Let’s say I have a surge protector that has a 15A cable that is rated 1875 watts at 125V.

If my voltage is low, let’s say 105V the amount of watts it can supply will drop? So its max safe output would be 1575 watts. Is this correct?

Lastly, won’t all the appliances pull more amps as well since the voltage is lower? For instance a charger that is stated to be 12W will simply pull more amps if the voltage is lower to reach 12W. Also if the voltage is higher it will pull less amps to reach 12W? It will not change how many watts it consumes?

I do not need an explanation on voltage and amperage just a simple answer to how it works in this scenario, nothing too complex.

Finally, if a surge protector is rated 15A can you calculate the amount of load just by adding the correct calculated amps based on voltage levels.For instance appliances of 0.2A + 0.3A + 0.5A = 1A load. So I can still use 14A safety with that surge protector?

  • \$\begingroup\$ are you talking about a power bar? \$\endgroup\$
    – jsotola
    Feb 2 '20 at 19:45

Cords and outlet strips are rated in current capacity which has to do with how large the conductors are and how hot the device can get safely (in addition to maximum voltage which has mostly to do with the insulation). They are not really rated in watts, even if they are labelled that way.

If the voltage drops, some appliances will draw less power (resistive loads) and some will draw more (switching power supply based appliances, etc). The total current should not exceed the maximum rated current for the unit, but what that means in terms of appliances depends on which appliances you are using.

Power = Voltage * Current

Current = Voltage / Resistance (for resistive loads like heaters)

or Power = Voltage * Voltage / Resistance

so as the Voltage drops, the power drops with the square of the change in voltage.

  • \$\begingroup\$ Is this an accurate way of measuring load “For instance appliances of 0.2A + 0.3A + 0.5A = 1A load. So I can still use 14A safety with that surge protector?” \$\endgroup\$
    – Luke
    Feb 2 '20 at 18:43
  • \$\begingroup\$ Yes, but be aware that some loads draw significantly more current when they are powered up (inrush current). Ratings are typically for maximum running current. \$\endgroup\$ Feb 2 '20 at 18:45
  • \$\begingroup\$ Would 1200watts constant power be safe with the rating allowing 1875 watts? Thanks for helping me understanding and that is a good though I did not think of. \$\endgroup\$
    – Luke
    Feb 2 '20 at 18:53
  • \$\begingroup\$ Probably - make sure the power strip is not covered by anything or placed inside an enclosure that limits air circulation, and don't use an extension cord with a power strip, or plug one power strip into another (fire code violation in most places). The NEC has rules (and the NFPA) for power strips if you are interested. \$\endgroup\$ Feb 2 '20 at 19:11

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