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277/480v 3 Phase Line to Line vs Line to Neutral

09/24/2016 12:23 PM

Please help us understand, thanks in advance.

We're building a commercial greenhouse, (all applicable codes will be respected) and using sixty 1000w metal halide lights. I understand the that line to line may save copper but my thinking is line to neutral can reduce amp draw running 480v 3 phase? What are your thoughts?

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#1

Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 1:42 PM

The higher the voltage the lower the amperage, the watts remain the same....The lower the amperage the smaller the wire size requirement the cheaper the wire....Light fixtures and bulbs sometimes vary in price depending on the popularity, this is also a factor that must be considered...Energy usage can vary from lighting type to type, this must also be considered...In this day and with what's available in the market I would certainly be considering LED lights which reduce energy costs and electrical requirements, as well as maintenance costs over time....

https://www.ledgrowlightsdepot.com/blogs/blog/19086795-best-led-grow-lights-2015

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#5
In reply to #1

Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 7:51 PM

We're growing food and the light spectrum needs to equal the sunlight. I considered LEDs and when light intensity and spectrum is realized I move on to them but at present I can't justify the expense and the additional labor required to readjust height.

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#6
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 7:54 PM

I see you didn't read the link at all....good luck

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#7
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 8:39 PM

So I read the article and it is as I expected. When LEDs are used above 70% the longevity decreases dramatically which means greater expense. The LED is a blue and red spectrum very good for vegetive growth and flowering of non food plants, but the LED needs to be quite close to the plants and in our system this's troubling because we need to inspect the plants everyday; so I'd need raise the lights then reset the height hourly.

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#8
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 11:00 PM
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#9
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/25/2016 1:24 AM

Growing varieties of the mustard family from seed to harvest about 38 days, and needs supplemental lighting during the dark winter at the 44th parallel in Minnesota when the heat of metal halide will be welcome helping to keep the facility at 78 F.

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#10
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/25/2016 8:13 AM

Well, if you're determined to use that much powered you can't worry about the amount of copper.

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#11
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/25/2016 8:48 AM

The lower current when a neutral is included if my thinking is correct a 1000W MH at 480v with neutral current is .86805555556 amps vs line to line current is 1.503516326 amps. The power supply is 112KW 480/277 high leg wye.

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#17
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/29/2016 4:47 PM

You are in error, view the following catalog....

http://hid.venturelighting.com/On-LineCatalog/Venture_Lighting_Interactive_Catalog_v1.pdf

page 55 gives 4.0 amp for a 1000W lamp with (essential) ballast @ 277V single phase.

2.4 amp...............................................................@ 480V single phase.

Note that the advantage of 3 phase/ 3wire over single phase 2 wire declines when you necessarily have to use 2 wires per lamp where you split off to 3 lamps in different positions.

Each lamp needs a ballast, the weight of which and accessibility for maintenance weighs against having it integral with the lamp (a 1000W lamp underneath cooks the ballast too!) and enclosure against water is needed. The more enclosures you have, the more the assembly cost - you have to decide how to subdivide the system so you have say 5 switches/breakers (3 phase)(12 lamps each switch) to avoid losing everything due to a fault.

Fundamentally, you have to double the copper cross section for a single phase lamp at 277V versus 480V. Four lamps/phase at 277V take 16 amp, needing 2.5 sq.mm copper rated 21 amp: while 4 lamps/phase at 480V take 9.6 amp, needing 1 sq.mm rated 12 amps. The wire ratings I give are UK ones for one 3 wire/3phase circuit in conduit - several circuits in one conduit have to be de-rated because of mutual heating.

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#18
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/29/2016 9:14 PM

I have a 277/480 wye 3 phase service and my calculations are:

The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by 3 times the power factor PF times the line to neutral RMS voltage VL-N in volts (V):

I(A) = 1000 × P(kW) / (3 × PF × VL-N(V) )

*1kw, line to neutral, 277v, PF 1,

1.2033694344 amps

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#19
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Re: 277/480v 3 phase Line to Line vs Line to neutral

09/30/2016 8:32 AM

Your formula is correct. However, your unit of load is a 1000W lamp. The lamp itself is, of course, 2 wires and single phase. The maker's data I referenced states one ballast & lamp draws 2.35 amp at 480V.

Since 480V x 2.35 A = 1128 VA and the consumption is listed as 1080 W, I think each lamp ballast is single phase input, high power factor - not a box which converts a 2 wire lamp to a 3 wire, 3 phase load. So each lamp is essentially a single phase, 2 wire load.

