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Illustrated Changes to the NEC, 2002 Edition - Part 1

Article 240

Overcurrent Protection

240.85 Applications

Author’s Comment: A 120/240V slash circuit breaker cannot be used on the high-leg of a solidly-grounded 120/240V delta system, because the phase-to-ground voltage of the high-leg is 208V, which exceeds the 120 line-to-ground voltage rating. Figure 240–6

FPN: Circuit breakers on systems other than on a solidly-grounded wye, particularly on corner-grounded delta systems, should consider the individual pole interrupting capability.

Author’s Comment: A slash rated breaker cannot be used on corner-grounded systems because phase-to-ground voltage is equal to the phase-to-phase voltage. For more information on this subject, visit www.mikeholt.com/Newsletters/240.85.doc or www.mikeholt.com/Newsletters/240.85.pdf.Intent: The change was the addition of the words “solidly grounded.” This was needed to emphasize that slash-rated devices were not appropriate on resistance-grounded and ungrounded systems.


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