Topic: new electric setup: 1-phase vs 3-phase (Read 284 times)

In North America it is NOT 2-phase (but yes such a thing does exist for some very limited applications). The technical name is "Split Phase" as it is 1 single phase that is literally split into 2 legs by using a transformer winding with a center-tapped Neutral connection. As such, both legs are in-phase with each other which is why you get an even 120V split referenced to Neutral. True polyphase has each leg out of phase with the others. In the case of 3-phase it's a 120deg shift between any 2 legs.

First I want to say that although I'm no electrician but end up with problems like this often enough in different applications.  What country are you in, and what are the voltages at your mains legs?  I ask because I always consider 220-240VAC as being "2 phase - more properly two single phase legs" - I have a shop with three phase and we have some equipment that is larger that does indeed need three phase.  Not mining equipment mind you, but compressors and steam generators.  So without three phase, we'd (my shop) be doing some expensive electric motor upgrades - we can't do like most (very small) miners and go either one or two legs of hot.  Again I consider each leg of 110-120VAC one phase.  So because you are just going to mining, I'm thinking it would be cheaper to go 220V - 2 legs of 1 phase 110-120VAC than just 1 phase if you are indeed 1 phase - and that may be the case in some places, but very few as far as I know.  My feeling is that you are in the US and really have 2 legs of 110-120VAC (2 phase in my mind, they are 180 degrees out of phase, thus I say two phase) along with a neutral and ground coming in from the grid. Voltage [V] x Amperage = Watts [P -Power in watts], or P/V=A, so Amps (current) is lower by half for each leg of 110VAC. Now,  {V=IR} or Ohms law brings in the resistance term, you would have lower current draw on each leg, thus lower resistance, getting you more efficient, safer wiring, and saving on electricity cost marginally if it's set up properly (and inspected by a real electrician etc).   Lower Amp draw running one phase per leg (phase) of your power supplies, splitting the load between two conductors.  Now if you have three phase you can send those phases around for different loads (using sub panels etc for specific areas etc) more efficiently and ultimately end up being able to distribute loads better, but that is really a matter for future expansion.  

More directly to your question - should you go 3 phase if you can?  If money is no worry, three phase allows you to run larger equipment like welders and other fun things you may want in the future, and split loads in creative ways.

I will take a crack at trying to explain.

For industrial power users they generally need three phase and it’s benefits for motors which are far simpler in design and more efficient than single phase motors. By adding the third wire there is also a good bump in available load rating without having to upsize the wire and panels feeding everything. Get three phase if you are going to have big HVAC or big ventilation fans.

150kW on single phase is around the 625A per leg range which needs some serious wire and larger gear.

150kW on three phase is closer to 425A per leg. This makes for smaller wire sizes and easier installations.

Like NotFuzzyWarm said, the line provider will do their best to balance loads as they connect services. Sure your load might tip the scales a little but in the grand scheme when a power plant puts out 400MW (1000 times the size you plan to be) your load won’t be perceived as unbalanced by the generator.

In an ideal world a mine should get 240/415V three phase but that is tough because that is a non-standard system voltage in North America.

Do the power supplies run more efficient at higher voltages? I do not believe so, at least not enough for it to really matter. Rectifiers and electronics are really efficient these days. What is nicer about 240V over 208V or 120V is that the breakers, plugs and wires to the miners can be smaller which is generally cheaper. Plus there is less chance of fire if someone accidentally brings a 18awg IEC cable into the facility. At 120V those will burn up right quick. At full 240V there is much less chance of running an individual circuit over its rated max, at least accidentally.

But profit is king. Do what is available fastest and most cost effective. You want to be running, not messing around with electrical services. 

I am scaling up to around 400kW and actually still on the phase conundrum, so now I'm asking why 150kW was "getting into 3-phase territory" and so this implies I should be getting 3-phase for 400kW facility?

That wild leg is considered a potential safety hazard because folks adding new (120v) circuits to a panel that is fed in that way MUST pay close attention to which breaker slots in the panel are fed by it. Every 3rd slot is the wild leg.

For new construction or service upgrades most local codes will demand you to have two breaker panels: 1 main panel for the incoming service main breaker followed by high line (208-240v) 2-pole or 3-pole breakers in it for single or 3-phase loads, and a 2nd single-phase panel fed from a large breaker in the main panel.

The 2nd panel is only fed by L1, L2 and Neutral. This 2nd panel is for all single-phase 120/208V lighting and wall outlet power, breakers in it will be either 1-pole or 2-pole to respectively deliver either 120v from L1 or L2 referenced to Neutral or single phase 208-240v from across L1-L2. The driving point is that new circuits can be added to this panel at will with no regard to that wild leg.

The most common wye service connection from the utility's transformer eliminates any potential for incorrect wiring. Leg to leg will always be 208-240v and any leg to Neutral will always be 120V (208V phase voltage) up to 138V (if phase is 240V).

As for actual voltage supplied, that is a bit of a sticky issue... Most utilities want to give you 3-phase 208VAC (usually more like around 213V) vs 230-240 because with a 208V leg referenced to Neutral you will get 120VAC. Them supplying 230-240VAC splits down to around 132V up to just over 138V when referenced to Neutral, that of course is a no-go.

