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The AC adapter supplied with my laptop is designed to accept voltage in the range of 100-240VAC at 50-60Hz, but the AC cable that plugs into the adapter unit itself is only rated to 125VAC 7.5A 2.5A. I know the adapter can accept 220V power, but is it safe to use this cable with the AC adapter to plug into a 220V socket?

Edit: The part in question is a 90W HP Smart AC Adapter. The laptop does not cause the AC adapter to draw more than about 80 watts from the socket (as measured with a Kill A Watt meter).

Edit 2: The amperage rating of the cable as marked on the attached label is 2.5A, not 7.5A.

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If it's UL approved, then it was probably only tested & certified for 120V use. Since you asked about "safe" rather than "is it OK", instead of using it with a plug adapter, you would be better off (i.e. safer) getting the proper power cord w/suitable plug. –  sawdust Aug 25 '12 at 0:53
    
Net/net -- It's only infintesimally less safe than using the "right" cable. IOW, you're more likely to reduce your life expectancy by driving 5 miles to purchase the "right" cable than you would by using what you have. –  Daniel R Hicks Aug 25 '12 at 1:49
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up vote 3 down vote accepted

It should be fine.

Your laptop's power consumption is probably less than 100 W (unless it's a particularly power-hungry workstation or gaming machine), which at 220 V works out to about 0.45 A,1 or way less than the 2.5 A the cable is rated for. In fact, since voltage and current are inversely proportional (for constant wattage), you're actually running less current through the cable than it was meant for. So current-wise, you're good.

As for voltage, as far as I know, the 125 V rating is merely an indicator of which mains system it was intended to be used with. The real concern here would be the insulation - if for some reason it's rated for less than 220 V, you'd be creating a fire and shock hazard. From what I've read about typical laptop power cords, the insulation should be good for at least 300 V, but you may want to inspect the cable carefully, the insulation's maximum voltage should be marked on it somewhere.

Nevertheless, if you want to be 100% sure, get a cable that's meant for use with 220 V mains systems.


1 - a bit more, actually, since for alternating current, the amount of power usable by devices (called real power) is less than current × voltage (which is called apparent power), but the number is in the ballpark.

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The label attached to the cable is marked 2.5A 125V~ (the squiggly indicates AC). The cable itself is marked 300V 60°C (note maximum temperature). How confusing... –  DragonLord Aug 25 '12 at 1:21
    
@DragonLord - first spec is the current and voltage (for power) rating. Second spec would be for the insulation. –  sawdust Aug 25 '12 at 1:26
    
@sawdust -- If the cable itself is stamped 300V then the cable is good for that. The cable assembly (including the connectors) is what the label refers to, and it was no doubt designed for standard US 2-prong 120V service. But that's really a statement of the plug design, not the voltage that the connectors can withstand. I've never seen any commercial wire or connector that couldn't withstand at least 300V -- in fact, it would be hard to design a connector that met UL standards but could not withstand 300V. –  Daniel R Hicks Aug 25 '12 at 1:41
    
Keep in mind that, to meet UL requirements, a cable assembly must withstand not only the standard line voltage but reasonably foreseeable "transients", including voltage spikes of 1000V or more. –  Daniel R Hicks Aug 25 '12 at 1:46
    
Good guess on the insulation rating, but the (1) footnote is incorrect. "Actual power" is never more than the volt*amp product. See this answer about power factor in superuser.com/questions/348103/pc-watts-usage-comparison/… –  sawdust Aug 25 '12 at 2:59
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