I have a background as a product designer/developer in the 240/415Vac control area for Clipsal/Heineman. At the simplest this involves circuit breakers and manual switches. The engineering principle here requires switch contacts to wipe each other during the action of closure to clean the contact area of oxides so that current can flow without overheating the contact surface. This is called "wetting". (Materials used on the contact are also important). Up until the 1970's and 80's the Australian electrical standards regulator actually tested mains connected products in a NATA laboratory, sadly no longer.
With the advent of very low current LED room lighting I am noticing a few seconds of brightness flickering develop in the bathroom. Investigation shows the lamp itself is good but only draws 50mA when on. I suspect now that the humid bathroom environment is contributing to contact oxidation which is not being cleaned by the wiping action. In turn, there must be a 240Vac arc needed to break through the partial oxide insulation on the contact surface.
If this continues there is potential (in the extreme case) for the erosion of the contact surface to eventually create sufficient heat to be a fire hazard.
Is anyone else noticing this phenomena? Materials and design of mains wall-switches could/should be adjusted to include low current (non-wetting) loads but it seems no one cares anymore.
With the advent of very low current LED room lighting I am noticing a few seconds of brightness flickering develop in the bathroom. Investigation shows the lamp itself is good but only draws 50mA when on. I suspect now that the humid bathroom environment is contributing to contact oxidation which is not being cleaned by the wiping action. In turn, there must be a 240Vac arc needed to break through the partial oxide insulation on the contact surface.
If this continues there is potential (in the extreme case) for the erosion of the contact surface to eventually create sufficient heat to be a fire hazard.
Is anyone else noticing this phenomena? Materials and design of mains wall-switches could/should be adjusted to include low current (non-wetting) loads but it seems no one cares anymore.
Ah, I spent a lot of time in relay land. We called that over-make between contacts "scrub". As the closing of the contacts then further motion tended to rub one contact against the other . This helped keep contacts fresh. For low current signal contacts, they were often gold plated or gold flashed (not sure if there is a distinction there) Contacts that carried current were subject to pitting, so it was extra important there. For that matter had to dress the contacts on a regular basis. Any unsmoothed pit had sharp edges which actually encouraged arcing.
To me, and I don't speak for other technicians, let alone entire industries, a wetted contact was one using mercury or other literally wet substance.
I currently (no pun intended) have a lighting fixture over my dining table with three LED lamps in the fixture. One of them is near life's end. WHen it is first turned on it flickers a little. Sometimes blinks a time or two. Once it warms up - 5-10 minutes, it is steady as a rock. It isn't faulty contacts in my socket, it is the circuits in the bulb waking up. I have had this action in multiple LED lights ever since converting to them.
Just my opinion, I suspect you have similar situation, rather than corroded contacts. And just for academics, is 50ma enough current to cause fire-starting arcs? Occasional creative flourish aside, I am on the technician side of the fence, I am not an engineer. Nor do I play one on TV.
To me, and I don't speak for other technicians, let alone entire industries, a wetted contact was one using mercury or other literally wet substance.
I currently (no pun intended) have a lighting fixture over my dining table with three LED lamps in the fixture. One of them is near life's end. WHen it is first turned on it flickers a little. Sometimes blinks a time or two. Once it warms up - 5-10 minutes, it is steady as a rock. It isn't faulty contacts in my socket, it is the circuits in the bulb waking up. I have had this action in multiple LED lights ever since converting to them.
Just my opinion, I suspect you have similar situation, rather than corroded contacts. And just for academics, is 50ma enough current to cause fire-starting arcs? Occasional creative flourish aside, I am on the technician side of the fence, I am not an engineer. Nor do I play one on TV.
In an instrumentation and telephony context wet vs dry means that a "wet" contact has a small DC bias added to a normally AC, very low amplitude signal to overcome surface resistivity effects: for example, you would add a 47K resistor connected to a clean 48V source on one side.
The parasitic resistance would have no effect compared to the 75 ohm impedance, and the 1mA DC wouldn't affect the operation of the input transformer, but the voltage applied would be sufficient to break down any parasitic layer.
Having dry contacts operating reliably can be very difficult, even in vacuum and with precious metals coatings, like gold or palladium. After a large number of operations, the contact area undergoes changes and compromises the conductivity.
A sure way of avoiding the problem was to actually wet the contacts, but it involved mercury, which is a no-no today
The parasitic resistance would have no effect compared to the 75 ohm impedance, and the 1mA DC wouldn't affect the operation of the input transformer, but the voltage applied would be sufficient to break down any parasitic layer.
Having dry contacts operating reliably can be very difficult, even in vacuum and with precious metals coatings, like gold or palladium. After a large number of operations, the contact area undergoes changes and compromises the conductivity.
A sure way of avoiding the problem was to actually wet the contacts, but it involved mercury, which is a no-no today
Yes it was noticed several times at work. When (high quantity) lighting is replaced for LED lighting the light switches will be defective after a while. LED lighting power supplies/current sources often turn out to be a capacitive load (which on itself became an issue for the diesel generator. The light switches here are 16A rated but that they were not meant to switch capacitive loads. It is better to have relays switching large amounts of LED lighting.
We also noticed the First Law of LED lighting: the more energy efficient LED lighting is installed the more expensive energy soon will be 🙂
We also noticed the First Law of LED lighting: the more energy efficient LED lighting is installed the more expensive energy soon will be 🙂
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Sorry I would not know for sure but one can divide LED lighting in groups with a few relays (designed for lighting) controlled by just 1 push button switch. That also divides the current. Relays probably are faster and mechanically more powerful in switching compared to a light switch (that may have some contact bounce). Contrary to the switches the relays last till now.
Classic use of relays I would say.
Classic use of relays I would say.
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