single phase or 3phase wiring?

Quote "86 x 13amp socket outlet for 43 computers , 2 x 13amp socket outlet for HP, 3 x 13amp socket outlet for computer servers ,2 x 2.5hp air conditioners"

This does not tell me anything. Get the name plate amps for the computers and the other loads.

If the building it is going into already has three phase power and in the correct voltages needed then use that otherwise single phase will work just fine. My math says the total load would be likely under 20 KW peak which is well within a single phase power supply capacity. So if you don't have three phase already available don't worry about it.

Be careful about what contractors recommend. Many are greedy lieing little weasels with huge markups on their labor and materials! Convincing you to install a three phase system in your building just for a computer lab could put $100K or more in their pocket after expenses for no real justified reason!

What voltage(s) are these pieces of equipment?

If the air conditioners are available in 1-phase versions, then at least in principle the whole system can be 1-phase. However, if the ACs are only available in 3-phase, then a reasonable system would be 208-120/3 with neutral. The loads should be analyzed so they can be balanced nearly equally among the 3 phases.

What are the line voltage choices commonly used at your location?

Hi Kuduk - I support your answer from all enginnering matematics aspects. A DED [Detailed Engineering-design baed Drawing] is needed for the circuitary design and defining the allied gears on each electrical phase [a] guide the contractors [b] verifying the completed works [c] support the operating staff even once Rohan is on another assignment. Best Regards, Furqan

GA for the first best (safe) answer when reading from the top down.

Anyone even thinking about single phase does not realize that the 3 phases have to be load balanced as much as possible to stop neutral current!!!

3 Phase is the way to go.

Furthermore, losing a phase means that you will only lose about a 1/3 of the sockets, not all of them!!!

UPS is ALWAYS a good idea....

I forgot to add, I would suspect this install in either in the UK or one of its dominions, ege. a "proper" 240 volt AC system, not a US 220 or 2x110.....

The 13 amp ring main sockets sort of gives it away......am I right?

If by some lucky coincidence the AC load equals very nearly half of the combined computer loads, this might work. Otherwise, it is likely to be unacceptably imbalanced, especially as the AC load varies.

A properly sized AC may not even be available in single phase. Each watt of equipment and lights is a 3.41 Btu/h load; each person about 400-500 Btu/h. Without building dimensions, insulation data, outdoor air conditions, and door/window sizes, an AC load estimate can't be completed.

Since each half of the computer group shares a line with the AC, I don't see how the AC can be considered as isolated any better (or worse) in either system.

Tornado,

He said 2 x 2.5hp air conditioners.

The "everything-on load test" would be interesting. Using 3 phase Air Conditioning would be my preference too.

More specifications would be nice to know.

Kuduk

Rohan,

I would agree with Kuduk, a Lab such as this needs more thought than the Electrical Contractor has added.

The Input to the room, if available in the facility should be 3Phase.

From that point you need to "Split" the the room into functions.

1) IT\Lab Load
2) Support Services

Item 1 - List the equipment that falls into what the room is for.
Collect the "Name Plate" ratings for this equipment and work out your maximum load, this is not the same as a maximum demand calculation as these units will always be ON and therefore the load will have a baseline that only varies between that point and 100%.
Source a 3phase UPS that is rated at 150% of the initial load with cabling installed to 200% adjustable breakers would be a good idea if not cost prohibitive.
Take a 3phase sub-board from that for your IT\Lab load and try and keep it balanced across the phases.

Item 2 - From the initial board all your Support Services can be fed (lights, 3phase airconditioning, printers or any non-critical equipment)

This way your IT\Lab kit is isolated from the "noisey" mechanical & electronic equipment.

UPSs can be connected to the ethernet so do it and install the software that will allow the UPS to command the PCs and Servers to shutdown Cleanly in case of a Mains Failure and protect the valuable Data.

Talk to a Mechanical Services E(e)ngineer and get him\her to do a load assessment that includes the people factor as well as the IT\Lab load, then you can get appropriatly sized HVAC units, possibly with a spare if your application requires it.

Regards,
Sapper.

Excellent point about the cooling capacity!

When I was setting up labs and dev centers I was usually presented with very warm to hot working conditions for the QA guys and developers because the air handlers were under capacity for the heat production from the computers and monitors. The servers were especially good at producing excess heat.

