1.73 Power calc. confusion

[CESllcTN]

I have (36) 277V - 1kVA lights on a 480/277V 3-phase panel. Would I calculate the circuit feeding the panel with 36,000W / 277 x 1.73? Or just 36,000W / 277? Thanks

 

[winnie]

If you've distributed the lights evenly across the three phases, then you treat the load as a 480V three phase load, and use 36000/480/1.73.

You could also think of this as 277V loading by dividing by the number of phases being used: 36000/277/3

-Jonathan

 

[charlie b]

Let me rewrite the equations a tad more clearly.

36000 / (480 × 1.732)
Or
(36000 / 277) / 3

Both yield the same result of around 43.3.

 

[tortuga]

I have (36) 277V - 1kVA lights

All the following presumes these are ballasted lights, not say old incandescent (that would be nuts in 2024!).

Would I calculate the circuit feeding the panel with 36,000W

Article 215 has the rules for calculating a feeder aka the "circuit feeding the panel".

215.2(A)(1) Says you calculate the load per article 220.
220.14 (D) Luminaires. says

An outlet supplying luminaire(s) shall be calculated based
on the maximum volt-ampere rating of the equipment
and lamps for which the luminaire(s) is rated.

So you need to go look at the nameplate of these '1000W' balasts and see how many amps they use at 277V, not the output watts of the fixture. Here is a sample data sheet (from 1000W MH lihgts used for sports area lighting)


So I'd use 4.1 Amps per light not 1000W.
Then I would figure Amps X Volts to get VA
4.1A X 277V = 1136 VA per light
Next 36 lights X 1136 VA = 40896 VA
Now 215.2(A)(1)(a) says we have to add 25% if its a continuous load (on for 3 hr or more)
so we take 25% of our total and add that on
40896 X .25 = 10224 VA
40896 + 10224 = 51120 VA
If its a evenly balanced load I divide by 480 * SQRT 3 or 831.36V
51120 VA / 831.36V = 61A feeder size
That is if the lights are the only load on the feeder.

To make sure its balanced I could figure the maximum imbalance or the maximum lights on a line
To do this we'd have to know if they are on 4 wire MWBC or 2 wire circuit and the size of the branch circuits.
If they are on a 2 wire 20A 277V branch circuit for example I'd figure the number of lights per circuit as
Limit of branch circuit in VA / Continuous VA of lights, since the same load calc rules apply to the branch circuits (210.11 & 210.19)
Limit = 20A X 277V = 5540VA
Continuous VA of lights = 1136VA * 1.25 = 1420 VA
5540/1420 = 3 lights per circuit
So 12 circuits will balance.

 

[ramsy]

220.14 (D) Luminaires. says
An outlet supplying luminaire(s) shall be calculated based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(s) is rated.

220.18(B) specifically requires nameplate current for LED drivers & Ballasted lights

 

[ramsy]

To make sure its balanced I could figure the maximum imbalance .. so 12 circuits will balance.

310.15(E)
When considering current carrying conductors, triplen harmonics on Wye xfmr Neutral loads are CCC's regardless of balanced loads.

310.14(A)(3)
Informational note paragraph (2), describes harmonic load that overheat terminations. So load should not max ampacity, after the continuous factor x 1.25.

4.1A x 4 lights x 1.25 continuous = 20.5A

The industry practice for harmonics typically upsizes the neutral, in this example to a #10cu.

 

[d0nut]

All the following presumes these are ballasted lights, not say old incandescent (that would be nuts in 2024!).

I would argue that for most applications anything other than LED would be nuts in 2024, and I would include sports lighting in the list of applications where LED is appropriate.

 

[kwired]

I would argue that for most applications anything other than LED would be nuts in 2024, and I would include sports lighting in the list of applications where LED is appropriate.

Seems to still be common to use HID in grow houses as questions involving HID issues that come up on sites like this often are involving grow houses.

Better lighting qualities for growing plants? IDK but kind of assuming that is the case.

 

[tortuga]

I would argue that for most applications anything other than LED would be nuts in 2024, and I would include sports lighting in the list of applications where LED is appropriate.

Agreed I think now in 2024 they got it worked out.
but for a while people resisted the change, coaches are suspicious of anything that might degrade players performance, they freak out when the brand of bottled water gets changed.
There was also the problem of random lights turning purple mid game.
In aging facilities on a tight budget, like a city tennis court, YMCA or high-school they might have a tendency to buy cheap junk LED retrofits that have poor performance when they would have been better off keeping what they had going.

 

[Hv&Lv]

.
There was also the problem of random lights turning purple mid game. .

Yeah, many street lights do that also.
Purple or blue.
Blue LEDs with the phosphor layer around the lights is disintegrating. The phosphor absorbs the blue wavelength leaving red and yellow wavelengths to pass creating a white light.
It’s a manufacturing flaw that manufacturers don’t want to take action on.
Wait until a municipality gets sued because the blue lights are causing a safety issue with drivers at night. Maybe then it will change.

