Wire Choices for CO2 Lasers
Posted: Mon Jun 22, 2020
This might be a little boring to some as most see wire as bits of copper inside a tube of something flexible but there is a lot more to it depending on the application.
I am limiting this to 'typical' Laser use cases so consider most of this applicable to say Sub 150W CO2 Lasers with 30-40kV maximum HV supplies and either Nema 17 or 23 Steppers. Happy to talk about other use cases outside this but this will cover most of us.
Mains Wire:
First the Elephant in the Room, the USA and Canada in particular have 110V or in some cases 220V 'Split Phase' ( Recommend watching this https://www.youtube.com/watch?v=fJeRabV ... e=youtu.be ) This matters a bit in terms of wire gauge here but is more a concern for Switchgear which I will discuss in another thread.
First thing to consider here is how much power does my base machine use? Is the Blower wired from it or is it separate? If we assume worst case and the blower is included then the following is a rough summary of power required.
Stepper Driver Supply 250W
Additional DC supply 100W
HV Supply (based on 150W Tube) circa 1000W peak
Blower 550 - 750W for the bigger end.
So we come up with a rubbery number of 2000W for a larger Laser. If we consider the 110V case that is around 18A peak, or 9A in the case of 220V or a bit less for those of us on 240V supplies. This now matters a bit because it goes to wire gauge from the Meterbox or if you use multiple extension leads to run your Laser off
(yep I have seen it done) There is a reason to consider the entire run from the meter box as will become clear.
Copper has a Resistance which is very small but it has one. The ability to pass current without generating to much of a voltage drop or heat is a function almost entirely due to cross sectional area (keeping this simple). Seemingly Random I am going to use AWG and Feet here even though I live in part of the Metric world, the Cable industry worldwide still uses AWG a lot. I have included a conversion to sqmm and most of you will know there is about 3 1/3 feet to the M.
What the first chart shows is two sets of numbers as an E Eng I dislike 3% drop but it is considered 'acceptable' so if you are marginal and are hard up for a $ then go with it.
What you will see from the chart is that if you double your voltage you also double the length of cable run to maintain that voltage this is simplified but it is Ohms Law at work V= IxR in this case Voltage loss = Current times Resistance.
So if we take a 110V worst case at 18A and we use in this case the 20A portion then the maximum length from the Meter using 8AWG is only 60' so 110V larger machines are really pushing it uphill to hook into a single circuit. If you split that into two circuits with the blower on the other then you are back in the relms of 'reasonable'. 10 or 12 AWG is really not going to cut it for wiring IMO unless your run is really short.
If we now look at the better case of 220 or 240V then 10 and even 12AWG becomes feasible and up to the job and in most cases a single circuit will be fine without needing to upgrade from domestic wiring.
Why this matters it that for larger Lasers you should be using heavier cable even from the wall and if possible NOT using extension leads unless of an appropriate gauge and only if you have to. Typically this would be 16AWG for 220/240 or 12-14 AWG for 110V from the wall and keeping the run short.
This also should apply to internal mains wiring of the Laser and generally keeping the same gauge is a good idea.
General Hookup Wire
This is the now Lower Voltage wire used within the machine be that 24 or 36V DC generally. I differentiate this to Gantry wiring as they have different 'mechanical' needs even though the Voltage remains the same.
Firstly V=IxR still applies and in particular this applies to the main DC power runs to the Stepper Drivers themselves and far less to the rest so it can be ignored to a degree (use something mechanically 'sensible' for these). This now becomes more important as we have less Voltage available to lose.
If we take something of a worst nominal case again of a 24V system running three Nema 23's which is more power than most will be drawing and the drivers are set to 4A each. So 12A 'peak' current at 24V input and that supply is located 2M by wire length from the drivers using this snipped up chart you can reasonably use 14-16AWG wire for this purpose and 18AWG is a bit underdone so buy and use accordingly. Something in the order of 30-50+ Strands of copper should be fine here.
The type of wire used here is not critical in the strand count as the wire remains 'static' so flexibility and diameter are generally unimportant. There is one type I would advise against which is cheap Automotive wire, typically the strand count is very low and the insulation not all that good around heat.
For the rest of the 24V Controller based wiring including safety and limit switches much lighter will be fine as the currents are below 1A. The only exception to this might be low voltage led lighting if fitted. Typical sizing will be circa 20AWG and a kit like this is 'reasonable value' if you are wiring from scratch https://au.element14.com/stellar-labs/2 ... ASSEMBLIES
Gantry and Stepper motor Wire
We are now back into the area of 4A maximum and 24 or 36VDC apart from the limit switches and Red Dot Laser if fitted. In this part of the system Flexibility and strand count are king. Each wire is going to be moved many thousands of times over its life so larger radius drag chains runs are also key.
There is massively expensive dedicated Cable available for heavy industrial use such as this https://lappaustralia.com.au/en/drag-ch ... hain-cable and then there is something 'sensible' for the rest of use
Single core un-shielded conductors will be generally fine for Laser use but for a CNC Router for example with an Inverter close by not really a good choice.
