4 off, 2 core swa terminated in Wiska boxes suppling LED pir lights, earth continuity - no!
Outside lighting, don't bother with the cpc,
- Thread starter vera121
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4 off, 2 core swa terminated in Wiska boxes suppling LED pir lights, earth continuity - no!
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EEBADS stands for "Earthed Equipotential Bonding and Automatic Disconnection of Supply." and has for a long time been the standard way to protect our electrical system. But it is not the only way, and outside an earth system can cause problems, we see this with EV charging, and using earth rods local to the charging outlet to either earth the outlet or activate disconnection of not only the lives, but also the earth.
The main problem is the use of a TN-C-S supply, where some where before the supply arrives in your premises the earth and neutral are combined, then split again before they enter premises, this combined earth and neutral is called the PEN, and should it break, then the earth wires in your premises may not be at true earth potential, but like the bird on the power cables, since all metal work is the same potential since bonded, there is no problem.
However export this outside, and there can be problems, so outside we tend to use double insulated equipment not needing an earth, or use a TT earthing system. So at some point the house earth and outside earth need to be isolated from each other.
So what you show could be where the TN-C-S earth is isolated from the TT earth, or it could be an error, there is no way to know with that picture, likely is an error, but I would not want to simply connect up earths without knowing.
However the rules say "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point." so we often have earth wires which are not connected to the appliance.
Some years ago I made this error, one of these
protected the installation, known as an ELCB-v now no longer used, we hope, but they measured the voltage on the premises earth and if this exceeded 50 volts to true earth it disconnected the supply. I fitted earth bonding, which effectively stopped the device working.
So I would not jump to conclusions any more, one needs to inspect whole insulation first and try and work out was the reason for the break in the earth, best option is read the installation certificate or minor works certificate covering that box.
The main problem is the use of a TN-C-S supply, where some where before the supply arrives in your premises the earth and neutral are combined, then split again before they enter premises, this combined earth and neutral is called the PEN, and should it break, then the earth wires in your premises may not be at true earth potential, but like the bird on the power cables, since all metal work is the same potential since bonded, there is no problem.
However export this outside, and there can be problems, so outside we tend to use double insulated equipment not needing an earth, or use a TT earthing system. So at some point the house earth and outside earth need to be isolated from each other.
So what you show could be where the TN-C-S earth is isolated from the TT earth, or it could be an error, there is no way to know with that picture, likely is an error, but I would not want to simply connect up earths without knowing.
However the rules say "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point." so we often have earth wires which are not connected to the appliance.
Some years ago I made this error, one of these
protected the installation, known as an ELCB-v now no longer used, we hope, but they measured the voltage on the premises earth and if this exceeded 50 volts to true earth it disconnected the supply. I fitted earth bonding, which effectively stopped the device working.So I would not jump to conclusions any more, one needs to inspect whole insulation first and try and work out was the reason for the break in the earth, best option is read the installation certificate or minor works certificate covering that box.
.... just for the benefit of readers, whilst that describes the bottom line of what an ELCB-v (probably more commonly known as "VOELCB") achieved, it's not a very correct description of 'how it worked', since it was a very simple device, not capable of "measuring" anything.
What actually happened was that any current flowing to the earth from the installation went through the coil of a solenoid, and if that current rose to a certain level, it operated the mechanism which disconnected the supply. The impedance of the solenoid coil was chosen so that when that 'threshold' value of current was flowing, there would be about 50V across it - hence ~50V potential difference between the 'earth' within the premises (i.e. the CPCs) and true earth.
I'm not sure that "stopped the device working" is quite the right way of looking at it. As I understand, bonding an extraneous-c-p to the 'earth' within the installation (on the installation side of the ELCB-v) might have prevented the device tripping in response to a fault (since some of the fault current would go though the extraneous-c-p, which might not leave enough flowing through the coil of the ELCB-v for it to trip), but the device always would still trip if the potential difference between installation's 'earth' and true earth tried to rise above about 50V.
Kind Regards, John
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Hopefully the source SWA armour is earthed. If not then that is the first thing to fix.
