My brother has recently purchased an inverter to run a 3 phase lathe, which has been wired to a 10A C rated RCBO so it's protected. The lathe is plugged directly into the front of inverter at the 415V outlet - does the lathe, or any other machine he decides to use, need to have it's own appropriately rated protection fitted before the plug, or is it covered by the inverter?
3 phase inverter advice
- Thread starter fuzzytrifle
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The user side of the inverter is NOT protected by the supply side protection system. It MIGHT be but the only prudent answer is to say it is NOT.
Thank you, does that mean that it isn't RCD protected either?
The input is but if the inverter contains isolation transformers (to switch 230 to 415) then the output is not necessarily protected by the input RCD.
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Hard wired machines generally aren't RCD protected.
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Most motor inverters I have used have within there software configuration the ability to set maximum current and replace the motor overload. This does need setting and every make seems to have a different way to set it so it is a case of reading the book.
Many inverters will in fact be damaged if they become disconnected from the motor and all reversing and overload has to be done in the inverter.
The inverters also often have the ramp up and ramp down settings plus motor speed.
However where a general inverter is used rather than a motor inverter then you will still need overloads.
It is a case of carefully reading the book. Some do have a form of RCD protection but not all.
Many inverters will in fact be damaged if they become disconnected from the motor and all reversing and overload has to be done in the inverter.
The inverters also often have the ramp up and ramp down settings plus motor speed.
However where a general inverter is used rather than a motor inverter then you will still need overloads.
It is a case of carefully reading the book. Some do have a form of RCD protection but not all.
Thank you - this is the inverter he's bought (not off ebay though)
http://www.ebay.co.uk/itm/TRANSWAVE...ial_Automation_Control_ET&hash=item232b071c42
I'll get him to contact the people who made it.
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Ah...
That is NOT an inverter ... it is a rotary converter. A different beast altogether!
(An inverter creates the missing phases electronically & allows you to vary the frequency & hence the motor speed. A rotary converter creates the missing phases using magnetic means inside a spinning machine. It cannot vary its speed & hence does not allow the output frequency to change & hence does not allow speed control of the users motor)
My advice would be to treat the red output socket exactly the same as you would treat the same socket fitted to the wall .... the lathe still needs it own local overload protection, no-volt release & stop/star controls . ie. a proper motor starter unit as is probably already fitted to it.
That is NOT an inverter ... it is a rotary converter. A different beast altogether!
(An inverter creates the missing phases electronically & allows you to vary the frequency & hence the motor speed. A rotary converter creates the missing phases using magnetic means inside a spinning machine. It cannot vary its speed & hence does not allow the output frequency to change & hence does not allow speed control of the users motor)
My advice would be to treat the red output socket exactly the same as you would treat the same socket fitted to the wall .... the lathe still needs it own local overload protection, no-volt release & stop/star controls . ie. a proper motor starter unit as is probably already fitted to it.
Motor-generator set-up so there is direct electrical linking between input and output. In that case an RCBO on the input circuit will provide phase-ground fault protection; which I think may have been the objective of your original question.
But be aware that making contact with 415volts might well prove lethal (either directly or indirectly) before the RCBO has done its work. An RCD or RCBO offers no guarantee you will survive an electrocution event.
As to a 10A RCBO managing to meet the demand of a 3kW inverter, I doubt it. I would have imagined at least 15A being required, possibly 20A.
You'll also ned appropriate starting gear (contactor and overload) on your 3-phase drive motors. Otherwise it'd be the same as plugging a 4HP machine directly into a 3-phase mains socket.
edit : pipped at the post by Adrian
But be aware that making contact with 415volts might well prove lethal (either directly or indirectly) before the RCBO has done its work. An RCD or RCBO offers no guarantee you will survive an electrocution event.
As to a 10A RCBO managing to meet the demand of a 3kW inverter, I doubt it. I would have imagined at least 15A being required, possibly 20A.
You'll also ned appropriate starting gear (contactor and overload) on your 3-phase drive motors. Otherwise it'd be the same as plugging a 4HP machine directly into a 3-phase mains socket.
edit : pipped at the post by Adrian
Why have you used a 10A devise when the manufacturer specs a 25A?????
