I don't understand your comment ? is it just humor that I have missed, or do you really think I am making up my own rules ? I'm not.
No protection - Alarm, Home Automation, Fridge & Freezer
100mA - fire protection 30mA - life protectionRick
Supply is PME ( TN-C-S)
Agree on life protection, and the 30mA RCD wil provide protection to the AC outlets, Radial and Ring Final circuits.
The Best Practise oft talked about is not to have lighting on a 30mA trip duwe to nusisance tripping, many on this group for example have advocated no protection for light circuits.
Now I prefer to have some protection to prvent fire hazard, and thus have all light ccts through a 100mA RCD which are much less prone to nuiscance tripping.
My question is really pretty simple - do I protect Imeesrion and cooker or have them unprotected. AFAIK the regs do not require protection, but that doen't mean i t's best practise.
Rick
"Rick Hughes" wrote | Now I prefer to have some protection to prvent fire hazard, and | thus have all light ccts through a 100mA RCD which are much less | prone to nuiscance tripping.
But having all your lighting ccts through a single RCD - of whatever rating - means you lose all lighting on the opening of one protective device.
| My question is really pretty simple - do I protect Imeesrion | and cooker or have them unprotected.
Well, if you need fire protection on your lighting circuits (and the only reason I can think of in a normal dwelling would be if you have thatch roof or straw bale walls), why would you *not* need it on cooker and immersion circuits?
Lighting circuits are low current and use generously over-specified cables in most cases, compared to cooker and immersion circuits which may be operating at close to maximum capacity for extended periods of time. If anything, they're more likely to cause a fire hazard through poor connections overheating that a lighting circuit.
Owain
With modern downlighters and other types of lighting, the current drawn can be quite substantial.
Says he who thinks his CU might have caught on fire because 'wires were a bit tight'
:)
Alex
In article , G&M writes
There are some misconceptions about what an RCD actually does, well modern ones.
An RCD (Residual current device) is designed to trip when there is a current UNBALANCE between what is coming IN and what is going OUT on the circuit it is protecting.
Now under normal operating conditions it matters not how much current is flowing through the device, provided that its within its ratings like 64 amps for example.
Now as long as the current in, through say the live terminal, is matched by the current out through the neutral terminal, then all is fine. Now if for some reason there is more going in than coming out above the nominal tripping current, say 30 ma ,actually slightly less, then the device will trip.
Supposing that you inadvertently touch the live wire somewhere in the house, assuming that that particular circuit is protected by the RCD, then there will be an element of current flowing through your body to earth. Now if that current that you are "conducting" is greater than the current trip level, then off goes the trip because it has detected less current flowing OUT than the current coming IN hence an UNBALANCE!.
It doesn't even matter if you touch earth or not or even if your house is on an earth or not, or even if there is no earth on your system, it doesn't matter as far as the trip is concerned. The reason is that the neutral line is earthed at the substation transformer, be that in a substation proper, or on a pole mounted transformer. Due to this if say you touch a live wire then you shunt some of the current via the trip and the earth mass back to the substation and if that value of current is greater than the trip level off will go the trip!.
Its down to a current unbalance through the trip, simple as that. If for instance a cooker element develops some leakage between the element casing then some current will flow to earth and if that current is greater than the tripping unbalance current then off the trip will go. Sometimes you may experience this as the element will only do this when it gets hot and then the insulation will breakdown and the trip current will be exceeded!.
Another "bastard" problem comes if there is a short betwixt the neutral line and the earth line in the wiring somewhere. Normally if most every thing is switched off then no tripping, but as soon as some appliances are switched on then off the trip will go!. The reason is that under light or no load conditions the trip will be sensing an unbalance state so the current flowing in will match the current out, because some of the current will flow back along the neutral lead through the trip and some direct to earth through the earth wire. Now as soon as some load is put on the system and the current flowing through the combined earth and neutral return starts to increase then the trip will sense that there is more coming in than going out via the "authorised" route via the RCD, so a unbalance exists and as soon as this exceeds the trip current off again.
In my opinion all the wiring in your gaff should be on a 30ma trip because there might be the time when you are working on something and forget to turn it off, or pull the wrong fuse or something similar I wouldn't fancy trying to trip a 100 ma trip with my body either thanks!.
