Skip to content
Open calculators

Distribution Panel Load, Headroom, and Phase Balance Estimate

Summarizes measured phase currents against separately entered panel bus and main overcurrent-device ratings. It also estimates phase balance and a maximum-phase equivalent kVA. This is an arithmetic screening tool, not an Article 408 rating, SCCR, or feeder/service compliance determination.

Inputs

Panel measured load and nameplate ratings

For single-phase panels, enter the load in Phase A and set B/C to zero.

Range: 1–100,000

Use the measured or nameplate nominal voltage at the panel. For three-phase systems, enter line-to-line voltage; this screen does not infer line-to-neutral voltage.

Range: 0–100,000 A

Use a same-time measured RMS current or a documented design current for Phase A. Do not combine readings from different operating states.

Range: 0–100,000 A

Use a same-time measured RMS current or a documented design current for Phase B. Do not combine readings from different operating states.

Range: 0–100,000 A

Use a same-time measured RMS current or a documented design current for Phase C. For single-phase use, enter zero as documented by the calculator instructions.

Range: 0.001–100,000 A

Enter the equipment nameplate bus rating. This is not the same as available fault current or the main OCPD rating.

Range: 0.001–100,000 A

Enter the installed or proposed main breaker/fuse rating for an arithmetic comparison only.

Result

Average phase current (A)
75.00
Arithmetic bus headroom (A)
20.00
Maximum phase vs bus rating (%)
80.00
Maximum deviation imbalance (%)
6.67
Arithmetic main-device headroom (A)
20.00
Maximum phase vs main rating (%)
80.00
Maximum deviation from phase average (A)
5.00
Maximum entered phase current (A)
80.00
Maximum-phase equivalent apparent load (kVA)
66.51
Scope and limitation
Arithmetic screening only. Verify the adopted NFPA 70 Article 408 requirements, feeder/load calculation, available fault current, SCCR, conductor ampacity, equipment listing, and AHJ amendments before design or approval.
Maximum entered phase current (A)
\operatorname{max}(\mathrm{Measured\ or\ calculated\ Phase\ A\ current\ (A)},\mathrm{Measured\ or\ calculated\ Phase\ B\ current\ (A)},\mathrm{Measured\ or\ calculated\ Phase\ C\ current\ (A)})
\operatorname{max}(80,75,70)
Average phase current (A)
\begin{cases}\frac{\mathrm{Phase\ Sum\ A}}{3}&\text{if }\mathrm{Panel\ phase} = \mathrm{3}\\\mathrm{Measured\ or\ calculated\ Phase\ A\ current\ (A)}&\text{otherwise}\end{cases}
\begin{cases}\frac{225}{3}&\text{if }\mathrm{3} = \mathrm{3}\\80&\text{otherwise}\end{cases}
Maximum deviation imbalance (%)
\begin{cases}0&\text{if }\mathrm{Panel\ phase} = \mathrm{1} \lor \mathrm{Average\ phase\ current\ (A)} = 0\\\frac{\mathrm{Maximum\ deviation\ from\ phase\ average\ (A)}}{\mathrm{Average\ phase\ current\ (A)}} \cdot 100&\text{otherwise}\end{cases}
\begin{cases}0&\text{if }\mathrm{3} = \mathrm{1} \lor 75 = 0\\\frac{5}{75} \cdot 100&\text{otherwise}\end{cases}
Arithmetic bus headroom (A)
\mathrm{Panel\ bus\ rating\ (A)} - \mathrm{Maximum\ entered\ phase\ current\ (A)}
100 - 80
Maximum phase vs bus rating (%)
\frac{\mathrm{Maximum\ entered\ phase\ current\ (A)}}{\mathrm{Panel\ bus\ rating\ (A)}} \cdot 100
\frac{80}{100} \cdot 100
Arithmetic main-device headroom (A)
\mathrm{Main\ overcurrent\-device\ rating\ (A)} - \mathrm{Maximum\ entered\ phase\ current\ (A)}
100 - 80
Maximum phase vs main rating (%)
\frac{\mathrm{Maximum\ entered\ phase\ current\ (A)}}{\mathrm{Main\ overcurrent\-device\ rating\ (A)}} \cdot 100
\frac{80}{100} \cdot 100
Maximum-phase equivalent apparent load (kVA)
\frac{\mathrm{Maximum\ entered\ phase\ current\ (A)} \cdot \mathrm{Nominal\ panel\ voltage\ (V;\ line\-to\-line\ for\ three\-phase)} \cdot \mathrm{Phase\ Factor}}{1000}
\frac{80 \cdot 480 \cdot 1.7320508075689}{1000}

Related calculators

Screening tool. Verify the adopted NFPA 70 edition, AHJ requirements, nameplate data, and project conditions before use.