Thank you - I'm not entirely certain of the converter's actual rating, the chap who made it told him to fit a 10A motor rated MCB, the link was just the first one I came across for a Transwave rotary machine that looked identical to what he has. As usual, it would help if I actually knew what I was writing about!
It would be a good idea to get the EXACT model number - just because it looks the same doesn't mean it is the same. I find myself wondering if that unit is actually a rotary converter, or is in fact like the one I have on the shelf in the garage - an autotransformer, pile of caps, and a voltage sensitive switch. Works quite well, starts a 3P motor, but there is no load side neutral and the 3 phases bear little relation to the 3 phases you'd normally expect to see on a 3P supply (one of them is more than 240V from supply neutral IIRC).
My brother took a look at the paperwork and it states that both the unit and plugged in device require adequate overload protection. I'm guessing that he just has to (get a qualified person to) put a breaker in a suitable enclosure either mounted on the wall behind the machine, or bolted to the cabinet, directly before the plug. Not sure how he's going to calculate the rating though as the cabinet houses two 3-phase motors, the main drive and one for suds, a small AC transformer for a work lamp, and a socket for a third 3-phase motor for the overhead drive. There's a second socket which we think is for the extraction unit and a second low voltage socket. Is it just a case of providing the electrician with all the ratings for the motors and transformer?
What you do for overload protection depends to a certain extent on how you use the converter. If it's only ever going to be used with the one machine, and especially if it were hardwired, then the overload protection on the supply will also cover the machine if it is sized correctly.
But if the converter might be used with different machines, then you'll need overload protection for the converter, and separately for the machines.
From the description, there may already be some protection installed. Motor starters are usually (but not always) fitted with overloads - if so fitted then that covers the motor controlled by it. Since the smaller items (eg light transformer) wouldn't normally be adequately protected by any supply fusing, there may well be a built in fuse in the device itself.
And while considering things like the worklight, it may be worth checking which is the synthesised 3rd phase on the converter output - and ensure that the worklight is wired across the other two. The synthesised 3rd phase is likely to be a lot less stable than the 2 that are created by transformer from the 1P input - so best not to link your light to it.
And if there is a 1P socket for anything, then (and again, you need to know about the internals of the converter) it may be best to remove it and and use a different socket direct from the workshop supply. As I mentioned earlier, we have a convertor in a box that looks very similar to that at home, it has no neutral, and the 3 phases really don't relate to the 3 phases you'd get ina real 3P supply. IIRC the input L-N is stepped up to 415V with an auto-transformer to give 2 phases - one of which is more than 240V to neutral, and the other is a lower voltage but "negative" relative to the input. The 3rd phase is generated by capacitors and varies considerably with the connected load and the unit setting. Yes, of course I've had the lid off to look inside
A genuine rotary converter could provide a neutral point - but for reasons of economy (it would add to the cost and weight of the machine) it's not likely to and/or it may not be as "earthy" as people are used to with neutrals - ie you'd want to treat it as live and not use any single pole switching downstream.
You may have noticed a certain amount of "if"s and "but"s - that's because to really answer the question means knowing details of both the converter (ie what it's got inside and how it's wired) and the machine (ie how it's wired). There are so many ways these things can be done that it's hard to generalise.
But if the converter might be used with different machines, then you'll need overload protection for the converter, and separately for the machines.
From the description, there may already be some protection installed. Motor starters are usually (but not always) fitted with overloads - if so fitted then that covers the motor controlled by it. Since the smaller items (eg light transformer) wouldn't normally be adequately protected by any supply fusing, there may well be a built in fuse in the device itself.
And while considering things like the worklight, it may be worth checking which is the synthesised 3rd phase on the converter output - and ensure that the worklight is wired across the other two. The synthesised 3rd phase is likely to be a lot less stable than the 2 that are created by transformer from the 1P input - so best not to link your light to it.
And if there is a 1P socket for anything, then (and again, you need to know about the internals of the converter) it may be best to remove it and and use a different socket direct from the workshop supply. As I mentioned earlier, we have a convertor in a box that looks very similar to that at home, it has no neutral, and the 3 phases really don't relate to the 3 phases you'd get ina real 3P supply. IIRC the input L-N is stepped up to 415V with an auto-transformer to give 2 phases - one of which is more than 240V to neutral, and the other is a lower voltage but "negative" relative to the input. The 3rd phase is generated by capacitors and varies considerably with the connected load and the unit setting. Yes, of course I've had the lid off to look inside
A genuine rotary converter could provide a neutral point - but for reasons of economy (it would add to the cost and weight of the machine) it's not likely to and/or it may not be as "earthy" as people are used to with neutrals - ie you'd want to treat it as live and not use any single pole switching downstream.
