Lightning strikes and RCD's

[AlienBiker]

Hi all, I'm hoping someone can help me with a bit of a problem. Ive had 2 professional electricians tell me two different things, so at this point I'm fairly confused.

The problem is that every time there is a lightning strike in my area, my RCD trips. I'm sure it used to only trip when the strikes were relatively close. It now seems to trip when there is a strike in about a 30 mile radius. I kid you not with the distance, we can now predict incoming lightning storms before we see a flash or hear anything ! The RCD never trips at any other time, other than obviously when the test button is pressed.

The RCD is a Proteus unit, about 15 years old and is rated 80A 30ma. My house is a 3 bedroom detached. Power supply comes from overhead cabling, since I live in the sticks. Earth goes underground from the main fuse box via a rod in the basement.

Ive checked my neighbours systems, they all have 30ma RCD's. Some of them experience their RCD's tripping in bad storms but none of them have it as bad as myself. My overhead power comes from a telegraph type pole that has been put in, only for my house and is taken from another telegraph type pole on the main road.

Ok, the first electrician told me that due to the size of the house and number of electrical devices in it, I need to change the RCD for a 100ma unit. The second electrician has told me, that will not make any difference and due to the type of overhead power supply coming to my house, I'm just going to have to live with it !

My fusebox is now too old to simply replace the RCD, ( Ive checked, they've stopped making compatible units ). At the moment I'm playing with the idea of getting an electrician to replace the whole box with a MCB based one ( mine has little round fuses in what looks like MCB's ) and to have a seperate incomer box ( I think thats the right term ) with the RCD in, connecting to the main fuse box. I dont know what rating RCD to have put in it. I have also read somewhere that you can get RCD's that can be "locked" disabling the RCD protection side of the device. This would be a possible way of getting through storms without having to stay up half the night reseting the fusebox.

Please could I have an ideas on where the problem is originating and what I can do about it. I'm trying to avoid throwing money away at solutions that dont work.

Sorry this was so long, I wanted to try and get all the details in first time, thanks for reading and any suggestions in advance.

 

[JohnD]

There is a possibility that your RCD is getting out of spec; or maybe you have a background earth leakage due to putting several circuits on it, that is not enough to trip it but brings it close to the tripping level so it does not need much extra to push it over the edge.

It will help if you have the 30mA RCD replaced by a 100mA RCD with time delay (this is only a delay of 100 milliseconds) and is recommended for installations with an overhead suppply and an earth spike.

You could protect your sockets likely to be used with equipment outdoors, and any outbuildings, and any electric showers, protected with 30mA RCD or individual RCBOs.

The idea is that by not protecting your whole installation with a single 30mA RCD (1) you will get fewer trips (2) a fault on one circuit will not bring down all other circuits.

An RCBO is a single small device that can (depending on brand) fit into the same space as an MCB but includes an RCD to protect that circuit only. They are a very good solution though if you have a number of them it naturally works out more expensive than just having one RCD to protect the lot. I use MEM and am very pleased with them. They are not very cheap but are very widely used in commercial and industrial installations.

I think you would benefit from using a maker like MEM because their Industrial devices also fit in the domestic CUs, and they sell TVSS devices which give some protection against surges including those caused by nearby lightening strikes (one of the members on here has a couple to protect his computers) though in your position I would probably try it with one circuit and see if it helps your situation. Get a good big CU with room for later expansion. The MEM 2000AD range is very flexible and can be converted to and from split-load layout even after installation.

I am sure the first thing to do is to stop using a 30mA RCD to protect your whole installation.

Also ask your electricity supplier if they can provide you with a PME (Protective Multiple Earth, also known as TNC-S) supply (this is a way of providing a supplier's earth instead of using your earth spike, they are able to do this even with remote overhead supplies now, and if they can do it, will probably cost less than £100.

(note: I have edited this a bit as more ideas struck me)

 

[sm1thson]

(note: I have edited this a bit as more ideas struck me)

no pun intended!?!
john covered all you need to know and more (inc his obsesion with rcbo's). his last piece of advice was what you should do first! -phone the electricity supplier and see if you can get changed to PME

 

[AlienBiker]

Hi, thanks for the feedback.

Ive contacted my supplier and they've contacted some form of contractor who'll be in touch with me in the next couple of days and let me know if its going to be a straight forward connection job (£21) or more "complex" ( didn't specify an amount ).

I'll still make some enquiries into getting the fusebox updated and having a 100ma RCD put in. My garage/workshop/external sockets are already protected by a 30ma RCD on a sub fuse box.

