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Thread: Three phase vs single phase

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    Three phase vs single phase

    Good morning - I am not an electrician, but cannot seem to get a consistent answer to my question anywhere else and accordingly would appreciate advice from the knowledgeable members of this forum.

    I have three phase power in my house, but recently installed a inverter for solar power which connects to one of the phases only. For various reasons I would prefer it if I can connect to all three phases, and it seems to me that the easiest (and cheapest) way to do it would be to combine the three phases into a single phase - I really don't have any need for three phase power, electricity load is not significant, have removed under floor heating in most of the rooms when I installed wood floors.
    By asking around I have received the following feedback:
    - Converting to single phase is easy - just join all three power wires into a single input wire (or bridge then 3 inputs on the DB board)
    - a transformer, which is very expensive is required
    - it cannot be done except by the municipality (when I live in a residential estate and is not directly connected to the municipal supply!!). The people who hold this opinion also tells me that I have to replace my meter - the current meter I have merely combines all three phases and is exactly the same meter as my neighbours, who don't have three phase power, have.

    Please guys - what is the correct way of doing this (and for which I can get a CoC) - preferably a method which allows me to reverse the conversion in the unlikely scenario I require three phases in future

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    Diamond Member AndyD's Avatar
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    You can't just bridge the 3 phases of a 3-phase supply together, there will be an almighty bang and best case scenario you'll lose eybrows....worst case is you won't be around to tell the tale.

    To convert to single phase it may be possible to simply remove two of the phases and make them redundant but this will leave you with a relatively small incoming supply which may not be sufficient for your needs. Also any 3-phase appliances you may have would no longer work and the DB may need reconfiguring accordingly. You can still meter the resulting supply using the existing 3-phase meter.

    It may be possible to convert to a larger single phase supply and double-up the conductors in the supply cable and increase the available supply at source but whether or not the existing meter could be used is dependant on the meter itself and its rating.

    A new meter isn't that expensive so I wouldn't let the fact it needs replacing govern your decision about whether to convert. I'd also suggest for a job of this nature you should get a competant electrician in to survey the requirements and give you a quotation.
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    Thank you Andy - next question, where do I find a competent electrical contractor who can do this for me? Can you recommend someone who can do a proper job which complies with all necessary standards?
    I am in Pretoria and never seem to get hold of the skilled people, long history of problems with service providers.

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    Diamond Member AndyD's Avatar
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    I don't know any contractors in Pretoria I'm afraid but maybe one of the other members here can recommend someone.
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    what rating is your 3 phase supply? look on your main circuit breaker and if you have an accessible council box,look there as well.(on your outside wall)

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    Good morning Bergie - I really don't know how you guys can survive with the weather in CT, sounds a bit unpleasant
    I attach pics of the meter (residential estate so not a council meter) and the main switches and trip switch on my DB board.Click image for larger version. 

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    hi solarfan . your main switch is 50 amps 3 phase. (3 x single pole breakers are used which is not compliant).if you can run your household on 50 amps single phase then you could rewire the db to have everything on 1 phase and not use the other 2. eskom want all the phases to be balanced ,but i wouldnt worry about that. your availability fee every month might be more for 3 phase than single phase.

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    If you discard 2 of the phases you will only have 50 amps available. this may or may not be enough for your house if you have everything on at the same time. you will need to get an Electrician to determine this.

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    Thanks for the input guys, Bergie - your immediate comment about non-compliant switches (the 3x single pole) is exactly why I appreciate the input - not one other electrician who has looked at the DB has mentioned anything.
    Now I just need a referal to a good electrical contractor up here in Pretoria - someone who will do things excatly by the book and who actually takes pride in his work, not just take a shortcut, grab the fee and run away. I really don't mind how much I spend (within reason!), I just want single phase to be installed exactly correctly (as you can probably tell I am a slightly anal accountant)

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    Hi me again, if you get someone to convert your wiring to single phase, make sure that the contractor is registered with the ECA (Electrical Contractors Association and is able to give you a Certificate of Compliance as this will be deemed a new installation and your insurance will not cover you without one.

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