3 phase machine wiring

[info_1marchco]

Hi folks
I wonder if any one can help me
I have a machine with a 3 phase motor that also has a transformer converting 230vac to 24Vac to power a start stop contact switch, the machine also has a digital counter that runs on 230vac and gives out 24vdc to power a couple of sensors, both the counter and the transformer are connected to L1 of the incoming 3 phase feed that also supply's the motor, but the 125mA fuse on the supply to the counter blows occasionally when I turn the power on, so I'm wondering if I were to connect the transformer to L2 instead of L1 would that change anything (or even be advisable)
Thanks

 

[sawtooth-9]

Sounds like you have three phases and a neutral running to your machine.
Picking up between L1 and neutral will give you your 230 volts.
The transformer input of 230 volt will come from L1 to neutral and supply the DOL with a 24V coil and the sensors.
You could connect to any of the three phases to get your 230 V, so changing to L2 or L3 would make no difference.
Either the 125mA fuse is too small to cope with the load, or you may have a problem with one or more of the sensors.
Try a 150 mA fuse - if it still blows, look deeper into the sensors for a possible fault

 

[sawtooth-9]

Hi folks
I wonder if any one can help me
I have a machine with a 3 phase motor that also has a transformer converting 230vac to 24Vac to power a start stop contact switch, the machine also has a digital counter that runs on 230vac and gives out 24vdc to power a couple of sensors, both the counter and the transformer are connected to L1 of the incoming 3 phase feed that also supply's the motor, but the 125mA fuse on the supply to the counter blows occasionally when I turn the power on, so I'm wondering if I were to connect the transformer to L2 instead of L1 would that change anything (or even be advisable)
Thanks

 

[info_1marchco]

Sounds like you have three phases and a neutral running to your machine.
Picking up between L1 and neutral will give you your 230 volts.
The transformer input of 230 volt will come from L1 to neutral and supply the DOL with a 24V coil and the sensors.
You could connect to any of the three phases to get your 230 V, so changing to L2 or L3 would make no difference.
Either the 125mA fuse is too small to cope with the load, or you may have a problem with one or more of the sensors.
Try a 150 mA fuse - if it still blows, look deeper into the sensors for a possible fault

Hi
Thanks for your reply
I'm more inclined to suspect the transformer than the sensors or the counter as that's the oldest component, the counter and sensors are both new

 

[sawtooth-9]

Hi
Thanks for your reply
I'm more inclined to suspect the transformer than the sensors or the counter as that's the oldest component, the counter and sensors are both new

Sometimes you can run into this issue if the transformer neutral is not also run to earth.

 

[sawtooth-9]

If the sensors and counters are new - do they draw the same current as the old ones ?
Is the 125 ma fuse just for the counter ? If so, you should check the current draw of the new counter.

 

[info_1marchco]

Hi
The 125mA fuse is the recommended fuse for the counter, the sensors run on 24vdc supplied by the counter, the transformer is fused separately to the counter at 2Amps with no earth, only the motor has an earth wire the transformer and the counter have no earth connection - the incoming earth and the earth from the motor connect to a terminal on a metal din rail connected to the machine casing - your comment about earthing the neutral on the transgggis interesting because it's shown on the wiring diagram but there isn't any earthing to the transformer or to neutral - would if just be a case of connecting a wire from the neutral to the earth terminal

 

[sawtooth-9]

Hi
The 125mA fuse is the recommended fuse for the counter, the sensors run on 24vdc supplied by the counter, the transformer is fused separately to the counter at 2Amps with no earth, only the motor has an earth wire the transformer and the counter have no earth connection - the incoming earth and the earth from the motor connect to a terminal on a metal din rail connected to the machine casing - your comment about earthing the neutral on the transgggis interesting because it's shown on the wiring diagram but there isn't any earthing to the transformer or to neutral - would if just be a case of connecting a wire from the neutral to the earth terminal

If you want to run an earth to the transformer, then yes, just connect a wire from the transformer neutral to earth.
Your supply neutral should be at ground potential ( either earthed at the power station or where power comes into your board ) so it should not cause any issues. In Aus, some councils insist on earthing your neutral and some don't. So might be worth checking this out with a local sparky.
I once had to build a control system for a small three phase extruder - which consisted of two VFD and 24 Vdc controllers. When I had the design checked by my sparky he insisted that the transformer neutral was earthed.

 

[Spectric]

then yes, just connect a wire from the transformer neutral to earth

There is no neutral on a transformers primary or secondary windings, both being Ac. If the transformers output is classed as extra low voltage, ie 50 volts Ac or less then under uk regs there is no requirement to provide any earth or ground connection.

 

[Dabop]

If you want to run an earth to the transformer, then yes, just connect a wire from the transformer neutral to earth.
Your supply neutral should be at ground potential ( either earthed at the power station or where power comes into your board ) so it should not cause any issues. In Aus, some councils insist on earthing your neutral and some don't. So might be worth checking this out with a local sparky.
I once had to build a control system for a small three phase extruder - which consisted of two VFD and 24 Vdc controllers. When I had the design checked by my sparky he insisted that the transformer neutral was earthed.

In Australia, its always got a bond between the neutral and the earth at the fusebox, and an earth stake connected to the earth bonding bar- its not up to the council lol
That's because we use the 'MEN' standard (Multiple Earth Neutral) system here- only the very oldest places didn't have it- and I'd be surprised if they hadn't been updated to it anyway- we are talking half a century or more ago that it became the standard practice here... (is required under Au/NZ 3000 section 5)
https://www.worksafe.qld.gov.au/__d...535/es-multiple-earth-neutral-connections.pdf

 

[sawtooth-9]

There is no neutral on a transformers primary or secondary windings, both being Ac. If the transformers output is classed as extra low voltage, ie 50 volts Ac or less then under uk regs there is no requirement to provide any earth or ground connection.

I would be interested to see a transformer with only a single phase wire on the primary and secondary windings. No potential difference means no current flow.
Maybe we have our " wires crossed " ?
Hey, at least you wouldn't blow any fuses.

 

[Spectric]

Ac is an alternating voltage and therefore neither output from the secondary windings will be positive or negative because they alternate. Maybe you are thinking of the phase relationship between the primary and secondary windings where dot notation is used to indicate whether the windings are in phase or 180° out of phase.

 

[Dazed]

I mean no disrespect to anyone here, but rather than try things at random I would try to find out by measurement why the fuse is blowing. IMO the best way of doing that is by getting an electrician to take a look - if you don't have the knowledge or tools to do that of course.

 

[Spectric]

but rather than try things at random

The only way to solve any problem is with taking the logical approach, a random one will just take you in circles. Often you are not looking for the fault but rather systematicaly working through a system to illiminate what is functioning and eventually you find the fault. Electrical fault finding is not difficult if approached logically, what is making things very difficult now is when there is an electronic module containing some type of coding which you have no access to and don't know what is going on behind closed doors, ie a blackbox.