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Why do switches have voltage ratings?
Switches that are going to be subjected to high-inrush inductive loads, such as an AC motor, will often be rated in horsepower in addition to volts and amps. This rating reflects the amount of current the switch contacts can handle at the moment the device is turned on.
Do switches have current ratings?
There are two basic parts to a switch rating-the current and voltage rating. For example, a switch may be rated at 250 volts dc, 10 amperes. Some switches have more than one rating. For example, a single switch may be rated at 250 volts dc, 10 amperes; 500 volts ac, 10 amperes; and 28 volts dc, 20 amperes.
What happens if a relay switches more than its rated current?
If you use a switch or relay to control more than its rated current, it will likely go to an early grave. Relays that switch more than their rated current often end up with their contacts welded together. They appear to be ‘on’ all the time. Note that contact ratings are for resistive loads.
Why do switches have lower current ratings at higher voltages?
A higher voltage should not lead to more power dissipation. So why do switches and relays have lower current ratings at higher voltages? I would imagine that the current derating at higher voltages would be due to arcing when the contacts open.
Which is the largest DC load a relay can switch?
The switching capacity is the largest DC load that the relay can switch, irrespective of current or voltage. It has nothing to do with power dissipation in the relay itself, which should be minimal. The quoted numbers on a relay are generally just indications of current at line voltage in a few countries.
What happens when the contact of a relay is closed?
The contacts of mechanical switches and relays are movable pieces of metal that are designed to open and close an electrical circuit. When the contacts are closed, an electric current flows through the contacts, and when the contacts are opened, the current stops.