RCBO instead of switched fused outlet?

Discussion in 'UK DIY' started by Charles M Atkinson, Jan 12, 2004.

  1. 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?
    Charles M Atkinson, Jan 12, 2004
    #1
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  2. Charles M Atkinson

    Lurch Guest

    On Mon, 12 Jan 2004 19:27:05 -0000, "Charles M Atkinson"
    <9.coREMOVE.uk> wrote:

    >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?
    >
    >

    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
    Lurch, Jan 12, 2004
    #2
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  3. Charles M Atkinson

    ARWadsworth Guest

    "Charles M Atkinson" <9.coREMOVE.uk> wrote in message
    news:hACMb.13900$9.net...
    > 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?
    >


    There are RCD fused spurs, such as
    http://tinyurl.com/3bgrf
    but if you have a 30 mA RCD whole house RCD there is no guarantee which will
    trip first.
    --
    Adam

    adamwadsworth@(REMOVETHIS)blueyonder.co.uk
    ARWadsworth, Jan 12, 2004
    #3
  4. "Lurch" <> wrote in message
    news:...
    > On Mon, 12 Jan 2004 19:27:05 -0000, "Charles M Atkinson"
    > <9.coREMOVE.uk> wrote:
    >
    > >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?
    > >
    > >

    > 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


    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.
    Charles M Atkinson, Jan 12, 2004
    #4
  5. Charles M Atkinson

    Owain Guest

    "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
    Owain, Jan 12, 2004
    #5
  6. Charles M Atkinson

    Guest

    In uk.d-i-y, Charles M Atkinson <9.coremove.uk> wrote:
    >
    > 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.
    >

    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
    , Jan 12, 2004
    #6
  7. Charles M Atkinson

    Guest

    Charles M Atkinson <9.coremove.uk> wrote:
    > 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.
    >

    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
    , Jan 12, 2004
    #7
  8. <> wrote in message
    news:btv4pn$boqc3$-berlin.de...
    > Charles M Atkinson <9.coremove.uk>

    wrote:
    > > 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.
    > >

    > 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


    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?
    Charles M Atkinson, Jan 13, 2004
    #8
  9. Charles M Atkinson

    Chris Oates Guest

    "Charles M Atkinson" <9.coREMOVE.uk> wrote in message
    news:Ha_Mb.14505$9.net...

    > Thanks to all for info. Am learning fast!
    >
    > Back to original question -- is an RCBO available?
    >

    yes

    > 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.

    the power breaker fused RCD spur is the easiest
    thing for you

    > 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?
    >

    the crabtree is for fire protection

    > If there wasn't much "base level leakage" then the ELCB
    > might allow nearly 100 mA through someone before tripping.
    > Not good.

    as above it's for fire protection not electrocution

    > 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?

    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.

    > 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?


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

    > Getting theoretical: even if the "whole house" was protected
    > with a 30 mA RCD

    no no no no - no more to say

    > 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.

    whole house = bad idea

    > Or are
    > RCDs so reliable that any improvement from using two RCDs in
    > series is so small that it is insignificant?

    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
    Chris Oates, Jan 14, 2004
    #9
  10. In article <40051ec2$0$9393$>,
    "Christian McArdle" <> writes:
    >>> 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?

    >> 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.

    >
    > 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.


    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
    Andrew Gabriel, Jan 14, 2004
    #10
  11. In article <40054877$0$9394$>,
    "Christian McArdle" <> writes:
    >> You are describing an old Voltage Operated ELCB -- they trip when
    >> the difference in voltage between the earth conductors and outside
    >> ground reaches 50V.

    >
    > 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.


    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
    Andrew Gabriel, Jan 14, 2004
    #11
  12. 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.
    Charles M Atkinson, Jan 14, 2004
    #12
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