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Split versus Dual CU

Discussion in 'Electrics UK' started by davidgpa2, 7 Oct 2020.

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  1. davidgpa2

    davidgpa2

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    In one of your forums someone stated that a split-load CU protects circuits by RCDs and a dual CU doesn't.
    So what protection DOES a dual unit provide?
    Surely ALL circuits are protected by an RCD even if several circuits use the same RCD?
     
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  3. AndyPRK

    AndyPRK

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    posting a picture of your board, we can help answer the question and explain

    Do you have red labels on one side and green the other?
    Do you have 2 RCDs ?
     
  4. EFLImpudence

    EFLImpudence

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    Split load has one RCD covering only one of two groups of MCBs.

    Dual RCD has two RCDs which cover one group each.

    Split load is just the name given to this arrangement as obviously both are split load.
    The electrical trade is full of such inappropriate names and terms.
     
  5. Taylortwocities

    Taylortwocities

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    And there is one forum member who will generate endless posts to try and belittle anyone who uses an incorrect term.
    Oh sorry, I should not have used the word belittle. He calls the process “education”.
     
  6. EFLImpudence

    EFLImpudence

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    To be fair, I also correct definitely incorrect terms - and I think so do you.

    It's just his manner that is a problem - and, of course, when he is wrong.
     
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  7. SUNRAY

    SUNRAY

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    Their ahh write and rong ways of putting that edyercasion over.

    But it does make it so much better when the education is actually correct.
     
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  9. sparkwright

    sparkwright

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    A split load cu 'typically' comprises of one side RCD protected, the other side RCD non-protected.

    But the non-protected side can have it's MCBs removed and replaced with RCBOs, which provide RCD protection.
     
  10. ericmark

    ericmark

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    I have often wondered where the names come from, we also have high integrity which means the board is split into three sections, two with a RCD and one with no RCD.

    Not worked out what name is given to my consumer unit with no RCD?

    When I say RCD I mean a stand alone device, you can get combined RCD and MCB called a RCBO, so technically speaking my board does have 14 RCD's as 14 RCBO's but that is not what I was counting.

    Likely the split load is a good compromise with a group of MCB's with a single RCD for all, and a group of RCBO's.

    The major problem is what will fit the board. The early boards were not tall enough to take the early single module width RCBO, we now have shorter versions, but consumer unit means a type tested distribution unit and if you fit items not included in the type testing it ceases to be a consumer unit.

    I know technically I should not fit wrong make, but the German Institute of Standards in German the acronym DIN stipulate a rail (DIN rail) which is reasonably standard, it can result in terminals not lining up, or the bit that sticks through lid not lining up, but it does mean often the wrong make will fit, but even if they fit spot on, it means not type tested.

    I am told some where there is a rule that where an ordinary person is in charge only type tested items should be used, not sure if IET/BSi or HSE rules, but if your living in the home and you can change them then your not an ordinary person, so it is rather muddy as to what can and can't be done.

    But if we assume with split RCBO's are used, then the comparison split to duel must show split as better option.

    But this house the sockets were split front/back and the lights split up/down, so it would be impossible to arrange so if a fault in any room trips the RCD it will not trip the lights in that room. I know we can loose all power at any time, but it is assumed a RCD will trip when some thing has gone wrong, like an electric shock, it is bad enough when you get a shock without being also plunged into darkness as well.

    So we have sockets which are more likely to trip to any other circuit so you could say sockets on their own RCBO, but lights are more essential so could say they need own RCBO, and freezer not working could mean dangerous food, so do you put freezer on its own RCBO so less likely to trip, or with something which is likely to alert you that it has tripped? Rechargeable torch that auto switches on will power failure is favourite.

    But where you group MCB's together you must assess the risk, I considered my consumer unit is in the old garage now classed as annex under the main house, and to reset any trip, I need to go outside on an unlit path and down steps to access the CU to turn them back on. So if I have all RCBO then less likely to trip, and if it does trip more likely outside lights will still work, and also unless freezer likely I can wait until morning to reset. I assessed the risk, and decided risk of falling while going to reset them too high, so have done all I can to reduce risk.

    Mothers house the CU was assessable without need to get dressed. My old house was in garage, but no steps, so each house different.
     
  11. AndyPRK

    AndyPRK

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    Yeah to me split load means 16th Ed. one side RCD protected, the other side RCD non-protected.
    Typically lights and immersion heater not RCD protected for 16th Ed.

    Regarding your tall RCBO's not fitting. I think this is probably down to specific brands. I've not had a problem with Wylex etc, or MK. Although the existing T&E routing can be a pain.

    To me you put lights on RCBO and a downstairs socket circuit & boiler
     
  12. ericmark

    ericmark

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    The main reason to fit split or duel boards is they are cheaper than fitting all RCBO, so if going for cheapness why use an expensive make of board? We look at Fuse box, British General, Chint, and like. OK industrial look for quality, but then also looking at all RCBO.

    "MK Electric, owned by US conglomerate Honeywell, has announced plans to quit the circuit protection business and discontinue the Sentry consumer unit product range." as a result there are clearance sales of MK stuff rather cheap, OK good quality, but rather short sighted buying what will soon be obsolete kit.

    The other problem is what is made, I used Fuse Box, and in hind sight maybe a mistake as I have had type A RCBO's on back order for quite some time. I had thought I was fitting type B however it turned out type AC curve B.

    As to if any manufacturer produces a type F with single modular width I don't know, even if they do, picking one up a local whole sale output may be a problem, but this WylexRCBO.jpg is typical type B TYPE A at least Wylex put both down even if the don't say what the type refers to, but try finding a type B curve B RCBO internet hunt will pick up a load of curve B but failed even to find type F RCBO single module width, type F RCD two module wide yes.
     
  13. AndyPRK

    AndyPRK

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    Wylex and Crabtree have had Type A RCDs in their RCBOs for decades

    The old generation MK's were also Type A.

    So if you will buy a cheap brand!
     
  14. ericmark

    ericmark

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    Fuse box do type AC and type A and Wylex do type AC and type A the only difference is the packet the fuse box one said type B only.

    I blaim the guy who decided it was OK to have type B for both RCD and MCB there were 18 other letters he could of used even without using two letters, it was not that hard.

    Had the fuse box packet said type B type AC I would have realised.
     
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