Question 1

How do I size a UPS for a network closet?

Accepted Answer

Add up the wattage of all devices in the closet (switches, routers, NVR, patch panels with active PoE loads). Multiply by 1.25 for headroom, then divide by the UPS power factor (typically 0.9 for line-interactive UPS). Size for at least 15 minutes of runtime at full load to allow graceful shutdown. For critical infrastructure, target 30–60 minutes. Example: 8 devices × 150W avg = 1,200W × 1.25 = 1,500W UPS minimum (APC SMART1500 or equivalent).

Question 2

What is the difference between line-interactive and online double-conversion UPS?

Accepted Answer

Line-interactive UPS provides AVR (automatic voltage regulation) and switches to battery within 2–6ms on power failure. Sufficient for most network closets. Online double-conversion UPS continuously runs equipment off the battery inverter, providing zero transfer time and complete isolation from power grid disturbances. Required for servers, NVRs with SSD arrays, and any equipment sensitive to micro-outages. APC Smart-UPS series (line-interactive) vs APC Symmetra or Eaton 9PX (online double-conversion).

Question 3

How long should a UPS runtime be for network equipment?

Accepted Answer

15 minutes is the absolute minimum — enough for a graceful shutdown sequence. 30 minutes is the practical standard for branch office network closets. 60+ minutes is recommended for environments without a generator, where the IT team needs time to drive to site. For 24/7 operations with generators, 15 minutes is sufficient as the generator will start within 10–30 seconds of utility failure.

Question 4

Should I put PoE switches on a UPS?

Accepted Answer

Absolutely — PoE switches are often the most critical devices in a network closet. A 48-port PoE+ switch can draw 400–800W including PoE load. Ensure your UPS is sized to support the full PoE load, not just the switch base wattage. Many UPS sizing mistakes come from forgetting that a 48-port PoE switch may draw 3–5x its listed base wattage when all ports are fully loaded.

UPS Size	Typical Runtime (50% load)	Best For	Example Models
600–900 VA	15–25 min	Small router + switch closet	APC BE850G2, CyberPower CP900AVR
1,000–1,500 VA	20–40 min	Branch office network closet	APC SMT1500, Eaton 5P1150
2,000–3,000 VA	25–50 min	Mid-size IDF closet	APC SMT3000, Eaton 5PX2200
5,000–10,000 VA	30–60 min	MDF / core network room	APC SURTD5000, Eaton 9PX6K
10,000+ VA	30–90 min	Data center / server room	APC Galaxy, Eaton 9395

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