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Power - Earth-RCD's- ISO/TX's and workshops.

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Power - Earth-RCD's- ISO/TX's and workshops.

Post by TVJON74 » Thu Jan 31, 2013 9:17 pm

My workshop is about 60 yards from the house in the back garden.
I installed armoured cabled underground in 2 inch ducting from the house to the workshop. At the house end I installed an RCD to protect the cable and at the workshop end I have my own consumer unit with built in RCD and my own earth stake, so I am totally separated from the house.
On the decorating side I have foil backed plasterboard with butted joints, the joint gaps were just filled with decorators caulk and painted.
In an earlier post it was mentioned about using plug in Ethernet devices, does anyone know if they will work over a mains install like mine?

Jon

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Thu Jan 31, 2013 9:25 pm

Hi Jon,

It is usually better to supply the outbuilding using armoured cable, and non RCD'd at the supply end, the RCD being at the remote end.

It would be better not to be on any RCD that the house is also using, as this can lead to nuisance/unwanted tripping the house out.

This is for two reasons.

1) two RCD's in series will not discriminate, ie. you cannot guarantee which one will trip first.
Unless the one at the supply end is a 100mA time delayed type, and the remote one is a 30mA type, a 30mA type required now for sockets for general use, or outdoor use.

2) the incovenience/danger in the dark of having to walk to the house to reset the RCD after it has tripped.

I see no reason why your network over mains would not work.

 
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Re: Power - Earth - RCD's and workshops.

Post by Michael Watterson » Thu Jan 31, 2013 9:31 pm

The Network over mains is a Transmitter and Receiver. It's a LIE. it uses the mains mainly for power. A pair lighting loops will couple one on a generator and one on public mains.

Older ones only wreck Short wave and high end of MW. Newer faster ones put out muck up to 200MHz!

If these are tested properly (i.e. on actual domestic wiring as a pair, transferring data) they are ALL 20dB above the interference limit. "Tricks" to pass them include only plugging one in or not connecting ethernet data.

 
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Re: Power - Earth - RCD's and workshops.

Post by TVJON74 » Thu Jan 31, 2013 9:34 pm

Thanks for the replies,
I forgot to mention that my workshop supply comes from the house before the consumer unit so I'm totally separated, ie my causing a fault can not blow the house trip. Yes my supply is the same phase as the house, but I had heard somewhere that the Ethernet adaptors didn't like RCB's

Jon

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Thu Jan 31, 2013 9:34 pm

ppppenguin wrote: However there is still the thorny problem of whether to export the earth from the house to the shed or run the shed as its own TT system with an earth rod.


Depends on the earthing system in use at the supply end, and if there is any metal water or gas pipes in the outbuilding.

If you already have an accessible duct, then I would pull in some cat5 cable (or similar) too.

 
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Re: Power - Earth - RCD's and workshops.

Post by TVJON74 » Thu Jan 31, 2013 9:47 pm

Unfortunately this was all about 13 years ago now and although I can get to both ends of the underground duct I won't be able to pull more cables through now!

House supply is overhead cable with earth stake, the cable armour is joined to house earth, the workshop then uses its own earth stake.

I'm currently using WiFi devices for internet connect via the house but distance and location slow things up a bit.

Jon

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Thu Jan 31, 2013 9:58 pm

TVJON74 wrote:
House supply is overhead cable with earth stake, the cable armour is joined to house earth, the workshop then uses its own earth stake.

I'm currently using WiFi devices for internet connect via the house but distance and location slow things up a bit.

Jon


So your house supply is more than likely a TT system, so by rights the supply cable to the out building should be protected with a 100mA time delayed RCD (30mA at the shed end), if it has two 30mA cascaded it is only really a problem Jeffrey and I mentioned further back (lack of discrimination/inconveniance) but is safe, also having another stake at the shed end is good, as this will work in conjunction with the house stake lowering the overall RA (the rods resistance to earth) which is a good thing. :thumbl:

Ethernet over power is something I have very little experience in, so I cannot really advise if RCD's affect this or not.

 
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Re: Power - Earth - RCD's and workshops.

Post by Michael Watterson » Thu Jan 31, 2013 10:01 pm

ppppenguin wrote:Red to Black is correct about cascaded RCDs and the hassle of having an RCD trip at the house. However there is still the thorny problem of whether to export the earth from the house to the shed or run the shed as its own TT system with an earth rod.


Here every house has neutral bonded to earth and earth rod at the meter.

The HF transmitter earth connects to several earth rods and it's connected to mains earth too. I can't see how else you run 80W at 3.7MHz on a metal chassis / metal cased Radio set designed to use mains Earth. I suspect a problem in some countries? France?

