Lighting Calcs for indiv. branch circuits

[starbright28]

He's not wrong, he's just showing more info than most people do. I've never seen anyone show watts in a schedule. I've only seen VA, because its technically the more important value when sizing a panelboard.

What I meant by is he doing the calculations correctly to show the correct # on his panelboard. I will agree that I have never seen the "watts" column until I started working here. Plus his panelboards are also set up different, and I would re-arrange to make them more clearer.

I understand how to get VA, that's not hard at all. I was a little confused with the post on what exactly I needed to be looking for.

 

[starbright28]

Okay - sicne I think we nailed down on how to figure out the ampacity and the VA for the fluorscent lighting or lighting that contains a ballast, and regular lighting (using lamp wattage only)....

how do you figure out lighting in a residential house, when you basically have receptacles and lighting on the same circuit? What is the good General thumb of rule on this? I have alsways been curious how you figure out how many to put on 1 circuit.

And for practical sake - how many on a 15amp circuit, and how many on a 20 amp circuit.

thanks

 

[starbright28]

Here we go again

Here we go again

I just had a meeting with our lighting sales rep. and our engineer here. We discussed the method on using the input watts x the # of light fixtures you have then divided by your voltage = amps.

The whole big ordeal totally blew me into a more confused state when I got done. I thought I had it understanded. Acutally I understand the formula, I just don't understand why we don't use that number and place it on our panel boards.

Also, i brought up the deal eith the continuous load, and needing to take the amps by 125%. Our engineer does not do that, nor the lighting salemen said was this really required? Since the engineer is still using the lamp wattage and adding them up and placing this under VA on our panel board, it doesn't make since. He calculates the power factor as being one, and said he's never been able to find a power factor for the type of ballasts in the fluorscent lamps. The whole deal about the 125% factor being added on stumped them that I guess we'll be calling later this week the Ballast Engineer who does these calculations in and out all day long.

What I am finding out that there is no "right or wrong" way in doing these calculations. The code book doesn't reall ynail down something, and the AHJ will depened if you need to watch your lighting loads or not. To me it doesn't make since in the reason why you wouldn't follow code book ruling all the time, unless I took some of there interpertation differently.

In the end it has left me confused on how on earth do you figure out how much to put on 1 circuit for lights, receptacles, etc. What numbers you use to figured out this calculation, what code articles you look at, what is the general rule in how much you fill up the circuit, etc. That is what still confuses me.

So if anyone can read through my mumble jumble and help decifier out what I'm trying to say - please help...

 

[W6SJK]

Amanda,

Is the engineer that you are working with a licensed/registered Professional Engineer (P.E.)? He certainly isn't acting like one. And at the risk of offending lighting reps... some salespeople are not qualified to design so don't take their word as gospel.

You already have the answers you need.

Never add up lamp watts. The lamps are most likely not being "driven" by the ballast at their rated watts. And it takes power to run the lamp ballast, as it is not a 100% efficient device. So that adds a few watts also.

Never assume a PF of 1 for a ballast.

Add up ballast input amps or ballast input VA and enter VA into the schedule. Plain and simple. Get the data from the lighting fixture mfr or a ballast catalog, or the actual ballast nameplate.

As to multiplying by 125%, if the engineer doesn't understand this simple requirement he is not qualified to be a lead engineer on a project. NEC Article 100 defines a continuous load as a load that operates 3 hrs or more. Clearly most lighting falls into this category!

NEC 210.19 (A)(1) requires branch circuits to be sized at 125% of the continuous load on the circuit.

NEC 210.20 Requires the overcurrent protective device to be sized at 125% of the continuous load, unless it is a 100% rated device, meaning that it can handle a load of 100% of the breaker amps for more than 3 hrs. No 20A branch CBs have this rating. So you must multiply the continuous load by 125%. The is the same as multiplying the CB rating by 80% (The recriprocal of 125%) So the max load would be 80% x 20A or 16A. Most people limit the load to 12 to 14 amps to allow for variations in ballast performance and to leave room for alterations to the circuit in the future.

