Voltage ratings on switches/illuminated switch questions

Hey guys,

This is going to be a super noob question (so apologies in advance) but what does the voltage rating on a switch actually mean?

I was in Jaycar yesterday looking at toggle switches, and found these really neat looking pushbutton switches:

https://www.jaycar.com.au/ip67-rated...-blue/p/SP0793

I asked the guy at the counter, because the specs listed DC Voltage 240 and Voltage 12, and I was unsure what that meant. He told me that the switch has to run on 240 V or the LED won't illuminate, which I suppose is probably true, but then he seemed to suggest that the switch would also only work in a circuit at 240 V, and I don't understand how that is true. I was under the impression that voltage ratings were maximum voltages that a part could withstand?

As a general rule the voltage rating is either the maximum or the typical voltage that the switch can withstand. Similar applies to the current rating.

Using a switch beyond its rating risks burnout or arc over, particularly when the switch is operated from on to off. Turn on is less of a risk than turn off as the contacts within the switch have to be able to interrupt the current it is carrying without damage. When opening or turning off a switch there is risk of a spark being created, and as the voltage and current rises this risk increases dramatically, and to the detriment of the switch.

Some are rated for AC only as they are not designed to handle the increased spark risk involved in DC current interruption. Special considerations must be included for switches that interrupt high DC voltages such as used as standby switches in tube guitar amps.

Your Jaycar switch will safely and reliably turn a 720W mains AC power device on and off (240VAC x 3A = 720W), however for it to light up you will need 12VDC for the LED.
Misleading Jaycar website information aside I would not used it to control a DC circuit unless the DC was less than 24V (1/10th the AC only rating) and less than 3A maximum. Unless there is a specific DC voltage/current rating then don't use it for DC or not more than 1/10th the AC rating.

Thanks Marcel, this is really helpful.

Earlier today I had a very interesting discussion with another tech local to my area. His working career in electronics started sometime in the late '60]s or early '70's and is still strong and active today so I and many others nationally value his vast experience.

While we digressed briefly onto the subject of voltage ratings he reminded me that it is important to note that excessively high capacitor voltage ratings can work to the detriment of the circuit they are used in.

Using a 50V rated cap in a 12V or 9V circuit is reasonable, but using 600V caps on the small 100mV signals such as within a guitar can actually de-rate the capacitive value of the cap. The problem is 100's of times worse with electrolytic caps as they require a minimum voltage to be applied to maintain their capacitive value. So right here and now I'd like to offer and personally strongly suspect that all caps have their ideal working voltage range, and that a bigger voltage rating isn't always better.

As an example, if you look at most tube amp circuits the cathode bypass caps are typically rated at 25V or 40V which is fine as most cathode voltages when operating normally are in the order of a few volts, and that is when there is a few hundred volts on the anode. It is always the case of using appropriate voltage ratings and capacity value for the job/task to be done. Throwing a 450V cap on a cathode bypass may work for a while or during testing but that cap will fail reasonably quickly as a 450V cap needs probably at least 50V or more on it to maintain condition internally and even the 10V or so on a self bias EL84 cathode will not be enough to maintain its health long term.

So, if the range of your tone pot in your build is not up to your expectations when using that 600V orange drop or whatever cap, then considering the work/task/job to be done maybe a 200V or 100V version might be a better choice...