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The total connected lighting load in the site trailer, in volt-amps.
Sum the volt-amp (or watt) ratings of all lighting fixtures and circuits in the trailer.
The total connected heating/cooling equipment load, in volt-amps.
Use the nameplate volt-amp rating of the trailer's window/split AC unit(s) and any electric heaters.
The total connected load from receptacles, computers, printers, and other plugged-in equipment, in volt-amps.
Sum the expected volt-amp draw of office equipment, chargers, and any other receptacle loads planned for the trailer.
The service voltage supplying the trailer.
Common temporary construction power is single-phase 120/240V — confirm the actual voltage of the temporary service or generator supplying the trailer.
Required service amperage
29.2 A
This is a simple connected-load sum with no demand factor applied — NEC Article 590 (Temporary Installations) governs the actual code requirements for temporary construction power, including conductor sizing, GFCI protection, and disconnect requirements, which this calculator does not address. Round up to the next standard breaker/service size and consult a licensed electrician for the actual installation.
- Total connected load
- 7,000 VA
They open the calculator with your figures already in it
Temporary Site Trailer Electrical Load Calculator: 29.17 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Total connected load (VA) = Lighting + HVAC + Receptacle Loads; Required amperage = Total VA ÷ Voltage — a straightforward connected-load sum with no demand factor applied (unlike a permanent dwelling service calculation), appropriate for a temporary construction trailer under NEC Article 590 (Temporary Installations), which governs the actual code requirements for temporary wiring.
Inputs used
- Lighting Load (VA)
- 1500
- HVAC Load (VA)
- 3500
- Receptacle/Equipment Load (VA)
- 2000
- Voltage (V)
- 240
Intermediate steps
- Total connected load
- 7,000 VA
Confidence note: This is a simple connected-load sum with no demand factor applied — NEC Article 590 (Temporary Installations) governs the actual code requirements for temporary construction power, including conductor sizing, GFCI protection, and disconnect requirements, which this calculator does not address. Round up to the next standard breaker/service size and consult a licensed electrician for the actual installation.
What this calculation does not cover
- Divides the whole load by the voltage, which only gives the per-leg current if the load splits evenly across both legs of a 120/240 V supply. It never does — the lighting, receptacles and office gear are all 120 V and land wherever the panel schedule puts them. A trailer that computes 29 A total can be pulling 40 A on one leg and 18 A on the other, and the leg is what trips.
- Connected load is not breaker size. A continuous load is sized at 125 % for the overcurrent device, and the trailer's air conditioner pulls several times its nameplate for the first second of every start. This figure is what the equipment eats while running, not what the breaker has to survive when the compressor kicks in on a hot afternoon.
- If a generator is feeding the trailer rather than a temporary pole, amperage is the wrong question. A set is rated in kW at a stated power factor, and it is the motor starting kVA of the air conditioner that sizes it — a genset matched to the running load sags and stalls on AC startup, and the office reboots with it.
Add the equipment this sizes
This result is a specification — 29.2 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Total connected load (VA) = Lighting + HVAC + Receptacle Loads; Required amperage = Total VA ÷ Voltage — a straightforward connected-load sum with no demand factor applied (unlike a permanent dwelling service calculation), appropriate for a temporary construction trailer under NEC Article 590 (Temporary Installations), which governs the actual code requirements for temporary wiring.
Which documents these citations point at
- National Electrical Code (NFPA 70) — Article 590 (United States)Electrical installations — conductor sizing and protection, load calculation, wiring methods, grounding and working clearances.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
Cite this page
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