The NEC (National Electrical Code) doesn't explicitly limit the number of reducers you can use in a conduit run. However, several rules and practical considerations govern this situation

Key Considerations and NEC Sections:
Fill



NEC 300.17 (Raceway or Cable Tray Systems)

”The number of conductors in a raceway shall not be more than will permit dissipation of the heat and ready installation or withdrawal of the conductors without damage to the conductors or to their insulation." This is arguably the most important. Multiple reducers can create constricted areas that make pulling wire difficult and can potentially damage the insulation.

Conduit Fill Calculation

Each size change requires recalculating the conduit fill to ensure you are not exceeding the allowable percentage as per Chapter 9, Table 1. The smallest conduit section in the run will dictate the maximum allowable fill.

Physical Damage

Too many connections introduce more points of potential failure and physical damage. You want a robust system.

Support

Each reducer adds a potential bending/breaking point to the run. Consider adequately supporting the conduit system to prevent stress on these joints. See

NEC 344.30 for rigid metal conduit support requirements. Pulling Force

Each reducer adds friction during wire pulls. You might exceed the maximum allowable pulling force for the conductors. Using pulling lubricant and considering the run's total length and bends is vital.

Bonding

If metallic conduit is used, you need to ensure proper bonding throughout the entire run, including at each reducer. This is critical for safety and requires proper grounding locknuts or bonding bushings per

NEC 250.92 and NEC 250.96. Practicality/Workmanship (NEC 110.12)

"Electrical equipment shall be installed in a neat and workmanlike manner." While subjective, an excessive number of reducers might be considered poor workmanship, especially if there are better, simpler solutions.

Is Your Example Scenario Acceptable?

Going from 4" to 2" using those four reducers could be acceptable, IF you meet ALL of the following conditions:1. Conduit Fill is Compliant

The 2" conduit must be large enough to handle the number and size of conductors you're installing, according to NEC Chapter 9, Table 1.2.

Pulling Force is Manageable

The wire pull must be feasible without damaging the conductors. Consider pull lengths, bends, and lubrication.3.

Support is Adequate

The conduit system must be properly supported to prevent stress on the reducers.4.

Bonding is Correct (if metallic)

Proper bonding must be maintained at each reducer.5.

Installation is Neat and Workmanlike.Alternatives to Consider



A Single 4" to 2" Reducer

This is the simplest and often the best solution. It reduces the number of connections and potential failure points.

A 4" to 2" Reducing Bushing

A reducing bushing fits inside the larger conduit, reducing the opening. This can be a very compact and clean solution.*

A Junction Box

If the wire count or pulling is an issue, using a junction box to transition from 4" to 2" might be a better approach. This allows you to make the wire splices/terminations in a controlled environment and makes pulling easier.

In summary: While the NEC doesn't strictly limit the number of reducers, practical considerations and compliance with other code sections often dictate whether using multiple reducers is an appropriate and safe solution. Carefully consider conduit fill, pulling force, support, bonding, and overall workmanship. It's usually best to minimize the number of transitions whenever possible. When in doubt, consult with a qualified electrician or inspector. Flag for review