Years ago in Norn Iron (1970s) the Bungalows all took three wires from pole and I presume the Earth and Neutral bonded at substation. But "earth" was also bonded to pipe (not plastic) in kitchen, at Hot tank and also at central heating pipe at boiler in garage.

 
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Re: Power - Earth - RCD's and workshops.

Post by Michael Watterson » Thu Jan 31, 2013 10:05 pm

TVJON74 wrote:Thanks for the replies,
... I had heard somewhere that the Ethernet adaptors didn't like RCB's


Maybe some models don't like some RCBs, but I'd honestly be surprised if it mattered much as the adaptors will work with a 2m or more gap between ISOLATED circuits! They will work badly or not at all if one end is on a properly filtered socket strip.

 
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Re: Power - Earth - RCD's and workshops.

Post by TVJON74 » Thu Jan 31, 2013 10:34 pm

Thanks again all,
Maybe I will get a set and try it.

Best regards
Jon

 
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Re: Power - Earth - RCD's and workshops.

Post by Michael Watterson » Thu Jan 31, 2013 11:38 pm

Please run Cat5e.

The Powerline Ethernet are horrible RF wise. Worse than any SMPSU, CFl or TV by up to 20dB :sad:

I install extra Cat5e and can run "IR" Remote, DC, Audio and even HDMI on it.
http://www.techtir.ie/howto/hdmi-via-cat5-cable

You can run SCART RGB, but that needs more cables and Baluns.

Shielded Cat5e is best if you don't have metal / shielded trunking.

 
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Re: Power - Earth - RCD's and workshops.

Post by TVJON74 » Fri Feb 01, 2013 12:13 am

Running any cables is a no go without digging up a patio and 60 yards of garden.
I will have to stick to the WiFi.
I won't bother using/trying Ethernet over mains.
Thanks for your help and advice :thumbl:
Best regards
Jon

 
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Re: Power - Earth - RCD's and workshops.

Post by Michael Watterson » Fri Feb 01, 2013 12:59 am

I do have a pipe, but it's full. So there are coax and Screened Cat5e going around the base of the wall and up the back of a drain pipe.

Here we have MMDS which is 2.5GHz. The older discarded ones have a N connector for downconverter and dipole. The current ones have the downconverter built into the stalk. A pair of those gives about 1km at full speed (8km at low speed)

Sticking ordinary Bridge Wifi on window sills gives easily 30m. (more at lower speed).

 
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Re: Power - Earth - RCD's and workshops.

Post by CTV » Fri Feb 01, 2013 8:15 am

Michael Watterson wrote:Please run Cat5e.

The Powerline Ethernet are horrible RF wise. Worse than any SMPSU, CFl or TV by up to 20dB :sad:

I install extra Cat5e and can run "IR" Remote, DC, Audio and even HDMI on it.



Well that's that dismissed then! :|

If I had followed that advice I would have missed the opportunity of a solution that worked and suited my needs.

The last 3 houses I installed a dedicated hardwired CAT5e network over the entire house to all rooms and the workshop. This time I could not be arsed with all the hassle of routing wires, crimping plugs etc so installed this solution. The proof is in the pudding it works and I suffer no issues. Perhaps you should let people decide by using and having their own experience. At £20 it's worth a try and you can always take it back if you find it's not for you.

Just my attempt to offer a balanced opinion.

Chris

 
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Re: Power - Earth - RCD's and workshops.

Post by GlowingAnode » Mon Feb 04, 2013 12:50 am

ppppenguin wrote:Red to Black is correct about cascaded RCDs and the hassle of having an RCD trip at the house. However there is still the thorny problem of whether to export the earth from the house to the shed or run the shed as its own TT system with an earth rod.


If you use the exported earth ie a continuation of a TNS/TNC-S, then you run the risk of a voltage difference between mains earth and local "true" earth, either induced or through IR voltage drop. This can cause a nuisance in the form of interference to radio reception amongst other problems.
Under fault conditions this voltage could be several tens of volts.
If you intend to bring external aerials and/or RF earths into your workshop, then TT (local earth rod) is to be advised.
By creating a local equipotential zone, this will minimise any voltage difference (and hence induced loop currents) between mains earth and true (RF) earth.
A double pole mains filter is also highly recommended, especially if you're operating a transmitting station.
The downside being the design of the installation requires careful consideration, and periodic testing of the earth is required.
Rob.

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Mon Feb 04, 2013 1:08 am

I was thinking of problems more on the lines of if it was TNC-S and extraneous metal parts, mainly water or gas pipes being present in the shed/outbuilding.
As then these pipes need bonding with at least 10mm^ back to the main earth terminal (MET) in the house.

