Electrical sockets for obsy, recommendations please

[Chris]

Safety is always paramount. As little as 35mA can cause a fatal fibrillation if you're unfortunate enough to have a current pass across your chest.

Well that would be an horribly ironic death considering I'm part of the cardiac team at my local hospital:D I Think you guys have helped me see that the whole things got to go and I'll start from scratch with some furher research:)

[freeflyjay]

A TN-S system with a failed sheath connection could have been converted to TT - it's been known.

a possability for sure,i`ve a lot of things over the years, but i`d have to look and get some meters out, a bit far for me i`m afraid, but DO NOT remove the earth wire, if this is a tt system you would leave your house with no earth.

[Chris]

If you're competent to do this then you can do it yourself by notifying your local building control and having them inspect and test. It'll still cost you but it might be cheaper - ask your BC department for advice first. Be warned though, SWA is horrible stuff to handle and terminate if you're not used to it. If you decide to go with the electrician sign off, then they'll accept you digging the trench but they'll want to do the connection themselves. Discuss it with them before you do anything.

That does make sense now you mention it, they can't sign off what they can't see:) it just makes me wonder about all the obsy build threads where they run armoured cable from the house and do it all them selves, with this in mind they can't be having it signed off because they have done it all them selves?

[Chris]

My wife just made me laugh, she said "just get a generator"

[freeflyjay]

as islander says, you can carry out the work yourself (not that i agree with non qualified people doing electrical work) any one can legally work on electrics if "competent", what you have at the moment is essentially just and extention cable as it is not hard wired into the mains, but that doesn`t mean it`s safe, you could always do your research buy the cable ect your self from an electrical wholesaler (city electrics or edmonsons are all over the place on industrial estates), run all the cables and then get a qualified electrian to check it and make the final connections to the mains to keep the cost down. by the way donn`t go adding more earth spikes it is unnessassery, it wouldn`t make it dangerous but not how it`s done, the main thing you need for an external installation is a 30ma rcd (any higher can still lead to fatal electric shocks), it is a fairly simple job but would be quite expensive as electrians will charge similar rates to a plumber (i really think it should be more considering your dealing with peoples lives all a plumber is going to do if he gets it wrong is flood your house)

[freeflyjay]

My wife just made me laugh, she said "just get a generator"

bit noisy that, you could always get a decent sized solar pannel, a charge regulator, battery and and invertor, armard cable is quite expensive, of coarse there is always the option of running an extention cable out on the nights your observing that would be substantially cheaper!

[Chris]

Thank you, thats made things a bit clearer for me, just one more thing if you don't mind? does it have to be wired into the mains, or is it much less acceptable to keep the extension cable theme just with better armoured cable and a 30ma RCD at the plug inside the house, this would keep it more simple for me, obviously I'd use the correct connections between the armoured cable and the flex after some research about it:)

Agreed, I can't think of a situation where a plumber would have the same responsibilty for life? I guess they have to do a lot smellier jobs though:D

Thanks again for the advice:)

[Chris]

bit noisy that, you could always get a decent sized solar pannel, a charge regulator, battery and and invertor, armard cable is quite expensive, of coarse there is always the option of running an extention cable out on the nights your observing that would be substantially cheaper!

hehe don't tempt me:D I probably would settle for this if I didn't wan't to run a dehumidofier in there, I personally think at least a small dehumidifier is a must when keeping optics and electrical equipment in an obsy.

I like the green approach though, that would be very cool, might cost it and see:D

[freeflyjay]

Thank you, thats made things a bit clearer for me, just one more thing if you don't mind? does it have to be wired into the mains, or is it much less acceptable to keep the extension cable theme just with better armoured cable and a 30ma RCD at the plug inside the house, this would keep it more simple for me, obviously I'd use the correct connections between the armoured cable and the flex after some research about it:)

Agreed, I can't think of a situation where a plumber would have the same responsibilty for life? I guess they have to do a lot smellier jobs though:D

Thanks again for the advice:)

of coarse you could keep it on the plug top, just make sure you use the rcd, you can acually buy rcd plugs to make it simple, just also make sure when you put the gland on the armard that you earth the sheath, if you terminate the armard into a metal box then there will be a brass loop that needs to be bolted on and the earth wire attached to this and the metal box.

[Chris]

Thank you:) I think this would suit my needs perfectly, I already have a good power tank for the mount etc, so the mains would mainly be needed for a simple 6W lamp, a lap top, and the forementioned Dehumidifier, so not too much demand really, nothing more than you would use with an extension cable inside.

