Okay, let's break down the scenario and address the potential code violations

Understanding the Components
Main Electrical Panel

The primary service entrance for the building's electrical power.

Subpanel

A distribution panel fed by the main panel, providing additional circuit capacity.

Gutter (Wireway)

A metal enclosure used to protect and route conductors. It's not intended as a primary splicing location for entire circuits, though limited splicing is permitted under specific conditions.

Romex (NM-B Cable)

Non-metallic sheathed cable commonly used for residential wiring. It includes insulated conductors and a bare equipment grounding conductor (EGC).

THHN Wire

Thermoplastic High Heat-resistant Nylon-coated wire, typically used inside conduit. It's a single-conductor type of wire.

EGC (Equipment Grounding Conductor)

Connects non-current-carrying metal parts of equipment (like the subpanel enclosure) back to the grounding system. Its purpose is to provide a low-impedance path for fault current to safely trip a breaker or fuse, protecting people from electric shock.

GEC (Grounding Electrode Conductor)

Connects the grounding system (e.g., ground rods, water pipe) to the service equipment (usually the main panel). Its purpose is to stabilize the voltage to earth during normal operation and to provide a path for fault current in the event of a ground fault.

Busbar

A conductive bar used for making electrical connections, often for neutral or ground conductors.

Issues and Potential Code Violations

Based on your description, here are the main concerns:1. Improper Splicing in Gutter



NEC 314.28(A) Splices and taps shall be permitted within a raceway that is accessible throughout its entire length and meet the following conditions

The NEC permits splicing in raceways, but they must be accessible. However, it's typically not intended for splicing entire circuits like you've described. It sounds like the gutter is being used as a junction box, which is not its primary purpose. Using a larger junction box would have been more appropriate.

NEC 312.8 In enclosures for switches or overcurrent devices, or control devices, splicing, tapping, or feeding through conductors shall not be any more than 40% of the cross-sectional area of the wiring space of the enclosure. You can not splice in a panel to free up space.2.

Mismatched Wire Types

The transition from Romex (NM-B) to THHN within the gutter raises questions. While permitted under certain conditions, it's crucial that the connections are properly made and protected. The transition from Romex to individual THHN conductors is typically done within an approved junction box with appropriately sized and rated connectors.

NEC 300.3(B) Conductors of Different Systems: Conductors of alternating current (AC) and direct current (DC) circuits, rated 600 volts or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. So the voltage is not an issue.3.

Grounding Electrode Conductor (GEC) and Equipment Grounding Conductor (EGC) Combined

This is a serious issue. The EGC must run with the circuit conductors (the hots and neutral) back to the source (main panel in this case). The GEC is separate and connects the grounding system to the service equipment.

You cannot simply use the GEC as the EGC for the subpanel.

NEC 250.24(A)(5) says: The grounded conductor (usually the neutral) shall not be connected to normally non-current-carrying metal parts of equipment, raceways, and other enclosures on the load side of the service disconnecting means. NEC 250.24(B) says: Where an ac system operating at 1000 volts or less is grounded at any point, the grounded conductor shall be run to each service.

NEC 250.64(C) requires the grounding electrode conductor (GEC) to be continuous or spliced by irreversible compression-type connectors or by the exothermic welding process.4.

Oversized Ground Wire

While using a larger ground wire isn't inherently unsafe, it's often unnecessary and doesn't compensate for other grounding issues. The EGC size is determined by the overcurrent device protecting the circuit (see NEC Table 250.122). Using a much larger EGC might indicate an attempt to compensate for a long run, but it's better to address the voltage drop with appropriately sized circuit conductors (hots and neutral).
5.

Workmanship

Improperly executed wiring practices can lead to loose connections, overheating, and potentially fire hazards.

Why Combining EGC and GEC is a Problem

Fault Current Path

The EGC provides a low-impedance path for fault current to quickly return to the source and trip the breaker/fuse. This fast trip minimizes the duration of a fault, reducing the risk of shock and fire. A combined EGC/GEC may not provide as reliable and low-impedance path as a dedicated EGC running with the circuit conductors.

Stray Currents

The GEC is connected to earth. If you connect the EGC to the GEC, you're potentially introducing earth currents onto the equipment grounding system. This can create objectionable neutral-to-ground voltage and potentially interfere with sensitive electronic equipment.

What Needs to Be Done1.

Correct the Grounding



Separate EGC

A properly sized EGC (based on the circuit's overcurrent protection) must be run with the THHN conductors from the subpanel back to the main panel. Terminate the EGC on the grounding busbar in the main panel.

Dedicated GEC

The GEC should run from the grounding system (ground rods, water pipe, etc.) directly to the main panel's grounding busbar.2.

Re-evaluate the Splicing

The gutter is likely being used beyond its intended purpose. Splicing entire circuits in a gutter is generally not best practice and may violate code. Consider using a properly sized junction box for the splices instead. Ensure all splices are made with appropriately sized and rated connectors. Make sure the transitions from Romex to THHN are done correctly within an approved enclosure.3.

Ensure Proper Bonding

The subpanel enclosure needs to be properly bonded to the EGC.4.

Consult with a Qualified Electrician

This situation requires immediate attention from a licensed and experienced electrician. They can properly assess the installation, identify all code violations, and make the necessary corrections to ensure the system is safe and compliant.

In summary, the described installation sounds like it has significant grounding and wiring issues that need to be addressed immediately by a qualified electrician.

Do not attempt to fix this yourself if you are not a licensed electrician. Incorrect wiring can be extremely dangerous. Flag for review