Wiring both power phases to my server room

[Mr Spock]

I estimate my server room's worst case current load could be just over 20A. I'm planning on routing two 20A dedicated circuits. Intuitively I'm thinking I should run both of the split phases of 120VAC to maintain balance. Some items would run off phase A and some off phase B. For example I'll have a Grand Concerto house audio amplifier and the expander unit (12 zones). I'm thinking I'd run one off of phase A and the other off phase B, along with splitting up everything else.

So my question is for those who have a lot of industry experience in this realm. I would expect that a properly designed power supply in all of my equipment would properly isolate their connections and make this a non-issue. However I can also think of scenarios where this might cause me trouble. At least there could be audio hum issues and such (I plan on asking Nuvo).

Does anyone have experience or advice on how best to work this or maybe some dos and dont's. For example should I tie both wire pair's neutrals together and (separately) the grounds together?

Thanks.

 

[tmbrown97]

The neutrals and grounds *are* tied together in your panel. Some of the A/V guys may know better about the noise issues - I can't think of any;

I think, given my background, I'd be tempted to run 240V in there as well if you plan to run servers and equipment; most of those components that use IEC sockets are compatible with 120-240V input - either with a switch or automatically. It's a much more efficient way to distribute power and keep the legs balanced. It takes a little getting used to the first time, but you get a power distribution strip that has the IEC sockets and a handful of the right cables from monoprice, and it's pretty straightforward. So much easier than balancing things across a couple different circuits, and a single UPS can protect everything. I've gotten some pretty good deals on eBay for UPS's that were brand new.

 

[gatchel]

I wouldn't tie the neutrals together in any other location than the main load center. Depending on how you wire them, if one neutral would fail then the other neutral would be carrying (or have the potential to carry) more than the rated ampacity of the wire.

 

[Mr Spock]

[sup]Yes the neutrals are tied together at the panel (so are the grounds). My though on tying them together at the load is to minimize imbalance on the neutral side of the line. I can see Gatchel's point. Might be others I'm not aware of that also make this a bad idea.[/sup]

[sup]If I do run both phases then I have 240V in the server room. I just have to wire up a 240V plug off both phases hot's accordingly. I'll look into your UPS advice.[/sup]

[sup]Anyone else with experience in this field care to comment?[/sup]

 

[jpmargis]

Intuitively I'm thinking I should run both of the split phases of 120VAC to maintain balance.

Circuits be circuits. It makes absolutely no difference which leg the load is connected. 240 VAC does not have "phases" and they don't need to be "balanced".

 

[Mr Spock]

Circuits be circuits. It makes absolutely no difference which leg the load is connected. 240 VAC does not have "phases" and they don't need to be "balanced".

My balanced statement was regarding 120V, which does have two phases (split) and optimally does like to have balanced loads.
They do not have to be balanced, but for a variety of minor reasons its a good thing to do.

240V in the US does not have phases. You get 240V by using each side of the 120V hot (no neutrals involved).

Looks like not a lot of experience in this field here. Maybe I'll consult an electrician.

 

[jpmargis]

You did consult an electrician!

 

[apostolakisl]

I don't quite understand why you need to balance such a tiny load as 20 amps between the two phases. Certainly you will have a myriad of other stuff running randomly about your house on one leg or the other causing "who the hell knows what" as far as which leg has how many amps at any moment in time.

While I am not an authority on this point, it is my understanding that the utility co. transformers don't give a hoot about balancing the load. . . they pull both legs from the same leg of the three phase running down the street.

And don't tie the neutrals together in the room unless the wire is rated for the full amperage of both legs.

 

[video321]

My opinion... screw the whole balanced load idea. That'll never work for a home environment anyway - who knows when each fridge will kick on or you run the dishwasher, laundry, etc. That is more for business environments that have a steady workload throughout the day and they could be calculated. With that said, I'd go the opposite and run 2 circuits on the same phase to reduce any issues.


And last... I'd measure what you're actually pulling before paying an electrician to run new circuits. I currently have (4) TVs, (2) computers, (2) A/V receivers, a decent size sub, network equipment, CCTV DVR and more all running on a single 20A circuit without issues.