I will be getting one of those plug in RCD for sure, and I'll also earth the cable how you describe.

Thanks very much for all your help:)

Chris

[Islander]

If you install SWA look for piranha nuts - they take the pain out of making off the earth connection. I think TLC do them.

[J_M_Franklin]

Safety is always paramount. As little as 35mA can cause a fatal fibrillation if you're unfortunate enough to have a current pass across your chest.

True, safety is always paramount, but your figure is incorrect, Ventricular fibrillation can be caused by a current as low as 20mA.

A TN-S system with a failed sheath connection could have been converted to TT - it's been known.

The only way this could happen is with full sign off of the local supply utility as it would be a breach of the Electricity Supply regulations. Importantly, the only way it could happen is if you already had a supply that had been converted from TT (Overhead) to a TN-C-S (PME), TT supplies are never converted to TN-S. If the sheath of a TNS feeder had been damaged or had degraded so far as to be dangerous, the law requires that it be replaced, and this would be at the cost of the utility unless a third party was responsible.

a possability for sure,i`ve a lot of things over the years, but i`d have to look and get some meters out, a bit far for me i`m afraid, but DO NOT remove the earth wire, if this is a tt system you would leave your house with no earth.

The earth rod should not be connected to the shed, the rod should be connected to the Main Earth terminal at the meter/head. Assuming the property actually has either a TN-S or a TN-C-S {PME} (The head can be used to identify which very easily) then the use of the Earth rod could actually introduce a hazard that would not otherwise exist. Fault currents have to flow back to the GME (General mass of earth) which will be back at the transformer and thus they would have a common equipotential, a local rod may be in conditions that will vary from that and thus a fault current may not flow properly and any protective device may not operate correctly. RCD's would still operate due to the manner in which they work, but MCB's may be compromised.

I have no idea where Starfox lives but if it is not too far from me I would be more than willing to take a look as it is always difficult from descriptions and images. Having said that the installation to the shed is a pile of poo and I would not recommend it being used. T&E is not outdoor rated and it certainly needs better mechanical protection than it has.

As has been said by someone above, the supply should be in properly installed SWA and protected by RCD's where necessary.

Starfox..let me know where you live, I am in Swindon.

[Chris]

If you install SWA look for piranha nuts - they take the pain out of making off the earth connection. I think TLC do them.

I will definately Google piranha nuts, cheers:)

[Chris]

The earth rod should not be connected to the shed, the rod should be connected to the Main Earth terminal at the meter/head.

I have no idea where Starfox lives but if it is not too far from me I would be more than willing to take a look as it is always difficult from descriptions and images. Having said that the installation to the shed is a pile of poo and I would not recommend it being used. T&E is not outdoor rated and it certainly needs better mechanical protection than it has.

As has been said by someone above, the supply should be in properly installed SWA and protected by RCD's where necessary.

Starfox..let me know where you live, I am in Swindon.

Hi, the rod is about 15' down the garden at the right hand edge, its just in the ground away from anything really, its not connected to the shed though. I have had no problems with my house electrics not one single switch has tripped in two years. Hopefully everythings ok, I live in Ipswich which is quite far from Swindon so don't worry, I appraciate the offer though:)

I agree, I've learnt that the current shed wiring is not up to scratch so I will be replacing it as suggested above with armoured cable and an RCD:)

Thanks

Chris

[Chris]

SOOoooo in answer to my original question:D I can use normal sockets in my shed if its dry but if theres a chance of damp then use outdoor sockets, right?

[Islander]

True, safety is always paramount, but your figure is incorrect, Ventricular fibrillation can be caused by a current as low as 20mA.

I'm sure it can given the right conditions but there's a reason that RCDs have a 30mA fault current rating.

The only way this could happen is with full sign off of the local supply utility as it would be a breach of the Electricity Supply regulations. Importantly, the only way it could happen is if you already had a supply that had been converted from TT (Overhead) to a TN-C-S (PME), TT supplies are never converted to TN-S. If the sheath of a TNS feeder had been damaged or had degraded so far as to be dangerous, the law requires that it be replaced, and this would be at the cost of the utility unless a third party was responsible.

Read it again. It's quite common for a DNO to remove earth connection because of degraded TN-S incomer sheaths. The usual option then is to convert to TT. Nobody mentioned converting TT to TN-S.