It is possible to use an Earth Marshalling Terminal (EMT) at the shed end, but then the supply cable earth has to have enough current carrying capacity (CCC) for both the expected Earth fault current and the bonding combined, and this leads to rather large supply cabling cross sectional area (csa), or a seperate bonding cable, which can be very expensive on long runs.

In this case it is sometimes better to segregate (insulate) the incoming earth at the shed and TT (earth rod) the shed supply, if armoured cable is used the armourings still have to earthed from the supply end but seperated/insulated from the shed earthing system.

The supply cable sizes are then more reasonably sized (and cheaper) for the TT at the shed end.

There is not usually as much of a problem with the TNS system as with the TNC-S system in this scenario, as again any bonding can be done with smaller csa cables.

 
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Re: Power - Earth - RCD's and workshops.

Post by GlowingAnode » Mon Feb 04, 2013 11:19 am

Yes, ok Baz good point.
Looks like another reason to favour a local TT installation, especially if it's a remote building.
Rob.

 
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Re: Power - Earth - RCD's and workshops.

Post by Terrykc » Mon Feb 04, 2013 11:59 am

There is a lot of useful information on earthing here:

http://wiki.diyfaq.org.uk/index.php?tit ... hing_Types
http://wiki.diyfaq.org.uk/index.php?tit ... ty_outside
http://wiki.diyfaq.org.uk/index.php?title=TT_Earthing
http://wiki.diyfaq.org.uk/index.php?tit ... nd_Bonding

Note that there is a link to an IEE Wiring Matters article in the first one, which is broken. The article in question is included in this:

http://electrical.theiet.org/wiring-mat ... mplete.cfm

 
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Re: Power - Earth - RCD's and workshops.

Post by CTV » Mon Feb 04, 2013 12:13 pm

Split the developing discussion about power/earth/RCD etc off from my workshop construction thread. It was starting to dominate and It warrants a discussion thread of its own really.

 
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Re: Power - Earth - RCD's and workshops.

Post by GlowingAnode » Mon Feb 04, 2013 12:28 pm

GlowingAnode wrote:
ppppenguin wrote:Red to Black is correct about cascaded RCDs and the hassle of having an RCD trip at the house. However there is still the thorny problem of whether to export the earth from the house to the shed or run the shed as its own TT system with an earth rod.


If you use the exported earth ie a continuation of a TNS/TNC-S, then you run the risk of a voltage difference between mains earth and local "true" earth, either induced or through IR voltage drop. This can cause a nuisance in the form of interference to radio reception amongst other problems.
Under fault conditions this voltage could be several tens of volts.
If you intend to bring external aerials and/or RF earths into your workshop, then TT (local earth rod) is to be advised.
By creating a local equipotential zone, this will minimise any voltage difference (and hence induced loop currents) between mains earth and true (RF) earth.
A double pole mains filter is also highly recommended, especially if you're operating a transmitting station.
The downside being the design of the installation requires careful consideration, and periodic testing of the earth is required.
Rob.


See here; http://wiki.diyfaq.org.uk/index.php?tit ... g_an_earth
(taken from one of Terry's links above)
Cheers.

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Mon Feb 04, 2013 2:00 pm

First off, Thanks Chris for splitting this, as the thread had taken on a life of it's own. :=D

Interesting links Terry and Rob, I hadn't seen this before (the DIY forum), as usually the DIY type sites don't go into much detail on this, and usually spread the the myth that ooh! you can't export TNC-S :O

I have actually done these types of jobs, and had to design and cost out the different ways of achieving it.
I have actual experience of doing this, it can be a bit of a balancing act, as each system has it's pro's and cons

Most of my information originally came from the IET Guidance Note 8, which is all about Earthing and bonding and goes into far more detail than the snippets I posted here.
I actually just posted off the top of my head without looking at any books, just by experience so I hope there are no mistakes in it. :roll:

The Wiring matters article is now quite out of date (16th edition), and out of step with current regs, but the basic principals are still valid, and it is still a good and easy to understand guide.

On a more serious note, anybody contemplating doing anything contained in this thread, then please get an electrician in to oversee it, as a forum limits the amount of advice that can be given, and the consequences of doing something wrong can be fatal.

 
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Re: Power - Earth - RCD's and workshops.

Post by valvekits » Mon Feb 04, 2013 5:39 pm

Whenever I have read threads on other forums about running power out to a shed I always end up being non the wiser. I get the strong impression that you can't do it yourself these days even if you are a qualified 17th edition electrician.
What I concluded rightly or wrongly, is that you need to be registered with the Competent Person Register; it would be great to get some clarification on this.
What also seems strange to me is that within the competent fraternity, there is debate about whether you are allowed to "export" an earth to your shed or not. I suppose export in this context means the physical act of running or extending an earth from the house, I mean why wouldn't you?
I did wonder at one point if this CPS was just some more red tape madness, but having followed a recent thread on here illustrating some poor building work, I'm starting to see why the Government might think it necessary.


