Electrical Estimator

What it does

A page with two tools. The first is a load and circuit estimator that sizes branch circuits, breakers, wire and conduit and adds up material, labor, permit and tax costs. The second is a voltage-drop calculator for a single run, which describes itself as a planning estimate, not a code-compliance determination.

When to use it

Use it to rough out branch circuits and installed cost for grow-room lighting fixtures and HVAC units, and to check voltage drop and ampacity on a single feeder run.

How it calculates

• Fixtures per 20 A circuit = floor(V × 20 A × 0.8 ÷ fixture W). The breaker is the next standard size at or above 125% of circuit current
• Wire is the smallest THHN copper size whose 75°C ampacity is at least 125% of the current and whose voltage drop (2 × L × R × I ÷ 1000) is within 3% of system voltage. Conduit size is looked up from the wire size
• Total = materials (wire, conduit, breakers, panel, connectors, 15% misc) + labor hours × rate + permits, then markup and state sales tax
• Voltage drop VD = 2·I·L·Z ÷ (1000·N) for single-phase or √3·I·L·Z ÷ (1000·N) for three-phase, where Z = R·PF + X·sinθ and R is temperature-corrected. Ampacity is derated for ambient temperature and conductor count

What you enter

Location(state)

System Voltage (V) and Phases

Wire Run Distance(ft)

Labor Rate ($/hr) and Markup (%)

Fixture schedule: watts and quantity

HVAC units: voltage, MCA, MOCP and quantity

Load Current (A) and Power Factor

One-Way Distance(ft)

Conductor type, conductor size and conduit type

Ambient temperature, current-carrying conductors, parallel runs and electricity cost

What you get

Materials, labor, permits, markup, tax and total($)

Circuit summary(breaker and wire per circuit)

NEC compliance issues and recommendations

Voltage Drop(V and %)

Voltage at Load(V)

Power Loss (W) and annual loss cost ($/year)

3% branch-circuit and 5% feeder guideline checks

Recommended conductor size

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