Yes, Steve, it was likely a mistake to run the printer circuit in the same conduit as the office lighting circuit, and the blinking lights are a good indication of why. Here's a breakdown of the potential problems and why it's happening

Why the Lights Are Blinking:
Voltage Drop

When the printer starts, it likely draws a surge of current. This sudden increase in current flow causes a voltage drop along the conductors in the conduit. Because both the lighting circuit and the printer circuit are using the same neutral conductor, the voltage drop affects both circuits. Your lights are blinking because the voltage to them is momentarily dipping below the level where they can maintain consistent brightness.

Neutral Conductor Overload (Potentially)

The neutral conductor in a circuit is designed to carry the unbalanced current between the hot and neutral conductors. If the lighting and printer circuits are heavily loaded, the shared neutral could be overloaded, leading to voltage fluctuations and potential overheating. Although this is less likely with an LED lighting installation than with older flourescent lights.

Harmonics

Printers and other electronic devices can generate harmonic currents. These currents can distort the voltage waveform on the neutral conductor and cause problems with other equipment connected to the same circuit. This is more of a concern in larger electrical systems with many nonlinear loads, but it's a potential contributor.

Improper Grounding

While less likely to cause blinking, inadequate grounding can exacerbate voltage fluctuations and make the system more sensitive to load changes.

Why Sharing Conduit Can Be a Problem



Load Diversity

Lighting circuits are typically designed for a fairly steady load. Printers, on the other hand, have very intermittent loads with large current spikes. Mixing these types of loads on the same circuit is generally not a good practice.

Code Compliance

Depending on your local electrical code (NEC in the US, CEC in Canada, etc.), it may not be permissible to mix lighting and receptacle circuits in the same conduit, especially if they serve different functions or areas.

Troubleshooting

When you have multiple circuits sharing a conduit, it can make troubleshooting electrical problems more difficult.

What You Should Do


Assess the Situation



Check the breaker sizes

Make sure the breakers for both the lighting and the printer circuits are sized appropriately for the wire gauge and the load they are serving.

Check the wire gauge

Is the wire gauge appropriate for the breaker size and the length of the run?

Examine the connections

Ensure all connections in the panel, junction boxes, and receptacles are tight and clean. Loose connections can cause voltage drops and overheating.2.

Ideally, Run a Dedicated Circuit

The best solution is to run a completely separate circuit for the printer from the electrical panel, using a different conduit or a new run of cable. This will isolate the printer's load from the lighting circuit and prevent the blinking issue.3.

Consider a Different Neutral

If running a new conduit is difficult, you might be able to run a new neutral conductor back to the panel within the existing conduit, but only if there's enough space and the existing wires aren't too crowded. This will at least isolate the return current for the printer, but it's not as good as a completely separate circuit.

Make sure this is code compliant in your area and you are properly trained to do this.4. Check for Grounding Issues

Verify that the grounding system is properly installed and that all grounding connections are secure.5.

Consult an Electrician

If you're not comfortable with any of these steps or if the problem persists after making adjustments, it's best to consult with a licensed electrician. They can properly assess the situation, identify any code violations, and recommend the best course of action.

Important Considerations



Safety

Always prioritize safety when working with electricity. Turn off the power at the breaker before working on any electrical components. If you are not comfortable working with electricity, hire a qualified electrician.

Code Compliance

Ensure that all electrical work complies with your local electrical code.*

Future Growth: Consider the future electrical needs of the office when planning electrical upgrades. It's often better to over-prepare than to have to make changes later.In summary, while it might have seemed like a convenient solution to run the printer circuit through the existing conduit, it's causing problems with the lighting due to voltage fluctuations. The best solution is to run a dedicated circuit for the printer. If that's not feasible, explore other options with the help of a qualified electrician. Flag for review