Scenario: Computers are turned off, power strip is turned off. If there were a blackout, lightning, or some sort of power surge, would the appliances be unaffected (since they are not drawing any power,) or does the electricity actually force its way through even an inert and turned-off power cord anyway?
Lightning pushed it’s way through thousands of feet of air. So if it’s a direct strike, it will go wherever it damn pleases.
A slight power surge won’t.
If you have an appliance plugged in and there’s a power surge, the wire of the cord will carry the surge to the appliance, and if it’s electrically delicate in some relevant fashion, it can damage it. It has nothing to do with the appliance not drawing electricity. It’s just that hey, here’s a piece of braided metal wire, and down here on this end the lightning can get in and over yonder it leads into the appliance.
The iron on your ironing board and your electric space heater won’t be likely to care. Your gigabit router, on the other hand, may be fried.
A blackout or power sag (brownout) etc won’t have any effect, or shouldn’t.
The problem with a blackout, lightning, etc. is that it can cause voltage spike between the hot an neutral terminals at the outlet. (There are other scenarios, but those are much more rare and I won’t get into those.)
Assuming the outlet is 120 VAC, the voltage between the hot and neutral terminals rapidly oscillates between +170 V and -170 V when everything is operating normally. When lightning strikes nearby, or there are problems with the incoming power, the voltage might briefly go very high, e.g. 500 V for 20 microseconds or -1000 V for 10 microseconds. Some appliances and devices don’t care a whole lot about these voltage spikes. But some do, especially ones with electronics in them.
Designers know this, so they will attempt to protect the devices using voltage-sensitive shunting devises such as MOVs or TVS. And because voltage spikes are rich in harmonics, the might also use frequency-sensitive devices such as capacitors.
So… when an appliance is on, it should be O.K. when low to moderate voltage spikes are present, assuming it has at least one MOV, TVS, or capacitor-based filter. But if a big spike comes through, all bets are off. Turning the appliance “off” will give you better protection, but only if “off” means “OFF” (mechanical switch on the incoming hot). With a lot of electronic devices, “off” is not really “OFF,” which means it may only offer mediocre protection or very little protection at all. Turning off the power strip will offer good protection since it uses a mechanical switch to disconnect the hot. The best protection? Unplug it.
Engineer_Comp_Geek’s quote is taken from a different post.
As quoted, just like a spark plug, higher voltages can jump from one conductor to another. So an off residential switch doesn’t provide much protection if you were to get a “big” lightning hit.
The solution for high voltage switches is to use dielectrics that don’t breakdown like air does
One of my household treasures is an OLD “Isolation Transformer.” It “transforms” household current…to household current. No step-up or step-down. But it does have a “gap” instead of a “wire” so, in extremis, a really nasty power surge would be stopped by the gap
Weighs an awful lot!
A power surge surely. But unless it is specifically designed for lightning strikes, it can jump between the primary and secondary coils (they are usually wrapped one over the other).
The OP used the terms “extension cord”, “power strip”, and “power cord” as if they were the same thing. And “appliances” and “computers” as if those were the same thing
They’re not. Better answers come from better questions.
Not much to add to the earlier answers: A big enough surge will overwhelm any protective features in your computers, appliances, or power strips. Power cords and extension cords by definition have no switches or protective features. Bigger surges are statistically more rare than lesser surges.
The question you have to ask and answer is “how big/rare a surge am I trying to protect from?” For a lightning strike on the wiring leading directly into your house, unplugged is pretty much your only hope and even then your computer may be destroyed when your house burns down.
[quote=“LSLGuy, post:8, topic:914542, full:true”]
Power cords and extension cords by definition have no switches or protective features. [/quote]
?
The power cord/surge protector strip in my house definitely has an on/off switch.
Power cord is like the cord you’d use to connect a PC desktop to the power outlet.
Extension cord is like the cord you’d use to connect an electric lawn mower or Christmas lights on your roof.
Power strip usually has a switch like you said.
Slightly off topic, but any conductor lying about is always picking up power from various radio-frequency sources. The power is low, but measurable.
As kids, we would take the earpiece out of old rotary dial phones (junkyard), connect a crystal diode across the leads and connect one lead to a clothesline (steel wire) outdoors.
We could hear the local AM radio station without using any batteries or power supply. 