Okay, let's break down your transformer installation and the application of NEC 240.21(C)(1) to ensure you're on the right track. Your understanding is mostly correct, but let's clarify a few key points and perform the necessary calculations to confirm compliance.

Understanding Your Setup 14 kVA Transformer

208 Delta primary, 480Y/277 secondary. This is a standard configuration.

Primary Protection

40A breaker at the panel (presumably 208V).

Primary Disconnect

Immediately before the transformer. Good practice.

Secondary Conductors

#12 AWG.

Single Load

13.6A (max) forklift charger located within 5 feet of the transformer.

NEC 240.21(C)(1) - Secondary Conductor Taps Without Overcurrent Protection at the Tap

This section allows you to tap secondary conductors from a transformer without secondary overcurrent protection at the transformer, under specific conditions. Here's a summary of the relevant requirements for your situation: (1) Tap Conductors Not Over 10 Ft Long

Your conductors are less than 5 feet, so this is met.

(2) Ampacity of the Tap Conductors

The tap conductors must have an ampacity that is: Not less than the calculated load.

Not less than 1/3 of the rating of the overcurrent device protecting the primary side of the transformer. (3) The Tap Conductors are Protected from Overcurrent by a Single Overcurrent Protective Device

This means that, in the event of an overload, the overcurrent protective device protecting the primary side will adequately provide overcurrent protection.

(4) Tap Conductors Do Not Extend Beyond the Equipment They Supply

This is essentially saying that you can't just tap these conductors and run them somewhere else to feed other loads. The tap conductors must run to a single device.

Your Calculations and Analysis

Let's revisit your calculations and ensure accuracy: Transformer Primary Current (Full Load)

kVA = (Volts Amps √3) / 1000 14 = (208 Amps √3) / 1000 Amps = (14 1000) / (208 √3) = 38.85 A

Your Primary OCPD (40A) is sized appropriately. You are within the limits in 450.3(B) Transformer Secondary Current (Full Load)

kVA = (Volts Amps √3) / 1000 14 = (480 Amps √3) / 1000 Amps = (14 1000) / (480 √3) = 16.83 A

Load Calculation

Forklift Charger: 13.6A 1.25 = 17A. This is the minimum ampacity your secondary conductors must have, according to 210.20(A)

Verification of 240.21(C)(1) Requirements1. Length

< 5 ft (Meets the <10 ft requirement)2.

Ampacity

This is where we need to be careful.

Calculated Load

17A

1/3 of Primary OCPD

(40A) / 3 = 13.33AYour #12 AWG conductors have an ampacity of 20A in accordance with 310.16. However, per 240.21(C)(1)(2), the ampacity of the conductors must be greater than both the calculated load, and 1/3 the size of the primary overcurrent protection device. In your example, the calculated load is 17a, and 1/3 of the 40a primary breaker is 13.33a. As such, using the minimum size conductors allowed in accordance with 310.16 will not meet the requirement in 240.21(C)(1)(2). I would advise to upsize your conductors to #10 which have an ampacity of 30A. By doing so, you will now have conductors sized larger than both the calculated load, and 1/3 the size of the primary breaker.
3.

Single OCPD Protection

The primary OCPD will provide protection in the event of an overload.4.

Single Load

The tap conductors run directly to the forklift charger, and do not supply any other loads.

Conclusion and Recommendation

You are correct that, based on your described scenario and if all the conditions of NEC 240.21(C)(1) are met, you are NOT required to have an overcurrent protection device (breaker or fuses) on the secondary side of the transformer at the transformer. However, you should upsize the secondary conductors to #10 in order to meet the minimum requirements in 240.21(C)(1)(2).

Important Considerations



Local Codes

Always verify with your local electrical inspector for any specific local amendments or requirements that might supersede the NEC.

Transformer Nameplate

Make sure the actual kVA and voltage ratings on the transformer nameplate match your calculations and the connected loads.

Short-Circuit Protection

While 240.21(C)(1) focuses on overload protection, ensure that the primary overcurrent device will also provide adequate short-circuit protection for the transformer. This is usually addressed through the transformer impedance and the breaker's interrupting rating.

Disconnect: You are correct that a disconnect will not be required on the secondary as the forklift charger can be disconnected with a cord and plug connection.By carefully following these guidelines and verifying your work with a qualified electrician and local authorities, you can ensure a safe and code-compliant transformer installation. Flag for review