 

[Big_Spark]

Alienbiker, from what you have said I would concur that the RCD has passed it's "sell by" date and should be replaced.

The likely cause is the RCD has been oversensitised and so trips with the slightest provocation. Electric storms produce bursts of electromagnetic radiation as well as discharge, and pulses of magnetic fields (a very much smaller version of that created just before a nuclear burst). These will induce a small current into the earth of installations, and when the RCD "sees" this, it treats it like any other fault and trips.

Regarding the upgrading of your service, if it can be PME'd that is a good thing, and in that case an RCD incomer is not required (but don't forget any sockets feeding external equipment need RCD protection for compliance).

If your service cannot be upgraded, then I would suggest a 80A 30mA Type S (Time delayed) unit. It gives the same level of protection, but the time delay will allow it to "ignore" electromagnetioc waves caused by electrical storms.

 

[JohnD]

You will need a new 16mm G&Y Earth Wire that will reach the service head by the meter. The contractor will supply a terminal for it to be connected to when he does the PME. Best for you to have this ready before he arrives. If you just have one Consumer Unit it can go straight into that; if you have more it can be useful to have an Earth Block (at least 4 way, an 8-way can be handy) with 16mm going to each CU. You will also need 10mm G&Y main bonding to the incoming services (water, gas, oil) either from the earth bar of the consumer unit, or the earth block.

You can do this yourself or get your electrician to do it; it is not difficult and does not need to be notified.

It is not necessary to remove your old earth spike, you can leave this connected to all the other bonding if you like (the "M" in PME means that it is earthed at Multiple points). Once you have PME you do not need the whole-house RCD, you may be able to get a switch to fit in its place, or your electrician may be able to remove it and give you an external main switch in the tails adjacent to the consumer unit. This should be quicker and cheaper than having a new CU.

 

[AlienBiker]

Thanks everyone for the new info.

I was reading the WIKI section on this site and found a bit under RCD's that states :

"Spurious tripping may be avoided by installing a filter upstream of the RCD at the origin of the installation."

My only knowledge of filters is that of the surge protectors available for computer, HI-FI etc that are basically trailing extensions. I had a look for mains "filters" but couldn't find anything. Anyone have any advice on this ?

At the moment, I'm envisioning a new setup with the incomer in separate housing to avoid future problems of replacing it, if it breaks down again. The incomer will be a RCD. The main reason for this is that I have a young son who no doubt will stick his finger in a socket at some point. The other reason, is Ive read somewhere on this forum that new laws are coming in soon that will require all installations to be protected by RCD's, so I may as well comply with that now. As to what value to put on it, that seems to be of mixed feeling here. 100mA or 30mA ?. My current RCD is time delayed and I assumed from what I'd read somewhere else that any main incomers had to be time delayed anyway. The RCD in the sub CU that I have in my garage ( that also protects outside sockets ) is 30mA. This is taken from the main CU as an extension, I think. As I understand it, if the main CU was only protected by a 30mA, a fault in the garden would trip the main CU RCD ( house ) first, therefore, I really need a 100mA for the house.

I want to have the main CU replaced, mostly to get rid of the fuses, would much rather have MCB's instead. Sorry John, I'll have to give RCBO's a miss due to cost, it would be great to cover each circuit with them, but I cant afford it at the moment. I'll have the MCB's upgraded to RCBO's at a later date when finances are a bit better.

I believe that all the utilities are already earthed. The house was built in the early 90's and as far as I'm aware was built to specs at that time. There are Earthing tags in various places, there is definately one coming from the main loop down into the basement and is attached to the incoming water supply. I dont know about the oil supply, that was added after I moved in, I'll need to have that one checked.

I'm sorry if I seem to be re-iterating some of the same stuff here, but I'm trying to get it all clear in my mind what needs to be done. I have to convey this to an electrician at some point ( when I manage to find a good one )( neither of the previous 2 mentioned or seemed aware of this PME as a possible solution to the problem )

 

[sm1thson]

At the moment, I'm envisioning a new setup with the incomer in separate housing to avoid future problems of replacing it, if it breaks down again. The incomer will be a RCD

if you get PME'd you dont need it and its more hassle than its worth! as when it trips your whole house goes out (dark).

as you say at the moment the requirement is all sockets that can be expected to supply outdoors (/allong them lines), but you want all your sockets. it is normal to cover all your sockets on a PME'd supply you can use a split load CU which some circuits are on RCD (sockets) and others arent (lights, cooker (if seperate), immersion heater). or ould you add RCDs after the CU? -probably better just to change the CU!