I would recommend at least an HVAC contractor be consulted but better yet an MEP firm to design the proper environmental solution. It will be money well spent.

Note that what is normally called single phase (110 VAC) residential power is in reality 2 phase 220 VAC. This is a significant difference when calculating if you have enough power available from regular 'residential' power service that you already have readily available.

No, what is normally called single phase is in reality SINGLE PHASE. In most residential installations both 120 volt and 240 volt services are obtained from the same secondary winding on the distribution transformer. The center tap of the winding comprises the neutral, which is required to be grounded at the service entrance.

Electric motors designed to run on single phase power require a starting circuit or device, usually a second winding that uses self-induction or a capacitor for phase shift to produce a rotating magnetic field

The phase difference in a two phase electric supply provided the means for a rotating magnetic field in induction motors without the need for a separate starting circuit.

http://en.wikipedia.org/wiki/Two-phase_electric_power

In most cases, two phase electric supply has been supplanted by three-phase supply.

Doug,

single phase (110 VAC) residential power is in reality 2 phase 220 VAC.

The single phase residential power is derived from a single phase input to a transformer that has a split single phase output to the power meter and breaker box in the house. The 230 and 115 Volt service is still single phase no matter how you look at it.

Kuduk

The single phase really is single phase. 1 110 leg and a second leg made of another 110 leg in phase but inverted. I missed an exam question because of it. My instructor reminded me the 2 circuits were in phase but opposite as the timing was identical, not the amplitude. Multi phase ( including 2 phase ) are time shifted.

Rebuilt,

I have noticed that a lot of people seem to have trouble understanding the difference between syncronous zero crossing to peak and non-syncronous zero crossing to peak as it pertains to phase.

Kuduk

The 13-amp circuits are not a US standard, so I'm thinking UK or other European. If so, this may be 220 volts rather than 120. It would be nice to know.

A 2.5 hp AC would be about 480/3/4 amps, 240/3/8 amps, 208/3/9 amps, 240/1/13 amps, or 120/1/26 amps. That's real rough for comparison. For 120 (or 110) volts, a 1-phase unit would be odd, but not out of the question (though I've never seen such). A 240 (or 220) 1-phase unit would be feasible.

Rather wildly assuming 400-watt loads for each 13-amp plug, 400 x 91 = 36.4 kW. This all gets dissipated as heat into the room; plus some unmentioned lighting; plus presumably 43 persons. 36.4 kW x 3415 Btu/kWh = 124,306 Btu/h heat load. To this we add 43 x 400 Btu/h-person = 17,200 Btu/h. After adding heat conduction through the building envelope, plus infiltration through openings, plus lights and ventilation, it will be around 200,000 Btu/h total. This equates to 16.7 tons of refrigeration, which requires about 14 hp or 10 kW. (Sizable error bars for all of this.)

Wattage ratings on the computer equipment would be good to have for refining this thumbnail calculation....

Please tell us where you are located...

British Standard 7671 will prove valuable reading, then.

A three phase system,such as 208/120Y is generally used to supply racks of computers.Each rack using one hot and 1 neutral to obtain 120vac, and alternating and balancing phases among the racks.The harmonics are very much suppressed by this method, and modern switch-mode power supplies are required to do their switching at the zero-crossing point, thus eliminating harmonics that were generated by the older switch-mode supplies.A three phase sytem has the advantage of delivering the same amount of power with 50% less copper than a single phase system.13Amps is an odd circuit for a receptacle in the USA, and if this is your actual load, you would have to use a 20 amp receptacle and #12 awg wire.(80% load allowed).Industries use 3 phase because of the inherent efficiency of the system.

I have seen a 3 phase 120 volt systems, and a 42 volt 3 phase system used in some German and British made machinery, but very rarely do you see this voltage configuration.

HiTekRedNek

Its a UK (and Dominions) standard system, called a "Ring Main".

You will enjoy reading the infos here:-

http://en.wikipedia.org/wiki/BS_1363

HI ALL,

forgive me in advance.was not able to be online for sometime.

Im from Malaysia. where single phase refers to 240v,50hz.

thanks alot for the advice as some of it are very new knowledge for me to learn.