So as we are typically looking for acceleration and rapid changes of direction in particular in the case of the Gantry drive getting the power which is Voltage times Current ( P = V x I ) we want to maintain the voltage and keep it as high as possible while considering the mechanical requirements.
If we take the last chart above 18AWG will be a reasonable choice and maybe for smaller Lasers 20AWG (not shown on the chart) but in this case look for wire with strand counts of 100+. Something like this evilbay listing would be a good place to look https://www.ebay.com.au/itm/30-28-26-24 ... 1195.m1851 and they have a good range of colours. Not a lot to be saved between 18 and 20AWG so go heavier IMO.
HV Laser Power Supply Wire
This doesn't apply to the Ground wire of the HV Laser supply and as the current is very low use some of the 20AWG will be fine.
So onto the HV wire and we have another different set of considerations Di-Electric Breakdown or Strength of the Insulation https://en.wikipedia.org/wiki/Dielectric_strength. There are numerous threads here about this breakdown including this one viewtopic.php?f=127&t=3559&p=22049&hili ... ric#p20494 but have a bit of a search should reveal some others.
From the Wikipedia link just above you will notice Air is one of the worse Strength materials. In air 1000V will jump a 1mm gap and expanding on that to some of the Larger lasers we have 30+kV so that voltage in Air (differs with environment) will jump well over an Inch. so at either end of the cable NO METAL PARTS should be even close to 25mm to those connections!
The only thing now to consider is the Di-Electric Strength of the Wires insulation and what the Breakdown of this Strength does. This is largely what was happening in the case of the Bodor thread. Clearly the Cable Insulation was failing. When the Insulation fails once it generally creates a carbonized path through the insulation and it will continue to leak through that same point ALWAYS. Secondary props additional sleeving are only masking the underlying issue and are no better than a band aid on a knife wound. Replacing the entire run is always the best and only real choice as any tape or heatshrink over a nick will always fail first as underlying that defect is effectively AIR.
Buy from a reputable source not a generic Evilbay or Aliexpress one that deals in Lasers even if yours is fine now add some into your next order it is CHEAP https://www.aliexpress.com/item/3258866 ... 1abadG0cvb
Extra Mechanical Considerations
Cable management and looming is partly art and partly science. Keep your wires tidy with zip ties and ducting and make it look nice because it is probably the right thing to do. Do not have your wires taught or stretched to make a connection EVER, add a few inches and let them curve between connections.
Importantly too in the case of Mains use Cable Glands so the wire can not be pulled from the machine and terminals if it gets a tug or kicked.
Lastly use Rubber Grommets where Cables and wires pass over metal plates most failures of the insulation will occur here regardless of being HV or LV DC
If you made it this far happy to take on board critique, questions, requests for expansion/modification of this as the groups sees fit.
I am limiting this to 'typical' Laser use cases so consider most of this applicable to say Sub 150W CO2 Lasers with 30-40kV maximum HV supplies and either Nema 17 or 23 Steppers. Happy to talk about other use cases outside this but this will cover most of us.
Mains Wire:
First the Elephant in the Room, the USA and Canada in particular have 110V or in some cases 220V 'Split Phase' ( Recommend watching this https://www.youtube.com/watch?v=fJeRabV ... e=youtu.be ) This matters a bit in terms of wire gauge here but is more a concern for Switchgear which I will discuss in another thread.
First thing to consider here is how much power does my base machine use? Is the Blower wired from it or is it separate? If we assume worst case and the blower is included then the following is a rough summary of power required.
Stepper Driver Supply 250W
Additional DC supply 100W
HV Supply (based on 150W Tube) circa 1000W peak
Blower 550 - 750W for the bigger end.
So we come up with a rubbery number of 2000W for a larger Laser. If we consider the 110V case that is around 18A peak, or 9A in the case of 220V or a bit less for those of us on 240V supplies. This now matters a bit because it goes to wire gauge from the Meterbox or if you use multiple extension leads to run your Laser off
(yep I have seen it done) There is a reason to consider the entire run from the meter box as will become clear.Copper has a Resistance which is very small but it has one. The ability to pass current without generating to much of a voltage drop or heat is a function almost entirely due to cross sectional area (keeping this simple). Seemingly Random I am going to use AWG and Feet here even though I live in part of the Metric world, the Cable industry worldwide still uses AWG a lot. I have included a conversion to sqmm and most of you will know there is about 3 1/3 feet to the M.
What the first chart shows is two sets of numbers as an E Eng I dislike 3% drop but it is considered 'acceptable' so if you are marginal and are hard up for a $ then go with it.
What you will see from the chart is that if you double your voltage you also double the length of cable run to maintain that voltage this is simplified but it is Ohms Law at work V= IxR in this case Voltage loss = Current times Resistance.
So if we take a 110V worst case at 18A and we use in this case the 20A portion then the maximum length from the Meter using 8AWG is only 60' so 110V larger machines are really pushing it uphill to hook into a single circuit. If you split that into two circuits with the blower on the other then you are back in the relms of 'reasonable'. 10 or 12 AWG is really not going to cut it for wiring IMO unless your run is really short.
If we now look at the better case of 220 or 240V then 10 and even 12AWG becomes feasible and up to the job and in most cases a single circuit will be fine without needing to upgrade from domestic wiring.
