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  1. #1
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    How to wire up an inverter. Properly.

    Little inverters are getting more and more popular in home workshops these days.

    However, judging by some of the questions being asked on the forum it that some people are feeling a little out of their depth wiring one up.

    So, here's how to connect a basic "1-phase in, 3-phase out" type. It's meant to be used in conjuncion with the manual that comes with your inverter, and is just a guide to good wiring practice.

    Here's the secret to doing a safe and good looking job.
    Insulated terminals, and the special pliers for crimping them on.
    They come in three basic sizes, 1.5mm (red), 2.5mm (blue) and 6mm (yellow). Make sure you have the right size for the cable you are using. Get them from any electrical supplier or by mail order. Just DO NOT buy them from your local car spares shop unless it specifically says on the pack that they are mains rated. Ok?
    For this job you will only need need small ring or fork terminals.




    The incoming mains cable.

    Strip the minimum amount possible of the outer sheathing off the cable.
    Bare no more than 5mm of copper wire and crimp on your terminals.

    On a 1-phase input the Live and Neutral connect to R and S, or L1 and L2. On this unit the terminals have both markings. It does not matter which way round you connect Live and Neutral.
    The earth terminal will be somewhere nearby, and should be clearly marked. Make sure you use it.

    On the other end of this cable is the standard 13 amp domestic mains plug. You do know how to wire one of those, right?





    The idea is, that when the terminal guards are back in place the the minimum of unsheathed cabling shows.





    This is SY cable. For any application where there is a risk of the cable getting abraded, trapped or damaged it is the perfect stuff for connecting your inverter to your motor.





    Start by stripping off the clear outer serving. Straighten out the braided steel wires and twist them together.





    Strip the sheathing off and cut the inner cores to length. Put some earth sleeve or tape on the twisted braid wires.





    Crimp your terminals on.
    Seal the end where you cut the serving. I've used heat-shrink tubing here, but insulation tape is fine. This is important, so don't neglect this step.





    The motor phase connections go to T1, T2, T3. Note that you now have two wires to the earth terminal.
    The U, V, W labels on the terminals relate to the labels on the motor terminals. If you connect them in the same sequence then the motor will rotate clockwise (viewed from the drive end) when the "run" or "forward" buton is pressed.




    So that's it, done. Nice tidy job. Should take about half an hour.






    Hope someone might find it useful.
    If anyone is interested I will go into how to sort out the motor end of the cable (although it's pretty straightforward).





    one_rod.
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    Re: How to wire up an inverter. Properly.

    thanks for taking the time to post this i think it will be helpful to some

    DC
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    Re: How to wire up an inverter. Properly.

    Thank you for taking the time to document this! - Ive just ordered a 2hp unit from 'Transwave' for retrofit to a grinder.

    I think it would be useful to show a couple of pics of the 'bars' inside the motor terminal box in either 'star' or 'delta' config. for the dual voltage motors, My (very basic) understanding is if your 'bars' are set for 400v youll only have half the torque ??

    Good points about keeping it all neat, with the amount of metalic dust from a grinder it wouldnt take much to get a short across terminals !

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    Re: How to wire up an inverter. Properly.

    Are you wiring in a remote start/stop speed control unit ? - very useful for putting the inverter out of dust and harms way, but if you can keep the inverter in sight you may be able to program it to display load or spindle speed or even surface speed

    Rab

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    Re: How to wire up an inverter. Properly.

    Thanks very much for taking the time to post that, it's very helpful
    I'm just about to do this (just waiting for some of the bits and pieces to be delivered) and will find this useful. I hope you don't mind if i ask some questions..

    I'm planning on putting a 3p+e plug and socket on the SY cable between the motor and the inverter. Am i right in thinking i should connect both the earth wire from the inverter and the braided steel wires on the SY cable to the earth terminal on the 3p+e socket? and then do the same on the earth terminal of the 3p+e plug with the wire that connects to the motor?
    Also, just to be sure, am i correct in assuming that the connection at the motor end is basically the same, with the earth wire and the braided steel wires both connected to the earth terminal on the motor?

    thanks very much

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    Re: How to wire up an inverter. Properly.

    good post but it wasnt made clear that the braided wire is NOT AN EARTH but is the way to earth bond the braiding as it is A conductive material that could hurt you if it was pierced by a nail or a cut and wasnt earth bonded to the main earth but left unterminated nice to see some clear pictures cheers

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    Re: How to wire up an inverter. Properly.

    Quote Originally Posted by Rab View Post
    Are you wiring in a remote start/stop speed control unit ?

    Rab
    Not really got any particular purpose for this unit at the moment. Just one I had laying around. Wired it up in the hope that the pics. would be a help to someone doing a similar job. If anyone is interested, I will wire out the remote functions to show how it's done.

