You're on the right track, but there are some crucial nuances, especially when dealing with a high-leg delta service and ensuring proper phase balancing. Let's break it down and clarify.

Understanding the High-Leg Delta Challenges



Phase Imbalance

High-leg delta services are inherently unbalanced. Phase B (the high leg) has a higher voltage to ground (208V), while phases A and C have 120V to ground. This means careful load balancing is even more critical.

Neutral Loading

Unbalanced 120V loads contribute to neutral current. This is important for sizing the neutral conductor and avoiding overheating.

Your Approach - Refined


Individual Panel Calculations are Correct, with Adjustments



3-Phase Panel (mostly 3-phase and 1-phase 240V loads)

Your calculation is correct for determining the total current draw,

but you need to further break it down by phase to ensure balance on the service. Calculate the total kVA for the 3-phase loads. You can use the formula you provided: `I = (kVA x 1000) / (240 x √3)` This gives you the current per phase for the 3-phase load. Assign this current equally to phases A, B, and C. Calculate the kVA for each 1-phase 240V load. `I = (kVA x 1000) / (240)` This gives you the current. Crucially, note which two phases each 240V load is connected to (A-B, B-C, or A-C). Assign the current to those two phases. For example, a 240V load connected A-B would add current to phase A and phase B. 1-Phase Panel (120/240V with 120V loads)

Your calculation is correct for determining the total current draw of the panel. `I = (kVA x 1000) / (240)`.

The critical step is to determine which PHASE is supplying the 120V loads. This is where the high-leg becomes tricky. 120V Loads off the A-N Leg

The line to neutral voltage is 120V. These 120V loads only go on Phase A.

120V Loads off the C-N Leg

The line to neutral voltage is 120V. These 120V loads only go on Phase C.

IMPORTANT: DO NOT USE THE HIGH LEG (PHASE B) FOR 120V LOADS. This is a major no-no in high-leg delta systems. There is no neutral available to reference from the high leg (phase B).2. Summing the Phase Loads, Not Just the Totals

This is where the nuance comes in.

Calculate the total current on each phase (A, B, and C) at the service. For each phase, add up the current contributions from: The 3-phase loads (equally distributed) The 240V single-phase loads (based on which phases they connect to) The 120V single-phase loads (only on Phase A or Phase C) Example

Phase A: (Current from 3-phase) + (Current from A-B 240V loads) + (Current from A-C 240V loads) + (Current from A-N 120V loads) Phase B: (Current from 3-phase) + (Current from A-B 240V loads) + (Current from B-C 240V loads) Phase C: (Current from 3-phase) + (Current from A-C 240V loads) + (Current from B-C 240V loads) + (Current from C-N 120V loads)3.

Demand Factors and Diversity

After you've calculated the total current on each phase, you can apply demand factors and diversity factors as allowed by the NEC and local codes. These factors account for the fact that not all loads will be operating at their maximum at the same time. This is critical to avoid oversizing the service. Different load types (lighting, HVAC, motors, etc.) have different demand factors. Consult NEC Article 220 and local amendments.4.

Calculating the Service Size

The service needs to be sized to handle the

maximum current on any one of the three phases after applying demand factors. You need to calculate the minimum service size for: Ampacity of the ungrounded (hot) conductors

The maximum of phases A, B, and C after demand factors.

Ampacity of the neutral conductor

This is the most complex. It depends on the amount of unbalanced neutral current, which is largely determined by the 120V loads. NEC 220.61 has specific rules for neutral load calculations. You must account for the neutral load carefully.

In summary



Don't assume simple addition of panel totals. You must track the phase connections. Pay very close attention to the neutral current. High-leg deltas can have substantial neutral current if the 120V loads aren't balanced. Consult the NEC and local codes for demand factors and neutral load calculations. Consider using a load calculation software tool. These tools automate the process and help prevent errors.

Important Considerations for High-Leg Delta



Wiring Color Code

The high leg (Phase B) must be identified with orange tape or markings everywhere in the system.

120V Load Distribution

Strive to balance the 120V loads (A-N and C-N) as evenly as possible to minimize neutral current.

Code Compliance

Ensure that the installation complies with all applicable codes, including NEC Article 220 and any local amendments. High-leg delta systems have specific requirements.

Professional Expertise: If you're not experienced with high-leg delta systems, consult with a qualified electrical engineer or master electrician. Improper installation can be dangerous.This is a complex topic. Take your time, consult the NEC, and consider seeking professional guidance. Good luck! Flag for review