Hi again! Soon I will be moving a rack of about 8-10 servers, two 48 port switches, an MD1000 full of disks, and some other odds an ends to a location equipped with a 240v 30A circuit. Naturally, I need something to plug into the L6-30R receptacle and because I will be remote of this setup I’d like to be able to flip a server or switch off entirely in case of issue. There are times where an iDRAC just goes brain-dead and the server needs to be unplugged to reboot it, but if you don’t have some hands at the location… So, combine the need for at least 20 power connections and the remote switching, I figured I’d pick up a PDU (Power Distribution Unit).

I ordered an APC AP7941 off of eBay for about $85 shipped. The key about this strip is that it has an acceptable input voltage range of 200 – 240v. So, a 240v receptacle off ordinary household mains will suffice. Be careful if you go to buy a PDU on eBay! I would say approximately 90% of them are for 3-phase power, and rated for 208v input which you will not be able to utilize without an expensive phase converter. Ordinarily, if you see them for really cheap, check the model. You don’t a 3-phase model for home (or some businesses!). You’ll also find that the 120v models tend to be pretty expensive – this is because they do cost more money new sometimes, but in the used market 99% of people buying a used PDU are at home or small office and have only 120v. Ordinarily you’ll plug the PDU into a UPS but for my purposes it will be direct into a receptacle.

That said, I received my Zero-U AP7941 except it was in a box about 12″ x 12″ x 20″. Oh boy – a Zero-U should be long and skinny. Turns out, it was an APC AP7900 – a 120v 1-U PDU… not what I wanted at all! I checked the listing and sure enough I did place a bid and buy the AP7941 so the company had just sent the wrong device. No big deal after sending them an email they realized the error, send me the right unit out and a shipping label for the wrong one (they were great to deal with). While I had the wrong one I figured I would reset the username/password of the device since it was not reset when I received it (it was an asset from a cloud hosting service in Houston, TX). Note to businesses – you should really zero out your configurations before selling off parts. This PDU had the community string for read/write SNMP settings, hostnames, domain, etc. for assets that I could ping externally! Rather than pull the hashes and such to try and crack some passwords, I reset it using the proper RJ12-Serial cable which the next person will not likely have and won’t be able to log into the unit. I reset it to the standard user of apc and password of apc.

Today my AP7941 showed up in a 6′ long box but before I got to messing with it I wondered – how much power does a PDU use itself?

While the unit booted up it only used 3w which was nice and I thought for a second that it would only use that at idle. But, once it finished booting up, even with the outlets turned off, it consumed between 8.2 – 8.6w of power. Not a huge deal at the end of the day but considering there are pfSense appliances drawing only 16w this is a little high. But, with the beauty of remote managed outlets versus not, it is what it is.

Mind you these two units are old and deprecated – the current offerings may consume less power.

I couldn’t test the power consumption of the AP7941 since it’s got an L6-30P connector but I assume it is similar if not higher considering it has 24 ports instead of 8.

Here’s the AP7941 powered up just for kicks:

Both units are in fantastic used shape though I suppose that’s to be expected as they obviously came from a real data center based on the configuration on the units. The AP7941 was from a different hosting center but it also had the read/write SNMP criteria set along with all host names, outlet labels, domain names, etc.

One thing worth noting – I flashed the PDU firmware and application firmware on the AP7941 since I am keeping it. I didn’t want to risk bricking the AP7900 though it’s a really easy process unlikely to fail. Unfortunately the only L6-30R receptacle I have is in my garage for my electric heater so I can’t really use this in full, but it’s meant for another location anyway. Just though some people might get a kick out of seeing how much power is consumed just by the PDU itself! Thanks for reading!

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