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How to wire the AC input wiring and power supplies in a FAST Neuron pinball machine cabinet

Wiring, high voltage, and electricity can be dangerous. Read this first!

The voltages and electricity discussed here can be dangerous and could cause property loss or death. It is your responsibility to ensure you are comfortable doing the things discussed here. Furthermore your local jurisdiction may have regulations or rules which differ from what we discuss here, including wiring colors, standards, techniques, etc. Seek professional guidance from someone local to you if you are unsure of anything you're doing here. Also there could be errors, omissions, or typos here. Use this content at your own risk.

This guide is for FAST Neuron-powered machines only

This wiring guide is for pinball machines powered by a FAST Neuron Controller. If you have a FAST Nano Controller, please see the Nano wiring guide.

The Neuron wiring guides are incomplete works-in-progress

NOVEMBER 2022 UPDATE: We are in the process of creating & updating the wiring guides for FAST Pinball Neuron-based systems. We are publishing our work-in-progress docs to get as much information out as soon as possible. If you have questions or want clarifications, please reach out via email to me (Brian), via

This guide is the first in our step-by-step wiring series which shows you how to wire the AC high-voltage to your power supplies in a pinball machine powered by a FAST Neuron Controller. It covers the components in the red box here:

What's covered in this guide

  • Only 48-volt and 12-volt supplies are needed.
  • How to choose power supplies.
  • Why we like the power supplies in the backbox.
  • Power switch options: traditional cabinet location, traditional switch, soft switch, etc.
  • How to wire your power supplies, the AC line input, AC line fuse, AC power switch

Before you read this guide, you should read these others first:

Design Choice: Will you use the Neuron's "low voltage" power switch option?

Most of our wiring guides provide a simple "just do it like this" way to do things, though occasionally you will have some design decisions to make. The first decision you need to make before you start wiring anything is whether you want to use the Neuron Controller's "low power / soft start" power switch option, or whether you want to use a traditional power switch.

Overview of the traditional power switch option

A traditional pinball machine uses a main power switch which switches the high-voltage AC power before it enters the power supplies in the pinball machine. This can be complicated, because if you want to locate this power switch in the traditional right-front cabinet location, that means you need to have high voltage AC power in your cabinet, which is potentially dangerous and makes the machine harder to get UL listed (if you care about that). Some pinball manufactures don't care and put the power switch there anyway. Others just move the switch up to the backbox so all the AC stays in the backbox, but then the switch is in an inconvenient location.

Overview of the soft power switch option

FAST Pinball has created a solution where the Neuron Controller uses a 2032 lithium batter with a solid-state relay which can be used to remotely switch the AC power via low voltage. This provides the advantage that you can keep your main power switch in the traditional under cabinet location, but that switch is actually a low-voltage pushbutton switch connected to the Neuron. This means you will have no high voltage AC in your cabinet while also having the switch where people expect it. You can build in a traditional switch to the backbox too which allows for the machine to be powered on via the breaker box (like most on location machines). This also lets you use the machine if the battery dies. The downside to the low-voltage soft start option is it adds a few steps and components to your wiring.

We'll cover the solid state relay and soft power option fully in the next step. You can read that now to get an understanding of what you'll need if you want to go that route.

Your machine's "power box"

In this step, we're going to start building your pinball machine's "power box". This is a section (typically in the lower right corner) of your backbox that contains all the high-voltage AC line power stuff, which is then covered by a protective panel of some kind. The purpose is to contain all the high voltage stuff in a protected place to ensure no one touches line voltage current when the backbox is open. This can be a literal metal box, or, more likely, a metal or plastic cover which separates the components here from peoples' fingers. Don't build this box just yet, as you'll need to include some more pieces from the next few steps.

If you really want to locate your power supplies in your cabinet, you can do that. However the same guidance for containing everything that touches AC under some kind of cover will still apply. Also you would most likely want to include your power filter board there too, and then probably the Neuron and your host PC also. Basically it's sort of "all or nothing", as your power wiring, supplies, Neuron, and computer are all pretty tightly connected, so you'll want to include them all in the same place.

You must use crimped connectors

An important thing to know is that you should not connect your bare stranded wire to the screw terminal of the PSU (or to any screw terminal, for that matter). Instead, use some type of connector which is crimped to the end of your wire. (See our guide to crimping if you're new to this.) The reason you need to use a connector is to ensure that a stray copper strand doesn't touch a neighboring terminal and short out. Also it ensures a solid connection with low resistance.

The specific type of connector you use is a personal choice. You could use a fork connector (shown below), or a ferrule, or a ring connector, or probably others.

Some people choose to use ring connectors thinking the ring will prevent the wires from coming off if the screw comes loose. Just be aware that many screw terminals are designed so the screws don't fully come out, making ring connectors annoying in those cases.