The DNOs are under no obligation whatsoever to replace an incomer with a degraded sheath nor to supply an earth. As long as they're happy that the incomer is otherwise safe, they'll simply say convert to TT.

There are DNO head arrangements still in place that would make your hair stand on end - typical example being fused phase AND neutral. They're under no obligation to change things - they operate under a completely different set of rules to the rest of us.

The earth rod should not be connected to the shed, the rod should be connected to the Main Earth terminal at the meter/head. Assuming the property actually has either a TN-S or a TN-C-S {PME} (The head can be used to identify which very easily) then the use of the Earth rod could actually introduce a hazard that would not otherwise exist. Fault currents have to flow back to the GME (General mass of earth) which will be back at the transformer and thus they would have a common equipotential, a local rod may be in conditions that will vary from that and thus a fault current may not flow properly and any protective device may not operate correctly. RCD's would still operate due to the manner in which they work, but MCB's may be compromised.

Again, read it properly. There's no suggestion of what may be an earth rod connecting to the shed - the cable disappears under the house which makes me suspect it may be part of a TT installation. Whether that installation is still extant or has been replaced needs professional verification. If it is a part of a TT installation then it will connect to the MET.

Aside of this, there are specific circumstances where you would use an earth rod and TT installation even if the main property has an earth provided by the DNO. It can be dangerous to export TN-C-S earths under these circumstances and the normal approach would be to export the phase and neutral only with the SWA sheath connected to earth at the house end to provide protection but isolated at the shed end. You would then use the normal TT earth arrangement with one or more earth rods.

It's common practice in Europe to add your own earth rod to a TN-C-S installation and it's been discussed a number of times by the IEE with a view to adding it to the regs here. It's a good idea too - it would protect against loss of neutral. It's certainly not forbidden under current regs and is perfectly OK to do as long as it's done properly and the implications are understood.

[Islander]

SOOoooo in answer to my original question:D I can use normal sockets in my shed if its dry but if theres a chance of damp then use outdoor sockets, right?

If it's weather tight then normal household sockets can be used. That's what will be going into my obsy next year

If the shed leaks then either fix it or fit something like MK weatherproof sockets.

[pwalsh61]

Get a qualified electrician to install power to your obsy properly. It may cost money, but that's better than dodgy electrics costing you your life!

Sent from my GT-I9100P using Tapatalk 2

[Chris]

Thanks, I was just double checking:) My obsy is pretty much compeletely water tight just traced a slight leak in one corner back to a knot hole which I have now filled, I'll use indoor sockets away from any possible water ingress.

Thanks and good luck with your build, I can definately recommend doing a build thread, its not only great for advice but I found its very good for motivation as well:)

Chris

[Islander]

Thanks, I was just double checking:) My obsy is pretty much compeletely water tight just traced a slight leak in one corner back to a knot hole which I have now filled, I'll use indoor sockets away from any possible water ingress.

Thanks and good luck with your build, I can definately recommend doing a build thread, its not only great for advice but I found its very good for motivation as well:)

Chris

I may well do that

[J_M_Franklin]

I'm sure it can given the right conditions but there's a reason that RCDs have a 30mA fault current rating.

Read it again. It's quite common for a DNO to remove earth connection because of degraded TN-S incomer sheaths. The usual option then is to convert to TT. Nobody mentioned converting TT to TN-S.

The DNOs are under no obligation whatsoever to replace an incomer with a degraded sheath nor to supply an earth. As long as they're happy that the incomer is otherwise safe, they'll simply say convert to TT.

There are DNO head arrangements still in place that would make your hair stand on end - typical example being fused phase AND neutral. They're under no obligation to change things - they operate under a completely different set of rules to the rest of us.

Again, read it properly. There's no suggestion of what may be an earth rod connecting to the shed - the cable disappears under the house which makes me suspect it may be part of a TT installation. Whether that installation is still extant or has been replaced needs professional verification. If it is a part of a TT installation then it will connect to the MET.

Aside of this, there are specific circumstances where you would use an earth rod and TT installation even if the main property has an earth provided by the DNO. It can be dangerous to export TN-C-S earths under these circumstances and the normal approach would be to export the phase and neutral only with the SWA sheath connected to earth at the house end to provide protection but isolated at the shed end. You would then use the normal TT earth arrangement with one or more earth rods.

