Aug 25 2016

CNC Machine Power Consumption

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Electricity is not the most expensive thing to worry about when running a CNC machine. But while it does account for a small percentage of your operating costs it is still a factor that you should be aware of. For the computer you use with your machine the power usage will be negligible, you do not really need to worry about it. The CNC machine itself should be your area of concern. Looking at your motors is a good way to identify power consumption; most of the power your machine uses is going to be directed towards the vacuums, air compressor and spindle. Say that all together these devices can draw a maximum of 50 horsepower if they are all running together. One horsepower uses up about 750 watts. This means that at peak efficiency you will be using 37,500 watts worth of power. Check how much you are charged per watt to determine what running your machine costs. Also remember to run the numbers based on the amount of power you usually use. If your machine can run at 50 horsepower but you usually only run it at 30, use the number 30 when figuring out your costs. The number you come up with should not be too high; it will likely only be a few dollars per hour. However, if you are using your CNC machine for business purposes the capital you spend on power could be figured into the cost of whatever items you make and sell.

CNC machine power consumption

CNC machine

A skilled machinist should also be aware of problems they can run into when it comes to power usage. Many machine shops use a 3-phase ungrounded service or a 3-phase, 4-wire grounded service. Either of these services requires a grounding electrode conductor to interface with the building grounding electrode system. Together the conductor and system provide low-impedance paths to the ground for lightning or electrical faults, provide low-impedance fault return paths to trip breakers and reference the building’s electrical system to minimalize voltage differences between various exposed metal parts. CNC machines use a regular wire, extending from their power supply, to connect to a ground plate. The ground plate is bonded to a grounding conductor, and subsequently to the grounding electrode system. This establishes a local signal reference with the CNC machine itself and with remotely connected devices. Stand-alone CNC machines should have good grounding, bonding and shielding but machines with data links or remote devices can be vulnerable to stray currents. If that is the case, take extra precautions to avoid electrical damage.
CNC machine manufacturers may recommend, or even require, the use of a supplemental ground rod with the machine they have produced. Usually this is an 8 ft. copper rod that goes through the floor, connecting to the ground plate. Different manufacturers will cite different benefits of using a supplemental rod but on-site examinations have shown that using one of these rods can actually increase the risk of electrical damage instead of decreasing it. The supplemental rod connects the electronic controller to the grounding electrode system and can attract stay electrical currents, such as lightning strikes or electricity generated from power system failures. Potentially the rod could attract a large enough electrical current that it would damage your CNC machine. If you decide to remove a rod, double-check the relevant safety codes and make sure you are not violating any of them. The same goes for implementing any solutions that you think could help to reduce the risk of electrical damages. CNC machine manufacturers can be a good source of relevant advice; they built the machines and should know them very well as a result. Also keep in mind that not all power problems stem from a grounding issue. If you have checked and rechecked your grounding and are still experiencing problems, explore other areas.