15A is a lot at 120 or 240VAC. For 120VAC, that’s 1800W.
Most things we plug in are DC. For DC, W = A * V. Your phone probably charges around 5V 3A, which is 15W. You could plug over 100 times that into a 15A power strip.
When going between AC and DC, the wattage will be the same, or close enough considering losses from heating during the conversion.
You look at the amperage rating and add them all together if that’s over your limit (usually 15 A like you mention) you would have a problem.
It depends on the type of device but very few of them draw more than 1-2 amp unless its a heater or has moving parts (like a blender or something) So you can easily plug in about 7-15 devices with no real problem.
Those are also their peak ratings. For example I have my desktop PC, 3 monitors, 2 phone chargers, and a VR head set, an all plugged into one outlet and running right now. The peak for all that is about 8 A but its currently drawing 0.54A
Read the max amperage of every device, and for safety’s sake assume they’re all taking that all the time. Add them up, and don’t use them all if they exceed the amperage listed on the power strip. You might think you’re just running your TV and PS5, no problem, but a PS5 and a big TV can pull over 6 amps together. So you decide to plug in a vacuum or heater because it’s convenient, and you can easily go over.
If you want to know how much each is actually pulling, they sell devices for that. You can buy a clamp meter that goes around a cable and measures, and you can get plugs that you can plug your device into, and it’ll show the amperage it’s pulling at any one time.
They are all added together so the sum of the power draw is limited to what it can handle which often is 15A.
It is technically not the rating that is listed on the device, that the max power it can draw but what is really draws when they are used that matters. But to be safe assume the use max power is a good idea.
15 A will result in 15 * 120= 1800W or 15* 230 = 3450 W depending on where you live.
That is quite a lot of power and stuff that is typically used in a household it will be objected that are designed to heat up stuff that uses lots of power. An electric kettle, electric oven, stove top, portable AC, space heater etc, I would suggest connecting them directly to a wall outlet or realy check so you might not draw to much with all of them on,
Most other stuff we use does not draw a lot of power. Even large 60-inch TV with LED illumination is sub 100, double that for an older LCD illumination system. A powerful gaming PC might be at 350W. Gaming computer is sub 100W and the phone charger are sub 20w. LED lamps are typically less then 10
So most of the time when you want to put in lot of devices that will not draw that much so the limit is not relevant.
Unless what you plug in produces a lot of heat it will not use a lot of power and filling up a power strip works fine.
So, there’s a hierarchy here.
At your circuit breaker (which is typically 100 amp, newer houses or larger houses have 200), this means that it supports up to 100 amp load (realistically it shouldnt go over 80 amp)
From there, each circuit (the switches on the breaker) correspond usually to specific rooms, or parts of a room. High load things like laundry, fridge, kitchen, might have a larger circuit, 20-50 amps. Most rooms are 15 amps.
15 amps circuit x 120 volts socket = 1800 watts max (again, realistically 1440w). When a circuit hits that 80% mark, typically that’s when the breaker pops and you have to go reset it. It’s usually pretty hard to hit that, because not a lot of things draw their rated power.
Easy example though… Kitchens. Eletric kettle. Microwave. Coffee Machine. All of these are resistive heaters that basically just run full steam of ~700-1000w. Run two of those at once and you trip the breaker.
Most desktop devices don’t pull a lot of power. Speakers, lights, usb devices, phones, printers.. They just don’t pull a lot of power. Even while gaming, we’re talking… half of what a kettle will pull. Maybe.
This is also (one of) the reasons they recommend not to daisy chain surge protectors, and they are often limited to ~6-8 ports. The less stuff you plug in, the less chance that it trips. But if you chain 2-3 and plug in 20 devices, especially if several are computers with a lot of other stuff, you might actually bump up against that limit.
It’s also the reason at the new house we’re working on, we’re using a 200 amp breaker with 20 amp fuses so that we can actually run multiple things at once.
Whereas many are mostly correct, it is also confusing. As some noted, only view amp numbers.
That wall receptacle can only provide 15 amps. Any plug that connects to it will always demand less than 15. If an appliance plug can mate, then human safety exists.
But a power strip connects many plugs to one receptacle. You are expected to read the nameplate on each appliance. Sum amp numbers from all. Verify that sum is less than 15. Then one power strip is not consuming more than 15 amp from one receptacle.
With experience, one can look at an appliance to know its amp number. But that experience comes from reading amp numbers on nameplates.
A safe power strip must have a 15 amp circuit breaker – the emergency backup protection. To protect you if you make an arithmetic error.
Actual amp numbers are far more complicated. And sometimes massively exceed 15. But that is not a concern. The amp numbers, listed on every nameplate, takes all that into account. We simply make it easy for you. Each appliance has one, simple, ballpark number that says everything necessary to be safe and informed.