An Eaton UPS on bypass is feeding your equipment straight from utility power: the equipment is powered but not protected, with no battery backup. On the 9PX and 9SX, Eaton lists four triggers: a user command, an internal failure, overtemperature or overload. Check the alarm, remove the cause, or call for service if the UPS failed.
This guide follows Eaton’s manuals for the 9PX and 9SX 700 to 3000 VA and the 9SX and 9PX 8000 and 11000. Other Eaton models describe bypass in their own manuals.
What Bypass mode means on an Eaton 9PX or 9SX
In Bypass mode, the UPS transfers your equipment to utility power. Eaton is plain about the trade-off: battery mode is not available and your equipment is not protected, although the utility power continues to be passively filtered by the UPS. The orange Bypass mode indicator lights on the front panel.
Bypass is not always short. Depending on the overload, the UPS stays in Bypass mode for at least 5 seconds, and it stays there if three transfers to Bypass occur within 20 minutes. A UPS that keeps falling back to bypass is telling you the cause is still there.
Why it went to bypass, and what Eaton says to do
| Cause | What the UPS does | What to do |
|---|---|---|
| Command from the front panel | Control, Go to Bypass transfers the UPS to Bypass mode on purpose | Return it to normal operation when the work is done (on the 8000 and 11000: Control, Go back normal) |
| Overload (above 100% of nominal) | The UPS continues to operate but may switch to Bypass mode or shut down if the load increases | Remove some of the equipment from the UPS; the alarm resets when the condition clears |
| Overtemperature (internal temperature too high, or a fan has failed) | If the temperature rises another 10°C above the warning level, the UPS transfers to Bypass mode, or shuts down if Bypass is unusable | Clear the vents, remove heat sources, let the UPS cool and check the airflow around it, then restart; it returns to normal when the temperature drops 5°C below the warning level |
| Internal failure | The UPS transfers to Bypass mode and remains on to alarm the fault | Check for a UPS failure alarm in the Fault log; contact your service representative |
For Bypass mode, Eaton’s troubleshooting table gives one first step: check for one of three alarms, overtemperature, overload or UPS failure. The Event log and Fault log in the front panel menu show which one. For the full list of alarm messages and beeps, see our Eaton 9PX, 9SX and 5PX alarm guide.
An overload on bypass has a time limit
Eaton’s specifications set how long the UPS will carry an overload on bypass, as a percentage of nominal load (the 9PX manual says nominal current in bypass mode). For the 9PX and 9SX 700 to 3000 VA:
- 102% to 110%: overload warning.
- 110% to 130%: shutdown after 5 minutes.
- 130% to 150%: shutdown after 15 seconds.
- Above 150%: shutdown after 300 ms.
The 9SX and 9PX 8000 and 11000 have their own limits on bypass: no alarm from 100% to 125%, shutdown after 1 minute from 125% to 150%, and after 1 s above 150%.
So an overload that sent the UPS to bypass can still end in a shutdown of the connected equipment if the load is not reduced.
Bypass settings to know
Eaton warns that changing these settings changes UPS behaviour and may result in decreased protection. On the 9PX and 9SX 700 to 3000 VA:
- Qualify Bypass: the default (In spec) allows a transfer to Bypass only when the bypass voltage is within the set limits and the bypass frequency is within 5% of nominal. You can prohibit Bypass (Never), always allow it with no voltage or frequency check (Always), or always transfer on a UPS fault and otherwise follow the default (Always on UPS Fault).
- Bypass voltage limits: by default, a transfer is disabled below the nominal output voltage minus 20% or above it plus 15%.
- Start on bypass: an On/Off setting, disabled by default.
- Bypass standby (8000 and 11000): defines whether the output is powered from Bypass when the UPS is off but still connected to its AC source; it is enabled by default, and Eaton notes the output is then powered but not protected.
Bypass mode, High Efficiency mode and manual bypass are not the same
- Bypass mode is the automatic transfer described above: the load is unprotected.