 

[Mr Spock]

Ok, now I'm starting to accumulate some useable feedback.

If I run both phases to this new construction server room that is not yet built and so the real loads are as yet unknown (other than worst case calculations) I have the option of having 240V if I want it.

If I run both 20A feeds off the same phase then there should be no possible hum and similar problems. 2x20A is probably over kill, but I'd rather have overkill and expandability. Phase balancing is admittedly[font="Arial""] [/font]a minor thing. Down side is no 240V if I should want it.

As long as the wires go to the breaker planel I can always change it afterward.

 

[video321]

As long as the wires go to the breaker planel I can always change it afterward.

Exactly

 

[Westcojack]

1. I have seen the av contractor call for 2 120v circuits run from receptacle to receptacle and then to a plug which then plugs into the power conditioner. Then both circuits are on the same phase of the same power conditioner. This eliminates any noise in the lines.
2. I have also run 2 separate hot legs, 2 separate neutrals, and 3 ground wires. 1 ground wire to ground the boxes, and 1 groung wire for each circuit using isolated ground receptacles. This keeps the receptacles off of the grounding system for freezers, refrigerators, a/c units. (The iso ground is only grounded at the main service.)

 

[apostolakisl]

If I run both phases to this new construction server room that is not yet built and so the real loads are as yet unknown (other than worst case calculations) I have the option of having 240V if I want it.

I wouldn't do it like that. I would run something like a 50amp line to a sub-panel. Electrically taking two separate 120vac lines on opposite phases and merging them together in your room would work, but it would be odd and confusing to anyone not privy to the original installers notes. Probably not something the inspector would be cool with either.

And your neutral's would be screwy again also since you would have two of them for what would end up being a single 240vac setup. . . .I just don't think you should do that. A subpanel is what you need to be future-proof and in code.

 

[JimS]

You could tie the neutrals together in this particular situation if you split the circuits. In fact if you split the circuits you could run 12-3 (with a single ground conductor) that would carry both circuits and a single neutral. You can use two independent single breakers or one dual. With one circuit on one leg (or phase, or whatever you want to call it) and the other circuit on the other leg there is no way you can put more than rated current through the single neutral. If both circuits are at 20A the neutral current will be zero. Even though it may be possible to run them on one circuit I think your objective (and I could be wrong) is to over do the wiring a bit so you don't have that as a likely point of failure - so running two circuits makes sense. That said, the fact that two 20 A circuits is such a small part of the total load makes running them both off one leg or splitting them probably not that important unless your entire system is near the limit anyway. But if the rest of your loads are balanced then splitting them is at least theoretically a bit better. And having 220 in the room is good as others have suggested. For universal input equipment it does reduce the current for each piece of equipment. But power is power so for example you have a two 600W loads. At 120V that is 5A, at 240V it is 2.5A. If wired for 120 and you put one thing on each circuit then each circuit has a load of 5A.

If wired for 240 each load is 2.5A for a total of 5A. Since it is 240V then the 5A flows in each hot conductor. So in each case the 20A conductors are each loaded with 5A each. NO DIFFERENCE! (except for second order effects such as slight efficiency differences of the power supplies at the different input voltages, which is going to be very small).

But 240 does allow a bit more flexibility. I would run 12-3 and split the loads. The most important thing for hum reduction is grounding everything to the same point. If you bring low level signals such as line level audio in from another location you may need to use an audio transformer but in many cases it will be fine without it. You can add the transformer if needed.

I design industrial power electronics if that counts for anything...

 

[JimS]

The isolated ground (no other loads connected to it) does have some merit but then this is a dedicated circuit so how could it be anything but isolated? (assuming it is wired to the main panel).

If you want flexibility for both circuits on the same 120V leg or 240 V don't run 12-3. You could Run 12-2 for each. But doing that and combining them for 240V is a bit odd and may not be to code. But down the road you could convert one to 240V by adding a colored tape to the white wire at both ends and using it for the other hot wire of the 240V circuit. One wire run would be 120V and the other would be 240V. That would meet code.

I really think you are over thinking this as there are a number of ways to do it. Unless you are running a server farm with LOTS of things I don't think it matters that much.