lamps in parallel max

[charlie b]

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

You are happy that you are still getting it backwards? I am not in a trap, you are.

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.

Your load on one circuit may be the number of lamps powered by that circuit. But what about the next circuit over? And the next? How many circuits will there be? Well, that starts with a load calculation. Either on a ?watts per square foot basis? or on an actual lighting layout drawing (reflected ceiling plan) basis, you need to know the total load. Then you know how large a panel you need, and how large a feeder to that panel. Then you can make design choices regarding the number of circuits and the rating of each.

You say you know the number of lamps? I say you don?t. You haven?t told us if you plan to use a set of 20 amp circuits, or 30 amp circuits, or 50 amp circuits. You just latched on to the number 20 (or 19, or 17, or fewer, depending on which comment you are using for your number). Your design is not done yet.

You select the breaker without a short circuit analysis?

I select a panel?s short circuit rating on the basis of the short circuit analysis. I require (in the specifications, not the drawings) that branch circuit breaker ratings must match or exceed the panel?s rating. As I said earlier, I don?t do a short circuit analysis of branch circuits.

When do you do the short circuit analysis then??

If I am only adding branch circuits to an existing facility, perhaps never. If I am doing the design for an entire new building, then the short circuit, voltage drop, and fault coordination studies are nearly the last items on the task list.

 

[Mayimbe]

me

You are happy that you are still getting it backwards? I am not in a trap, you are.

Ok

Your load on one circuit may be the number of lamps powered by that circuit. But what about the next circuit over? And the next? How many circuits will there be? Well, that starts with a load calculation. Either on a “watts per square foot basis” or on an actual lighting layout drawing (reflected ceiling plan) basis, you need to know the total load. Then you know how large a panel you need, and how large a feeder to that panel. Then you can make design choices regarding the number of circuits and the rating of each.

Ok


You say you know the number of lamps? I say you don’t. You haven’t told us if you plan to use a set of 20 amp circuits, or 30 amp circuits, or 50 amp circuits. You just latched on to the number 20 (or 19, or 17, or fewer, depending on which comment you are using for your number). Your design is not done yet.

I know the number yes. Im not using any, Im using mine. No my design is not done yet, theres a lot of other things that are not involved with lamps that I have to do. So?

I select a panel’s short circuit rating on the basis of the short circuit analysis. I require (in the specifications, not the drawings) that branch circuit breaker ratings must match or exceed the panel’s rating. As I said earlier, I don’t do a short circuit analysis of branch circuits.
If I am only adding branch circuits to an existing facility, perhaps never. If I am doing the design for an entire new building, then the short circuit, voltage drop, and fault coordination studies are nearly the last items on the task list.

Ok. So basically you believe im wrong, and I believe you are wrong. Good luck with that.

Same old

 

[LarryFine]

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:

At least you only had the same number of CCC's.

 

[buldogg]

me



Ok. So basically you believe im wrong, and I believe you are wrong. Good luck with that.

Same old

With that attitude, good luck to you. You're gonna need it

 

[Cold Fusion]

...I select a panel?s short circuit rating on the basis of the short circuit analysis. I require (in the specifications, not the drawings) that branch circuit breaker ratings must match or exceed the panel?s rating. As I said earlier, I don?t do a short circuit analysis of branch circuits. ...

Interesting way to say that. Let's look at a common installation (for me anyway - couldn't tell you about this pansy commercial stuff): 480V, 3ph, 1000kva xfm feeding 25kA rated switchboard, with 800A feeders to MCCs or panels. So if you are specifying say an 800A MLO panel, a common rating is 65kA. One would likely to have to pay extra to get a lower rating.

So in this case, you are telling the material provider to get 65kA Cbs in the 800A panel?

I'm pretty sure you didn't have that in mind - but that's the way it came out.

With that attitude, good luck to you. You're gonna need it

dogg -
Could be May is actually reading charlie's posts.

cf

 

[charlie b]

So in this case, you are telling the material provider to get 65kA Cbs in the 800A panel?

Good point, cf. The requirement is that the breakers must have a short circuit rating at least as high as the amount of short circuit current that is available at the panel location. But how is that requirement imposed by the contract documents? Perhaps I should take another look at the way the specs are written.

 

[Cold Fusion]

But how is that requirement imposed by the contract documents? Perhaps I should take another look at the way the specs are written.

I don't know. This is what you do for a living, and this language has been working, and I knew what you meant. If this came up on one I was putting in, all that would happen is you would get an RFI with a suggestion: "Would 25KA CBs be okay for this application?"

I don't write that stuff, but it seems very difficult to get boilerplate to fit all.

Okay, let me rephrase: I don't write that stuff at all. I wouldn't have a clue what would be right.:grin:

cf

 

[skeshesh]

me

Ok. So basically you believe im wrong, and I believe you are wrong. Good luck with that.

Same old

Mayimbe, I'd have to respectfully say that you wrong. I dislike your attitude towards Charlie b since, while being on this forum for a relatively short period, I've found a sound understanding of engineering in his posts.

As far as lighting calcs, you should first determine how much illumination you need and how many lamps/fixtures you need to accomplish the task. Only then do you make the design decision of how many fixtures per circuit you'd want which is when you size the OCPD. Like charlie mentioned, I've personally never used a breaker bigger than 30A but its permissible upto 50A.

Charlie is again correct about the short circuit analysis. When working with an existing system I usually take a look at the closes transformer upstream and specify the panel KAIC based on that. The circuit breakers should obviously match the panel. When designing a complete new system, I usually use software (SKM or ETAP) and draw out a one-line diagram of the system with available short circuits + VD and size the equipment & feeders based on that. Then, finally, I start playing with the IV curves if selective coordination study is required. Charlie is correct that it's improper, if not impossible, to do the SC, VD, protective coordination studies if you don't have an overview of the entire system.

BTW, I'm actually surprised by Mayimbe's comments since I've met a lot of foreign engineers, at least here in LA, many of them South American who had a solid knowledge of engineering.

 

[cycotcskir]

It seems that maybe Mayimbe and Charlie are looking from two different directions.

Mayimbe said that he " is designing it", but what is "it"? I don't think that he clarified enough.

Is he referring to the entire building and project, or is he referring to someone's request for additional lighting in a stuffed panel?

I may have missed something, but it seems that the latter is true of Mayimbe and that the former is true for Charlie.

If that is true, I agree with both of them