(100ma time delayed is used for an incommer, 30 ma is used for supplying sockets. this is because 30ma on an incomer it will nucence trip too often, and 100ma on sockets isnt suffient protection for outdoors etc)

 

[JohnD]

The only filters I know that could stop lightening tripping an RCD would be the TVSS devices, I'll see if I can find them in the MEM price list. (edited: looks like about £40 per circuit, or £500 for a big one that will do the installation - but I am not experienced with this technology) Other major manufacturers will have other products.

They are rarely used outside industrial installations and I don't know if your local electrician will be familiar with them.

If I were you I wouldn't worry about that yet; if you get your supply PME'd and get rid of your old whole-house RCD that will I'm sure stop the nuisance tripping so it should come off your priority list. (as sm1thson says, you won't need it) You still need 30mA RCD protection on your outdoor sockets (which you say you already have on the submain) and preferably (as you say) on the other sockets as well.

There are some pictures of a good-quality installation by RF Lighting
including TVSS on //www.diynot.com/forums/viewtopic.php?t=70551&start=0 but be aware that it is a post mainly designed for amusement of people with minority interests who like looking at pictures

 

[AlienBiker]

From the price you've given for a whole system filter, I think I'll leave that one as an absolute last resort, or even consider moving house first !

Wonderfull pictures of systems, unfortunately, I have limited space to play with, somehow I think my wife may get a bit upset if I take over half her wall space in the kitchen

I wanted to apply some sort of RCD protection to all the circuits in the house, not just the sockets. The reason being, as a kid, I pulled a light bulb out of a socket and stuck my thumb in to see what would happen I mentioned this to a mate and he'd done the same thing, so I know its not exactly an isolated case. There are 3 ring mains in the house, upstairs, downstairs and kitchen. Unfortunately the fridge and freezers are plugged into the kitchen ring main, not on a seperate circuit, so I cant just miss out putting an RCD on the kitchen circuit because I'd loose the protection on the remaining sockets in the kitchen. Ideally its the one circuit to miss out on a RCD because of trips to the power supply leaving the fridge and the freezer without power. Anyway, thats the reasoning for wanting to maintain a 100mA RCD covering the whole lot.

So, any of you lot heading down to sunny Devon in the near future and fancy a fairly straight forward CU replacement job ?

 

[securespark]

MEM price list.

John's book of worship, kept under his pillow...

 

[JohnD]

No, but I found the soft copy on the interweb

 

[AlienBiker]

Hi again, only me

Ok, I've found an electrician that knows his stuff on PME's etc.

He's provided a quote for replacing the consumer unit and setting up everything ready for the PME connection, which I'm happy enough with.

Bonding the oil supply, which I'm going to discuss with him about doing myself.

Also, he has quoted me for cross bonding the hot and cold water pipes along with running earth cabling to re-bond "breaks" in the metal hot and cold pipework supplies that I had created by installing new plastic pipework. This part confuses me. I had read on these forums that plastic plumbing made bonding unnecessary and it was actually more dangerous to re-bond the pipework. Is this a special requirement for PME installation ? or did I read something wrong earlier ?

[edit]

Ok, Ive just found the pdf about earthing plastic pipes with respect to PME installations. I'm still confused by it though, since its first words are "You do not have to Earth Plastic pipes" and then it goes on to tell you how and where to earth pipes.

 

[AlienBiker]

Apologies in advance for bringing this one up again, but my head is starting to hurt trying to understand certain needs for earth bonding and I obviously want to make sure everything is safe.

In preparation for the electrician coming, I have bonded the hot and cold water pipes and the oil line with 10mm wiring, running back to the CU area ready for hooking up.

I am however confused as to what needs to be done with the radiator circuit. All the information I've read states that it should be bonded if metal pipes are used and not bonded if plastic pipes.

My plumbing has been "evolving" since I moved in and is now a combination of metal and plastic ( it was before, but is even more so now ). The pipework connecting radiators upstairs is now mostly plastic below the floor, downstairs it is still mostly metal. If it was a case of having to bond all the metal segments together, it would actually be easier ( by a long way ) for me to cut sections out of the metal and replace with plastic, effectively making the whole system plastic, or at least 95% of it.

Please, what are the bonding requirements in relation to a mixed system ?

 

[Pensdown]

If you have a look around the Wiki section all will become clear.