    Quote Originally Posted by happy camper View Post

    I'm planning on putting a 3p+e plug and socket on the SY cable between the motor and the inverter. Am i right in thinking i should connect both the earth wire from the inverter and the braided steel wires on the SY cable to the earth terminal on the 3p+e socket? and then do the same on the earth terminal of the 3p+e plug with the wire that connects to the motor?
    Also, just to be sure, am i correct in assuming that the connection at the motor end is basically the same, with the earth wire and the braided steel wires both connected to the earth terminal on the motor?

    thanks very much
    The answer to the first two questions is yes.
    As for terminating at the motor, it would be better to use a proper SY gland. This earths the cable braid securely, as well as protecting the cable from damage where it passes into terminal box. It also prevents dust getting inside, so it's worth the extra bit of time it takes to fit.

    Quote Originally Posted by dugaboy View Post
    good post but it wasnt made clear that the braided wire is NOT AN EARTH but is the way to earth bond the braiding as it is A conductive material that could hurt you if it was pierced by a nail or a cut and wasnt earth bonded to the main earth but left unterminated nice to see some clear pictures cheers
    Absolutely right.
    I was trying to make it more of a "how to" rather than a "why". Perhaps it might have been better to have gone into the reasons for things a bit more?





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    Re: How to wire up an inverter. Properly.

    Quote Originally Posted by one_rod View Post

    The answer to the first two questions is yes.
    As for terminating at the motor, it would be better to use a proper SY gland. This earths the cable braid securely, as well as protecting the cable from damage where it passes into terminal box. It also prevents dust getting inside, so it's worth the extra bit of time it takes to fit.

    one_rod.
    Thanks for that I've managed to find a 20mm threaded gland for the motor terminal box that (just about) fits the thick sy cable, but i didn't manage to get a proper sy gland unfortunately. I was hoping that twisting a tail from the steel braid and connecting it to the earth terminal inside the terminal box would be ok. I want to do it right though, so if that isn't the way then i'll have to try and find an SY gland.
    Thanks again

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    Re: How to wire up an inverter. Properly.

    Yes, yes and yes to any add ons like star-delta configuration or remote speed controls any way this could be made a sticky?
    It's not that I expect not to make mistakes; it's that I'd rather make new ones.

  10. #10
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    Re: How to wire up an inverter. Properly.

    OK, following a couple of PM conversations about terminating the motor end of the cable, I thought I would extend this thread a little.

    So here it is, the poly-phase, squirrel-cage, asynchronous induction motor. Nikola Tesla's immortal legacy, and the single most important electrical machine ever invented. Around 60% of the worlds commercially generated electricity is reconsumed by these things.




    If you are buying a new motor from a reputable supplier you can skip the next bit and go straight to the wiring.
    If you are looking at a scrap-yard or salvaged ex-machinery motor you may save yourself a little heartache by finding the "tally plate" on the side of the motor. Do this before you part with any money, and if the plate is missing then don't buy the motor.

    This is the bit you need to see. If can't find that upside down Y and the little triangle (they are known as "STAR" and "DELTA" respectively) or the 230/400v rating somewhere, then the motor is probably not going to work with an inverter. Many older industrial motors are hard wired in star mode, and others are 400/600v rated. Not a lot of use, either way.




    If the motor is ok, then when you open the terminal box you will hopefully see something like this.
    This is the motor set up in STAR mode, for use on a 400v supply. Most motors are supplied this way as it's the way most are used in industry.




    Although you can only see two, there should actually be three of those brass shorting bars. One link is usually made from two bars, doubled up.
    Remove the nuts and alter the links to this position. This is known as DELTA mode, and is the set up for a 230v supply.




    Bring our cable into the terminal box through a proper gland, and connect the three phase connections to one end of each shorting link. Obviously it does not actually matter which end you choose.
    Make sure the phase connections are very secure on the terminals. I would seriously recommend you use crimp-on lugs. Modern inverters are very good at defending themselves from phase-to-phase short circuits, overloads and thermal effects. The one thing they will not survive is a direct phase-to-earth short. One wire coming adrift from a terminal can wipe out the output transistors, and your inverters warranty, instantly. You have been warned.





    If you are using SY, or some other type of armoured cable, then don't forget to connect the cable screen to earth as well as the the earth wire inside the cable.
    This is a new type of SY gland called a bite-clip and it makes wiring in the earth connection a doddle. Get one from any trade electrical wholesaler.





    Hope this may be some help to someone.





    one_rod.
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  11. #11
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    Re: How to wire up an inverter. Properly.

    This is a brilliant thread, I have a motor very similar to the one shown and it'll be a great help
    Richard
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  12. #12
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    Re: How to wire up an inverter. Properly.

    Very kind of you to take the time. I think this one should be pinned to the top of the page ! Could save a lot of people trouble. :

  13. #13
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    Re: How to wire up an inverter. Properly.

    nice one mate

  14. #14
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    Re: How to wire up an inverter. Properly.

    Great tutorial Mick. I agree this should be stickified!! oh those glands look handy, I used brass ones which were a nightmare; they made my fingers sore and severely tested my patience!

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    Re: How to wire up an inverter. Properly.

    Good post,
    thank you,
    Rab

 

 

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