RCDs/RCBOs in series

Discussion in 'Electricians' Talk' started by Mr.AwesomeHandyman, Feb 8, 2016.

  1. fire

    fire Well-Known Member

    I can't disagree with what you just said there and if everyone agreed with me i would most likely think something is wrong :D

    [​IMG]

    And they clearly wish to keep the general public in the dark.
    Some amongst us are so self important they will go to every length to discredit someone for their own selfish gain.

     
  2. madhatter1uk

    madhatter1uk Screwfix Select

    You may not want to put a fridge or freezer circuit on an RCD / RCBO. It would have to be used for the appliance exclusively though, and you may not want to put smoke alarms on an RCD / RCBO
     
    Brian_L likes this.
  3. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Maybe so but at least what I state is factual and I am still awaiting the link for the time delayed 30mA Residual device you bit on a while ago. . .
     
  4. fire

    fire Well-Known Member

    True, you may or may not but a risk assessment needs be carried out to ascertain how you would design the circuit prior to installing it.
    In all fairness as i have said before, you can do what you want regardless of regulation but if you do something that directly contributed to the loss of life or property then you are in big trouble.

    Funny thing is I get the feeling many electricians, registered or not just seem to think a risk assessment is that annoying bloke that keeps coming round looking over their shoulder holding a clip board.

    If you need to for whatever reason install a smoke alarm without RCD protection then you need to figure out how you can do this safely within the guidelines set out in the regulations. Of course first part is that the cable can not be concealed or if it is, must be buried into a wall greater than 50mm while being mechanically protected such as SWA cable.
    So as an example using an SWA cable clipped to a wall or cable tray or put into a wall deeper than 50mm then you can get away without needing it to be RCD protected for whatever reason it is that you would not need RCD protection for. Better to find a better smoke alarm lol

    Grade D (with battery backup)

    The mains supply to smoke and heat alarms should either be a single independent circuit from the dwelling's main distribution board or a separately electrically protected regularly used local lighting circuit.

    Grade E (without battery backup)

    The mains supply to smoke and heat alarms should be a single dedicated independent circuit from the dwelling's main distribution board.
    Smoke and heat alarms should be interconnected and, in this case, must be supplied from the same circuit.
    The circuit supplying the smoke and heat alarms should preferably not be protected by an RCD unless one is required for reasons of electrical safety, then either the RCD should serve only the circuit supplying the smoke or heat alarms or the RCD protection of the fire alarm system should operate independently of any RCD protection for circuits supplying socket-outlets or portable equipment.


    To me that sounds like it is in case a fault on the sockets or some other circuit that may trip the split type consumer unit design RCD and would not only isolate sockets... but your fire alarm as well.
    Makes sense, if each circuit has its own dedicated RCBO this generally kind of fixes the problem anyway.

    I guess you could go the extra mile to avoid the RCD and the possibility of a false positive RCD trip which would power down your fire alarm. This is all part of a good thought out well educated decision when you design your circuits.
    I have no doubt a fridge freezer would have similar reasons for avoiding and RCD too.

    If a DIY person has not already passed out from information overload yet then i guess this probably just topped it off.:D

    Clearly there are multiple ways to do this and as had been said for the past decades on decades there is more than one way to skin a cat.

    An Electricians design is just that a design of their making. Regulations are a guide to make sure you do it safely and in the event of something going horribly wrong people will live through it. After all the regulations are created from past experiences, catastrophes and fatalities from bad wiring and how technology has evolved over the years. We learn from mistakes made and find innovative ways to make sure they don't happen again or at least minimize that risk to the minimum possible.

    I will never advise anyone to install an unprotected circuit. I need look at it myself in detail and decide very carefully how to go about doing it, if not i would opt for it to be protected. If a DIYer is capable of doing this themselves then who am i to judge, it is their call not mine.

    All we can do is make sure they have all the information so they can make a sound decision and carry out the installation safely and sound.
     
  5. fire

    fire Well-Known Member

    Oh yea I forgot to say, if you do make a NON RCD protected circuit using lets say SWA or put cable in the wall deeper than 50mm. If you terminate the circuit into a wall socket then you once again need RCD protection. Could there really be someone out their in the world that would do this? :confused:

    It literally is more simpler to just RCD protect everything wherever possible. Aaaaaaand that's miraculously what i had said at the very beginning... :p
    If you want to make it complicated oh yes we can do complicated and over-bloated, how far down the rabbit hole does one want to go...

