Is there any practical way of modifying a Crabtree Starbreaker CU from
6+6 split to 8+4? Ideally I want to move two of the circuits (immersion heater and air conditioner) to the non-RCD-protected side, to reduce nuisance trips. There are no spare positions.Richard.
I have no idea about your Crabtree, on an MK it is simple but you would have to replace one of the copper bus bars with a longer one and cut the other down. If my immersion heater was tripping the RCD I would not call it a nuisance trip, I would want to investigate the problem and correct it.
I haven't managed to find a longer busbar for the Crabtree. I know MK boxes are easy to modify but replacing the entire unit isn't really an option for me (and even if I did, wouldn't I have to do it to the 17th edition regs?).
It's not (in fact it's switched off, so it can't), but the FAQ says an immersion heater should be on the non-RCD-protected side.
Richard.
17th edition regulations. If it works and is not tripping your RCD then leave it where it is.
Cheers
Adam
When the air conditioner was installed (recently) they wanted to put it on the non-RCD side, but there wasn't a spare position. I can't believe it would be "against the regs" to move it to where the installers wanted to put it in the first place! It's a largish 'inverter' type with no doubt a substantial EMC filter, potentially resulting in a significant leakage to earth.
The situation is that we suffer rare but annoying nuisance trips. It's not surprising because there are lots of items with Switch Mode Power Supplies that are usually left on standby (computers, microwave oven etc.) on the RCD-protected circuits, so it's probably close to tripping all the time. I have no reason to think any single item of equipment is faulty, it's just the cumulative effect of all those EMC filters. Moving things which *should* be on the non-RCD side would be a practical step which might mitigate the problem.
Richard.
I said "could" not "would" be against the regs! If the cable is surface mounted or armoured then it would not be against the 17th regs.
Is it the Crabtree Starbreaker with the plug in MCBs that you have? I have not fitted one for a while but I am sure that they only available in 7, 10 or 15 way versions (with a choice of split between the RCD and Non RCD sides) There was an older version that did a 6+6 split but was not available with a choice of split. A photo would help. There is certainly nothing showing on Crabtrees website that fits what you need.
Cheers
Adam
Yes, surface mounted.
That will be the one (it was installed in 2007).
That's what I suspected.
As the range of consumer equipment using SMPS technology increases, nuisance tripping is bound to become a greater problem IMHO. Do you happen to know whether a standard CU RCD takes account of power factor (in other words, does it trip just on the imbalance current or is phase a factor)? Since EMC filter leakage will invariably be capacitive, whereas a through-the-body circuit is likely to be primarily resistive, the RCD could in principle discriminate between them.
Richard.
Just on imbalance AFAIK.
Is there any way you could add a second CU to feed the A/C if needed?
Adam
immersion heaters mix lots of electrickery and water, why not add another consumer unit with its own RCD for the trippy circuits (and why are they tripping) (2 of mine tripped in the thunderstorms last nght)
[g]Can you put the immersion on an RCBO?
Reason being immersion elements do breakdown, an IR test would confirm. RCBO can be cheap on Ebay at least in pinning down a fault.
In fact there already is a second CU which feeds outside circuits (garden lighting, pond pumps and shed). I suppose it might be acceptable to connect the A/C there. It would be on an RCD, but there are no other loads on that CU likely to cause leakage.
Richard.
If something is switched off only on the live wire then it could trip an RCD if theres a leakage from neutral to earth
but the FAQ says an
The FaQ says an imemersion heater should have no RCD?
I put a link here some months back of a TV programme investigating cheap RCBOs which didnt have the correct circuits in them , one exploded!
beware!
[g]
Depending on the neutral-earth voltage, yes, but IME it requires a low- impedance connection like a dead short for that to happen. Anyway, the immersion heater switch is double-pole (Hamilton).
"Immersion Heaters are run off the non-RCD side. Immersion Heaters are a common cause of earth leakage, and can thus make an installation unreliable if on an RCD":
DIY FAQ being inconsistent again!
Richard.
Cheap =3D "Boxed New" from genuine sellers with good feedback :-)
Recalls do happen. Wylex/Crabtree MCB have had recent recall. MK/MG/Schneider RCBO/RCD had a recall for 2003-2004 product.
There are also intentionally counterfeit devices. BS1361 house-sized HRC fuses without sand, this one is obvious due to the weight and they ain't arf going to go with a bang. Counterfeit MCB which were in fact a continuous link, this one was rather odious since it could result in damaged wiring or ejection of material from steam generation (cable overheating). Chester just had an underground cable blowup in a street today causing flash damage & ejecting material.
I am wondering when the bad caps issue or similar hits RCD/RCBO in the future, since I am rather dubious about product quality these days re hidden outsourcing from lousy screws to electronic components. I have two RCBO fail on me in 6yrs.
xxxx
[g]
An electrode water heater is *not* an immersion heater. It is where the current is passed through the water in order to heat it. Many years ago I used to operate a pair of 3 phase electrode boilers used off peak for a heatbank for space heating. Earthing has to be well up to spec, and earth leakage *is* expected. I can't imagine that single phase ones are permitted.
On Tue, 15 Jun 2010 00:19:38 +0100, wibbled:
I've seen electric showers in China (these have a small tank that requires preheating as most people's supplies wouldn't manage a 9-11kW instantaneous device) based on electrode heating. That scared me. Especially as RCDs are only recently appearing on new builds (ironically the new build I looked at for fun was RCBOs on all circuits - talk about extremes!).
However, after noting exactly where the socket for the shower was mounted (in the shower, albeit at ceiling height) I stopped worrying so much about the electrode heaters :-|
Or outdated. But the wiki also says- NOTE - The current set of IEE Wiring Regulations, the 17th Edition are more onerous in the requirements to install RCD (or RCBO) protection than the previous 16th Edition. In general, ANY cable which is less than 50mm below the wall surface AND is NOT mechanically protected as defined by the IEE Regulations (which generally means armoured cable [SWA], pyro cable [MICC, mineral insulated copper clad], cable in steel heavy guage conduit or a limited use of highly specialised cables incorporating an earthed foil screen MUST HAVE a 30mA non timed delayed RCD protecting that circuit, in addition to all other requirements. Such circuit protection may be derived from either an RCD protecting several circuits, or individual RCD/RCBOs on each circuit. This statement and it's implications now overrides anything else in this article which was written to the 16th Edition, pending more detailed updates to this article.
Adam
anything else (all the other CUs on their site have different busbars to alter the split) then could have a 3rd CU? I am still not sure that the immersion need to be RCD protected unless it causing you problems (ie is it usually off when you get a nuisance trip). I have not checked yet but you might be able to change the bus bar and then use RCBOs for the circuits that you want RCD protection on. Please sit down before looking at the prices on Crabtree RCBOs.
Adam
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