Is the higher phase-to-phase voltages better? Yes. As you said there is lower current pulled so less stress on the front side of PSU's. Plus, it gives you greater margin to keep running if there is a brown out where the line voltage drops though in the US the brown out margin rarely matters.

I'm in the US. Do miners such as antminers run more efficiently on higher voltage? (this is why I was aiming for 240v) as well as the increased effiency gain from higher voltage (less current).
For larger setups I keep seeing that a 415/240 volt transformer is ideal, so I figured 240 delta was similar.

What specifically do you mean "voltage imbalance" between the high leg and neutral? As long as you ignore the 208V between it, everything is fine right? you have 120v and 240v available no?

You're over-thinking things....
Unless you are pulling mega-watts of power, load balance on the utilities transmission lines is not your concern. If you have 3-phase power you only have to reasonably balance power from your distribution panel. If you have single-phase power it is still the utilities concern - not yours. Of course this also assumes that you are in a fairly well developed country with stable & modern power grids.

In most countries 3-phase is typically delivered to a building as a wye connection with a center Neutral connection - not delta. However, that also depends on the local power loads. Wild leg or high leg grounded delta is usually only found where most area loads are single phase and only a few select customers need 3-phase. Unless it is your only choice, due to the voltage imbalance between the wild leg and Neutral I do not recommend grounded delta.

What country is this in? How power is distributed varies between countries and even between regions within a country.
What voltage is your typical wall outlet at home or business? 110v or 220v?
ref https://en.wikipedia.org/wiki/Three-phase_electric_power

If you want 208-240v 3-phase power, and if the location also needs a lower voltage for wall plugs & lighting just tell the utility that. They will decide on the type of transformer used as it all depends on how they distribute power in the area where you are.

Are you just saying that the TDU should be able to balance things on their side easier than I make it seem?

Also, you're not referring to "high-leg delta" voltage are you? I am considering requesting 240 3 phase in the delta config:


This setup is as true of 3 phase as 120/208 right?

I assume that "TDU" is your utility supplying power to the building?
If so, yes and no. Yes it is a load on only 1-phase of their (usually 3-phase) transmission lines BUT it is their job to monitor the lines and divvy up the loads on them between you and other customers so no it should not really be an issue for them.

If you are in North America, depending on what kind of power is needed for other businesses nearby, their '3-phase' may not exactly true 3-phase but rather 3-phase created by using a 'wild leg' as referenced to Neutral. Voltage across all 3 or any 2 lines is the same. Voltage from either L1 or L2 referenced to Neutral is balanced to 1/2 the L1-L2 voltage. For 208 VAC that is 110V for L1 or L2 to Neutral. Voltage on the 3rd or Wild leg referenced to Neutral is much because it is is NOT reference to Neutral. The 3rd leg is supplied only to places needing 3-phase to run motors, refrigeration, and other application requiring it that are powered by all three phases. If that is the case the utility is already supplying single phase power over very heavy lines feeding several other locations nearby.

Would they prefer a load split across all 3-phases? Sure, but it should make no difference in what you pay.

Is drawing 150kw on a single phase an issue for the TDU since it is extremely unbalanced on the transmission lines, right?

150kw is getting into 3-phase territory but still very practical for single phase service. It comes down to cost of the panel (size and amount of copper in it) and if the power company needs to supply you with a different service transformer to feed the building. As Mikey said, go with what is cheaper.

Why would anyone recommend 3 phase over a single phase for mining? it really makes no difference, since you are going to be using nothing but PSUs that need only a single phase.

Remember that by the end of the day you will be using 3*single phase which is just like running 3 separate single-phase wires, what you should focus on are only the total allowance and the cost.

You tell your electric guy that you need for example 100kw at 220v in the cheapest form possible, I don't know about the cost in your country but I'd say a single-phase set-up would be cheaper.

I have 3 phase but only because I really don't have any other option, the nearest supply I have is 3 phase 11KV, so I have an 11KV to 380V (3 phase) transformer (the only type of transformers available here), it does come in handy sometimes, for example, I was able to get some 3 phase exhaust fans ( certainly a lot more robust than a single-phase fans) but I then have to worry about load balancing and shit, so with everything else equal, a single-phase will be it for me.

This question has been asked a couple times with variations and I haven't quite got an answer so I'm posting this here.

I found a small shop to use for mining, aiming for about 150kw total 24/7 power draw. I'm discussing with TDU and electrician about setup but neither of them are very helpful in giving advice for what I need. Their attitude is mostly just like "just tell us what you need and we'll do it". The shop has a small 1 phase 200 amp panel, but they are willing to make the upgrades.

From my research, it seems the question of 3-phase vs 1-phase delivery just comes down to cost. All mining hardware uses 1 phase but still many people seem to recommend to go with 3 phase because of reduced delivery costs. I'm not 100% sure the reason for this, so that is part of my question. Secondly, I might be able to take the panel and any other electrical equipment from the shop with me to later expand, so if 3 phase isn't strictly neccesary, maybe it is a good investment anyways?

Anyway my main question here is, should I give the TDU a load sheet requesting 3-phase power or just 1-phase? Any advice on this is appreciated because I am really unsure.

Thanks.