When you are wiring a relay coil into a circuit,
you must be sure that the voltage rating of the coil matches the
circuit voltage within +/- 10%. Some industrial-grade relays have
color-coded coils so that you can determine the voltage rating
for the coil by its color as well as from printed specifications
on the relay. A red coil is rated for 110 volts ac and a black
coil is rated for 220 volts ac. On the other hand, the contacts
can be rated at any voltage equal to or above the voltage of the
circuit in which they are used. That is, one can use contacts rated
for 208-volts ac in a circuit that has a power supply of 110 volts
ac. The current rating of the contacts should never be exceeded.
The contacts will be rated for a specific amount of current or
power. If the rating is for power, it may be expressed in VA (volt-amperes)
rather than wattage and you will need to do a calculation...
current = volt-amperes / voltage
...to determine the maximum current rating. Some relays will also
provide a chart to help you determine their ratings. AMAZON multi-meters discounts
AMAZON oscilloscope discounts
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