Can a 3-phase QO load center be used on a 240 V "high leg" system?

Issue:
Application

Product Line:
QO Load Center

Resolution:
Yes, but it is important to understand some limitations. This "high leg" delta system referred to is actually a 3 phase, 4 wire, 240/120 V delta system. It has a number of common names, including high leg, wild leg, stinger leg, etc. This system provides 240 V phase-phase power between all 3 phases, plus 120 V phase-neutral power on 2 of the 3 phases. The problem, however, is with the phase-neutral on the 3rd phase: it measures 208 V, which is not a usable downstream voltage since it is too high. This is what gives the system its nickname, high leg. This high leg is commonly the B phase, but could be the A or C phase.
Selecting QO breakers for this system must be done carefully. Here are some guidelines:

1-pole QO Breakers

• Standard 1-pole QO breakers have a voltage rating of either 120/240 V (e.g., QO120) or just 120 V (e.g. QO120GFI). These should only be applied on phases measuring 120 V phase to neutral, never on the phase measuring 208 V phase to neutral.

2-pole QO Breakers

• Standard 2-pole QO breakers have a voltage rating of 120/240V (e.g., QO240). These should only be applied on phases measuring 120 V phase to neutral, never on the phase measuring 208 V phase to neutral.
• Special 2-pole QO breakers with "H" suffix have a voltage rating of 240 V (e.g., QO240H). These may be applied on any of the phases, including the high leg phase.

3-pole QO Breakers

• Standard 3-pole QO breakers have a voltage rating of 240 V (e.g., QO330). These may be applied on any of the phases, including the high leg phase.

NOTE: The installer should be careful to follow NEC and/or local electrical codes regarding the wiring, marking, and usage of this system.

Released for: Schneider Electric Canada