You may have noticed a certain amount of "if"s and "but"s - that's because to really answer the question means knowing details of both the converter (ie what it's got inside and how it's wired) and the machine (ie how it's wired). There are so many ways these things can be done that it's hard to generalise.
What you do for overload protection depends to a certain extent on how you use the converter. If it's only ever going to be used with the one machine, and especially if it were hardwired, then the overload protection on the supply will also cover the machine if it is sized correctly.
But if the converter might be used with different machines, then you'll need overload protection for the converter, and separately for the machines.
From the description, there may already be some protection installed. Motor starters are usually (but not always) fitted with overloads - if so fitted then that covers the motor controlled by it. Since the smaller items (eg light transformer) wouldn't normally be adequately protected by any supply fusing, there may well be a built in fuse in the device itself.
And while considering things like the worklight, it may be worth checking which is the synthesised 3rd phase on the converter output - and ensure that the worklight is wired across the other two. The synthesised 3rd phase is likely to be a lot less stable than the 2 that are created by transformer from the 1P input - so best not to link your light to it.
And if there is a 1P socket for anything, then (and again, you need to know about the internals of the converter) it may be best to remove it and and use a different socket direct from the workshop supply. As I mentioned earlier, we have a convertor in a box that looks very similar to that at home, it has no neutral, and the 3 phases really don't relate to the 3 phases you'd get ina real 3P supply. IIRC the input L-N is stepped up to 415V with an auto-transformer to give 2 phases - one of which is more than 240V to neutral, and the other is a lower voltage but "negative" relative to the input. The 3rd phase is generated by capacitors and varies considerably with the connected load and the unit setting. Yes, of course I've had the lid off to look inside
A genuine rotary converter could provide a neutral point - but for reasons of economy (it would add to the cost and weight of the machine) it's not likely to and/or it may not be as "earthy" as people are used to with neutrals - ie you'd want to treat it as live and not use any single pole switching downstream.
You may have noticed a certain amount of "if"s and "but"s - that's because to really answer the question means knowing details of both the converter (ie what it's got inside and how it's wired) and the machine (ie how it's wired). There are so many ways these things can be done that it's hard to generalise.
Thank you for all of that - I spoke to my brother this evening, it's a Transwave MT21210B Rotary Converter with 415V output, no motor rewiring is necessary for any of his machines, and it's also capable of running machines with more than one motor. When he originally ordered the converter my brother provided the info for the lathe to the chap who owns Transwave (who just happens to be a relative of my sister-in-law) and he specified the converter so that it will cope adequately with the lathe, a Schaublin 102, plus a couple of other smaller 3-phase machines (used one at a time).
As for the lathe, the motor ratings according to the motor plates are:
Main motor - 415V 3.6A, 1.5kW
Milling motor - 220V 1.34A, or 380V, 0.78A
Extractor - 220V 1.5A, or 380V 0.9A, 0.37kW
Suds - unknown
Transformer (work lamp) - unknown
The milling motor is wired to all 3 phases, not sure about the extractor though, but it connects to a similar, but slightly differently shaped 3 pin socket at the back of the lathe cabinet - each motor can only be plugged into it's specific socket. As for the suds motor, it's buried somewhere inside the cabinet, there are six wires connected to the on/off switch, although it only has an on/off function, but I can't imagine that it's all that powerful. The same goes for the single phase (connected to L1) work lamp transformer which is always running, whether the lamp is in use or not.
Very occasionally all three motors will be used at once.
There's a separate 2 pole MCB for the work lamp transformer and a bank of six narrow single MCBs which he hasn't identified.
According to the chap at Transwave all he needs to do is get the relevant MCB and plug fitted and it's ready to go.
The main motor is wired like nothing I have in my workshop, all six terminals are connected to the rotary on/off/reversing switch giving two motor speeds - that coupled with a physical variable drive system makes my Myford look like a toy!
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