected to anything at the garage end.

One thing which will undoubtedly be considered when decisions are taken about earthing is the situation of the container. If it is (or effectively is) sitting on bare ground, then it's probably going to be fairly well connected to 'local earth', anyway, even if one didn't formally locally TT it (with a rod) - so that might be an argument in favour of separate TTing.

dhutch said:

Can you TT the earth and then have the RCD at supply? Sounds find to me if it works,....

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An RCD does not know, and is not 'interested' in, anything about what earths are connected to what in the installations - all it knows about are L-N current imbalances, due to some current finding a return path to the supply transformer (via some connection to true earth,any connection to truth earth) other than the neutral conductor. So, yes, it will work.

When considering protective devices and the arrangement of the wiring, the usual worries about a single fault having the potential to take out lighting in the container if/when someone was using a power tool within the container (no matter how unlikely it is that someone may do that) will presumably need to be taken into consideration.

Kind Regards, John

JohnW2 said:

One thing which will undoubtedly be considered when decisions are taken about earthing is the situation of the container. If it is (or effectively is) sitting on bare ground, then it's probably going to be fairly well connected to 'local earth', anyway, even if one didn't formally locally TT it (with a rod) - so that might be an argument in favour of separate TTing.

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Container is sat directly onto the tarmac that forms the work area and road, spaced about 6 inches away from the metal perimeter fence.

An RCD does not know, and is not 'interested' in, anything about what earths are connected to what in the installations - all it knows about are L-N current imbalances, due to some current finding a return path to the supply transformer (via some connection to true earth,any connection to truth earth) other than the neutral conductor. So, yes, it will work.

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Yes, that makes sense.

When considering protective devices and the arrangement of the wiring, the usual worries about a single fault having the potential to take out lighting in the container if/when someone was using a power tool within the container (no matter how unlikely it is that someone may do that) will presumably need to be taken into consideration.

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Yes, this is to a point also valid point.
- I solved this in my own garage, in which I do quite a lot of work, but installing a small emergency light (8w floro, £12 from tlc).
- That said, in many ways the bigger issue would be if the flood lights went off on the work area on the same tack.
- You could solve that by having the floods, or atleast one flood, off the garage directly. Or, taking the container feed off a non-rcd-protected circuit, and putting two rcds, or a main switch and rcbo, in the container.


Equally, there is an argument that (like my garage was) the whole lot is currently run of a single extension, and feeding more reasons to add costs is unnecessary given that although working in low-light in not uncommon, working in the night is very rare indeed, and there is a lot of light pollution around from other facilities on campus, and the public road the other side of the perimeter fence.


Daniel

dhutch said:

Yes, this is to a point also valid point. - I solved this in my own garage, in which I do quite a lot of work, but installing a small emergency light (8w floro, £12 from tlc).

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Indeed, that is the best solution, and the only solution that will cope with sudden loss of electricity due to any cause.

dhutch said:

- That said, in many ways the bigger issue would be if the flood lights went off on the work area on the same tack.
- You could solve that by having the floods, or atleast one flood, off the garage directly. Or, taking the container feed off a non-rcd-protected circuit, and putting two rcds, or a main switch and rcbo, in the container.

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None of those measures would maintain lighting in the case of, say, a 'power cut'. However, I'm not sure that this is necessarily a 'bigger issue' since, as you go on to say, you do not envisage much/any work being undertaken during hours of darkness. I suppose you could have some sort of outdoor emergency light to provide at least some lighting in the case of power failure.

Kind Regards, John

Just to clarify; I'm talking about joining the internal earth cable (i.e. the one joined to the earth terminal in the garage CU) to the container end of the steel protection. The garage end of the steel protection is also joined to earth (probably directly to the garage MET). The earth wire from the container CU/MET goes to the rod. This gets rid of any "spare" wires and completely separates the garage earthing system from the container earthing system, whilst ensuring that there is an earth for all parts of the system.

viewer said:

Just to clarify; I'm talking about joining the internal earth cable (i.e. the one joined to the earth terminal in the garage CU) to the container end of the steel protection. The garage end of the steel protection is also joined to earth (probably directly to the garage MET). The earth wire from the container CU/MET goes to the rod. This gets rid of any "spare" wires and completely separates the garage earthing system from the container earthing system, whilst ensuring that there is an earth for all parts of the system.

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AsI said, that's what I thought you meant. It would perhaps be less potentially confusing if you simply said (I assume that this is what you mean!) that the earth core of the SWA (assuming there is one) would be connected to the SWA armour at both ends and both would be connected to the 'MET' at the garage end, but that neither (earth core or armour) would be connected to anything at the container end (the container being separately TT'd to a local earth electrode).

That is the standard system when using a separate, isolated, TT earth for an 'outbuilding'.

Kind Regards, John

Yes, apologies for poor use of the English language. We agree on what is required.

Thanks for clearing that up.

For interested, what is gained from joining the third core to the swa armor at the container end, rather than just cutting back the internal wire?

Obviously if you where to use two core swa, the whole issue goes away, and again I presume the only reason for using three core in this application is its being more available than two core.



Daniel

dhutch said:

Thanks for clearing that up. For interested, what is gained from joining the third core to the swa armor at the container end, rather than just cutting back the internal wire?

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Not much, electrically, other than removing the possibility of an induced voltage arising between the core and armour at the container end, if they were not connected at that end. It's also always nice to have all conductors connected to something (and available for future use), rather than 'floating or 'cut back'.

dhutch said:

Obviously if you where to use two core swa, the whole issue goes away, and again I presume the only reason for using three core in this application is its being more available than two core.

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Two-core is pretty available. However, if (for whatever reason) 3-core is being used, I can see no particular electrical reason why that third core could not be doubled up with (i.e. wired in parallel with) the L or N core, thereby reducing VD and Zs a bit.

Kind Regards, John

dhutch said:

what is gained from joining the third core to the swa armor at the container end, rather than just cutting back the internal wire?

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Wash your mouth.

Never cut back unused cores.

Therefore it has to be made safe so connect to earth (the swa).

In this case the core is already connected to earth and swa at the origin.

JohnW2 said:

Not much, electrically, other than removing the possibility of an induced voltage arising between the core and armour at the container end, if they were not connected at that end. It's also always nice to have all conductors connected to something (and available for future use), rather than 'floating or 'cut back'.

Two-core is pretty available. However, if (for whatever reason) 3-core is being used, I can see no particular electrical reason why that third core could not be doubled up with (i.e. wired in parallel with) the L or N core, thereby reducing VD and Zs a bit.

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Fair enough, as you say, paralleling it with the live (or maybe better, neutral) would work too, sleeve it the right color, etc.

EFLImpudence said:

Wash your mouth.
Never cut back unused cores.

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Ok, yes, there is that...


We're off aon a bit of a tangent, but it gives my something to read over lunchtime in the office!


Daniel