So as long as you see the trip as a device that monitors the current in and the current out are in balance, then all is fine if however there is a difference between these two values greater than the trip level, then the device will operate.
Hope this helps....
On Mon, 9 Aug 2004 14:42:28 +0000 (UTC), "Rick Hughes" strung together this:
Bit of both.
Fair enough, just wondered. Nothing wrong with it, just don't see domestic installations, or many installations in general come to think of it, with 3 classes of protection.
Do try to read things properly.
On Mon, 9 Aug 2004 14:51:52 +0000 (UTC), "Rick Hughes" strung together this:
You've obviously mis-read something somewhere. RCD=earth fault protection, MCB=overload protection.
RCD's work by measuring the amount of current on the live cables and ensuring they are equal, if they aren't, by an amount determined by it's rating, then it assumes the current has gone to earth, either through a faulty appliance or you, and trips.
A light bulb isn't earthed so wouldn't take out an RCD. You're thinking of MCB's which protect final circuits, light bulbs can easily take out type B MCB's as the bulb takes a surge of current as it blows which overloads the circuit but by fitting a type C or a HRC fuse to the lighting circuits this nuisance tripping can be reduced.
Type C MCB's and HRC fuses react slower so won't always trip\blow.
If that's what you based the 3 classes of protection on then you might not be the best person to be doing this project.
The immersion doesn't require RCD protection. The cooker doesn't either, unless the manufacturers instructions say so or if the switch incorporates a socket that can be reasonably expected to supply portable equipment outdoors.
On Mon, 9 Aug 2004 20:42:25 +0100, tony sayer strung together this:
Wrong way round, out from the RCD through the live and back in through the neutral.
I have on occasions tried overloading circuits fed by 30A fuse wire, using just myself as 'the load' and failed, and I've never managed to trip an RCD by using me as a load across live and earth.
Agreeed 100%, but it's the leaqkage that causes the nusianace trips I would assume.
So my question on whether to protect a cooker is a valid one?
Sometimes you may experience this as the element will only do this when
I had such a fault on a previous house .... trip would operate once a week or so .... after hours and hours of fun, eventually could re-create it as soon as I put a high current on the ring (toaster & kettle) eventually found that SWMBO after loosening a socket for painting some months previous - had crushed a neutral wire under the socket plate screw ...
If I didn't have an RCD on the cct ..... when would I have found the fault ? when it burst into flames ?
Rick
No not at all .... I refer to nusicance trippingt of RCD that is nothing at all to do with overload protection.
Wrong here I'm sorry I referred to lighting circuits not to light bulbs, (but it could just be the sequence you are reading mail in) ... floreescents are earthed and it is these that typically give the nuiscence tripping reports, again an RCD would actiuvate not an MCB as there is an imbalance but no overload.
No I'm not - I am specifically referring to RCD protcetion.
The 3 classes of protection are deliberate .... unprotrected, fire protection and life protection - all defined separte calssses of protection - exactly what I want on this project.
Do you have a comment on my qusetion ? I would be interested in your answer.
Q was - To RCD protect a cooker and immersion or not .... the regs do not require it, but that may not be best practise.
Rick
My 'reading' and I'll admit it's not personal experince is that some lights, such as Floureseents can have leakage which can cause a 30mA trip to activate ... whether this is on switch on , or when choke gets hot, I'm not sure.
Rick
On Mon, 9 Aug 2004 21:28:10 +0000 (UTC), "Rick Hughes" strung together this:
Ah, with you now. Not heard that one too often, the lightbulb scenario I presentede is a far more common aoccurence so I assumed that it was that you were referring to. TBH, all circuits are likely to trip at some time or other. I don't think the technical basis of your plans is particularly sound. I think with a bit more electrical knowledge and experience you would see this whole ting as a 'fiasco', (as I do)!
I've answered that, twice. Only you can decide how much additional protection over and above the regs you require. I think from what you've said you'd be better off with RCBO's for all final circuits, then all circuits have their own RCD and MCB so any earth fault or overload will affect that circuit only.
