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Thread: Electricians Question

  1. #1
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    Default Electricians Question

    I'm hoping someone can help me with this rather simple and at the same time complicated dilemma.

    The simplest way I can put it, is I'm looking for a "3"/"4"-way switch.... let me explain:

    Objective: Power a light (example) /Route A.
    Power Sources: Mains/ Route B | Generator/Battery/Route C.

    OK, so to sum it up, I'm looking for a switch, that will allow me to choose between two power sources.

    What device/product can allow me to manually switch between Route B and Route C

    I know I sound stupid explaining this, but all I really want is the name of the Switch/Toggle Switch that is required.





    Thanks again for any help, it's much much appreciated!

    P.S If I remember correctly, it's the live that needs to be used for switching, as that's the wire that carries the electricity, right?
    Last edited by kwaggawerner; 17-04-2010 at 12:58 PM.
    Si vis pacem, para bellum

  2. #2

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    Quote Originally Posted by kwaggawerner View Post
    OK, so to sum it up, I'm looking for a switch, that will allow me to choose between two power sources.
    Power source selection switches are common on boats (domestic or equipment battery banks). I am not sure of the voltages available, but you should try them (chandlers).

  3. #3

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    I'd recommend getting a proper electrician for this. These switches are a problem from a building code & fire viewpoint. Not exactly an occasion to DIY it.

    Make sure the switch you get has an empty position between the two options. i.e. Between the two options there is another setting that isn't connected to anything.

  4. #4

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    The switch you are looking for is a "Change over Switch".It has a neutral position between change over positions.You will need to know what amps you will be drawing to decide on what size switch you will need.

  5. #5
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    Thanks so much for the replies guys.... I'm glad I finally got the official term for it... The amperage wont be too much, It will basically power a couple computers, and several lights, nothing major, the Generator, supplies 7 kVa, 21.7 Amp Max, but I won't consume nearly that much, I just want an easier way, of 'toggling' between Mains and the Generator. What price range will I be looking at if I want something like this


    Also, I won't be installing this in the existing DB board, 'cause I don't want it to run to all the plugs,etc... just the plugs on the extension cord (heavy duty, permanent position), I will get a dedicated IP65 enclosure for the switch. The 3 Core cable, running from the generator, is one thick mother fluffer... I think it was 4.5mm... I know we paid R2700 for 100 meter roll....
    Last edited by kwaggawerner; 17-04-2010 at 02:30 PM.
    Si vis pacem, para bellum

  6. #6
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    I found the above at Waco's website.... When choosing electricity components, is it safe to assume, I can use any component, regardless of amperage, as long as it's rating, is MORE than what the incoming power source is? - IOW, the Generator, provides 7 Kva/6900watt, 21.7 Amps, and the mains input for this switch, will come from the plugs circuit breaker, which is 20A.... so a change-over switch, that can handle 25A, and 400VAC will suffice?

    I'm thinking, these manual change over switches, when wiring the switch, what is referred to as 3 poles or 4 poles, is that 3 core (live,neutral,earth) wiring? - or is it reference to the phase?



    My Mains: Plugs are 20A and Light are 10A... There won't be more load with this proposed new setup, the current power consumption from the mains will remain the same.
    Last edited by kwaggawerner; 17-04-2010 at 03:22 PM.
    Si vis pacem, para bellum

  7. #7

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    Quote Originally Posted by kwaggawerner View Post
    Also, I won't be installing this in the existing DB board, 'cause I don't want it to run to all the plugs,etc... just the plugs on the extension cord (heavy duty, permanent position), I will get a dedicated IP65 enclosure for the switch. The 3 Core cable, running from the generator, is one thick mother fluffer... I think it was 4.5mm... I know we paid R2700 for 100 meter roll....
    If thatís what you want to do, you are involving yourself in a lot of unnecessary PT. This is an extract from my blog and is a budget (and safe) way to compensate for Eskom screw-ups. If you are doubtful, get an electrician to look it over.

    Eskom: Household electrical power distribution

    This procedure assumes a generator as a power source. If you are uneasy about this, check it with an electrician. He would be unhappy about some safety aspects, but it would work.

    NOTE: The safety aspects relate to disconnecting and connecting. There is not a permanent danger while using the system.
    A major issue (I cannot emphasize this enough) is to SWITCH OFF the main switch (leave it off). It is easy, like switching-off a normal switch. It is usually green on the distribution board. Switch off the geyser and stove as well for power conservation reasons.

    Switch it on again (**after disconnecting your scheme**) when power returns. If Eskom power returns, the main switch is on and you havenít disconnected your stuff, Eskom power will overwhelm your scheme and there will be sparks, burnt-out equipment, expense and tears. Disconnect (pull the plug on your scheme) before returning to Eskom power.
    You need a patch cord between the gen. set outlet socket and your chosen house input socket (to power-up your house). The patch cord needs to have a male plug on both ends to transfer power. This is bad practise (safety issue). If you prepare the house and plug everything in except for the gen. set plug, you are OK (the house is Ďdeadí) Donít plug in the gen. set until itís started as that will place a load on the generator and make the engine difficult to start. There is always stuff that is on (electronic gate, pool pump [switch this off] etc.)

