Let's break down the NEC requirements to determine if you need a main breaker in your 125A panel. This revolves around NEC 240.21(C)(2) - 10-Foot Tap Rule.Here's a step-by-step analysis:1. Transformer Secondary Conductor Ampacity

First, we need to calculate the ampacity of the secondary conductors from the transformer to the 125A panel. The transformer is 25 kVA with a 240V secondary. kVA to VA: 25 kVA 1000 VA/kVA = 25000 VA Secondary Current: 25000 VA / 240 V = 104.17 AmpsTherefore, the secondary conductors must be rated for at least 104.17 Amps.
2.

240.21(C)(2) - 10-Foot Tap Rule Requirements

This rule allows a tap from a transformer secondary without overcurrent protection at the tap point, provided specific conditions are met:

(1) Length

The tap conductors cannot exceed 10 feet in length. You state your run is 5 feet, so this requirement is met.

(2) Ampacity

The tap conductor ampacity must be at least: Not less than the calculated load Not less than the overcurrent protective device from which the tap is made (2p50A breaker)

(3) Enclosed in raceway

The tap conductors must be enclosed in a raceway (conduit).

(4) Overcurrent Protection Location

The tap conductors must terminate in a single overcurrent protective device (OCPD) that is rated for not more than the conductor's ampacity. This is the key condition here.3.

Applying 240.21(C)(2) to Your Situation



Length

The 5-foot distance meets the length requirement.

Ampacity

You'd need conductors rated for at least 50 amps (based on the 2p50a primary breaker) and at least 104.17 amps (based on the secondary load).

Since this panel is rated 125A, the conductors are likely rated to 125A or above, thus meeting this requirement Raceway

Assuming your conductors are in a raceway, this is met.

Overcurrent Protection

This is the determining factor. The 125A panel with individual breakers, without a main breaker, acts as your single overcurrent protective device.4.

Do you need a Main Breaker? Likely YES.

The 10' tap rule requires the panel to be protected by a single overcurrent device not more than the ampacity of the conductors. The absence of a main breaker makes this not a single overcurrent protection device.

Important Considerations



Conductor Size and Ampacity

Verify that the conductors from the transformer to the 125A panel are sized appropriately (at least 104.17A, but likely higher). Using a conductor table like NEC 310.16 (or similar based on your conditions) to confirm the ampacity.

Grounding and Bonding

Ensure proper grounding and bonding throughout the system, including the transformer, panel, and enclosures, according to NEC Article 250.*

Local Codes and AHJ

Always consult with your local Authority Having Jurisdiction (AHJ). They have the final say on code interpretation and may have additional requirements.

In summary, while the 5' distance and other factors point towards potentially using the 10-foot tap rule, the lack of a single main breaker in your 125A panel likely means you are NOT exempt from needing overcurrent protection at the transformer secondary, and a main breaker will be required. Flag for review