The 3 phase cable I have that's still connected up to this rather large lat he I bought has some unfamiliar colours making it up. There's a braided shi eld round the outside which I assume is for grounding purposes. Then four e qual thickness conductors inside: brown, grey, black and blue. I have to so mehow marry these up to the inverter box where the appropriate terminals ar e marked 'U','V' & 'W' which is neither helpful nor meaningful to me. Can a nyone clue me up here? I'm starting to develop a complex over all the flash es and bangs I've experienced recently. Don't want to end up a nervous wrec k. Thanks.
Surely Adam the Blue is more likely to be Neutral, with the CPC/Earth conductor being the braid that he refers to ? Many machine tools bring in a neutral to allow 240v contactors, lights and the like.
CY cable that I've used is either 4 core - 3 phases + earth + braid or 5 core 3 phases, neutral earth plus braid.
The theory is the the earth must be used for earth continuity to the motor but the braid should only be connected at the inverter end so it can act as a true RF shield to minimise the crap from the inverter interfering with other equipment. If any current passes down the braid (however small) the braid itself turns into an antenna and radiates the RF energy.
However what I am saying is that the number of times I have seen 4 core SWA used on a 3 phase supply with the 4th core used as a cpc and not as a neutral far outweighs the number of times I have seen the 4th core used as a neutral.
So basically you're saying I can just connect *any* phase wire up to the u, v or w and the order doesn't matter? I mean I don't need to specifically connect a certain colour to a certain lettered connector?
So long as you don't mind which way the motors revolve then yes. However if you are running off a static phase converter you need to ensure that your contactor coils are driven by a phase other than the generated phase.
Reference the Star-delta question, are you sure that the motor is modern en ough to have all the coil ends brought out so that you can change configura tion. Most electronic inverters - at least the less expensive ones - are 2
40vac 3ph output rather than the 410vac required for star.
Older motors are hard wired for star as I discovered on a friend's Graduate lathe for which I recommended an inverter, and then had to dismantle the m otor to reconnect the coils.
First. Look in the terminal box at the lathe end of the cable. What are the terminal markings in there, and which cable colours are connected to them?
Usually: Phase 1 is L1 / Red / U / R / Brown Phase 2 is L2 / Yellow or white / V / S / Black Phase 3 is L3 / Blue / W / T / Grey Neutral is N / Black / N / N / Blue
Although variations exist. :)
If a neutral connection is used for the lathe then you will need to source it from the inverter somehow (or make some other arrangement) as it will be used for the control circuit. You can't omit it. Even if the motor is star connected the neutral may not be connected to the star point of the winding (that is very unusual).
As others have said, if you reverse any 2 phases of a 3-phase motor it will run in reverse. So no, you don't have to be specific in colours & markings. If the lathe was properly installed then it will probably have been connected as one of the above sequences.
Unless the lathe was originally fed from an inverter or speed controller it will almost certainly be using the braid as protective earth. The blue (usually neutral for brown/black/grey/blue cable) wire may or may not be connected. You MUST check. You also MUST check whether the braid is used as protective earth and make sure that it is terminated correctly at both ends if it is.
If it is dual voltage it will be delta for 220 volt (Phase/phase) and star for 400 volts (phase /phase). There is not much requirement for this sort of thing now, as we and the EU are similar voltages.
The neutrel is not needed for the motor iself but may be needed for ancilliaries. If it is a dual voltage motor & starter, the starter coil will be the low voltage so you would need a neutral if is were run in high voltage configuration.
enough to have all the coil ends brought out so that you can change configu ration. Most electronic inverters - at least the less expensive ones - are 240vac 3ph output rather than the 410vac required for star.
te lathe for which I recommended an inverter, and then had to dismantle the motor to reconnect the coils.
The motor is 1998 manufactured and dual voltage 230/415 3 phase 3hp/2.2kw a ccording to the plate on it. My converter puts out 230V 3 phase from a 230V single phase input supply. There appears to be a box mounted atop the motor where the delta/star conne ctions can be changed. I say "appears" because it looks like it's going to be a devil of a job to get the lid off and I can't say for sure until I do, but we'll find out eventually by which time I'll no doubt have shed yet mo re grey hairs.
THanks, Mick. I was wondering if I should make the addition of an earth spi ke within the workshop itself to be on the safe side, since there is a run of about 10 meters from the lathe back to the existing earth in the house's distribution board. Any thoughts on the advisability of that and if so, ar e those cheaper, copper plated spikes good enuff for the job? Come to think of it, I've got some 15mm copper pipe laying around that woul d probably do just as well as a spike...
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