This varies a bit. 120 +/- 10% was what we guaranteed when I worked for Ohio Edison, but a lot of utilities now are 120V +/- 5% (114 to 126 volts).
If this was the case and there was a broken neutral somewhere, that would explain the computer blowing up. If the neutral on the 240 circuit was broken, the voltage on the power strip’s neutral is going to vary depending on the load balancing of the two hot lines. If the loads are perfectly balanced, then you’ll have 120 volts from either line to neutral. If they aren’t balanced, then you could easily end up with something like 200 volts from one line to neutral and 40 volts from the other line to neutral.
This is a very good reason why you should never construct a power strip like this.
Back to the OP - do you actually know for sure that it was (or is) 240V(‘220V’) coming from the strip?
I have a feeling it may be something like ecg suggested. It could also be a fault in the computer. Was the fizz-pop more inside the computer itself (motherboard, presumably) or just at the computer power supply(where the cord comes in)?
Agreed, and that makes me wonder; are electric clothes dryers like that? Do they have a 240V heating coil, but a 120V motor? (I really don’t know) For that matter didn’t a lot of (older?) 240V stoves/ovens have a 120V convenience outlet?
If so, could a broken neutral make the case “hot”? (The cases don’t ‘float’ or do they?)
I am pretty sure that newer dryers (and stoves?) now have a 4-wire plug with a true ground in addition to the neutral. But there’s a lot of old 3-conductor dryer receptacles out there.
This is a fairly common setup in data centers. In our data center we have rack-mounted PDUs with IEC C13 female sockets such as the ones on the left side of this image. The PDUs are hard wired to the UPS.
Of course, folks will recognize the male version of this connector as the one on the back of their computer. This led to a fried power supply on a few occasions when I had to install some rickety old development servers in the rack, and completely forgot to check to see if they had the 110/220V switch on the back of their power supplies. One loud POP and the power supply is dead.
We also have a couple of C14 to to NEMA 5-15 (typical american wall socket) cables zip-tied to our racks to plug in laptops and such. I’m waiting for someone to bring a laptop power supply that doesn’t accept 220V, but I doubt any are made any more. These cables AFAIK violate the NEMA ratings.
More than you ever wanted to know about US power connectors is available here.
And the transformers don’t adapt from one type of current to the other instantaneously. Very fast, yes, but slow enough that I’ve seen a laptop fizz like that when the owner plugged the transformer into the laptop first and the 240 power supply second (the laptop had previously been used only on 110).
It was a 220 outlet on the wall (big, dryer type plug) with the plug running to a power strip that had standard 110/120 plugs. This power strip was labeled “220V”. THere was another power strip plugged into that that was unlabled. Then the computer was plugged into its own power strip. The computers power strip was plugged into the unlabeled power strip.
So there were three strips involved; only one labeled with 220.
I’m glad I didn’t do this. I’m sure the fire inspector would have a cow.