To have a balanced 3 phase load, you must connect

  • 3 single phase 277 volt lamps [with ballast] line to neutral (known as Y connection) or
  • 3 single phase 480V lamps line-line (known as delta connection, because the voltage vector diagram looks like a greek alphabet Δ ). Note the angles in that Δ are 120 degrees.

Each line conductor in Δ connection has two lamp loads connected to it. Because the currents to the two lamps are sinusoids 120 degrees apart their currents do not sum arithmetically, but with a cos 60 degrees (0.866) factor. Line current = 2 x 480V load current x 0.866.

Taking the makers values for 480V lamps, 2 x 2.35 x 0.866 = 4.07 amp - near enough the current listed for a 277V lamp (the power factors may be different or values rounded). So, as someone noted in their "post", 3 lamps of 1000W at 277V draw essentially the same current as 3 lamps of 1000W at 480V when connected as a balanced load to a 480/277V system.

The clever thing about 3 phase is that, with a balanced load 4 wire system, there is negligible current in the 4th neutral wire so negligible voltage drop & losses in the 4th wire. In effect, the two wire final loads are being supplied with zero voltage drop in the return wire!

In fact, you can manage with 3 wires, three EQUAL 277V loads can be connected in a Y to 480V 3 wire. The "rub" is that single phase loads to different customers are never equal - you would get unstable voltages without the fourth (neutral) wire from the "star" point of a Y transformer winding source.

I note your 1.203 amps: 1.203 x 3 = 3.6 A for 3 lamps - but the losses of the ballasts have to be added - without a ballast to limit current, a discharge lamp will run-away to excessive current/power and explode.

As another post commented, 277V gear may give the lowest cost solution because it is more used and available for lighting. Cable size and cost is only part of the system cost. Minimum length of conduit and cable, minimum number of control cabinets, junction boxes and flexible control are important as well as current.

I hope this helps.

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#2

Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 1:56 PM

In a balanced Wye system (3 phase + neutral) with resistive load there is no current in the neutral. The amount of current in each phase line would be the same for the same amount of power whether the load is connected Wye or Delta.

Having said that, metal halide lights may have higher harmonics present in the current waveform which will return in the neutral regardless of whether the load is balanced or not. In that case you should have a little less in each of the phase wires with a Wye connected load.

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#3

Re: 277/480v 3 phase Line to Line vs Line to neutral

09/24/2016 3:09 PM

Not true.

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#4

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/24/2016 7:13 PM

60- 1000 watt metal halide lights? Sounds like enough light for growing in Hanger 1, it's already wired, so wire according to already existing. And, it's well secured too

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#12

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/25/2016 11:42 AM

"High leg wye"? No such thing, which show that you don't know what you are doing. You should hire a professional.

Watts are watts are watts. The higher current is irrelevant. If you are going to try to run all of those lights on one circuit, a) you are nuts and b) at 480V it is a 60A circuit, so by the time you get to the end of the run, the voltage drop will get bad and you will need impossibly large conductors.

The reason why you use 277V for lighting is that you will end up breaking these up into multiple circuits anyway. So because you are in charge of balancing your load, you run 3 hits and one neutral in a conduit and split off one hot and one neutral to each fixture, then have 3 separate 1 pole breakers on each hot leg. It's called a Multi Wire Branch Circuit (MWBC). In fact it's best in a large space to stagger them so that if one breaker trips, you have nearby lights still on because they are a different circuit, so the spillover light still gets something on the area and you aren't left with big dark areas.

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#13
In reply to #12

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/25/2016 1:25 PM

Thank you and yes I was using the designation 277/480 wye until the Gillette genset nomenclature stipulated 277/480v high leg wye, and I do have an electrician doing work though I like to have understanding too. I've seen 277/480 wye noted as, high leg, red leg, orange leg etc., and as you indicated it's not an accurate description. I intend to employ staging allowing for expansion and unknowns.

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#14
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Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/25/2016 11:27 PM

Higher current leads to larger copper investment to keep the IsquaredR heat losses reasonable. Compare the two methods, 3 small copper return conductors at 480V to 1 larger copper neutral at 277V, and the raceway considerations to get the equipment installed and wired. You may need to consider a larger gauge neutral than supply if harmonics mentioned earlier are considered.

I don't know of any rule of thumb that sets you one way or the other, even equipment selection, circuit breaker selection could tip the scales...

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#15

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/25/2016 11:51 PM

"I've seen 277/480 wye noted as, high leg, red leg, orange leg etc., and as you indicated it's not an accurate description."

If you have heard that, you have been listening to nincompoops... No such term for 480V systems, Wye or Delta. Does not exist.