Some people have asked if it's ok to "tin" the wires (to ensure stray strands don't come out) and then screw the bare tinned wires into the screw terminals rather than using crimped-on connectors. This is not recommended, as the solder on the tinned wire essentially freezes the wire into a circle shape, meaning the screw terminal can't mash it down, resulting in less conductive surface area contact which results in higher resistance. There's a reason that fork connectors are standard.

Wire gauges & wire type

We discussed wire gauges in our guide to wire types, sizing, and colors, which you definitely read already, right? So you know AC wiring should be 16 gauge, stranded, UL 1007 listed wire.

IEC power cord socket + EMI filter

Starting from the back of the machine and working our way in, the first component is the socket that the power cord plugs in to. That hexagonal plug is called an "IEC" plug, and it has three pins for AC hot (sometimes called "line"), neutral, and ground. We like the sockets that have EMI filters built-in. (You could also get a standalone socket and EMI filter, but that's just more steps.)

If you want to build a machine that is compliant to UL listing standards, then you do NOT want to use an IEC socket that has a fuse holder built-in to it. The reason for this is to be compliant, the AC line fuse cannot be "user accessible" from the outside of the machine. (Their reasoning is that a user wouldn't know the importance of proper fuse selection, meaning they could install a fuse that a higher current rating then intended which would create an unsafe situation due to the improperly fused machine.)

If you are building a homebrew machine and don't care about commercial certifications, then you could choose an IEC socket which has a built-in EMI filter and fuse holder.

You'll mount this through your backbox wood so that the socket end is accessible to the outside rear, and then the terminals on the inside are in the area covered by your power box cover.

AC line fuse

It's important that you have a fuse on the AC input line (hot wire) to protect the machine overall. we will cover this in more detail in our guide to fuses, but using default values of 8A for 120V countries and 5A for 240V countries is probably fine.

As we just mentioned above, we like a standalone fuse holder for your AC line fuse so that it's not accessible from the outside of the machine. You could choose to mount this through your power box cover (like in the diagram above), or you could get a surface-mount style fuse holder and screw it into the backbox plywood. (Again just keep it under the power box cover.)

Connect the black (hot) wire from your IEC socket to one of the lugs on your fuse holder.

Fuse and AC power switch: which order?

There's been some discussion around what's the "correct" order for the switch and fuse? Line in to fuse to switch? Or line in to switch to fuse? There are pros and cons to each, and again different jurisdictions and inspectors have different views on this. (Bottom line those is either is probably fine for your machine.)

The thinking for putting the switch first is that way when the switch is off, everything is off, and you don't have to worry about trying not to touch a fuse piece since everything is off. On the other hand, people could argue that the fuse should be first so that if it blows, everything is now unpowered, which should also include the switch. Again it probably doesn't matter. In our drawings we do AC line, then switch, then fuse.

AC power switch

Next you need to pick a switch to interrupt the main AC high voltage incoming power. The exact switch you select will depend on whether you are going to use the soft-start power option or you will use a traditional switch.

If you are NOT using the soft start power switch option, then this switch is your main switch

If you are NOT using the soft start option, then mount this switch through your backbox so it's accessible from the outside. This is how people will turn on your machine. Any simple rocker switch will do, just make sure it's rated for the voltage and current you machine will need. (There are lots of switches with ratings like 15A 250V AC, which is plenty.)

Connect the free lug of your AC line fuse holder to one of the AC switch lugs. (You can also use an all-in-one IEC input + fuse + EMI filter + switch combo.)

If you will use the soft start option

If you're planning to use the soft start option, then you want to find a three-way (ON-OFF-ON) SPDT switch. You'll mount it in a way that is NOT accessible from the outside of the machine. (So maybe mount it so it sticks out of the cover of your power box?) This switch will control the following three modes of operation for three switch positions:

  • ON Machine is "always on", meaning when it's plugged in, it's on, and unplugging the machine turns it off. This is the mode used in many arcades where a whole row of machines are powered on or off by flipping a breaker. In this switch position, the low power main pushbutton switch under the cabinet won't do anything.

  • OFF Machine is "always off", meaning it won't turn on even if it's plugged in and the front power button is pushed. This is great for taking a machine out of service since curious members of the public wouldn't be able to turn it on just to see if it's "really broken".

  • SOFT Machine power is controlled via the "soft" low power pushbutton switch in the right front underside of the cabinet. This position utilizes the solid state relay and is what allows that switch to be in the cabinet while all your AC high voltage power stays in the backbox.

For now you can choose just to wire up the ON/OFF positions, and you can add the SOFT position wiring later when you get your solid state relay.

In this case, connect the free lug of your AC line fuse holder to the "common" lug of your SPDT switch. (This is probably the center lug but check your switch docs or use your meter to confirm.)

