RCBO instead of switched fused outlet?

Hi,
I'm installing a bathroom heater and, for maximum protection, would prefer to connect its power circuit spur via an RCBO rather than via the more usual switched fused double pole isolator. The power circuit is still fed from a fused consumer unit with a "whole house" RCCB -- not something I'm planning on changing soon.
Anybody aware of an RCBO (= combined RCCB and MCB) that comes in a single wall box sized package? Heater is rated at 750 W so looking around 5 Amps trip current.
Or is my difficulty in finding a suitable product because there isn't enough demand -- showing that I'm thinking too far off the mainstream way of doing things?
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On Mon, 12 Jan 2004 19:27:05 -0000, "Charles M Atkinson"

Readily available at most wholesalers, powerbreaker H92 is what you want or equivalent. 13A RCD combined with switched fused spur. Just fits on a standard single box. I use them all the time for powering outside sockets mainly, brilliant things they are too! I would prefereably go for the powerbreaker because i've had no problems with them but you could use a cheaper one if you wanted.
Look here, http://tinyurl.com/3bgrf SJW
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wrote:

spur
from a

rated
too
what you

spur. Just

powering
would
problems with

Thanks for that, S. Good news!
The PowerBreaker is favourite for being less "industrially" styled. Specification says "13A max, DP switched". DP? Does that mean it can be configured to less than 13 Amp nominal trip current? Have checked Powerbreaker (Greenwood) website but could not find that info.
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"Charles M Atkinson" wrote | > Readily available at most wholesalers, powerbreaker H92 is | > what you want or equivalent. 13A RCD combined with switched | > fused spur. | The PowerBreaker is favourite for being less "industrially" | styled. Specification says "13A max, DP switched". DP?
Double Pole - which is what you need.
| Does that mean it can be configured to less than 13 Amp | nominal trip current?
It's not an RCBO, it's a fused spur + RCD. So you could take the fuse down to 5A.
However there is no point in fitting a 30mA RCD if you already have a whole house 30mA RCD - there is no discrimination between the two.
Owain
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DP means "double pole", which in turn means that when it trips, it disconnects both the live and the neutral "load" terminals from the supply. This is a Good Thing (and standard across just about all RCBs).
As to your other question: you've got knickers twisted around two different things. The "trip current" is the imbalance between wot-goes-out versus wot-comes-back, and is a nominal 30mA: that is, if a relatively weeny bit more or less than the full current going out to the load along the live wire comes back along the neutral, the PowerBreaker will, um, break the power, on the grounds that if it's not coming back along the neutral, it's probably going somewhere it really shouldn't (e.g., through you).
Whereas the "13A max" refers to the *total* load current. For your towel rail - 800W or so, wasn't it? - a 3A or 5A fuse in the PowerBreaker would be a little more appropriate than the 13A fuse probably supplied, as it'll give closer protection to the cable than a 13A one would.
Your remaining problem, though, is that if your whole-house RCB is also a 30mA non-time-delayed unit, there's no way of telling which one of them will trip first in the event of an earth leakage fault on your towel rail. In fact it's a little more likely that it'll be the whole-house one which will go, just because there will be small, harmless earth leaks on appliances on the other circuits (particularly on various appliances with mains suppressors, such as washing machines, dishenwashen, compteren and similar), which will "preload" the whole-house RCB closer to the point of tripping than your towel-rail-dedicated one. If, On The Other Hand, your whole-house RCD is a 100mA time-delayed one, then you're on a Win, as it will reliably "wait" for the non-delayed one to do its job firstest.
HTH - Stefek
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Pointless adding another RCD device 'in series', a fault will probably trip the upstream one anyway as that will have other leakage through it as well.
--
Chris Green

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wrote:

spur
fused
from a

will probably

leakage through

Thanks to all for info. Am learning fast!
Back to original question -- is an RCBO available?
If not then a combined RCD and fuse (13 A changed for 5 A) is the best available. It still offers better protection than a traditional switched fused double pole isolator.
Have just checked the "whole house" RCCB and found it's actually an ELCB with a 100 mA trip current -- marked "Crabtree SB6000". Given this extra information, is it useful (= significantly greater protection) to fit a 30 mA RCD in series with it?
If there wasn't much "base level leakage" then the ELCB might allow nearly 100 mA through someone before tripping. Not good. And, if an ELCB measures current in the supplier's earth conductor (as opposed to a live/neutral flow imbalance) then someone could be conducting current to some other earth. Equally not good?
If I do end up with two RCDs (or an ELCB and an RCD) in series, I don't care which one goes first because I'm not expecting frequent faults. Is that a sensible view or have I failed to consider something important?
Getting theoretical: even if the "whole house" was protected with a 30 mA RCD, I see some benefit in protecting an individual outlet with another 30 mA RCD -- in case the "whole house" one failed to operate when it should. Or are RCDs so reliable that any improvement from using two RCDs in series is so small that it is insignificant?
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yes
the power breaker fused RCD spur is the easiest thing for you

the crabtree is for fire protection

as above it's for fire protection not electrocution

definition of ELCB
ELCB is a device installed to detect imbalance in currents flowing between the AC active and neutral lines. This imbalance current is also known as earth leakage current. When ELCB detects the imbalance, it trips and disconnects the AC power supply. Hence, ELCB protects people from electrocution.

