General Tools and Instruments CT103 - Manual (Page 4)

• If 110V is present, the bottom neon
bulb on the tester will glow.
• If 220V is present, the bottom
two bulbs will glow.
• If 277V is present, the bottom
three bulbs will glow.
• If 460V is present, all four bulbs
will glow.
Each bulb has two filaments. If only one
filament glows, the voltage is DC. If
both filaments glow (making the bulb
appear brighter), the voltage is AC.
To detect voltage at a two-wire AC
outlet, insert either test lead into the
narrow “hot” slot and touch the other
lead to the metal mounting screw
(see Fig. 2).
To determine which slot of a three-wire
AC outlet is “hot”, insert one lead into
the lower (ground) slot and the other
lead into both upper slots in turn (see
Fig. 3). The bulb will glow when the
lead is in the “hot” slot.
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