It's common practice in Europe to add your own earth rod to a TN-C-S installation and it's been discussed a number of times by the IEE with a view to adding it to the regs here. It's a good idea too - it would protect against loss of neutral. It's certainly not forbidden under current regs and is perfectly OK to do as long as it's done properly and the implications are understood.

And that is why non-qualified people should not play with electrical installations. I suggest you also read my posts as written not as you interpret them. I would also suggest you don't make assumptions, I don't give a rats rear what they do in Europe and in all the years I have been a member of the IEE and now IET I have never come across a discussion about adding earth rods to TN-C-S installations. Further, adding them to it is, as I said, fraught with dangers. Installing an earth rod to compensate for a lost Neutral is simply ridiculous and avoiding the problem.

Network utilities have a legal obligation to ensure your installation (to their head) is safe and complies with not only BS7671, but also The Electricity Safety, Quality and Continuity Regulations 2002. With regards your comments about the head, behave, it is ILLEGAL to place a fuse into a neutral (Check out section 7 para 2 of the above regs). Any device placed into a Neutral must be interlocked with the phase conductor(s) so that all operate simultaneously...

Islander, I have no dsire to get into a spat with you on this, as that does not help Starfox you or I, but as I have been employed by the Electrical Installation industry for the last 29 years and am an registered NICEIC Qualifying Manager I suspect I know this a little better. There are lots of misconceptions out there, and as I know your in Scotland and on an Island things are done differently to the mainland...but I can assure you that you are not allowed to convert a TN-C-S system or a TN-S system to a TT when the cable is buried in the ground..if it is overhead, this would be doable, but it would be a simple matter to replace any damaged or degraded cables. Here in England the majority of overhead supplies have been converted to TN-C-S already or are in the process of this being done...

[J_M_Franklin]

Darn it...when do we get the ability to edit our posts...I always spot spelling and grammar errors AFTER I have posted!!

[Chris]

Get a qualified electrician to install power to your obsy properly. It may cost money, but that's better than dodgy electrics costing you your life!

Sent from my GT-I9100P using Tapatalk 2

I hear what your saying and I agree nothing is as important as safety, I do care about safety which is why I'm ripping it all out and doing it properly after lots of research, I guess the guy who installed this was not as safe as most people. From what I can gather the main thing which will safe your life is the RCD which I was always going to use, I am also going to mechanically secure the system with armoured cable properly earthed, after consulting with experienced and qualified people on this thread. I plan on taking their advice about how to make it safe, if I couldn't be bothered to learn how to make it safe then I would of course call in an electrician after I've saved for a while:)

Thanks for your concern though, I guess I can offset this danger against my very safe lifestyle of not partaking in extreme sports, smoking, or eating an unhealthy diet:D

Chris

[dwc]

Thanks, I was just double checking:) My obsy is pretty much compeletely water tight just traced a slight leak in one corner back to a knot hole which I have now filled, I'll use indoor sockets away from any possible water ingress.

So one question I've long been meaning to ask: when it comes to roll off shed electrics, doesn't dew count as a water source, and does that mean that the open to air part of an obsy needs waterproof sockets?

[Islander]

The ability to edit them doesn't last for that long after you've posted once you do get the ability. I was intending to tone down my post a bit as I realised it came across a bit on the terse side but the edit button had disappeared. Please accept my apologies for that. However...

The advice I've given to the OP is sound and based on good practice - I'll get that out of the way first.

The situation I outlined with TN-S systems being converted to TT is commonplace. DNOs are NOT bound by BS7671. A DNO's interpretation of safe is far different to that of a domestic electrician. They are not legally obliged to provide an earth connection and if a TN-S cable is considered no longer suitable for providing a DNS earth but otherwise safe for supply by their standards then they'll remove the earth and tell you to install TT. Double fused head connections were commonplace in the dim and distant past and they still exist - I've seen several. DNOs only replace those heads when they have to. The same applies to cast metal head installations which, quite frankly, are dangerous.

The IET forum has mentioned the discussions on earth rods for TN-C-S installations several times and they have been considered for inclusion in the regs. It will happen at some point in the future of that I'm sure. It's not unsafe if the implications are understood and can only be a good thing overall for PME systems.

Don't make assumptions about my qualifications,experience or knowledge please. I may live on an island now (and that makes no difference to BS7671 or DNO standards) but I lived in London for many years before I moved here and have been familiar and fluent in electrical installations and regs since the 15th edition.

Apologies to the OP for the digression from the original thread.

I'll bow out now.