48-volt and 12-volt power supplies

Now that you have filtered, switched, and fused AC coming in, the next step is to connect it to your power supplies. (We often use the acronym PSU, which technically means "power supply unit".)

As mentioned already, FAST Neuron-powered pinball machines only require 48-volt and 12-volt supplies and do NOT require 5-volt power supplies. The reason for this is that 5 volts is difficult to distribute throughout your machine due to it being low voltage yet high current, so it's particularly susceptible to voltage drops from wiring and connector resistance. Therefore the various FAST boards which need 5 volts (like for the LEDs) are connected to the 12-volt power system and use that to locally generate their own clean 5-volts.

If you have a combo 12V/5V supply from a previous project, you can still use it, you just won't need the 5 volt output. (If you do this, DO NOT use the 5 volt output. You do NOT want to mix-and-match 5 volts from a power supply with the local 5 volts each board generates.)

Selecting power supplies

We sell 48-volt and 12-volt power supplies in the FAST shop which should be fine for a typical pinball machine. However if you want to source your own power supplies, we have an entire guide choosing the right power supplies for your pinball machine.

We cannot overstate how important it is to select appropriate power supplies. This is not a scenario of "just pull out whatever you have in your drawer". The guide to choosing power supplies discusses current ratings, failure modes, why it's important to choose switching supplies, inrush current, etc.

Mounting your power supplies

You'll most likely screw your power supplies to the plywood of the back of backbox. (Read the next few sections first, as you'll need to run a ground braid under them first.) You'll need to decide if you want to enclose the entire power supply under your power box cover, or just the high-voltage connector terminals.

Part of this decision will be based on what clearances and air circulation requirements your specific power supply has. The concern is you don't want to pack your power supplies too close together and then cover up their vents with your power box cover, as that could cause them to overheat. (The good news is that most supplies, as we discuss in our selection guide, simply turn off when they overheat, so this can be a problem you don't have to solve unless you need to.)

Connecting wires to your power supplies

Power supply wiring is pretty straightforward. They have three AC input connections, typically labeled "L" (line, or hot), "N" (neutral), and "G" or the ground symbol for AC ground. Then they have DC outputs, which is just positive (usually labeled something like "+V) and negative (labeled "-V" or "C" or "COM" for common). So your AC wires go in one side, and your DC wires come out the other side.

Run a black hot wire from your AC switch to the line or hot input terminal on each power supply. You can simply connect from the switch to one power supply, then use a second wire on that same terminal from one power supply to the other.

The green ground wire and white neutral wire can be run directly from your AC line input socket directly to your two power supplies.

Connecting multiple power supplies

Since you'll have two power supplies, you'll have connect the hot, neutral, and ground lines from your AC line in to both. The diagram at the top of this guide shows a daisy-chain connection from the first PSU to the second. (Just note that each wire has its own fork connector crimped to it, with two connectors attached to each screw terminal. This is totally fine.)

Some people don't like this idea and instead prefer to run each of the three AC lines (hot, neutral, and ground) to their own breakout terminal connectors, and then run dedicated branch lines to each PSU. That's fine too. Here's a drawing showing how this would look with lever wire connectors. You could also use screw terminal barrier strips or some other approved method for connecting multiple high voltage wires inside of appliances. Just keep everything you do here under the protective cover of your power box.

Measuring power supply voltage might be weird at this point

If you measure the DC output voltage of your power supply, you might find that it's not accurate and cannot be adjusted to an accurate range when the PSU is not loaded. (e.g. when there's nothing connected to it.) This is expected, as the voltage regulators in many switching power supplies need a load to get the voltage dialed in. So don't be surprised if you see 13+ volts on your 12V, or over 50V from the 48V DC output with no load.

Once you connect your supply to your power filter board and through all the connectors, that will provide enough load and your power supply should regulate itself properly. In the future when you're verifying voltages, you'll want to measure from the output side of the smart power filter board so you can see the voltage that's actually being delivered to your machine. Measuring at the PSU output doesn't really tell you anything.

Next steps

By this point, you have power supplies wired up to receive AC power. In the next guide, we'll look at wiring up the pieces for the soft start option. Then we'll cover earth ground wiring and look at the smart power filter board wiring and fuse values. After these first five guides, you can start wiring your actual pinball components!

Shopping list for this step

  • 16ga stranded wire in black, white, and green.
  • Fork crimp connectors for wires
  • IEC line input receptacle + EMI filter
  • Fuse holder
  • SPDT switch, rated for AC power. (Most are 250V / 10A rated which is great.)
  • 48-volt power supply
  • 12-volt power supply
  • Power cord

Documentation Feedback? Requests? Confused?

Hi! I'm Brian, and I'm responsible for the documentation at FAST Pinball. If you have any feedback, requests, corrections, ideas, or any other thoughts about this documentation, please let me know! You can email me at Thanks!

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