 

[electrofelon]

I would argue that for most applications anything other than LED would be nuts in 2024, and I would include sports lighting in the list of applications where LED is appropriate.

Seems to still be common to use HID in grow houses as questions involving HID issues that come up on sites like this often are involving grow houses.

Better lighting qualities for growing plants? IDK but kind of assuming that is the case.

HPS actually typically has a higher lumens per watt than LED, although HPS is omnidirectional so you need a reflector and there will be some losses there. Not sure how it typically works out for "delivered" lumens per watt.

 

[electrofelon]

310.15(E)
When considering current carrying conductors, triplen harmonics on Wye xfmr Neutral loads are CCC's regardless of balanced loads.

310.14(A)(3)
Informational note paragraph (2), describes harmonic load that overheat terminations. So load should not max ampacity, after the continuous factor x 1.25.

4.1A x 4 lights x 1.25 continuous = 20.5A

The industry practice for harmonics typically upsizes the neutral, in this example to a #10cu.

With modern PFC power supplies I dont consider those things to be an issue anymore.

 

[ramsy]

With modern PFC power supplies I dont consider those things to be an issue anymore.

Does that include unlisted equip, with no FCC testing, which everyone buys from Amazon?

Did utilities stop charging commercial & industrial customers for non-linear loads, because everyone uses PFC?

I don't think so.

"In the United States, the voluntary Energy Star guideline states that any computing equipment must have a PF of at least 0.9 when working at its maximum rated output."

If mandatory can't be enforced, when is voluntary going to happen?

Do you specify PFC for lighting, or measure THD, before ignoring neutral CCC's on a balanced Wye per 310.15(E), before ignoring prohibited neutral reductions per 220.61(C), or ignoring the up-sized neutral bus over 1000 volts, per 368.258?

An oscilloscope is not a typical tool in the quiver of construction trades, and inspectors don't ignore up-sized neutrals on permitted plans.

 

[ramsy]

With modern PFC power supplies I dont consider those things to be an issue anymore.

My service business is seeing orders for surge protection (SPD) from HVAC contractors, to prevent circuit board damage. Clients are calling with end-use equipment instructions requiring SPD. Never seen this before, much less NEC mandates for SPD wherever AFCI is installed. Shielding against utility excursions & EMP is increasingly difficult, as is adapting xFCI's to electronic warfare of harmonic appliances.

It seems the great wall street scam of 2008, which foreclosed on municipal funding everywhere, replaced sequestered electrical inspectors / plans engineers, and permit enforcement, with design-build installers who are ignoring harmonics, and escalating utility line noise in the wild.

 

[electrofelon]

Does that include unlisted equip, with no FCC testing, which everyone buys from Amazon?

For larger commercial projects no one is buying lights from Amazon. Luminaires are required to be listed and unlisted ones would not pass inspections.

Did utilities stop charging commercial & industrial customers for non-linear loads, because everyone uses PFC?

I have never come across a utility that measures and charges for non-linear loads

Do you specify PFC for lighting, or measure THD, before ignoring neutral CCC's on a balanced Wye per 310.15(E), before ignoring prohibited neutral reductions per 220.61(C), or ignoring the up-sized neutral bus over 1000 volts, per 368.258?

No I do not specify or measure. Yes I just ignore.

 

[ramsy]

No I do not specify or measure.

I can learn something from honesty, which may share the proof to support the practice, and teach us both.

 

[electrofelon]

I can learn something from honesty, which may share the proof to support the practice, and teach us both.

Maybe if I was doing a data center and there were feeders or MWBC's supplying only servers I would give it a closer look. Other than than I cant imagine the stars aligning for it to be an issue with the type of work I do.

 

[kwired]

For larger commercial projects no one is buying lights from Amazon. Luminaires are required to be listed and unlisted ones would not pass inspections.



I have never come across a utility that measures and charges for non-linear loads




No I do not specify or measure. Yes I just ignore.

I don't think distortion power factor is as much of a concern to utilities as displacement power factor either.

For one thing I think distortion tends to be lesser per watt of energy consumed than displacement power factor tends to be.

Take a motor that runs at .86 PF. Now run it on a VFD. The displacement power factor on utility has gone to 1.00. But some distortion had been added because of the high speed switching, but much less effects on distribution loading than displacement power factor has.

 

[tortuga]

I think just doing a correct load calc takes care of most modern harmonics but I am no expert.
Using 'lamp watts' and omitting the continuous factor resulted in almost a 30% reduction in feeder size for the OP (43A vs 61A).

 

[Knightryder12]

Seems to still be common to use HID in grow houses as questions involving HID issues that come up on sites like this often are involving grow houses.

Better lighting qualities for growing plants? IDK but kind of assuming that is the case.

Not any longer. The lighting manufacturers have really got the LED grow lights on point these days. They can make any spectrum of light with different LEDs in one fixture. All of the grow facilities I have designed in the last 3 years have all been LED.