End of story.

 

[W6SJK]

Maybe that's not the end of the story I should clarify one thing.

The VA shown for each circuit is the actual VA, without multiplying by 125%. Then most schedules show a subtotal for each phase, and a "subtotal" VA for the panel. Then and only then do some engineers show an additional 25% value, arrived at by adding all the continuous loads and multiplying by 0.25. This value is added to the previous subtotal to arrive at a grand total VA. This is then converted to amps. This amperage is the minimum size of the panelboard bus, and the main CB if it has one.

Going one step further:
If you were to sub feed this panel 'B' from another panel 'A', you would show the actual load for each phase of panel 'B' in the load columns for the circuit in panel 'A'. The 25% value shown in panel 'B' carries forward and is added to any 25% factor calculated for the other loads in panel 'A'.

If this confuses you just stick to the lighting load calcs for now

 

[starbright28]

Sparky001

Thank YOU! I thought I had understood everything the right way. Then I questioned the engineer in regards to why we are showing that other number, and the way he explained it, i got lost with the first word. It just didn't make sense.

I haven't had the meeting with the Ballast Engineer (the one that comes up with the input watts, and maybe will tell us the power factor), but will post once that meeting happens. Since both the other 2 didn't understand the continous load deal - and I have no clue if it is even shown on the panelboards as so.. then I can't really coment on that.

So... your story helps me out. Now to nail down why exactly the panelboards are calcualted the way they are so (and hopefully not let me lash out at the person!)

BTY: he is a PE, holds a Master's lisence, and a contractor lisence.

 

[e57]

Amanda, you do realize that anything you cobble together will be ignored or tossed as soon as the electrician on site arrives.... We never trust those lists.... Just a fixture spec will do. Whats next? Circuit design - line diagrams - most of us would just scrap that too, or bid high just to match it. And if your calcs are wrong - we have no responcability....

 

[W6SJK]

Amanda, you do realize that anything you cobble together will be ignored or tossed as soon as the electrician on site arrives.... We never trust those lists.... Just a fixture spec will do. Whats next? Circuit design - line diagrams - most of us would just scrap that too, or bid high just to match it. And if your calcs are wrong - we have no responcability....

Electricians may ignore them but city plan reviewers don't! BTW, do you normally make a habit of ignoring contract documents? [not to hijack the thread...]

 

[starbright28]

Here's where it gets interesting.

I was an electrician before I came a drafter. I understand what the engineers specify and don't think it is always necessary either, however now that I work for one, I make sure the plans at least look understandable to the electrician.

I am just cya'ing here because you never know with the situation at my company. And I would be required to know things like this.

And I still don't fully like engineers (electrical) but put up with them for that's my work currently. So in some ways, I'm in the middle person.

Never had that meeting yet with the ballast engineer. Engineer here cancelled the meeting and never told me. Good thing the lighting sales rep called me up to say that, and boy was I ever fumed!

 

[starbright28]

starting to get some answers

starting to get some answers

I have a few "clarification" issues that I want to be sure that I am understanding correctly.

First: with this continuous load deal ebing 3 hours or more, this applies to anything that is connected with wires and controlled by a circuit breaker, correct? So it doesn't necessarily mean "just motors", but also means lighting and other things. So really is anything not a continous load?

The 125% you multiply is with the amps that you get at the very end of the calculation.

Now for our panelboards - what then do you show for the P.F. since the ballast itself will vary. The power factor is already in the calculation of doing the amps - so why is the point of showing something on the panelboard schedule?

And watts - what is exactly shown for watts - just the lamp wattage, or is the VA and the watts usually (or always) going to be the same.

 

[W6SJK]

I have a few "clarification" issues that I want to be sure that I am understanding correctly.

First: with this continuous load deal ebing 3 hours or more, this applies to anything that is connected with wires and controlled by a circuit breaker, correct? So it doesn't necessarily mean "just motors", but also means lighting and other things. So really is anything not a continous load?

It applies to any load connected to a CB or fused switch where the CB/switch is not "100% rated."

