Interesting observation on 120/208 panel schedule - someone can clarify?

[tankfarms]

I'm reviewing a new installation drawing and found this: the listed load VA is always 1.44 times that of the listed Watts, what's the reason behind this?

I doubt that's a conversion from power facotr, if so, the power factor is 0.7 which is way too low for lighting loads.

This is a typical 120/208 3-phase installation.

As you see, this 1.44x "multiplier" is one each circuit of this panel as shown in the picture.

Any thoughts?

 

[GoldDigger]

I doubt that's a conversion from power facotr, if so, the power factor is 0.7 which is way too low for lighting loads.

I would guess that the calculation was in fact being done for a estimated PF of 0.7, which used to be common for magnetic fluorescent light ballasts before power factor correction became a specification requirement.
Without control over what ballasts will be used, the schedule is taking the conservative approach so that the VA figure can be used safely for sizing upstream components and circuits.

 

[steve66]

I think they have added an extra 25% for continuous loads.

Then it looks like they have divided the load (increased it) by about another 0.87 for some type of ballast factor or power factor.

 

[Smart $]

I think they have added an extra 25% for continuous loads.

Then it looks like they have divided the load (increased it) by about another 0.87 for some type of ballast factor or power factor.

Panel schedule phase loading should not list exaggerated values (i.e. 125% for continuos loads), or should indicate in some manner if such is applied... but that's just my opinion. I'm not aware of any rules on the matter.

The wattage figures are likely lamp wattages. Ballast supply current is always higher than equivalent for lamp wattage to some degree because none are 100% efficient.

 

[tankfarms]

Thanks all for the feedback. I take this is just another safety multiplier for sizing equipment when they did the design.

 

[petersonra]

Thanks all for the feedback. I take this is just another safety multiplier for sizing equipment when they did the design.

maybe something empirical in nature.

 

[iceworm]

Thanks all for the feedback. I take this is just another safety multiplier for sizing equipment when they did the design.

Actually none of those (or maybe some of all of the above + another reason):slaphead:
I'd want to look at the load calc before I guessed at safety factor, load padding, assumed pf

Consider this:
With 208/120, the issue shows up if one considers the 120V loads calculate a VA of 120 x I. Now take that same current and put it on two legs, and the VA is 208 x I. Compare the two.
L1 = 20A
L2 = 20A
Is the VA = 208 x 20 = 4160VA
Or is it (120 x 20) + (120 x 20) = 4800VA

Also shows up in 120/208 single phase. That's in 220 (I think - I don't do much of that)

Doesn't show up if the loads are all three phase. Just another reason why I like industrial.

ice

 

[GoldDigger]

Actually none of those (or maybe some of all of the above + another reason):slaphead:
I'd want to look at the load calc before I guessed at safety factor, load padding, assumed pf

Consider this:
With 208/120, the issue shows up if one considers the 120V loads calculate a VA of 120 x I. Now take that same current and put it on two legs, and the VA is 208 x I. Compare the two.
L1 = 20A
L2 = 20A
Is the VA = 208 x 20 = 4160VA
Or is it (120 x 20) + (120 x 20) = 4800VA

Good Morning ice,
Have some coffee.

The diagram shows individual circuits, each of which is connected only to one phase conductor. Given that, the lamps appear to be set up for line to neutral 120 volt use, and the wattage of the lamps will be figured at that voltage.
If the lamps were wired from phase to phase (208 volts) then the diagram would have shown a two wire breaker with connection to two phases.

The discrepancy between 20 amps on two phase wires being 20 amps times two at 120 or 20 amps at 208 is taken care of by the famous square root of three factor used for three phase load when looking only at the phase wire current. In the case of two single phase loads, there will also be current in the neutral, so the result (and the power) will not be the same as for a single phase-to-phase load.

And in any case, the way you calculate the watts will not have any effect on the ratio between the watts and the VA.

 

[iceworm]

Good Morning ice,
Have some coffee.

Good idea - I'll get another cup. Its 9:30 - I've got to go to work. And you guys are addictive. Shame on me.

... The diagram shows individual circuits, each of which is connected only to one phase conductor. Given that, the lamps appear to be set up for line to neutral 120 volt use, and the wattage of the lamps will be figured at that voltage.
If the lamps were wired from phase to phase (208 volts) then the diagram would have shown a two wire breaker with connection to two phases.

I can't see the picture, so thanks

... The discrepancy between 20 amps on two phase wires being 20 amps times two at 120 or 20 amps at 208 is taken care of by the famous square root of three factor used for three phase load when looking only at the phase wire current. In the case of two single phase loads, there will also be current in the neutral, so the result (and the power) will not be the same as for a single phase-to-phase load.

And in any case, the way you calculate the watts will not have any effect on the ratio between the watts and the VA.

You are absolutely correct. Although the .87 factor discussed is suspiciously close to (sqrt3)/2 - which, of course, is the ratio in my example. And I can't see the load calc. And I have seen people stumble ove single phase load calcs in 3ph panels (not me, of course, :angel: cause it is not something I would ever have to do - okay rarely have to do). None of which changes - "You're still absloutely correct"

The Worm (turneth)

 

[Fordean]

I'm reviewing a new installation drawing and found this: the listed load VA is always 1.44 times that of the listed Watts, what's the reason behind this?

I doubt that's a conversion from power facotr, if so, the power factor is 0.7 which is way too low for lighting loads.

This is a typical 120/208 3-phase installation.

As you see, this 1.44x "multiplier" is one each circuit of this panel as shown in the picture.

Any thoughts?

It may be if load is on for 3 hours or more. 125% OF Load

 

[Smart $]

It may be if load is on for 3 hours or more. 125% OF Load

Perhaps... but 125% is not quite 144%

 

[Little Bill]

Apparent power and true (RMS) power?

 

[mivey]

It appears to be HID lighting. 0.84 amps for 70 W lamps and 1.2 amps for 100 W lamps. Looks like HPS but not the most efficient version.