Can a power surge harm a PSU while it remains connected to a mains socket, even though the switch is turned off?
Can a power surge harm a PSU while it remains connected to a mains socket, even though the switch is turned off?
I frequently disconnect my PSU from the rear, yet I rarely unplug it from the mains socket because it wears the prongs with repeated use. Would it still be safeguarded against power surges when connected to the socket but turned off in the back? I’m currently using a Silverstone Strider Essential 700w plugged into a standard thick-wired extension cable, which appears to last well so far.
The answer is yes, it would work. The switch is designed to block terminals at a specific voltage when not connected. Exceeding this limit could cause a spark on the button, disabling it and possibly blowing a fuse in the power supply. Such a scenario usually involves much higher voltages than normal, like lightning striking the house and affecting that circuit.
Changing the power supply unit's ATX PSU on and off at the rear of the unit isn't advisable. A colleague often does this each time he uses his computers, but eventually the switches become damaged. When I replaced the switches for him, I discovered the metal contacts were covered in blackened soot and deep pitting. Please note that as an electronics design engineer involved in industrial communications systems, I'm familiar with the dangerous voltages present inside a PSU. The cause of the switch failure is straightforward—it's highlighted in every test from Tom's PSU reviews. A screenshot below illustrates the mains supply inrush currents during switch activation for an Asus 550W power supply. For a 115V, 60Hz AC source, the peak inrush current reaches 78.580A. With a 230V, 50Hz AC supply, the current spikes even more to 93.990A. To reference the review: Inrush current, or switch-on surge, describes the maximum instantaneous current drawn by an electrical device when it first powers up. Sufficient inrush can trigger circuit breakers and fuses to trip, potentially harming switches, relays, and bridge rectifiers. Therefore, lower inrush during startup is preferable. The brief inrush occurs during the charging of the 400V DC bulk electrolytic at switch-on. These currents would be significantly higher without a series varistor in most PSU line inputs (with an optional bypass relay). Once the current stabilizes, repeated surges gradually erode small metal sections from the switch contacts, forming an arc each time. You might assume the on/off switch can handle surge currents of 100A+, but the ratings listed are typically 6A, 10A, or 15A for continuous operation. The surge current rating isn't mentioned. For details, you'd need to consult the manufacturer's data sheets. Plugging an ATX PSU into a power outlet at night with lights off often causes a flash of light when an arc forms between the plug and socket contacts. You'll also see a flash when connecting a laptop power supply in darkness. It seems manufacturers assume most users won't frequently operate the switch, so they install cheaper switches that can survive a few cycles before failing. TLDR. Avoid using the back switch on your ATX PSU unless absolutely necessary. Opt for a sacrificial mains extension block instead. It's wiser to replace an easily swappable and affordable extension rather than risking premature failure of the PSU or wall outlet switch, which are harder to replace. Additionally, a standard IEC mains lead for a PSU is only a few dollars. It doesn't matter if it gets damaged—your PSU is significantly more costly and should be handled carefully.