Most receptacle loads are not continuous. Some motors are not continuous. Water heaters and water coolers are normally not continuous. Hand dryers are not continuous. Think about it.

The 125% you multiply is with the amps that you get at the very end of the calculation.

You multiply the continuous load amps, if any, by 125% and then add the non-continuous load amps, if any. The resulting amps must be less than the CB or fuse size, unless the CB or fused switch is rated for continuous loading (i.e. 100% rated). Panelboard CBs under 400 amps are not 100% rated.

Now for our panelboards - what then do you show for the P.F. since the ballast itself will vary. The power factor is already in the calculation of doing the amps - so why is the point of showing something on the panelboard schedule?

I have never seen anyone show PF on a panelboard schedule in 25 yrs. You are the first. You're right, just show VA and don't show watts and PF.

And watts - what is exactly shown for watts - just the lamp wattage, or is the VA and the watts usually (or always) going to be the same.

We've told you before... Showing lamps watts is never right when there is a ballast involved, due to ballast losses and how hard it "drives" the lamps.

I have never seen anyone show WATTS on a panelboard schedule in 25 yrs, only VA. We told you before, WATTS never equal VA except when the power factor is 1 which is almost never.

 

[haskindm]

Amanda,
Everyone is making this much more difficult than is neccesary. There is no reason to worry about watts on a panelboard schedule, electricians are concerned with volts and amps. Have we supplied the equipment with the voltage for which it was designed? Is the ampacity of the conductor and overcurrent device adequate? Is the ampacity of the panelboard sufficient for the load to be served? Watts do not enter directly into these concerns. ANY load that stays on CONTINUOUSLY for 3-hours or more must be considered a continuous load. Usually equipment that is controlled by a thermostat or runs intermittently is NOT considered a continuous load. Most commercial lighting would stay on for three hours or more, so it is considered a continuous load.
Take the amperage input of the ballast(s) connected to a circuit, multiply this number by 125% and you have the load on the circuit. Period, you need do no further calculation. Take an existing circuit ampacity, multiply it by 80%, and you have the maximum CONTINUOUS load that may be connected to that circuit. Period, you need do no further calculation. You do not need to be concerned about lamp wattage, power factor, or anything else for the calculation that you are doing. Any discussion about power factor, harmonics, lamp wattage, etc., while interesting does not impact your calculation. I agree with some of the others, that the "engineer" on this job needs to do some studying on load calculations. Nothing can be determined by figuring the wattage of the lamps in a fluorescent fixture, unless you know the power factor of the ballast. In this case you may take the apparent wattage (from the lamps) and multiply it by the power factor of the ballast. This will give you the true wattage of the fixture. This number will usually be higher than the lamp wattage as some energy is wasted in heating the ballast.
Stick with the amperage draw of the ballast and you can't go wrong.
Hope that helps.

 

[starbright28]

My clarification issues weren't really clarification issues after all. I do understand thw whol calculating the amps deal, and I know that is what you base you whole circuit off of, is the number of amps to that circuit.

The whole reason this question of mind started is that I couldn't figure out what the engineer was doing and how he figured out how many fluroscent lights he could put on a circuit. Now that I have been told time and time again, this many with room to spare I understand.

But the I continued to question this further with the deal on the Continuous load and that they need to times everything that is like this situation by 125%. That's where I got resistance. 2 people in that meeting that I wrote about a while back never heard of doing it. I told both of them, it's in the CODE! Don't you follow the CODE????

And since that meeting, nothing else has been said about calculations, etc. for projects, and I'm not going to bring anything up becuase A) I think he doesn't want to be proved wrong B) I think he can't handle being outsmarted by a women C) stuck in the ways and won't change.

So I decided to continue this quest by myself and keep stuff to myself. I just recently talked to someone that is a rep of some kind for Advance Ballasts. I told him about the 125% factor that you use on the amps from the ballast information. He also hasn't heard of this. He was going to do some digging, and get in contact with a "old jigger" that's been with Advance Ballasts many years. Since he called yesterday, I have not had a call back. So it will be interesting to see what they come up with.

