I am having a 50 foot trench dug to sink a 6mm SWA mains cable in between my house and my new studio.
At the meter box (house) end, I will put in a new set of meter tails which I want to connect to an RCD and then the SWA cable to the studio. Would this device provide adequate protection or would you recommend another:
http://www.tlc-direct.co.uk/Products/WYWRM100slash2.html?source=adwords&kw=100mA+RCD&gclid=COiX8uPBu6sCFUMOfAodpD2cuA
The studio will be fitted with a 10 way 17th Edition Wylex consumer unit and the earth will be provided via an earth rod driven well into the ground.
Electrical RCD Protection question
Re: Electrical RCD Protection question
So the studio is going to be TT earthed?
Firstly you will want some overload protection for that 6mm^2 cable (probably a 32A or so trip), and you if I were you I would be looking at a 100mA time delay RCD to give some discrimination between the RCDs in the consumer unit and the one at the house end.
You might also want to consider where you earth the Armour on the cable, as you do not want to bring the domestic earth (that may well be PME) out of the equipotential zone, on the other hand bringing an external earth into the zone is also a bad idea.....
Also, one earth stake may not give you an adequately low Ze, this needs to be measured.
This system really needs to be designed, you cannot decide on your source end protection without knowing the parameters of the source of supply, and the discrimination needs to be considered bearing in mind the characteristics of the breakers in your consumer unit.
Show us your calc's and we will see if we can spot anything missing, but this is not something anyone here is going to design for you.
Oh and 6mm 2 core is a bit smaller then I would willingly direct bury, put it in a duct or go a couple of sizes up (The duct is better because you can also stuff a phone and data line down it).
Also, yellow 'buried electric cable' tape is a good thing before you fully backfill that trench.
Regards, Dan.
Firstly you will want some overload protection for that 6mm^2 cable (probably a 32A or so trip), and you if I were you I would be looking at a 100mA time delay RCD to give some discrimination between the RCDs in the consumer unit and the one at the house end.
You might also want to consider where you earth the Armour on the cable, as you do not want to bring the domestic earth (that may well be PME) out of the equipotential zone, on the other hand bringing an external earth into the zone is also a bad idea.....
Also, one earth stake may not give you an adequately low Ze, this needs to be measured.
This system really needs to be designed, you cannot decide on your source end protection without knowing the parameters of the source of supply, and the discrimination needs to be considered bearing in mind the characteristics of the breakers in your consumer unit.
Show us your calc's and we will see if we can spot anything missing, but this is not something anyone here is going to design for you.
Oh and 6mm 2 core is a bit smaller then I would willingly direct bury, put it in a duct or go a couple of sizes up (The duct is better because you can also stuff a phone and data line down it).
Also, yellow 'buried electric cable' tape is a good thing before you fully backfill that trench.
Regards, Dan.
Audiophiles use phono leads because they are unbalanced people!
Re: Electrical RCD Protection question
I'm not generally in favour of stopping people doing what they want with their own property, but I hope you know the whole thing will need signing off by a proper electrician, else it's illegal? Not that anyone really needs to know until you sell the house, mind, but non-regs electrics would almost certainly cause problems with your insurance if you ever (god forbid) have a fire and need to make a claim.
Re: Electrical RCD Protection question
Not at all sure it is illegal actually.
Part P applies, so you will have to get building regs approval and sign off, but the 'wiring regs' are actually purely advisory (for all that councils and insurers like them).
Building regs departments vary widely in terms of what they will accept as test documentation prior it sign off, but may want to look in your trench!
Regards, Dan.
Part P applies, so you will have to get building regs approval and sign off, but the 'wiring regs' are actually purely advisory (for all that councils and insurers like them).
Building regs departments vary widely in terms of what they will accept as test documentation prior it sign off, but may want to look in your trench!
Regards, Dan.
Audiophiles use phono leads because they are unbalanced people!
Re: Electrical RCD Protection question
dmills wrote:Not at all sure it is illegal actually.
Part P applies, so you will have to get building regs approval and sign off, but the 'wiring regs' are actually purely advisory (for all that councils and insurers like them).
Building regs departments vary widely in terms of what they will accept as test documentation prior it sign off, but may want to look in your trench!
Regards, Dan.
This is my understanding of it (but feel free to correct me if things have changed):-
Indeed it is classed as notifiable work meaning that it needs building regs approval which only in turn means that it should comply with wiring regs. It is up to building control to pay for any testing they deem necessary as part of the sign-off. A third party electrician is not really allowed to sign off someone else's work as being compliant with part p unless they are acting on behalf of building control. The work itself can actually be carried out by anyone capable but bear in mind that if building control don't inspect the work at the relevant stages they can ask you to expose everything to do so.
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- Dark Fader
Regular - Posts: 136 Joined: Sat Jan 03, 2004 12:00 am Location: Death Star
...rubbish at words 'n' stuff.
Re: Electrical RCD Protection question
Forgot to add that there is generally just a flat fee to pay to building control but this obviously varies from one lock authority to another.