The ONLY place where the term '"High Leg", "Red Leg", "Orange Leg", "Stinger Leg" etc. is used in a power system description is for 240V Delta systems. That describes a specific transformer arrangement where you want 240V 3 phase for 3 phase loads like motors, but you also need 120V in small amounts for office lighting, plugs and receptacles. So ONE of the 3 transformers for the 3 phase bank will have a center tap, which is referenced to ground, giving you 240/120V Split Phase on that ONE circuit.

The term "High Leg" applies to the fact that you will measure 120V referenced to ground on 2 pf the legs, in this drawing, A and C to ground, but if you measure B to ground, it will measure 208V, so it is "High" with relation to the other two, but not really intended (or advisable) to be used for anything. In some jurisdictions, you are required to mark that phase with Orange phasing tape, in the past it used to be Red, hence those two terms. "Stinger" means if you forget and plug a single pole breaker into B phase, it burns out 120V devices and that stings, particularly in the pocketbook. Officially, the limit on this type of 240V Delta system is 5% of your total load can be 120V single phase, because it is inherently unbalanced. If more than 5% of your load will be 120V single phase, you are supposed to use 208Y120V.

Again, this has NO RELATION to any voltage other than 240V; there is no 480V equivalent. 480V systems are either Ungrounded Delta, Corner Grounded Delta, or 480/277V Wye.

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#16

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

09/26/2016 1:39 PM

So this is a 60 kW lighting system? That is impressive!

I can see where using metal halide lights will result in some heat residual in the greenhouse, but it is hardly enough to even keep a barn warm in Texas, much less Minnesota. Good luck with the endeavor.

Listen to the old bulls here. They do know their electricity.

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#20

Re: 277/480v 3 Phase Line to Line vs Line to Neutral

02/01/2021 5:47 PM

Hello folks-

Reading online to educate myself I found this thread. It didn't answer my question so I thought maybe I could get some related answers signing on here to engage with your large minds on the subject of AC power. My situation is not unlike the original posters but so I thought to add on to this thread as opposed to a new thread since it might help them out as well.

I am partnering with folks to grow Hemp indoors in the state of NY and they have obtained the license to do so. The facility is going to run about 80 1000watt HPS lights and about 55 8 bulb T5 (432 watts a piece). Rough calculations put the HVAC system at about 30 tons, plus a little energy for additional dehumidification, water pumps, etc, surplus juice.

The facility currently has 300 amps of 3-phase power but I think this is about 400 amps shy. Would it be much trouble to ask recommendations on how to best wire this system up? All of the lights and mechanical will be run 277v 3-phase.

At 277v the 1000w HPS pull 3.8 amps (lets call it 4), at 277v the 8-bulb T-5's pull 1.66 (call it 1.75). 320 amps for the HPS and about 96 amps for T5. I am guessing a 30 ton AC unit pulls right at 220amps at 480v? Could this be accurate?

Calculation on that is:

One ton of frig.=12000 BTU
1 watt=3.412 BTU
30 tons x 12,000=360,000 BTU
360,000/3.412=105,510 watts

105.510/480 volts=220 amps

If the project gets full green light, are there methods to wire this up to reduce the size of the current draw on the panel? I'm grateful to all who can deepen my knowledge on this subject.

Very Best!

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#21
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Re: 277/480v 3 Phase Line to Line vs Line to Neutral

02/01/2021 7:35 PM

The first thing is that you need to use your SEER to convert tons of refrigeration to electricity, so if you have a SEER of 16, divide the converted BTU by 16.

277v is line to neutral voltage for 480V 3 phase loads, so your ac unit will likely be 480V and 3 phase, for lowest cost. Look up internet conversions for kw per BTU for mechanical refrigeration, about 80 amperes at 460v 3 phase, for a Carrier 30T unit.

Your lighting at 277 volts is single phase, so you need to distribute them among the 3 phases, so it you have 60 amperes of 277v load, you can figure on 20 amperes per phase to supply that load. With your numbers, about 140 amperes, so a 300A service is adequate, they would likely give you a 400A if National Grid felt it needed to be changed out.

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#22
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Re: 277/480v 3 Phase Line to Line vs Line to Neutral

02/01/2021 8:16 PM

That is an informative and helpful post Mr. Williams. Thank you so much for your reply...that got a "helpful answer" mark from me. Also, thank you for tying in SEER rating into the equation; I didn't know how that was connected to the equation.

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#23
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Re: 277/480v 3 Phase Line to Line vs Line to Neutral

02/02/2021 12:17 AM

Good luck, impressive project, and you actually provide the details needed, good work on your part too!

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