Now, you take that input watts of the ballast (which has the PF factored in) and divide it by your source voltage to get your amps for that light fixture. From those amps you take 125% to get your final amount of amps, and then start adding them up to do your circuits.

That's it, correct? Nothing more, nothing less. and seems so easy too!

As far as the panelboards currently being shown for the drawings I put together and go out the door, I have no control over. If that engineer no longer works there, then I will suggest and/or implement a better panelboard schedule that shows information an electrician would really think is necessary. Until that point however, I put up with what I see.

Thanks again, for everyone's help. I guess I didn't realise this was out there, and will "ponder" with the inspector I know in 2 months about this formula. I'm just so curious to hear his opinoin.

 

[AllenC]

Hi,

I'm based in the Philippines (220VAC/60Hz) and I need real help getting the actual energy consumption for fluorescent lighting fixtures.

Here is the test system I used for measuring the amps:
- 36W 4-ft T8 fluorescent lamp (G13 lamp base)
- Conventional/Normal Power Factor Magnetic Ballast 40W rating (0.43A printed on the ballast)
- 40W regular starter

I got an actual 0.43A using a clamp meter on the power cord.
Note that after adding a capacitor to the system, I got 0.22A reading.

FORMULAS:

1) System Input Wattage = Amps x Volts = 0.43A x 220V = 94.6W

2) Energy Consumption = 0.0946kW x hrs of operation x energy rate


QUESTIONS:

1) 94.6w seems to be too high for a single 36W lamp. Is this normal? (In our country we don't have the 32W T8 linear and mostly we use ordinary NPF magnetic ballasts.)

2) Do I need to factor in Power Factor?

3) Is it correct to use the System Input Wattage as basis for the actual energy consumed especially when calculating/estimating total lighting consumption for a small (say 3-floor) office building assuming the lighting used was basically similar to my test system?

Thanks!

Stick with the amperage draw of the ballast and you can't go wrong.
Hope that helps.

 

[W6SJK]

First, you should start your own thread topic.

1) 94.6w seems to be too high for a single 36W lamp. Is this normal?

Yes. Check out the ballast mfrs web site for actual watts.

2) Do I need to factor in Power Factor?

Yes, if you want watts, not VA. Watts = Volts x Amps x PF

3) Is it correct to use the System Input Wattage as basis for the actual energy consumed especially when calculating/estimating total lighting consumption for a small (say 3-floor) office building assuming the lighting used was basically similar to my test system?

You use VA to size the wiring. You use watts to figure (kilo)watthours that will appear on the utility bill. You shouldn't need to run your own test. The data should be available from major manufacturers.

 

[AllenC]

OK, I've started a new thread topic "System Input Wattage for Lighting".
(Sorry about this. Pls reply using the new thread.)

I'm confused. I need to estimate the actual cost of energy for a particular lighting setup. So I need to get the kWh and use the Watts = Volts x Amps x PF, right?

I'm based in the Philippines and most conventional ballasts here don't have a model number. If I don't have the data from the manufacturer, will my method (using the clamp meter to get the actual amps) and formulas mentioned give me an accurate KWh rate?

Another problem is that I don't have the PF of the ballast. Lets say I'm computing for the actual utility cost of a client's lighting setup and I want to compare the cost when a capacitor is added to correct the PF. So, for the client's present setup, can I get the PF from their latest utility bill and for the setup with capacitor can I just assume a conservative 0.9 PF? Using the formulas mentioned, I'll use the 0.43A for the setup without capacitor, and use 0.22A for the one with capacitor (based on our own testing using a clamp meter). Is this method valid?

Also, I'm still wondering if 0.43A is too high (90+ watts per 36W T8 lamp).

Thanks.

First, you should start your own thread topic.



Yes. Check out the ballast mfrs web site for actual watts.



Yes, if you want watts, not VA. Watts = Volts x Amps x PF



You use VA to size the wiring. You use watts to figure (kilo)watthours that will appear on the utility bill. You shouldn't need to run your own test. The data should be available from major manufacturers.