failed miserably - when the crabtree trips the lights go out ....bad idea.

no no no no - no more to say

whole house = bad idea

it's called discrimination - when RCDs in series you never know which one will trip if they are rated similarly ...reliability ? - don't connect a powerbreaker spur backwards it'll either smoke or won't work properly
most RCDs will operate upside down & I've not yet had one fail
I use Powerbreaker spurs in a commercial environment ....toilet hand driers - perfect solution
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The ELCB doesn't actually measure current imbalance directly like an RCD. It just measures the earth voltage. If it rises, then it cuts the power. It is not very effective for shock protection and only works if the current flow is directly to the electrical installation earth. In a bathroom, supplementary protection may mean that the likely earth path is NOT through the electrical installation, particularly if no CPC is part of the supplementary bonding system. An ELCB does not provide sufficient shock protection for a bathroom, even before you consider the fact that it is 100mA instead of 30mA.

But, this is what happens already. The addition of the RCD outlet will reduce the chance of the Crabtree device tripping and cutting the lights.

There is more to say.
What should happen is that the Crabtree ELCB should be retired. Assuming it serves a purpose (i.e. TT earthing, or to fix a dodgy earth loop impedence), it should be replaced with a 100mA Type S time delayed RCD.
The consumer unit should be upgraded to a modern DIN rail, if necessary. There are two options:
1. (best) Insulated consumer unit with 100A isolator incomer. Socket circuits and anything feeding outside or in the bathroom should use RCBOs. Other circuits should use MCBs. You may be able to replace the 100A isolater incomer directly with the time delay RCD, removing the need for a separate RCD enclosure.
2. (cheapest) Insulated split load consumer unit. Socket circuits (and other high risk) should use MCBs on the RCD side. Other circuits should use MCBs on the non-RCD side. Again, it may be possible to replace the overall incomer with the time delay RCD.
The cheaper option is more likely to be subject to nuisance trips. These trips will also have more serious consequences in cutting power to otherwise unaffected circuits. However, both solutions should prevent the lights cutting after an earth fault in the high risk circuits.
Christian.
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I think there's some confusion in terms here.
You are describing an old Voltage Operated ELCB -- they trip when the difference in voltage between the earth conductors and outside ground reaches 50V. They don't normally have current ratings like 30mA, 100mA. They aren't intended to protect against electrocution.
An RCD is also an ELCB, but it's a Current Operated ELCB (the term RCD didn't appear until some time after the devices appeared).
The easiest way to tell which you have is to see how many earth terminals the device has. A Voltage Operated ELCB has two separate ones -- one connected to the installation's earthing, and the other connected to an earth rod (it works by monitoring the voltage between these). A Current Operated ELCB (RCD) doesn't need any earth terminals, although some have one to allow it to check for other faults such as live-neutral reversal, broken neutral, and sometimes the test button requires it.
--
Andrew Gabriel

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Ah. I've never seen a current operated RCD labelled as an ELCB, only old voltage operated ones. I hadn't realised there had been a period when RCDs were sold under that name.
In any case, the solution is the same. It is still best to replace the entire house unit with a 100mA time delayed one, with RCBOs for individual circuits. However, provided the old RCD works, it isn't quite as urgent. The main problem is lack of discrimination under an earth fault, causing the lights to go out.
Christian.
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The wiring regs of that time (14th Edition) calls them Voltage Operated ELCB's and Current Operated ELCB's. Manufacturers each invented their own names for Current Operated ELCB's initially, leading to much confusion because consumers had no idea if all these differently named things were the same or not (main problem was in the plug-in RCD market). It was a campaign by Which? and That's Life! that got a common name agreed across the industry, RCD. The terms RCCB and RCCD still persist a little in the installation business.
--
Andrew Gabriel

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Thanks to all -- again. Thank you, especially, for education.
I'm going to go with Christian's suggestion, bite the bullet and replace the consumer unit. Was on the list of things to do, anyway. Little point in adding protection (and spending money) for the bathroom heater only when that will be redundant when planned CU upgrade is done.
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