I'm an electrician, please never use the argument that all inspectors are competent as well.
Panelboard has the wrong voltage rating
- Thread starter ken44
- Start date
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I'm an electrician, please never use the argument that all inspectors are competent as well.
- Location
- Simi Valley, CA
UL Panelboard Marking
UL Panelboard Marking
Per the UL Marking Guide for Panelboards:
6. VOLTAGE RATING
The basic voltage rating markings must be visible without disturbing wiring and other interior parts. A panelboard designed and intended for use only on a supply circuit involving two different potentials (for example, 120/240 volts, three-wire; or 208Y/120 volts, three-phase, four-wire) is so marked.
In many cases, however, the basic voltage rating marking ? for example, 480 volts, 3-phase ? indicates that the panelboard is suitable for various supply systems (such as 208Y/120 volts, 3-phase, 4-wire; 120/ 240 volts, 3-wire; 240/120 volts,3-phase, 4wire delta, etc.). These voltage ratings may be shown on a wiring diagram affixed to the panelboard or its enclosure.
A single-phase, 3-wire panelboard is not permitted to be marked with a 120/240 volt, 3-phase, 4-wire delta rating. 3-wire panelboards should not be used for this system. The use of a delta breaker to adapt a 3-wire panelboard to the system has been prohibited by Section 408.36(C) of the NEC.
Although delta breakers could be used properly in 3-wire, split-bus panelboards, they were being misused in 3-wire panelboards with a single main disconnect.
Misusing delta breakers in this manner allows voltage to backfeed through the delta breaker load when the panelboard main disconnect is opened. This allows voltage to be present on the main bus bars when none is expected
UL Panelboard Marking
Per the UL Marking Guide for Panelboards:
6. VOLTAGE RATING
The basic voltage rating markings must be visible without disturbing wiring and other interior parts. A panelboard designed and intended for use only on a supply circuit involving two different potentials (for example, 120/240 volts, three-wire; or 208Y/120 volts, three-phase, four-wire) is so marked.
In many cases, however, the basic voltage rating marking ? for example, 480 volts, 3-phase ? indicates that the panelboard is suitable for various supply systems (such as 208Y/120 volts, 3-phase, 4-wire; 120/ 240 volts, 3-wire; 240/120 volts,3-phase, 4wire delta, etc.). These voltage ratings may be shown on a wiring diagram affixed to the panelboard or its enclosure.
A single-phase, 3-wire panelboard is not permitted to be marked with a 120/240 volt, 3-phase, 4-wire delta rating. 3-wire panelboards should not be used for this system. The use of a delta breaker to adapt a 3-wire panelboard to the system has been prohibited by Section 408.36(C) of the NEC.
Although delta breakers could be used properly in 3-wire, split-bus panelboards, they were being misused in 3-wire panelboards with a single main disconnect.
Misusing delta breakers in this manner allows voltage to backfeed through the delta breaker load when the panelboard main disconnect is opened. This allows voltage to be present on the main bus bars when none is expected
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