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I am not an electrician. I am a sysadmin. I am trying to hook up a power-hungry blade server in my home and I am woefully ignorant on the subject. I have researched enough to ask a questions that I believe may be understandable to professionals. I am hoping to get enough information so that I can contact a professional to do the work and waste as little of his or her time as possible.

Here is a picture of my box:

my fuse box

I've read that these things can handle breakers totaling double the amperage of the main fuse. As I understand it, that means that this box can have 200A worth of circuits. By my count this box is at 135. Can this box handle a 60 Amp Breaker?

Furthermore, even if this box can take such a circuit. That's kind of the beginning of the road. According to this document: http://media.community.dell.com/en/dtc/attach/white_paper_c07-443792.pdf

My server should be powered by a 48 Amp Single-Phase (as three-phase is out of the question, according to my wife) Power Distribution Unit, and that the recommended mating receptacle for such a PDU is Hubbell 363R6W 60 Amp.

As far as I've been able to gather, this is the outlet to which they are referring:

https://www.stayonline.com/detail.aspx?id=11661&gclid=CjwKCAiAk4XUBRB5EiwAHBLUMfHDSBq6p2fD5vwVQ9Vvg2bPGYg-EmMhikH0OYumQXcFSWXHSBtDvhoCnPgQAvD_BwE

So, I guess what I'm wondering is, am I crazy? Is this even possible to do for $1000 or less?

Please also consider the alternate solution.

Alternately, I could have 2 x 30 Amp breakers with the more common NEMA L6‐30R plugs.

I don't really want two special outlets. I'd prefer to have one. But if running a 60 AMP circuit with the unusual Hubbell 363R6W is preposterous, I suppose that would be the only viable solution.

Thanks again for your consideration. Your input is valued, even if you are just laughing at me for being inexperienced.

migrated from electronics.stackexchange.com Feb 12 '18 at 18:45

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  • Isn't it like illegal in a lot of the USA to change wiring stuff like that connected to the grid without being a certified electrician? – BeB00 Feb 12 '18 at 17:05
  • I don't know. I'm not doing the work. I'm just trying to figure out whether this is something I can have a qualified electrician do. – Donzo Feb 12 '18 at 17:10
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    "I've read that these things can handle breakers totaling double the amperage of the main fuse." Maybe. But exceeding the main breaker in current draw will still trip it. – Ignacio Vazquez-Abrams Feb 12 '18 at 17:10
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    Damn crypto miners rabble – Bryan Boettcher Feb 12 '18 at 18:34
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    @BeB00 only EEs. EEs are at a huge disadvantage because they have learned too many things that are "wrong" for mains electrical and then must un-learn. Mortals have an advantage: Easier to teach Russian to a toddler than an Englishman. – Harper Feb 12 '18 at 20:20
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Since your 100 amp, 240 volt service consists of 100 amp, 120 volt branches, you can have 100 amps of load on each of the two branches. Note that the AC has two 120 volt breakers with the handles connected together. That uses both of the 120 volt branches to make a 30 amp, 240 volt breaker. As shown the box has breakers totaling 75 amps on one branch and 80 amps on the other. If you add a 60 amp, 240 volt breaker you will have 135 amps on one side and 140 amps on the other.

You can have breaker capacity in excess of the main circuit breaker rating based on the assumption that many of the load devices will only be used for short intervals of time during a day. However if the server uses 48 amps all of the time, it would not be difficult to imagine a day when the AC is running a lot, the refrigerator is cycling on occasionally, you stick something in the microwave and your wife is vacuuming.

It may not be out of the question, but it is somewhat doubtful. The service is already nut up to today's code. Today, a residence should have two 20 amp circuits dedicated to kitchen counter outlets and one 20 amp circuit dedicated to bathroom outlets. A microwave and garbage disposer often have their own circuits.

The box itself is likely capable of handling 200 amps at 240 volts, but you may have service entry wiring only rated for 100 amps. An electrician may come and quote a price at no charge. You can not get a good answer without that, but there is likely a way to get it done. Note that 48 amps at 240 volts is a lot of power. That is like having the oven and all the burners going at one time in an electric stove.

You don't need the Hubbell 363R6W. Use a standard electric range outlet.

  • Thank you for your thoughtful response. It is greatly appreciated. – Donzo Feb 12 '18 at 18:30
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Beware cost of electrical power and cooling.

The max limit on a 60A circuit is 48A actual.

A Siemens 60A breaker is $10. 6-2 w/ground cable is like $2/foot. A 2-gang steel box is $1. That Hubbell connector is Hokey smokes!

Um, two Siemens 30A breakers are $20. 10-2 w/ground cable is $1/foot x2. Two 1-gang steel boxes are $2. Two NEMA 6-30R's are $30ish. You cannot parallel, use two PDUs.