Why this matters it that for larger Lasers you should be using heavier cable even from the wall and if possible NOT using extension leads unless of an appropriate gauge and only if you have to. Typically this would be 16AWG for 220/240 or 12-14 AWG for 110V from the wall and keeping the run short.
This also should apply to internal mains wiring of the Laser and generally keeping the same gauge is a good idea.
General Hookup Wire
This is the now Lower Voltage wire used within the machine be that 24 or 36V DC generally. I differentiate this to Gantry wiring as they have different 'mechanical' needs even though the Voltage remains the same.
Firstly V=IxR still applies and in particular this applies to the main DC power runs to the Stepper Drivers themselves and far less to the rest so it can be ignored to a degree (use something mechanically 'sensible' for these). This now becomes more important as we have less Voltage available to lose.
If we take something of a worst nominal case again of a 24V system running three Nema 23's which is more power than most will be drawing and the drivers are set to 4A each. So 12A 'peak' current at 24V input and that supply is located 2M by wire length from the drivers using this snipped up chart you can reasonably use 14-16AWG wire for this purpose and 18AWG is a bit underdone so buy and use accordingly. Something in the order of 30-50+ Strands of copper should be fine here.
The type of wire used here is not critical in the strand count as the wire remains 'static' so flexibility and diameter are generally unimportant. There is one type I would advise against which is cheap Automotive wire, typically the strand count is very low and the insulation not all that good around heat.
For the rest of the 24V Controller based wiring including safety and limit switches much lighter will be fine as the currents are below 1A. The only exception to this might be low voltage led lighting if fitted. Typical sizing will be circa 20AWG and a kit like this is 'reasonable value' if you are wiring from scratch https://au.element14.com/stellar-labs/2 ... ASSEMBLIES
Gantry and Stepper motor Wire
We are now back into the area of 4A maximum and 24 or 36VDC apart from the limit switches and Red Dot Laser if fitted. In this part of the system Flexibility and strand count are king. Each wire is going to be moved many thousands of times over its life so larger radius drag chains runs are also key.
There is massively expensive dedicated Cable available for heavy industrial use such as this https://lappaustralia.com.au/en/drag-ch ... hain-cable and then there is something 'sensible' for the rest of use
Single core un-shielded conductors will be generally fine for Laser use but for a CNC Router for example with an Inverter close by not really a good choice.So as we are typically looking for acceleration and rapid changes of direction in particular in the case of the Gantry drive getting the power which is Voltage times Current ( P = V x I ) we want to maintain the voltage and keep it as high as possible while considering the mechanical requirements.
If we take the last chart above 18AWG will be a reasonable choice and maybe for smaller Lasers 20AWG (not shown on the chart) but in this case look for wire with strand counts of 100+. Something like this evilbay listing would be a good place to look https://www.ebay.com.au/itm/30-28-26-24 ... 1195.m1851 and they have a good range of colours. Not a lot to be saved between 18 and 20AWG so go heavier IMO.
HV Laser Power Supply Wire
This doesn't apply to the Ground wire of the HV Laser supply and as the current is very low use some of the 20AWG will be fine.
So onto the HV wire and we have another different set of considerations Di-Electric Breakdown or Strength of the Insulation https://en.wikipedia.org/wiki/Dielectric_strength. There are numerous threads here about this breakdown including this one viewtopic.php?f=127&t=3559&p=22049&hili ... ric#p20494 but have a bit of a search should reveal some others.
From the Wikipedia link just above you will notice Air is one of the worse Strength materials. In air 1000V will jump a 1mm gap and expanding on that to some of the Larger lasers we have 30+kV so that voltage in Air (differs with environment) will jump well over an Inch. so at either end of the cable NO METAL PARTS should be even close to 25mm to those connections!
The only thing now to consider is the Di-Electric Strength of the Wires insulation and what the Breakdown of this Strength does. This is largely what was happening in the case of the Bodor thread. Clearly the Cable Insulation was failing. When the Insulation fails once it generally creates a carbonized path through the insulation and it will continue to leak through that same point ALWAYS. Secondary props additional sleeving are only masking the underlying issue and are no better than a band aid on a knife wound. Replacing the entire run is always the best and only real choice as any tape or heatshrink over a nick will always fail first as underlying that defect is effectively AIR.
Buy from a reputable source not a generic Evilbay or Aliexpress one that deals in Lasers even if yours is fine now add some into your next order it is CHEAP https://www.aliexpress.com/item/3258866 ... 1abadG0cvb
Extra Mechanical Considerations
Cable management and looming is partly art and partly science. Keep your wires tidy with zip ties and ducting and make it look nice because it is probably the right thing to do. Do not have your wires taught or stretched to make a connection EVER, add a few inches and let them curve between connections.
Importantly too in the case of Mains use Cable Glands so the wire can not be pulled from the machine and terminals if it gets a tug or kicked.
Lastly use Rubber Grommets where Cables and wires pass over metal plates most failures of the insulation will occur here regardless of being HV or LV DC
If you made it this far happy to take on board critique, questions, requests for expansion/modification of this as the groups sees fit.