Wire Power Supply to AC Supply 1

Wire Power Supply to AC Supply


These instructions will show you a couple of ways to wire a Power Supply Unit (PSU) to your AC supply.

The first way will be directly connecting a power cord to the PSU. Wiring it this way is simpler but has you turning your machine off and on at the power point.

The second will be connecting a power cord to the PSU via an IEC power chassis. This way is a little more complicated but will give you two additional features, being able to turn your machine off and on at the chassis, and, the chassis will add a fuse to the circuit giving you an extra layer of protection.


Check that you can see all pronged plugs of your router, electronics and other devices, ensure they are not plugged in.

Best practice – hold the plugs of your devises in your hand and visually trace the cords back to the individual devices. This will confirm they are not plugged in.

Parts Required

1. Power Supply
A power supply with suitable voltage and amperage for your project’s electronics and motors.

2. Power Cord
You’ll need a cord long enough to travel from your wall socket to your PSU. It will also need to be rated high enough for the amount of power you PSU is going to draw.

3. Fork Crimp Terminals
Fork Terminals x3, these are used connect wires to screw terminals and are a tidy way to terminate a wire. They are fairly cost effective and can be used by people who  don’t have access to soldering equipment. 

The parts above are suitable for directly wiring the PSU to a power cord and you can skip the rest of the parts listed below. If you intend to us and IEC power chassis you will need all the parts listed above and the ones listed below.

4. IEC Power Chassis
The power chassis will allow you to connect power using a standard IEC cord (like you would find used with a PC) but give you the added ability to turn your PSU off and on with a switch instead of unplugging it. It also adds an added lay of protection to your project as the power chassis also has a fuse.

5. Spade Crimp Terminals (Female)
These will be required to attach wiring to the back of the power chassis. You will need 5. You can omit them if you intend to solder the wires to the chassis’ connectors. 

5. Additional length of AC wiring
This will be used to wire the the power chassis to the PSU. You’ll need enough length to travel from where the chassis is mounted to the AC terminals on the PSU. You will need to remove the outer sheath to create individual wires.

What size power supply do I need for my project?

Generally speaking, you’d need to determine the overall power consumption for the electronics of your machine and allow for around a 10-20 % buffer on top.

However, as a general guide for a 3 axis, 3 motor machine that has a separate supply for the spindle, you’ll find you fall in to one of three basic categories:

Small Machine – using Nema 17 motors and Arduino style electronics –
a single 200-250watt 12-24 volt PSU will most likely cover your needs.

Medium size Machine – using Nema 23 or 24 motors and a USB or LPT breakout board –
a 350-400 watt 36-48 volt PSU will most likely cover your needs.

Large size Machine – Using Nema 34 or 42 motors and a USB or LPT breakout board –
3x 400-500 watt 48-72 volt PSUs (one per Driver/Motor) will most likely cover your needs.

These are just rough guides based on common setups that are available on eBay, Amazon, Alixpress, etc..

I don’t have a page on “calculating” power needs but will endeavour to get one up and running.
Place holder for “Calculate Power Needs”


Tools Required

Wire cutter

Wire stripper

Crimping Tool

Philips head screwdriver

Small flat head screwdriver

Optional – Soldering iron

When dealing with AC power it is recommended that all joints be soldered where possible.


Unplug Any Power Cords

Make sure all cords you are going to use and any others associated with your CNC project are unplugged. Visually identify the male plug ends of your cords and that they are not plugged in to wall sockets, place them on the bench beside you. If I sound like I’m repeating myself, I am – its important!