Motor protection

[normspanners]

I have been asked to look at a couple of 2post lift that uses kraus Naimer rotory switches (that have burnt out on a few occasions) to control the 3ph motor but that is ALL they have, a 3ph rotary isolator on the incoming and a kraus naimer switch for the motor start, no motor protection at ALL !! the problem is a rotary switch will do it ( it has for 3 years or so) but IMO they are not totally accurate at the point they switch, as they work on plastic cams etc and that is not ideal for DOL motor starting and is that fact that is burning them out, they also are VERY expensive at £70 +
My idea is too use a 415 coil contactor and momentary switch to switch the motor in with an overload at the bottom (obviously set to the motor current), I would use some protection for the 415v coil and switch wiring but would it be better to use double pole protection ? because if one side trips the other is still live, through the coil, or use a small 415v isolation tranny and use single ph 230 protection or even go to 24 v?
the way it has been designed leaves a lot to be desired IMO as having no motor protection seems crazy with a 4/6amp ish motor dol on a 32a C MCB.

 

[MattH]

As per pdg, or go down the route of how a 3ph lathe with reversing is wired.

A contactor with overload on the incomer acting as the NVR and then two contractors (one for each direction). You could use 6 way contactors on the secondary pair to be able to run two motors.

 

[daleyd]

If your running remote switches/buttons then I'd be tempted to go for a 110 or as you say even 24V supply rather than using the 415 to power the control side of things, there's no problem with the switchgear handling it (If you buy decent stuff...) but it's just a whole lot safer if your able.

Either buy a DOL starter ready made or get an enclosure and make your own. What rating motors are they? I may have some stuff here that's suitable?

 

[daleyd]

 

[frank horton]

my 3 phase Hoffman lift had a rotary but the firm went bust......(think they r up and running again) so couldn't at the time buy a new'un.......
my sparks used a push button up/down unit to control a contactor in another box...........




works an absolute treat.........BUT WARNING, had to do away with the auto stop, no probs for me as it's only me that uses it.......
hope this helps Frank

 

[normspanners]

What's wrong with using a normal DOL start switch?

thanks for the reply, there is nothing wrong apart from it requires momentary operation, ' dead man operation' to control hydraulics and the incomer isolator is quite high up the post, so needs a remote momentary switch, siting it on the face of the motor terminal box would be good as that is where the 'up' switch is now, sort of in yer face obvious.

As per pdg, or go down the route of how a 3ph lathe with reversing is wired.

A contactor with overload on the incomer acting as the NVR and then two contractors (one for each direction). You could use 6 way contactors on the secondary pair to be able to run two motors.

thanks for the reply, the motor doesnt need reverse it is simple as it is hydraulic, the motor just needs switching on or off

If your running remote switches/buttons then I'd be tempted to go for a 110 or as you say even 24V supply rather than using the 415 to power the control side of things, there's no problem with the switchgear handling it (If you buy decent stuff...) but it's just a whole lot safer if your able.

Either buy a DOL starter ready made or get an enclosure and make your own. What rating motors are they? I may have some stuff here that's suitable?

Thanks for the offer Dale but I need to make both exactly the same and as we have spent quite a bit on switches, even though we have bought the 'correct' switch through Klaus N according to the part numbers etc they are NOT right config and I have to strip them and make them work, if you have ever stripped one and tried to rebuild, WOW !! you will understand how complicated it is it takes hours !!! to get the right config
So I was just going to make my own control out of replicatable new parts. using Schneider or some such? coz I have CEW round the corner! and I mot their cars !

Yes I think I might go with making my own box with a small control isolation tranny 110/ 24 v control and contactor /OL as it is only 3ph and earth 4 core I believe no neutral , then run the remote switch down to the motor terminal box through the same trunking and back to the control box.
I was just concerned that if a phase goes down as happens here quite a lot, as we are mostly overheads, and they go in to the control box messing, one side of the control gear COULD still be at 230v through the coil etc but if a control tranny goes down it is isolated.

I realize things are made to a price but having no motor protection seems crazy to me, and IMO rotary switches are 'not good' at dol motor switching because of wear and causing timing issues.
Also these have been designed, fitted and commissioned by qualified people with this inexcusable lack of thought IMO.

 

[normspanners]

my 3 phase Hoffman lift had a rotary but the firm went bust......(think they r up and running again) so couldn't at the time buy a new'un.......
my sparks used a push button up/down unit to control a contactor in another box...........

Sounds like the same scenario, there are that many Chinese / Italian lifts etc etc.
I am not knocking anyone here BTW but amazing to me, how many so called qualified sparks dont know how a lot of control gear works though !!

 

[daleyd]

I have 7 of those overloads so if you need a couple then let me know.

 

[normspanners]

Which part requires momentary operation?

Thanks'
No most hydraulic lifts use the UP or start switch to switch the motor on, you switch the pump on and as soon as the pump starts its up to pressure and lifts the arms, so you have to hold the button in to continue lifting and when doing intricate stuff IE 'inching' maybe with a stand under a bottom arm to compress a strut etc you could be pressing for milliseconds, just a dab, that is why a rotary is not good, for the switch or the motor because of the inrush.

