Switch Contact Rating Question

If you look at the power handling ability (W) it is the same! In effect the contacts are rated for a certain maximum wattage. It is difficult to think of it in those terms but that is the way it is.

Rolf

** Groper Alert !!!!!

** Cos it is a **switching ** current rating !!

Means the ability of the switch to BREAK a current flow of so many amps in a circuit with so many volts available after that break opens.

Its all about how DC current arcs behave - the more the volts, the harder it is break the circuit successfully.

Too many DC amps at too many volts with too small an opening gap = a * continuous DC arc * that heats and melts the metal surfaces to bits.

...... Phil

** BOLLOCKS !!

** No it is not - you know nothing, bullshitting ass.

....... Phil

The ratings are also different, in general, for AC vs. DC and for different types of load (resistive, tungsten, motor).

Some types of current and/or load simply cause more contact wear due to arcing (or the switch may even have difficulty in breaking the arc at all), or the type of load may have a large surge current on 'make' that tends to weld the contacts.

Best regards, Spehro Pefhany

--
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Switch ratings have more than one limiting property.

When the switch is closed, the contacts are heated by the RMS current passing through them, and the current limit for this operation depends on the contact material, whether the contact point just meets or wipes at closure, the contact pressure, the thermal conductivity to the surroundings that heat sinks the contact point, etc.

As the contacts open, an arc is drawn that cumulatively degrades the contact surfaces. So the load current and voltage limits depend on both the off state voltage, the load current, whether the current is AC or DC (AC has two moments per cycle when the current goes through zero, letting the arc go out, easier), whether the load is resistive or inductive, how fast the contacts separate, how far the contacts separate, the expected cycle life of the contacts, etc.

As the contacts close, they approach, bounce, possibly wipe, and increase their contact pressure, just as the load current through them is rising. The load current limit here depends on whether the load is inductive or resistive (resistive load currents rise almost instantaneously) and if resistive, if they are incandescent (low cold resistance produces large inrush current), how many bounce cycles, whether or not the contacts wipe (to smear the arc oxide damage out and freshen the metallic surface), etc.

Different cycle conditions (closing, carrying, opening) produce different kinds and quantity of damage, so either different life expectancy for a given rating (voltage, current, AC or DC and load character), or different ratings for the same life expectancy.

Banging two pieces of metal while they carry current or block voltage, with predictable results, is an art form.

more stuff here

martin

That's a good question. Doubling the voltage shouldn't halve the current rating. Why not ask the makers?

"Homer J Simpleton"

** See the Derating Curves on page 2.

10 amp ( switching capacity) rated relay contacts drop to 1.5 at 50 volts DC and nothing at 100 volts DC - even with purely resistive loads.

....... Phil