Technical FAQs

Ask a Question

Bypass operation of Symmetra Power Array 3:1 (3-Phase Input / 1-Phase Output)


How does my 3:1 Symmetra UPS operate when in bypass mode?

Product Line

Symmetra Power Array
Symmetra LX


3:1 (International) systems only


This document describes the bypass operation of a 3:1 Symmetra UPS system.  Due to the design, power will be drawn differently when the UPS is on inverter versus when it is in bypass.


Due to Symmetra's redundancy it is expected that the bypass operation will be a rare occurrence.

Symmetra has 2 types of Bypass modes:

Automatic Bypass - controlled by the Symmetra, initiated by the MIM or from the PowerView
Maintenance Bypass - manually set by switching the Maintenance Bypass Switch on the Power I/O section to the up / on position

There are 3 possibilities when using Symmetra 3:1 in bypass
1. With the APC Bypass transformer (part no SY-BPXFMR - for use with Power Array only)
2. Without the APC Bypass transformer 
3. Use a separate feed

If the Symmetra is in Bypass it will behave as follows:

1. Without the APC Bypass transformer
When in Bypass mode the Symmetra 3:1 will draw all the current from one dedicated phase. This particular phase must have a circuit breaker rated at 100 Amps due to the fact that it will be used to provide power to the whole load. This is only applicable for loads above 12 KVA. For loads below 12 KVA you can use a 60 Amp Circuit breaker.

2. With the APC Bypass transformer (SY-BPXFMR)
When using the Bypass Balancing transformer you will not need to have a 100 Amp circuit breaker on phase one. The Bypass transformer will draw current from 2 (L1 & L2) of the 3 phases, but no more than 60 Amps per phase. This allows the user to rate their 3 phases with 60 Amp circuit breakers.

See Symmetra Users Manual for wiring instructions of Bypass Transformer

3. Separate feed
The user can have a 100 Amp separate feed for the bypass. (100 Amp is necessary to provide for current protection). If the source of the separate feed is different from mains, there is a possibility of asynchronous transfers causing the load to reboot. This solution is possible but not recommended.

NOTE: While in bypass you will still have surge protection.

Was this helpful?
What can we do to improve the information ?