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- Dark Fader
Regular - Posts: 136 Joined: Sat Jan 03, 2004 12:00 am Location: Death Star
...rubbish at words 'n' stuff.
Re: Electrical RCD Protection question
Oh, and that actually getting building control to supply the sparks to do the inspection and test that they often insist upon is sometimes a good trick, they often expect you to pay for the inspection and test.
Not at all sure about the legality of that, but they will try it on.
Regards, Dan.
Not at all sure about the legality of that, but they will try it on.
Regards, Dan.
Audiophiles use phono leads because they are unbalanced people!
Re: Electrical RCD Protection question
dmills wrote:Oh, and that actually getting building control to supply the sparks to do the inspection and test that they often insist upon is sometimes a good trick, they often expect you to pay for the inspection and test.
Not at all sure about the legality of that, but they will try it on.
Regards, Dan.
Yeah I've heard that they often try to get you to foot the cost but as I understand it, it is for THEM to do and if they don't have the expertise themselves, THEY have to pay for it, even though they will try to convince you otherwise! I've even heard some stories of them signing stuff off without testing (probably to save money)!
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- Dark Fader
Regular - Posts: 136 Joined: Sat Jan 03, 2004 12:00 am Location: Death Star
...rubbish at words 'n' stuff.
Re: Electrical RCD Protection question
Thanks for your response guys.
The question about eathing the SWA is interesting. At the house end meter cabinet, there is no seperate earth provided - its basically derived from the incoming Neutral. So I was thinking of not connecting the SWA at that end but maybe connecting it at the studio end via the earth rod/s?
I have an approved electrician coming to look at my plans at the weekend so I'll take his lead and advice on these matters.
Of course, it is a notifiable works as far as building controls are concerned.
The question about eathing the SWA is interesting. At the house end meter cabinet, there is no seperate earth provided - its basically derived from the incoming Neutral. So I was thinking of not connecting the SWA at that end but maybe connecting it at the studio end via the earth rod/s?
I have an approved electrician coming to look at my plans at the weekend so I'll take his lead and advice on these matters.
Of course, it is a notifiable works as far as building controls are concerned.
Re: Electrical RCD Protection question
So the supply is TN-C-S, and possibly PME.
Note that if you do the earth the end at the studio thing then the minimum allowable Ze for the studio will be set by the protection device at the supply end, this is however probably the way I would tackle it.
Also the house end of the SWA must be inside a insulated box so that accidental contact with the armor is not possible (Note that the armor includes the gland in this case!).
Personally I would fit the supply end breakers in the existing consumer unit, which has the advantage that unlike anything involving meter tails and henley blocks you will not have to work live (Or get the DNO involved to pull the supply fuse).
A note on the SWA termination that the armor is earthed TT to an external earth domain would be a good thing.
Regards, Dan.
Note that if you do the earth the end at the studio thing then the minimum allowable Ze for the studio will be set by the protection device at the supply end, this is however probably the way I would tackle it.
Also the house end of the SWA must be inside a insulated box so that accidental contact with the armor is not possible (Note that the armor includes the gland in this case!).
Personally I would fit the supply end breakers in the existing consumer unit, which has the advantage that unlike anything involving meter tails and henley blocks you will not have to work live (Or get the DNO involved to pull the supply fuse).
A note on the SWA termination that the armor is earthed TT to an external earth domain would be a good thing.
Regards, Dan.
Audiophiles use phono leads because they are unbalanced people!
Re: Electrical RCD Protection question
Thanks Dan. I can confirm is a PME system.
Unfortunately, its not possible to take a spur from the house consumer unt - no spare space and access too difficult - practically impossible even.
The existing feed is an underground cable that comes into the meter cabinet (plastic, circa 1998 when the house was built. It is a 6mm SWA cable that has a shroud fitted over it but it does come into the meter box and I can't see that the SWA is connected at the meter box end to anything. I was aiming to terminate the studio supply at the meter box end in the same way.
Would the shroud (It looks like a black plastic heat shrink shroud) be considered enough of an accidental SWA contact preventer?)
Do I really need the DNO to take out the fuse? Couldn't I just snip the seal and pull it and when the Approved Electrician has come and connected all the new stuff up and certified it call them to come and re-seal?
Good idea about the TT label!
Unfortunately, its not possible to take a spur from the house consumer unt - no spare space and access too difficult - practically impossible even.
The existing feed is an underground cable that comes into the meter cabinet (plastic, circa 1998 when the house was built. It is a 6mm SWA cable that has a shroud fitted over it but it does come into the meter box and I can't see that the SWA is connected at the meter box end to anything. I was aiming to terminate the studio supply at the meter box end in the same way.
Would the shroud (It looks like a black plastic heat shrink shroud) be considered enough of an accidental SWA contact preventer?)
Do I really need the DNO to take out the fuse? Couldn't I just snip the seal and pull it and when the Approved Electrician has come and connected all the new stuff up and certified it call them to come and re-seal?
Good idea about the TT label!