Voltage drop sa emergency circuits: NEC 700/701 at UPS
I-size ang emergency at standby circuits gamit ang NEC 700/701, IEC 60364-5-56, UPS/generator paths, at numeric examples.
Ang emergency circuit ay hindi lang ordinary branch circuit na may ibang source. Egress lighting, fire control, UPS output, at generator path ay dapat magbigay ng usable voltage sa worst case. Sa 277 V, 12 A, 260 ft one-way gamit ang 12 AWG copper, nasa 3.6% ang voltage drop.
Buod
- NEC 700/701/702 and IEC 60364 classify the source duty.
- 3%, 5%, and 2% targets must be documented against the actual load path.
- UPS and generator modes need separate voltage-drop checks.
NEC 700/701, IEC 60364
NEC 700 para sa emergency systems, NEC 701 para sa legally required standby, at NEC 702 para sa optional standby. Sa IEC work, tingnan ang IEC 60364-5-56 at IEC 60364-5-52. Karaniwang target ang 3% branch, 5% total, at 2% para sa critical loads.
National Electrical Code and IEC references are used here as public authority links. Use the NEC standards page and the voltage drop calculator for project checks.
“Sa emergency circuit, hindi sapat ang breaker size. Puwedeng tama ang 20 A breaker pero kung ang dulo ng 120 V UPS load ay 113 V lang, kulang ang design margin.”
— Hommer Zhao, Technical Director
277 V / UPS / generator example
Kung 12 AWG copper ay 1.588 ohm/kft, ang 260 ft one-way ay 520 ft current path. Sa 12 A, drop ay 9.91 V o 3.6% ng 277 V. Sa 10 AWG, bababa sa mga 2.25%, o hatiin ang circuit.
Para sa UPS, kalkulahin mula inverter output hanggang pinakamalayong device. Para sa generator, hiwalay na tingnan ang running current at starting o pickup current. Sa 24 V, ang 2 V loss ay 8.3% na.
Comparison table
Ikinukumpara ng table ang emergency loads ayon sa voltage, code anchor, at drop risk para pumili ng mas malaking conductor o split circuit.
| Circuit | Voltage | Code | Decision |
|---|---|---|---|
| Egress lighting | 120/277 V | NEC 700 | 3% branch target |
| UPS output | 120/208/230 V | NEC 700/701 | Check inverter to load |
| Generator feeder | 208/480 V | NEC 445.13 | Check running and pickup |
| Fire alarm supply | 24 V DC | NEC 760 | 2 V loss = 8.3% |
| Standby distribution | 120/208 or 277/480 V | NEC 701 | Document 5% total |
Mga tanong
Anong voltage drop ang gagamitin sa NEC 700?
Walang iisang percent ang NEC 700. Sa practice ginagamit ang NEC 210.19(A)(1) at 215.2(A)(1): 3% branch, 5% total, at 2% para sa critical loads.
Paano kalkulahin ang UPS output?
Gamitin ang UPS output voltage, real current, one-way length, at conductor resistance. 120 V, 14 A, 10 AWG, 180 ft ay mga 5.0 V o 4.2%.
Bago i-finalize ang conductor, ikumpara ang normal, UPS, generator, at transfer path.
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