Okay, let's break down this scenario and address the potential violations and best practices.

Regarding the Shared Neutral (White Wires Spliced in J-Box)



This is a serious violation and poses a significant safety hazard. The contractor is essentially trying to create a shared neutral scenario with two circuits that are not operating as a multi-wire branch circuit inside the garage. Here's why it's wrong: Overloaded Neutral

With two 20-amp circuits, it is possible for both circuits to be heavily loaded simultaneously. When both circuits are on the same phase (which they are in this case), the neutral will carry the sum of the current from both circuits. That means the neutral could be carrying close to 40 amps on a wire designed for only 20 amps. This is an overload.

Loss of Neutral

If there's a loose connection or break in the shared neutral anywhere in the circuit (either in the garage or back at the panel), the voltage on the two circuits in the garage will become unbalanced and unpredictable. You could get dangerously high voltages on one circuit (potentially damaging equipment) and very low voltages on the other. This is especially dangerous for sensitive electronics.

Backfeed

If one circuit is heavily loaded while the other is lightly loaded, current can backfeed onto the "off" circuit potentially causing a shock hazard.

NEC References



NEC 300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, cable, trench, cord, or cable armor unless otherwise permitted in accordance with 300.3(B)(1) through 300.3(B)(4). NEC 310.15(B)(3)(a)

addresses the requirements for neutral conductors in multi-wire branch circuits. It is for multi-wire circuits with shared neutrals on different phases not two circuits with the same phase.

Regarding Not Pigtailing Neutral Conductors at Receptacles



Violation and Very Poor Practice



NEC 300.13(B) Continuity of Grounded Conductor. The continuity of a grounded conductor shall not depend on device connections, such as lampholders, receptacles, and so forth, for the interconnection of the grounded conductor conductors to electrically connected equipment enclosure(s). The way the installer has done this is that the continuity of the grounded conductor will depend on the device. Pigtailing grounded conductors is a very important safety practice and is required by code. Reasons for Pigtailing



Maintain Continuity

If a receptacle is removed or fails, the rest of the circuit downstream will still have a solid neutral connection. Without pigtails, removing a receptacle breaks the neutral connection for everything beyond it.

Reduce Fire Hazard

A loose or corroded connection at a receptacle terminal can create resistance, leading to heat buildup and a potential fire hazard. Pigtails allow for a more secure and reliable connection.

Regarding Phase Identification of the Red Conductor



Best Practice/Code

NEC 200.6 addresses this. Since the red conductor is being used as the ungrounded (hot) conductor on one of the circuits, it's a good practice to mark it with black tape at all terminations. It is not specifically required, as long as it is a different color than white or green, but it definitely improves clarity and reduces the chance of future confusion.

Overall Recommendation


Correct the Shared Neutral Immediately

Disconnect the two white conductors from the garage circuits in the J-box. The multiwire home run from the home will need to be split at the home panel into two separate breakers.2.

Pigtail All Neutral Conductors at Receptacles

Go through all the receptacles and lighting fixtures in the garage and ensure that the neutral (white) conductors are properly pigtailed. That is, do not use the receptacle or device as a splice.3.

Correct the wiring by installing a 3 conductor w/ground cable to each receptacle.4. Consider using three-conductor cable throughout the garage. It makes wiring more straightforward and helps ensure that all circuits are properly isolated.

Why This Matters

Electrical safety is paramount. Cutting corners on wiring can have devastating consequences, including electrical fires, shocks, and even death. This is not an area where you want to compromise.

Important



Hire a Qualified Electrician

Given the extent of these violations, it is strongly recommended that you hire a licensed and qualified electrician to inspect and correct the entire wiring in the garage. They can ensure that everything is up to code and safe.*

Contact the Electrical Inspector: If the work was recently inspected, contact the electrical inspector and explain the issues. They will be able to require the contractor to correct the deficiencies.Do not attempt to make these corrections yourself unless you are thoroughly knowledgeable about electrical wiring and code requirements. Flag for review