Having done that, it may be possible to install a couple of banjos to provide earth continuity. Alternatively as that box looks like a Wiska 308, then adding a WISKA EARTH BAR will sort it.
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3 more whiska boxes, 4 in total, all the same.
it’s not right, it’s relatively easy to fix.
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It seems very likely there is an error, my point is however this is not always the case. Some boxes have the earth links built in
and I have seen where we had a load of these then some arrived without the metal plates, and clearly the electrician was not paying attention or testing when finished. You can also get earthing nuts,
but at £25 for 10 I normally used the banjo washers which came with the gland. However to keep box water proof one has to consider where the banjo washer is fitted.
As to the ELCB-v which it seems unlikely you have, I found them fitted to static caravans, and it connected the incoming earth to the chassis of the caravan, I was sent to bond the caravan chassis, which I did, with no access to caravan, so was unaware the devices were being used, so I had effectively shorted out the protective device.
It was only latter I was asked what the device was, and next job was to fit RCD's on the supply, this was before the regulations required all caravan supplies to be RCD protected.
The point was I was doing as I was told, I was not designing, or inspecting and testing, I was only doing the installation, which could have been done by the electricians mate, i.e. brainless, just doing as I was told. Which is likely what has happened with you. The this is the way we always do it, without thinking hang on this box is non conducting plastic.
As to the ELCB-v which it seems unlikely you have, I found them fitted to static caravans, and it connected the incoming earth to the chassis of the caravan, I was sent to bond the caravan chassis, which I did, with no access to caravan, so was unaware the devices were being used, so I had effectively shorted out the protective device.
It was only latter I was asked what the device was, and next job was to fit RCD's on the supply, this was before the regulations required all caravan supplies to be RCD protected.
The point was I was doing as I was told, I was not designing, or inspecting and testing, I was only doing the installation, which could have been done by the electricians mate, i.e. brainless, just doing as I was told. Which is likely what has happened with you. The this is the way we always do it, without thinking hang on this box is non conducting plastic.
I’m redoing it next week including new 3 core swa as some of the cable is taped over, damaged and some of the terminations have let water and the armouring has gone rusty. It’s already supplied from a 30ma rcd. probably use galv conduit boxes.
Ah, right - so you meant "4 off, 2 x 2 core swa terminated in Wiska boxes"?
Kind Regards, John
Again for the benefit of other readers, "shorted out the protective device" is a bit misleading. Even with the bonding connected, the device would still have done what it was meant to do (disconnect the supply if the potential of the CPCs within the caravan relative to true earth rose to 50V) - as I see it, the only effect of the bonding would be that, if enough of the fault current flowed through the bonding/extraneous-c-p that that PD fell to <50V then the device would not operate (but would not need to operate to achieve what it was designed to achieve).
Of course, the main downside of ELCB-vs (as compared with RCDs) was that they would only operate in response to high fault currents, due to low/negligligible impedance faults. They were therefore fine for clearing such a fault before anyone had a chance to get a shock but, unlike RCDs would do nothing in the face of a 'tiny' current ('fault current')( flowing through a human being if they did get a shock, in the absence of an 'electrical fault' (whereas an RCD would).
Kind Regards, John
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If the bonding inside the building is connected to bonding outside the building then how would you ever get 50 volt between them, best you could get is milivolt.
Last week my customer mentioned that the RCD on the CU in the summerhouse could not be reset. I opened the CU and discovered (incidentally) that none of the 230v switch cables running back to the house or the cables suppling the lights in the garden had been earthed in the CU. The earths just hadn't been connected.
Mind you his previous "electrician" had used the wrong sized MCBs on the CU in the main house and bent the busbar to accommodate them, and hadn't bothered sourcing blanking plates- just leaving holes.
Mind you his previous "electrician" had used the wrong sized MCBs on the CU in the main house and bent the busbar to accommodate them, and hadn't bothered sourcing blanking plates- just leaving holes.
Sorry, I think you'll have to clarify what you are talking about.
What are these two 'bondings' and, indeed, what are you bonding 'outside the building'?
Kind Regards, John
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