I;m about to replace my existing metal cased wylex consumer unit,the one with the big grey RCD on/off switch which has a penchant for nuisance trippage,with a new unit which will have an isolator and mcb,s. Do i really need an rcd though ?. My biggest issue is nuisance trippage once or twice a year leading to fridge /freezer defrost. There is no apparent fault,it may just be a fault on an adjacent property or something or just nothing at all. Are newer rcd's less prone to trippage?
joe
CU units are available with mcb on the RCD and other that supply the freezer, alarm, etc, not on the RCD. get one of these.
The problem is that whole house RCD units are both prone to trips, and their consequences, as you've found out.
The best, but most expensive solution, is to use RCBOs instead of MCBs for socket and exterior electrical circuits. This way, any trip only affects that circuit, and trips are less likely anyway, because they only measure leakage on that individual circuit.
The next best solution is to use a split load circuit. This has only a single RCD, but this only covers high risk circuits, like sockets and exterior circuits as above. Some circuits (such as lights) are not covered by the protection.
In either case, a fridge freezer should actually be on a dedicated circuit and not be RCD protected.
Note that if you have a TT type supply, the circuits MUST be RCD protected. This is normally achieved using a time delayed 100mA RCD, with 30mA RCD protection provided as above. Alternatively, RCBOs could be used for every single circuit without exception.
Christian.
"tarquinlinbin" wrote | I;m about to replace my existing metal cased wylex consumer | unit,the one with the big grey RCD on/off switch which has | a penchant for nuisance trippage,with a new unit which will | have an isolator and mcb,s. Do i really need an rcd though ?.
You *must* have RCD protection on:
- a TT (earth rod) installation
- sockets likely to be used for appliances out of doors
In practice, it is usually easier to provide RCD protection to all sockets as this saves proving by calculation that the MCB alone offers sufficient protection.
You should NOT use a whole-house 30mA RCD main switch. This is contrary to the Regulations.
If you have a TT installation then use a 100mA Time-Delay RCD main switch and 30mA RCD on socket circuits (either a split load CU or RCBOs on individual circuits).
If you do not have a TT installation then use either a split load CU or RCBOs on individual circuits.
| My biggest issue is nuisance trippage once or twice a year | leading to fridge /freezer defrost.
You should try to identify which circuit(s) is tripping the RCD. There may be a fault such as poor insulation or ingress of damp.
If you use a split load CU, then the freezer can be wired on the non-RCD side, as should be lighting and smoke alarms.
Owain
Yes the thing is it would be troublesome to provide a dedicated supply just for the fridge /freezer as its just a typical upright model plugged into a socket in the kitchen so its a little impractical to run a separate supply just for this as i;d have to take upstairs apart(solid floor downstairs). BTW i have a passing recognition of supply/earthing types. Mine is PME so is it acceptable for me to have an isolator,no rcd and just mcb's?
ta joe
It only happens about two ccasions a year but inevitably,when it happens there are usually 2 or 3 offs per occasion then it settles for another year!!. Tried everything to try and proove a fault on my installation but I'm now thinking it must be a duff RCD or a fault in a neighbouring property
Not questioning that this is the recommended case - but I've found this recommendation to be curious...
I *would* put *all* my appliances on RCD just as an extra line of defence in the case of either multiple mode failure (live to case + case earth fault) or to cover someone plugging some other appliance into that socket now or in the future.
I see why the recommendation is the way it is (I think - food going mouldy?), but I'd rather have a freezer full of mouldy food than a shock.
Is there any other reasoning behind the recommendation that I've missed?
Timbo
Since you are not on a TT supply, then you don't require RCD protection for ALL circuits. However, you should have RCD protection (30mA trip) on any socket circuits that might conceivably supply power to portable appliances that could be used outdoors.
So in answer to your question, the strict answer is likely to be "no". Whether you need RCD protection for the particular circuit in question however will depend on the layout of your house etc.
That's a decision for you to make - when Christian wrote that freezers "should" be on a non-RCD circuit, he wasn't expressing a Regs requirement, just a trade-off which most households would find appropriate: the multiple-mode failure you mention is pretty unlikely, while the spoiling of food is a pain in the fundament to many. But it's your choice to make. For those who go for the non-RCD option, the possibility of other stuff being plugged into the socket can be eliminated by supplying the freezer & fridge through FCUs, or through non-standard sockets, e.g. 15A round-pins, Schuckos, IEC-320s, Powercons: there's a shedload of safe, approved connectors you can choose to use, mostly unfused - with a dedicated 10A or 16A radial for the fridge-n-freezer supply you can usually readily demonstrate that the flex to the appliance is adequately protected by the MCB; if you want the reassurance of an appliance-specific fuse, you can use an FCU to feed the non-standard socket of your choice, possibly using a cable-mounted rather than a wall-mounted one, so you have a way of wheeling the fridge/freezer out of the way for the once-every-four-years clean-behind-the-fridge session ;-)
Yet another possibility, if you want RCD protection on the fridge-n-freezer but not lose power to them unless there's a fault in those appliances themselves, is to feed them with their own RCBO-protected circuit, or on a circuit fed without RCD protection but to use a plug or socket incorporating RCD protection.
HTH - Stefek
Stefek
As it is not a TT supply then what about no RCD on the CU and have a couple of these
Provided you wouldn't conceivably use any outside appliances (i.e. you don't have a garden). The provision of some outdoors sockets with RCD could support you not providing RCD protection on socket circuits inside. However, you should realise that you are greatly increasing electrocution and fire risk by not RCD protecting all socket circuits.
Christian.
There can be ways. Do you have a cooker circuit, for example? A quick diversity calculation might allow you to use this for the fridge/freezer.
Christian.
You make it sound like this is fixed. On mine, you decide the combination.
OK, "should not be be covered by the protection, as doing so is more dangerous than providing shared RCD protection with other circuits."
Christian.
Thanks to all for your feedback,i'll give it some thought. Coincidentally i have had a plug socket that hasnt worked more or less since i moved in the house (new build about 20years ago). It was one that was little used anyway and i suspected a duff switch. I bought a new socket yesterday and on taking the old one off,it became apparent that the earths from the ring main were not connected!. They had never been in place because the earth screw was fully home and had never been in contact with the socket connector!. I'm just wondering now if this has been the cause of my spurious trippages,time will tell..night just do the consumer unit anyway.
thanks,,
joe
Sounds like you could do with a full system electrical test. This will test continuity, insulation resistance, polarity, earth loop impedence etc.
That RCD tripping might have actually been saving your life all these years. People who want to remove RCDs are often those most likely to be protected by them! My RCDs never trip. (Unless I'm using my RCD tester to piss off my TV watching daughter!)
Christian.
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.