- High Efficiency mode is a setting, not a fault. The UPS operates normally on Bypass and transfers to Online or Battery mode in less than 10 ms when the utility fails; the display shows High Efficiency mode and Eaton describes the equipment as powered and protected. Eaton recommends using it only to protect IT equipment.
- Manual bypass is a switch you turn. On a 9PX 700 to 3000 VA with a HotSwap MBP module, rotary switch 33 in the Bypass position supplies the load directly from the AC power source. On the 8000 and 11000, Eaton defines the manual bypass as a rotary switch that connects the loads directly to the AC source so the UPS can be maintained without interrupting power to the loads. Eaton’s sequence there puts the UPS in Bypass mode first (Control, Go to Bypass) and checks that the Bypass LED is on before the HotSwap MBP switch is turned.
- Reading the panel: the green indicator means Online or High Efficiency mode, the orange Bypass indicator means Bypass mode. High Efficiency mode engages only after 5 minutes of bypass voltage monitoring, and the UPS stays in Online mode if the bypass quality is out of tolerance.
Larger systems add a separate maintenance bypass. Schneider Electric’s White Paper 75 describes UPS modules above roughly 20 kW with internal static bypass switches, and an external maintenance bypass that lets the whole UPS system be shut down for maintenance; that circuit is meant to close only when the UPS module is in static bypass.
What not to do
- Do not leave the UPS on bypass and treat the load as protected: Eaton says it is not.
- Do not keep adding equipment to an overloaded UPS: on a 9PX or 9SX 700 to 3000 VA on bypass, an overload above 110% ends in a shutdown (above 125% on the 8000 and 11000).
- Do not change Qualify Bypass or the bypass limits to make the alarm go away; Eaton warns this may reduce protection.
- With a HotSwap MBP module, do not plug equipment into the UPS outlets: Eaton warns that operating switch 33 cuts supply voltage to them.
Pressing ESC silences the alarm on the 9PX and 9SX, but the condition remains; if the alarm status changes, it beeps again.
When to call for service
- The Fault log shows a UPS failure or internal fault.
- Overtemperature persists after you have cleared the vents and let the UPS cool, or a fan has failed.
- The UPS returns to bypass after the load is reduced, or it stays in bypass after three transfers in 20 minutes.
- You need the load kept up while the UPS is worked on.
We service Eaton 9PX and 9SX units across Canada: see emergency repairs, UPS maintenance or contact us at 438-800-0382. Have the model and serial number and the Fault log entry ready.
Frequently asked questions
What does bypass mean on an Eaton UPS?
The UPS has transferred the equipment to utility power. Eaton says the equipment is powered but not protected and battery mode is not available, although the utility power is still passively filtered.
Why did my Eaton 9PX go into bypass?
Eaton lists four triggers: a command from the front panel, an internal failure, an overtemperature condition or an overload. Check the alarm for overtemperature, overload or UPS failure.
How do I get an Eaton UPS out of bypass?
Remove the cause first: reduce the load, or clear the vents and let the UPS cool. On the 9SX and 9PX 8000 and 11000, Eaton’s menu path back is Control, then Go back normal. A UPS failure needs service.
Is High Efficiency mode the same as bypass?
No. In High Efficiency mode the UPS runs on bypass by design and transfers to Online or Battery mode in less than 10 ms when the utility fails. Eaton recommends it only for IT equipment.
How long can an Eaton 9PX stay overloaded on bypass?
For the 700 to 3000 VA models: a warning from 102% to 110%, shutdown after 5 minutes from 110% to 130%, after 15 seconds from 130% to 150%, and after 300 ms above 150%. On the 8000 and 11000: no alarm up to 125%, shutdown after 1 minute from 125% to 150%, and after 1 s above 150%.
Sources
- Eaton, 9PX 700-3000 VA RT installation and user manual. Operating modes, bypass settings, troubleshooting, specifications.
- Eaton, 9SX 700-3000 VA installation and user manual. Same sections.
- Eaton, 9SX/9PX 8000 and 11000 installation and user manual (international edition). Transferring between modes, bypass standby, glossary.
- Schneider Electric, White Paper 75, Comparing UPS System Design Configurations. Static and maintenance bypass.