How to use this calculator
- Enter one-conductor ampacity. Use the base ampacity per conductor from the adopted table, equipment listing, manufacturer data or project schedule before correction factors.
- Set parallel paths. Enter the number of same-phase conductors carrying the load in parallel.
- Apply correction factors. Enter ambient correction, conductor-count adjustment and any other project derating factor.
- Set terminal and sharing limits. Enter the terminal cap for one conductor and any conservative allowance for uneven current sharing.
- Compare against design load. Use total usable ampacity, per-path current, utilization and margin to decide whether the selected arrangement still clears the screen.
How it works
Start with the entered ampacity of one conductor. Apply the same correction and adjustment factors you would use for that conductor path: I_adj_each = I_base_each x F_temp x F_count x F_other Then cap that value by the entered terminal or equipment limit and apply any current-sharing allowance: I_use_each = min(I_adj_each, I_term_each) x F_share
The parallel total is the usable per-conductor value multiplied by the number of parallel paths: I_use_total = I_use_each x N_parallel The design load is still the entered load current multiplied by the load multiplier: I_design = I_load x M_load The result reports total ampacity, per-conductor current, design utilization, remaining margin and maximum load current under the same multiplier.
Use this after the per-conductor ampacity and parallel-path layout are known. The parallel conductor ampacity worksheet captures the same derating, terminal-cap and current-sharing workflow for exact search wording. For single-path derating, use the ampacity derating calculator. For long feeders, run the voltage drop calculator. Then check conduit fill, equipment grounding conductor size and pull tension for the same route.
Worked example
Verified against the live calculator
Suppose one conductor has a base ampacity of 115 A, the ambient
factor is 0.91, the conductor-count factor is 0.80,
no other derating applies, and two parallel paths are used. The adjusted
per-conductor ampacity is 115 x 0.91 x 0.80 = 83.72 A. With a
115 A terminal cap and 100% sharing allowance, total
usable ampacity is 83.72 x 2 = 167.44 A. A 130 A
load at a 125% multiplier needs 162.5 A, leaving
about 4.94 A of margin in this arithmetic screen.
Reference data
This page intentionally does not publish conductor ampacity tables or parallel-conductor permission rules. Enter the governing per-conductor ampacity, factors and equipment limits from the adopted source, then use this calculator for the multiplier and margin arithmetic.
| Input | Role |
|---|---|
| Base ampacity per conductor | User-entered table, listing or schedule value before correction/adjustment. |
| Parallel paths | Number of same-phase conductors carrying load in parallel. |
| Ambient correction factor | Temperature correction factor from the adopted source. |
| Conductor-count factor | Adjustment for current-carrying conductors in the raceway, cable or bundle. |
| Terminal cap per conductor | Upper limit from terminal or equipment temperature rating. |
| Current-sharing allowance | Optional conservative allowance for uneven path current. |
Source: User-entered values from the adopted electrical code, equipment listing, manufacturer data or project schedule.
Frequently asked questions
What is parallel conductor ampacity?
Parallel conductor ampacity is the combined current capacity of multiple same-phase conductors sharing the load. This calculator starts with the ampacity of one conductor, applies the derating factors you enter, limits each path by the terminal cap, applies any current-sharing allowance, then multiplies by the number of parallel paths.
Does this calculator choose a conductor size?
No. It does not publish ampacity tables or decide which conductors may be paralleled. Enter the per-conductor ampacity, factors and terminal limits from the adopted code edition, equipment listing, manufacturer data or project schedule.
How do derating factors apply to parallel conductors?
The calculator applies ambient correction, current-carrying conductor adjustment and any other entered factor to one conductor first. It then multiplies the usable per-conductor ampacity by the number of parallel paths.
What is current-sharing allowance?
Current-sharing allowance is an optional conservative multiplier. Use 100% when the parallel paths are designed and installed to share evenly. Lower it when you need to reserve capacity for uneven length, termination, impedance or layout concerns.
Is this a code-approved parallel feeder design?
No. It is an arithmetic screen. Final work still needs the adopted electrical code, local amendments, equipment instructions, conductor material/size/length checks, raceway conditions, overcurrent protection, grounding and qualified review.
Method & assumptions
- Uses user-entered per-conductor base ampacity and user-entered derating factors; it does not select a wire size.
- Assumes the entered parallel paths are allowed by the adopted rules and are intended to share current evenly unless you reduce the sharing allowance.
- Uses the smaller of derated per-conductor ampacity and the entered terminal/equipment cap before multiplying by parallel paths.
- Does not size overcurrent protection, grounding, neutral conductors, parallel-conductor eligibility, conductor length matching, raceway grouping, fault current or permit-ready installations.
- Final work needs the adopted code edition, local amendments, listed equipment instructions and qualified electrical review.