    Fire it all up and note the loading on the generator meter for each item you switch-on. Determine equipment you can run simultaneously without overloading the generator. You may have to switch some stuff off occasionally. For example Ė if you want to run the pool pump (a greedy user) this may require you to switch-off other stuff.

    You are basically going backwards here. You are isolated from the Eskom supply (switching-off the main switch) and pumping-in electricity via a wall socket thus electrifying your home. The electricity will spread throughout the wiring via the distribution board (which you **HAVE** isolated from Eskom by throwing the main switch). You switch-on what you want as is normal practise. Switching-on too much or high power users, will overload the generator.

    Normal generator rules apply. Well vented area bla, bla. A special SA precaution Ė make sure the gen. set is secure, you donít want it stolen.

  8. #8
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    Thanks Palimino, I didn't really think about having power spread through the house via the plug socket, This sounds like plan, I was just concerned that power is supposed to run in one direction. I will definitely discuss your proposition with an electrician friend of mine, not that he will approve, but nonetheless, I want to hear his perspective. The thing is, I live outside the city (Pretoria) so our power is out much more often than city-folk, for example, CURRENTLY our power is off every Wednesday from 8 AM to 6 PM, as part of Tswane's plan to "upgrade the network"... we believe it's load shedding in some form, in Winter, and during heavy rains in the week, it's not uncommon for the entire communities' power to be out for longer than 3 days. Therefore, My old man bought a couple generators, 5 to be precise, one for my free-standing apartment, two for the 'main house', one for the fences, flood lights and gates, and one more that's on standby.

    I know, overkill, and when they are all running, they collectively consume 15 liter's of fuel an hour! - yes... my eyes tear just to turn the key on one of these gennies.

    Therefore, I want a slightly more "professional" approach to the switch-over between power sources, the "generator" source will also have a UPS connected to it, so that when the Generator is switched off, The lights outside my apartment, will still be on for a couple hours, hopefully deterring any "baboons" out there...
    Si vis pacem, para bellum

  9. #9
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    You're on the right track there with the single phase selector switch and york box approach. It should set you back about R800-R1k. Your 7kVA 1ph generator can give out a true rating of 31.5Amps, but you're ultimately limited by the circuit breaker sizes. a 4mm wire will handle about 36amps, before it turns into a fuse, so you're fine there.

    Regarding the number of poles... A 3-phase selector switch will be much bigger and has 9 or 12 poles and is conventionally much bigger than your domestic 1ph ones. a 3 or 4-pole setup is generally divided into:

    1: source1 live
    2: off (4th pole absent in 3pole setups)
    3: source 2 live
    4: load

    You do not need to break your neutral, but in a single phase setup, always treat it as live regardless of the live being switched off.
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  10. #10
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    Thanks Voicy for your input, much appreciated!
    Si vis pacem, para bellum

  11. #11
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    OK! - So I've decided to get :

    I will be getting the 2 pole version, So now.... I'm going to assume that this switch has 4 contacts for incoming power, and 2 for outgoing... I'm told that I must isolate BOTH live and neutral, so the 2-pole version, is exactly it, right? Source 1, and Source 2 have their own Live and Neutral contacts?

    So, will it look something like this?
    Last edited by kwaggawerner; 17-04-2010 at 06:36 PM.
    Si vis pacem, para bellum

  12. #12

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    All you need is a Break before make change over switch. Available from any good electrical supplier or AC/DC dynamics

  13. #13

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    Quote Originally Posted by kwaggawerner View Post

    P.S If I remember correctly, it's the live that needs to be used for switching, as that's the wire that carries the electricity, right?
    I don't know!
    Quote Originally Posted by I.am.Sam View Post
    dont waste your money rather get the cheese jizz ....
    Quote Originally Posted by Nicci View Post
    Oh yes that is a nice one!!
    DEL PythonFSi

  14. #14

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    Quote Originally Posted by kwaggawerner View Post
    OK! - So I've decided to get :

    I will be getting the 2 pole version, So now.... I'm going to assume that this switch has 4 contacts for incoming power, and 2 for outgoing... I'm told that I must isolate BOTH live and neutral, so the 2-pole version, is exactly it, right? Source 1, and Source 2 have their own Live and Neutral contacts?

    So, will it look something like this?
    Yes you must break the neutral.

  15. #15

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    Quote Originally Posted by PythonFSi View Post
    I don't know!
    Thatís the convention but you donít know what cowboys have butchered around before you and how they have stuffed-up the system. Treat the neutral as live. However, you should continue the convention in your connections (do it right).

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