lamps in parallel max

[Mayimbe]

How many lamps of 1000 W can I conect in parallel?? According to the NEC.

The lamps have this data:

V = 480 V
P = 1000 W
I op = 2 A

_________________ Lamp#1 _________ Lamp #2 ..._____ Lamp #N

Nmax = ??

 

[Johnmcca]

OCPD size, continuous or non continuous use?

 

[Mayimbe]

OCPD size, continuous or non continuous use?

OCPD stands for what?? not familiar with the acronyms.

they will work only at night, all night, so I guess they are for continuous use.

 

[Smart $]

How many lamps of 1000 W can I conect in parallel?? According to the NEC.

The lamps have this data:

V = 480 V
P = 1000 W
I op = 2 A

_________________ Lamp#1 _________ Lamp #2 ..._____ Lamp #N

Nmax = ??

210.23(D) Branch Circuits Larger Than 50 Amperes. Branch
circuits larger than 50 amperes shall supply only nonlighting
outlet loads

 

[Johnmcca]

OCPD = Over Current Protective Device

 

[Mayimbe]

210.23(D) Branch Circuits Larger Than 50 Amperes. Branch
circuits larger than 50 amperes shall supply only nonlighting
outlet loads

Oh. Ok. All that I have to be careful is that my total operating current stays under the 50 Amp barrier.

But is there something in the NEC that says: "You can connect only 5 lamps of 1000 W for each branch", or something like that.

OCPD = Over Current Protective Device

I need to know how much lamps can I connect for a single branch to specify the protections, dont you think?

Im designing. It doesnt exist yet.

 

[charlie b]

My answer would be 19, but I suspect from the wording of the question that the person who wrote the question is looking for the answer of 20. Now, show me your work, and what answer you come up with, and then I'll tell you how I came up with those two possible answers.

 

[Smart $]

OCPD stands for what?? not familiar with the acronyms.

they will work only at night, all night, so I guess they are for continuous use.

50A ? 125% continuous loading = 40A

... ? 2A/lamp = 20 lamps

 

[charlie b]

Oh. Ok. All that I have to be careful is that my total operating current stays under the 50 Amp barrier.

No, there is another barrier you have to be concerned with. That was the reason for the ?continuous or non-continuous? question. Do you know what that other consideration might be?

But is there something in the NEC that says: "You can connect only 5 lamps of 1000 W for each branch", or something like that.

No. There is no specific requirement that is written in that context.

I need to know how much lamps can I connect for a single branch to specify the protections, don?t you think?

No, I don?t think so. You are looking at the situation backwards.

I?m designing. It doesn?t exist yet.

Then you get to make the choices. For my part, most of the lighting circuits I have designed have been 20 amp circuits. A few have been 30 amp circuits. I have never yet come across a 50 amp lighting circuit, but perhaps other members have. And as we see you can?t go over 50 amps in this application.

So you have a choice to make. The considerations include length of run, availability of unused circuit breakers, cost of copper (fewer large wires as opposed to more smaller wires), and the standard practices used by the client company, and in particular their maintenance department.

 

[charlie b]

50A ? 125% continuous loading = 40A ... ? 2A/lamp = 20 lamps

OK. That's how I got the answer of 20. Now how did I get the answer 19?

 

[Smart $]

...

But is there something in the NEC that says: "You can connect only 5 lamps of 1000 W for each branch", or something like that.

...

Well there is, indirectly, if your ocpd is less than 50A. How many lamps you can place on the circuit is limited to the circuit rating divided by 125% divided by the current rating of each lamp [fixture... meaning, especially in the case of non-incandescents, that it is stipulated by the fixture's current rating, not the lamp rating].

 

[Smart $]

OK. That's how I got the answer of 20. Now how did I get the answer 19?

I'm waiting for you to tell me... 'cause my brain isn't registering any other method of calculation right now.

Hmmm... perhaps 1000W ? 480V = 2.083A per lamp, disregarding the possibility of a power factor of less than 1.

 

[Johnmcca]

1000 /480 = 2.083a

40/ 2.083 = 19.2

 

[Mayimbe]

My answer would be 19, but I suspect from the wording of the question that the person who wrote the question is looking for the answer of 20. Now, show me your work, and what answer you come up with, and then I'll tell you how I came up with those two possible answers.

Well, from what 210.23 says.

Taking care that this kind of lamp have a huge starting current, for a very short period, and that each one will have a ballast that will drop this value, to normal values. I will say that each lamp at worst will operate with a current of 3 amps. Im being very conservative, because they are going to be connected to a small diesel plant of 250 kVA.

so #lamps = 50A/3A = 16.66 ~ 17 lamps.

Either way, I was planning on using a max number of 4 lamps for each branch. But I was scared about violating any rule of the NEC (which I found that is very similar to my country electric code)

Thanks guys

 

[Mayimbe]

No, I don?t think so. You are looking at the situation backwards.

Backwards how? How do you design a protection?? Do you place the protection equipment and then you do the short circuit analysis??

 

[mivey]

Backwards how? How do you design a protection?? Do you place the protection equipment and then you do the short circuit analysis??

First, he gets a check from the customer to set the budget. Then he buys a panel & #lights that fit in the budget. Then he installs the equipment, then the customer can decide what kind of work they can do in that area based on how many lumens they get. :grin:

 

[charlie b]

Nice answer, mivey. But I am an engineer, not an electrician, so I don't get to do it that way. :grin:

First, I calculate the load. Then I choose a conductor size. Then I select a breaker size. Short circuit analysis does not come into play at the branch circuit level.

 

[charlie b]

Hmmm... perhaps 1000W ? 480V = 2.083A per lamp, disregarding the possibility of a power factor of less than 1.

Yep, that's it. If power factor were a player, the number of lamps would be fewer still.

 

[mivey]

And don't forget the distance between fixtures. But you can go a long way at 480 volts.

I thought I had a nice lighting layout one time until the customer decided to order fixtures with ballasts that only went up to 277 volts. :roll:

 

[Mayimbe]

First, he gets a check from the customer to set the budget. Then he buys a panel & #lights that fit in the budget. Then he installs the equipment, then the customer can decide what kind of work they can do in that area based on how many lumens they get. :grin:

Thats a good way to optimise the budget problem.

First, I calculate the load.

Calculate the load. You fell into your own trap. Which make me happy

My load is a number of lamps. Thanks to this thread I know this number. So I can go on to the sizing part as you say.
Then...
you select the breaker without a short circuit analysis?
When do you do the short circuit analysis then??