Eddie

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Mon Feb 04, 2013 6:37 pm

Hi Valvekits,

I will try to answer your questions for you.

Since Part P was introduced several types of electrical work became notifiable, running a supply out to an outbuilding was one of them.

See here for a more in depth look, note there are different versions of the document.

http://www.planningportal.gov.uk/buildi ... p/approved

Basically if you are not a Part P registered Electrician (whether qualified or not) then you have to go through building control before you are allowed to do notifiable work (see documents above).

If you are a Part P registered electrician you can do the work and then self test and self notify (again see documents above).

Part P is about to be ammended in a couple of months, there are quite a few changes afoot.
Looking at the '2013 draft document' (also in the link above), it looks as though running a supply to an outbuilding is not on the list, however adding a new circuit is notifiable., so not much change there then.

'Exporting' is not really the best word to use, as you are 'extending' the earthed equipotential zone.

There can be problems exporting the Earth (see some of the previous posts and links earlier in this thread), it all depends on the earthing system at source, and if there are metal pipes in the outbuilding or not, or if the outbuilding is made of metal or not, there are other things you need to know, as it is not as simple as just running the earth cable out, there are other serious considerations to take into account too, the choices are not 'black and white' as each situation is different, it also depends on the intended use of the outbuilding to some extent.
Costs to comply also come into the equation too (see earlier posts).

There are also technical pro's and con's to consider. (see some of the links earlier in this thread)

Things like power to metal greenhouses also come under different regs too (horticultural regs).

What else causes confusion is that some DNO's (Electricity supply companies) at one time prohibited exporting TNC-S, and so some electricians think this is still the case, even some DNO's can't give a straight answer if asked, and it depends on who you speak to at any given time, at any given DNO.

It is quite a complex subject, and not particularly easy to advise someone what to do on an internet forum, without seeing the situation on the ground so to speak.

I hope I have answered some of your questions. Phew! :omg:

 
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Re: Power - Earth - RCD's and workshops.

Post by valvekits » Mon Feb 04, 2013 8:53 pm

Okay R to B some heavy reading there but I think I got it. You can't create a hypothetical shed scenario because although there appears to be great similarities, each case can be slightly different.

I think I understand this now and basically there are three avenues that I can see:

I chose to do it myself, I must contact building control before work commences.
Building control may chose to inspect themselves or get a third party to check the work, but they will be looking to recover their inspection costs so it might not save me any money.

I get my 17 edition electrician who isn't Part P registered but able to test to BS 7671 to do it, building control still need to be notified before work commences.
When he completes a BS7671 installation certificate, Building control will issue a completion certificate if they are satisfied, but may well request a third party approved inspector to verify the work. So it still might not save me any money.

I get a registered Part P installer to do it, they self test and provide me and building control with a compliance certificate. It won't save me any money but it could save me a lot of hassle.

It isn't possible to circumnavigate all this by making the cable to the shed plug in to an outside waterproof socket on my house (Not fixed installation) as this socket installation would have to comply with Part P anyway.
If I choose avenue 1 or 2 and don't involve building control at the outset, I can't get the work approved retrospectively even by an approved inspector because BS7671 cable routing requirements might not of been met and they have no way of checking.


Eddie

 
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Re: Power - Earth - RCD's and workshops.

Post by Red to black » Mon Feb 04, 2013 9:28 pm

Hi VK,

Jeffrey is of course correct, it is generally cheaper to use a part P sparky, who will notify it on your behalf, as BC charges vary enormously depending on the local autority.

I hate Part P with a passion, it is just a money making scam as far as I can see, and yes I am a part P registered spark :=D and for which I have to pay about 400 and odd quid each year, to renew just to stay legal, IOW Iam competent just so long as I have paid my cheque :\'(

During the new amendments, at the consultation phase, the government listed scrapping it altogether as one of the options, which they should have done IMO, but the Scams (Part P providers) lobbied heavily against this (vested interests ?), and produced some dubious data to prove electrical accidents in the home had decreased since it's introduction.
Then there was the fact that if the government scrapped it, that would imply they were wrong to introduce it in the first place!, and we cannot have that now. :O

It was also flagged up during the consultation that the scams (Part P providers) had a vested interest, ie. the person/trader they are supposed to be monitoring is also paying their wages.


I would much rather have had a Gas Safe type of registration, one governing body for all, Part P could and should have been great, but as always the implementation of it was a farce, although with the new version some parts have been improved, whilst other parts have been watered down.

BTW it is not policed at all ;) , it is just insurance companies and some mortgage lenders have began to insist on certain requirements.

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