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


Product Line:
QO Load Center

Load Center on 3PH/4W Delta

Application clarification

Yes, but it is important to understands some limitations. This ``high-leg`` delta system referred to is actually a 3-phase/4-wire, 240/120V Delta system. It has a number of common names, including ``high-leg``, ``wild-leg``, ``stinger-leg``, ``red-leg``, and ``bastard-leg``. This system provides 240V phase-phase power between all 3 phases, plus 120V phase-neutral power on 2 of the 3 phases. The problem, however, is with the phase-neutral on the 3rd phase: it measures 208V, 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:
-Standard 3-pole QO breakers (e.g., QO330) may be used in any place in the load center.
-Standard 2-pole QO breakers (e.g., QO240) may be plugged onto either phase measuring 120V phase-to-neutral.
-Special 2-pole QO breakers (e.g., QO240H) should be selected if plugged onto the high-leg phase.
-Standard 1-pole QO breakers (e.g., QO120) should only be applied on phases measuring 120V phase-to-neutral, never on the 208V phase-neutral phase.

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

LAST POINT: This system is NOT the same as the ``grounded B-phase``, or ``corner-grounded`` system.
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