    Bare in mind a fridge or freezer fridge/freezer would need a fused isolation switch above the worktop in the kitchen so one could also simply flick the switch accidentally and defrost all their food. You could go on forever with this stuff really.:rolleyes:
     
  6. Coloumb

    Coloumb Screwfix Select

    Amd. 3 pretty much rules out any kind of socket outlet without rcd protection no matter what the install method or if it's used by skilled or unskilled persons.

    How do you propose to terminate the swa in the alarms?
     
  7. fire

    fire Well-Known Member

    Good question, i personally have never installed a domestic smoke alarm without RCD protection because i have never needed to. A battery backed wired smoke alarm tends to warn you if the main power feed fails so the extra cost for avoiding the use of an RCBO is just not done, at least i don't do it. If you did do this for a domestic setting you would have to send the SWA Gland into a junction box and feed the device from that. Not something i would do but hey ho... Of course you could steel conduit and put them in the wall and do it that way.

    As for a Fire alarm system, industrial commercial fridge freezers, that is different. Of course the industrial scene is very different to your domestic wiring and is well beyond the scope of this thread, after all we are talking about purpose built appliances which will be designed to accommodate particular cables, steel conduit etc. ;)
     
  8. nffc

    nffc Active Member

    A fridge freezer does not need to be on it's own circuit. A complete myth.

    Smoke detectors and definitely fire alarms should not be on a RCD.
     
  9. Coloumb

    Coloumb Screwfix Select

    If they are rcd protected, and I can't realistically think of any other way to get round NOT having rcd protection in a domestic situation, then the rcd must protect only the smoke ctt.
     
    fire likes this.
  10. fire

    fire Well-Known Member

    Well then you better pull out the bright red cable and conduit then lol
     
  11. fire

    fire Well-Known Member


    You can send it up to the alarms in the red conduit surface mounted to the wall. If you really must install it that way. It is done in allot of the student accommodations and dorms.
    Could look pretty in your home, if you are into that sort of thing...

    [​IMG]
     
  12. nffc

    nffc Active Member

    It is not beyond even a 5WW to be able to install a circuit flush and not require RCD protection.

    That or FP400.
     
  13. Coloumb

    Coloumb Screwfix Select

    We have already been over this. As you choose not to bother with keeping up to date with the regs you are completely misunderstanding the need for rcd protection under the 17th. It's has been designed so that it's now more or less impossible NOT to use them for socket outlets, regardless of the install method.
     
  14. nffc

    nffc Active Member

    We are not talking about socket outlets?

    All socket outlets require RCD protection in a domestic installation. Regardless of installation method. No one is arguing that.
     
  15. Coloumb

    Coloumb Screwfix Select

    Oh right - so you mean you can use fp400 and no rcd so long as no sockets regardless? Who would do that in a domestic? This is just getting stoopi.d
     
    madhatter1uk likes this.
  16. nffc

    nffc Active Member

    The conversation had moved to fire alarms???????
     
  17. madhatter1uk

    madhatter1uk Screwfix Select

    If you've run a non rcd socket, to a freezer, which is allowed, why would the socket mean that it needs an rcd. A designated freezer socket is allowed if the customer feels it warrants one. He may have thousands of pounds of meat in it.
    Most of this is over kill and paranoia.
    If smoke alarms aren't on a lighting circuit then they shouldn't be on an rcd if possible, niceic give this in their notes.
     
  18. nffc

    nffc Active Member

    what installation method would you use? For the non-RCD fridge socket?

    And it is absolutely not the customers desicion.
     
  19. madhatter1uk

    madhatter1uk Screwfix Select

    Everything is the customers decision. You can't force them to have their freezer on an rcd.
    As I don't know where it would be I couldn't possibly say. It could be in conduit. Maybe the consumer unit is at ceiling height. If a cable is 50mm deep then it can still terminate in a socket outlet
     
  20. Coloumb

    Coloumb Screwfix Select

    If you did what the customer wanted in a way which did not comply with 7671 which later led to the customer (or anyone else living in the property) sustaining damage then you could be found to be negligent. It depends on what the damage was/is and how negligent you have been, ie if the regs clearly say don't do it, and you did, then you would be negligent. It doesn't matter what the customer says or wants. Most likely it would be the customers insurance company who would pursue the damage costs anyway, and they are not the customer so didn't agree to nowt.
     
    nffc likes this.

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