 

[normspanners]

I have 7 of those overloads so if you need a couple then let me know.

Thanks Dale, you can come and do it if Ya want----=-- save me some time !!! I get dragged into jobs kicking and screaming sometimes !!
seems difficult to get people who know what they are doing !!
not knocking anyone here BTW

 

[normspanners]

Thanks Dale, you can come and do it if Ya want----=-- save me some time !!! I get dragged into jobs kicking and screaming sometimes !!
seems difficult to get people who know what they are doing !!
not knocking anyone here BTW

It is mostly mates, that know what they would like to happen with something, but dont know how or where or who to myther !!!
but they know me !!

 

[daleyd]

Thanks'
No most hydraulic lifts use the UP or start switch to switch the motor on, you switch the pump on and as soon as the pump starts its up to pressure and lifts the arms, so you have to hold the button in to continue lifting and when doing intricate stuff IE 'inching' maybe with a stand under a bottom arm to compress a strut etc you could be pressing for milliseconds, just a dab, that is why a rotary is not good, for the switch or the motor because of the inrush.

It wouldn’t be a big leap to have a couple of buttons, one for latched operation and one for inching, if that’s what they wanted.

I’d certainly agree a rotary switch doesn’t sound ideal for what they are doing with it, they’re ok for stuff that’s on and left on in my experience but anything more than a really small motor and I’d be looking at chucking a proper starter at it.

 

[MattH]

thanks for the reply, the motor doesnt need reverse it is simple as it is hydraulic, the motor just needs switching on or off

I understand now. I'd still be inclined to use contactors.
I'd have two, the first would be an overload equipped latching acting as the NVR for the lift and then a non latching with a push button to "jog" the motor as required.
You are always going to have issues with switches that are switching motor current.

 

[normspanners]

It wouldn’t be a big leap to have a couple of buttons, one for latched operation and one for inching, if that’s what they wanted.
I’d certainly agree a rotary switch doesn’t sound ideal for what they are doing with it, they’re ok for stuff that’s on and left on in my experience but anything more than a really small motor and I’d be looking at chucking a proper starter at it.

THANKS CHAPS BTW !
The rotary switch is momentary also------ so to 'inch' it they have to turn it through about 30 deg for it to switch on, then they can release immediately, and the lift may raise 15mm or so, if the contacts are not exactly timed, (and how many old used switches actually can be ?) one of the switch contacts is getting more arcing, IMO. that is causing the burn outs.
Also because of head room with some large box vans latching is not a good idea and I think they have to have a 'dead man' switch for the insurance purposes, ie if the operator dies at the controls it stops.
It also has auto mechanical /manual sawtooth latches that click in on the way up every 150mm these have to be held out with a lever and boden cable to the other post, as it is lowered, but the hydraulic lowering is done by a spool valve, and chains to force the rams to travel together.
we bought a brand new lift 2 yrs ago that was 3ph or 1ph choice obviously 3ph is better but they sent 3ph motor and 1ph switch box! and then said-- oh cant you just mod it ? so I had to start moding the box over, but it was easier in one way coz there was 5 core with neutral in it IIRC. that had solenoid hydraulic release and electrical safety latches.

 

[normspanners]

It is a mates place and the boss my mate, has lads there that will have ago ! but one of the problems, I find, is lack of knowledge hence wanting to try and make it fool proof -------- for instance they needed a new compressor coz the one was too small, I managed to get them a large 3ph broom wade old school proper beast, before I could get there to wire it, they had wired it into a 5pin three phase 32A socket, 'JUST TO TRY IT' I had previously wired a single phase scissor lift to it, that they are using, they had removed the plug and copied the wiring from the new single phase lift colours to the old 3ph motor wiring and said the compressor was faulty !!! yep they had wired the red to the brown one of the yellows to the earth pin and the blue to the neutral !!
so that is why I am concerned about using 415 v control, because of the poss 'messing' factor. No matter what I say, they think they know better.
Its easy electrical work init you just stick the wire in and tighten the screw !

 

[MattH]

The trouble with anything other than 415v is that you are going to have to add a control transformer and then you are just making the whole thing more complicated for the "messers".

To make is fool and tamper proof you are going to have to build a small metal control enclosure with an interlocked door isolator, and then have a 24v control with maybe a pendent with push buttons.

 

[normspanners]

I dont need a pendant, because you have to stand clear whilst operating as said the control up switch will fit nicely into the same place as the present switch on the motor body terminal box which is quite large and at chest height, I will do away with the incoming isolator and build a box up there about 6ft to house the contactor etc with interlock door isolator etc I think, then if they remove that isolator cover it is isolated and there is only control voltage present at the motor till the contactor is operated.
at the end of the day he has spent over £200 on switches to date plus my time and now we need more spare switches ordering, another 150 that will just burn out. And the job is still crap !
do it once now and forget plus if anything does happen it is easily / quickly repaired. without complicated switches.etc also will be more user friendly.

BUT does make you think about designers and installers etc allowing such to be used each having 32A c mcb's !! the switch is 20 amp ish and the motor wiring looks to be 1.5mm

 

[normspanners]

This is the isolator and the trunking to the motor ,that is where the up switch resides just to give you a visual