Or heck with it! Just put in a bunch of 120V/15-20A circuits or 240V/15-20A circuits. Why bother with a PDU, just put the outlets somewhere reasonable.

This is very straightforward work, and you certainly do have the spare spaces in the panel.

Cooling

48A@240V is 11,520 watts or 39,300 BTU/hour of heat.

The 48A, with regular household loading, is pretty much at limits for your service. Adding 4kw of air conditioning is not an option.

I gather right now you're heating the house, but you want the heat in the house, not in one room.

So I recommend, if able, put the heat generators all over the house where the heat is wanted / where air conditioning is. Through a happy coincidence, this is also where the power is already wired with many 15A (1440W) circuits all over the house. In your case too few; you could fix that.

Alternately: Water (antifreeze) cooling would solve the problem by removing the heat entirely from the house. These guys did it, but with a hokey outside radiator "solution". A junkyard SUV radiator (with cooling fans and fan thermostat) will suffice.

Electricity cost

Consider this poor fellow. His utility tricked him onto a rate which charges him 1 cents per KWH, but $7 per kw of peak. If you could find a way to make the load "back off " when other appliances are pulling load, your monthly cost would be set by the servers, and your household loads would be essentially free.

Talk to your power company about rates like that. That weirdo rate is because Georgia is glutted in nuclear power, and nuclear power plants Do Not Like to be throttled down.

  • Thank you for the thoughtful, detailed comment. You knowledge is apparent. You should know, however, that I am not mining bitcoin. Mining bitcoin with self-hosted servers is a fools game. I'm doing something else. :D – Donzo Feb 14 '18 at 1:02
  • @Donzo sorry, we see so much of it I tend to assume. Here's the link to the whole house/dump it outside water cooling setup I saw, – Harper Feb 14 '18 at 2:13
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+1 on the cost issue. To give it relevance, your panel has a 30A breaker feeding your AC unit. You will need a 60A circuit for your blade server. But unlike an AC unit, that blade server will likely be running 24/7/365, consuming TWICE as much energy as your AC does on a hot day in the summer. Non-stop, every single day. No idea where you live, but if you pay the average electrical rate in the US, which is 7 cents/kWh, that is going to cost you roughly $1.26 per HOUR to run it. That's almost $40/month ADDED to your electrical bill. And as mentioned, this will ALSO increase your cost of air conditioning by quite a bit, so that figure could easily double in warm months. I hope you are doing something that makes it worthwhile.

But CAN it be added to your service, sure. That thing you heard about a 100A service being able to handle 200A is pure bunk; it can ONLY handle 100A, actually legally, 80A. But you can use a "diversity factor" based on knowing that all circuits will not be 100% loaded 100% of the time, so you can add this. keep in mind though that things like servers tend to run at full load most of the time, so that 48A load is coming right off the top of your 80A max load on that 100A main, leaving you essentially 32A for EVERYTHING else in the house, INCLUDING the AC unit. You will be constantly flirting with tripping that main, especially on hot days.

  • I really appreciate all the help that everyone gave me. The wealth of knowledge that you have given to me for nothing raises my hopes for humanity. Buried in Appendix A for this server enclosure is functionality for limiting the power to 24 amps. Based on the feedback everyone has given me, I think that I'm going to wire the 30 amp breaker, use a single PDU, and limit the power on the unit to 24 amps. Thanks everyone! Lord knows my wife will beat me to death if the AC cuts out in June. – Donzo Feb 14 '18 at 19:57
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When I finished my basement, I added a subpanel via 80 Amp breaker in the main panel (200A service). The subpanel has circuits totalling 135A. This includes a sauna oven on a 40A circuit. I did pull a permit and the inspector was quite pleased with my work.

My 200A main panel has a breaker capacity over 500A total, including another 80A breaker for a 2nd floor subpanel (that has a 240V circuit for a washing machine), two 30A breakers for the pool pump and AC units, etc etc.

I don't have problems with overload. I have never managed to trip the 80 Amp breaker for the basement, even with the sauna oven running on full load during start-up.

The primary challenge and cost driver for your project will be the wiring imo. You will need to run 4 or 6 gauge 4-conductor wire, which gets pretty expensive at longer distances. Challenging because the wire is heavy and stiff and not easy to pull through walls etc.

If I understand you correctly, you want to power one M1000e? At full build-out with 16 blades, this only draws a little over 30A (according to https://www.dell.com/community/PowerEdge-General-HW/Power-Requirement-for-M1000e-16-Blades/td-p/5077478). I think you will be ok with adding the 60A circuit.

  • Sounds like a nice project. I ended up wiring 2 x 30 amp circuits and using 2 x 24 amp PDU to power the server. I used 10 gauge wire. I only need to run it a few feet. I learned a lot from everyone here. Sincere thanks! – Donzo Feb 26 '18 at 2:02

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