On Mon, 9 Aug 2004 21:28:10 +0000 (UTC), "Rick Hughes" strung together this:
Only if the leakage is not about to cause a fire\damage to equiopment etc... If it goes off for a reason, i.e. a fault, then it's not a nuisance trip. If it goes off for no apparent reason then it is a nuisance trip.
Yes, as is any question that involves the words "shall I RCD protect my"? In your case, it may or may not be neccesary to install an RCD on the cooker circuit, if it does require one then that's your answer, if it doesn't require one then you can fit one if you want some additional protection.
No, it would probably have never done anything at all. If you are on PME, (which I seem to think you are), then neutral and earth are connected together in the service cutout, and that hasn't burst into flames has it? Having the neutral and earth connected together throughout the house on a PME system would never cause any problems whatsoever.
On Mon, 9 Aug 2004 23:14:31 +0100, "G&M" strung together this:
Not really, if the RCD tripped then you would get a cold supper _and_ cold bath if you put the immersion and cooker on the RCD. I would say the immersion and cooker would cause more nuisance tripping which is exactly what the deluded chap who started this is trying to avoid which only further convinces me that he really shouldn't be doing this. I think RCBO's would be the only way to prevent nuisance tripping affecting anything else, he's coming in at this from the wrong angle.
Been reading through this thread with some interest.
Correct me if I'm wrong, but I can't see the 100mA RCD offering any useful protection against fire hazard at all in this installation, and nothing useful against electrocution.
Rick correctly identifies the need for 30mA RCD as protection against shock hazard for socket circuits, the rationale of course being that if you touch a live part then as soon as the current through you to earth reaches 30mA the protection trips, disconnecting the supply. Fine, so we certainly install 30mA non-time-delay on all circuits likely to be used for any external portable appliances, and personal preference dictates whether other socket circuits (such as upstairs) are similarly protected. Some appliances within various zones of the bathroom will also require this protection.
This doesn't provide any protection against circuit overload (one of the causes of fire in fixed wiring), though, because unless it's implemented as a RCBO then this isn't it's job - the MCB takes care of that. As I see it, the other likely cause of fires (loose connections in the circuit giving localised high resistance and therefore heat generation) isn't protected against by either the MCB or RCD.
So, what's the 100mA RCD for? It can't be against electrocution, because
100mA represents a fatal shock hazard. Whole-installation 100mA time-delay is used in TT systems due to problems with the earth impedance and disconnection times for MCBs under fault-load conditions.I don't see that earth leakage is a significant fire hazard. The most likely ones are chronic circuit overload (MCB's job to protect against this) or loose connections (and neither will protect against this, unless the insulation breaks down to such an extent that there is significant leakage to earth, and once this happens then it's likely to produce a fault current that the MCB will protect against).
Not sure about reports of "nuisance tripping" that the OP talks about either. All the ones I have read have been concerned with blowing bulbs taking out the MCB due to high fault currents generated. Either that, or deprecated whole-house 30mA RCDs taking out all the lighting circuits due to earth leakage from either a portable appliance on a socket circuit, or mineral insulated heating elements leaking to earth. There's a jolly good reason why whole-house 30mA protection is deprecated.
Finally, for the OP, there could be a very good reason coming up on 1/1/05 why you shouldn't start introducing unneccessary RCD protection. (as opposed to "necessary" RCD protection - I'm NOT advocating that they are always unneccessary !)
My reading of Part P is that RCDs are always "notifiable" devices for the DIYer. So, if your superfluous 100mA RCD develops a fault, and you're the type to obey the letter of the law, you've just landed yourself with a bill for a self-certing spark to change it, or for BCO approval.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
I would argue that my solution of two smaller CUs each with RCDs plus some careful wiring around the house to ensure there is always a working light nearby is safer. If room lights are on one but staircase and exits on the other you'll never be far from a working light switch.
In any case one should either have some form of emergency lighting or a torch nearby for power cuts which are frequent where we are and are predicted to get worse everywhere.
In article , Lurch writes
Well that is another way of saying the same thing. Mind you a drawing would be worth a 10000 words in this instance:)
Something wrong there...your still here to tell the tale!....
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.