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I have a Back-UPS ES 550 from APC, and I'm wondering if that 550 wattage rating is for the battery backup side only or all outlets? It has 8 outlets. 4 that say battery backup, and 4 that say surge protection only.

I'm using all the outlets, and even though I don't think I'm overloading it (wouldn't it sound a tone?), I'm just a little paranoid.

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up vote 3 down vote accepted

It's the peak output it can deliver on battery backup outlets

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It is best to aim to load it at about half that. –  BillThor Mar 11 '11 at 4:13
    
Thanks. Seems like I would have to have something major in those 4 outlets to reach 550? –  Welsher Mar 11 '11 at 4:14
    
@Welsher Remember: it's not 550W each –  Sathya Mar 11 '11 at 4:16
    
Well, I meant things that added up to a lot of watts. Just not sure what that might be. A printer plus a gaming machine? Not sure. Seems like my usage (notebook, readynas) is pretty light. –  Welsher Mar 11 '11 at 4:21
    
@Welsher for your usage, it should be fine –  Sathya Mar 11 '11 at 4:22
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It's worth noting that 550 isn't Watts, it's a "VA" rating, which is meant to account for 'power factor'. For wattage, 2/3rds of the rated VA is a safe rule-of-thumb.

But to the question; Yes, the rating is for the battery outlets (combined) only. The limiting factor is the inverter that turns battery back into AC. The surge outlets are pretty unrelated to the rest of the UPS, and merely included for convenience.

And to the paranoia; If it's overloaded, you will know about it. It'll either make a (loud) constant tone, or it'll just power off; depending how far over it goes. It'll do this so that you can't run it overloaded, but you won't cause damage doing so. Unless it's overloaded and trying to use the inverter (providing power from battery). This would be very problematic, and the automatic shutoff is to protect against that scenario.

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