Combination Circuit Question School

Carultch said:
It's an academic example. It wouldn't meet code to solve this just with the materials given.

The premise is that the room in question only has the 240V circuit. No information on whether this is center-grounded like we do in the US, or end-grounded like 220V thru 240V circuits are in most of the world.
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Like we always do, we made the question far more complicated than was its intent. The obvious answer they were going for is the series parallel arrangement with two lamps in series connected in parallel with the other two lamps in series. Every lamp gets 120V and if a lamp burns out, it and its series partner go out while the other pair stays lit.
 
ggunn said:
The obvious answer they were going for is the series parallel arrangement with two lamps in series connected in parallel with the other two lamps in series. Every lamp gets 120V and if a lamp burns out, it and its series partner go out while the other pair stays lit.
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Yeah, that's grade school electrical theory and the obvious answer for a school project or after the Apocalypse. Anyone who decorated their Christmas Tree with old series light strings knows that.

But in the real world, it's part carter multipoint switching and part places where the electrical infrastructure looks like this.
 
Joethemechanic said:
Yeah, that's grade school electrical theory and the obvious answer for a school project or after the Apocalypse. Anyone who decorated their Christmas Tree with old series light strings knows that.
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Before that the bulbs were 120V all in parallel, but that was a significant fire hazard. A friend of my parents was having a big holiday party where the tree caught fire; he grabbed it, ran out through the French doors with it, and threw it into the swimming pool.
 
ggunn said:
Before that the bulbs were 120V all in parallel, but that was a significant fire hazard. A friend of my parents was having a big holiday party where the tree caught fire; he grabbed it, ran out through the French doors with it, and threw it into the swimming pool.
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Was the tree still plugged in? Did it get electrocuted?
 
Carultch said:
... It wouldn't meet code to solve this just with the materials given.
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A customer comes to you and want's four 100w lights installed in a boiler room. There is only 240v available. There wouldn't be any materials specified and none were here. It's completely up to you to come up with how to do it and with what. You quote four LED high bay fixtures with installation. The farthest thing from my mind would be cobbling up some kind of series/parallel arrangement with regular 100w light bulbs. That would be DIY for sure.

If you want to learn how resistors work in series and parallel arrangements and the calculations use actual resistors, not something that exhibits resistance. If I saw that question on a test I would think it was a trick question.

-Hal
 
hbiss said:
A customer comes to you and want's four 100w lights installed in a boiler room. There is only 240v available. There wouldn't be any materials specified and none were here. It's completely up to you to come up with how to do it and with what. You quote four LED high bay fixtures with installation. The farthest thing from my mind would be cobbling up some kind of series/parallel arrangement with regular 100w light bulbs. That would be DIY for sure.

If you want to learn how resistors work in series and parallel arrangements and the calculations use actual resistors, not something that exhibits resistance. If I saw that question on a test I would think it was a trick question.

-Hal
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It wasn't a question on a test. It was a question in homework, and maybe a darn good one.
 
hbiss said:
Just wondering what class or school the OP is in.
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Maybe an EET (electrical engineering tech) type, sort of a hybrid between straight trades electrician and full fledged engineer? This sort of series-parallel question would be the sort of thing I had in my basic circuit class, prior to starting on things like node/mesh analysis, norton and thevenin equivalents, and the like.
 
They often have test light panels with 5 120v bulbs in series for subway work. I have seen them used for temp fixtures and also getting hung from the catenary with a clip to the rail. Both Boston and NYC have 600v subway feeds.

I have built up test loads with 3 parallel pairs of 3 series bulbs each as test loads for some 347v dimmers I was designing at a past job

So there are reasons to use series bulbs, just not common ones :)
 
n1ist said:
So there are reasons to use series bulbs, just not common ones :)
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I remember using (3) 4x40W in series on the input phases to slowly power up a VFD during troubleshooting, or testing the inverter by using a wye arrangement of 3x4 on the output.
 
Yes, it's quite common to have a test setup with a variac and incandescent light bulbs in series with the load to test new or old electronic equipment before powering it up at full voltage. The lamps act as current limiters to keep the magic smoke from coming out if something is wrong.

-Hal
 
Joethemechanic said:
Nowhere does it say that the "lamps" are 120 volt.View attachment 2579768
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Yes, but remember that this is a very elementary test. I can easily imagine some nerd getting up in class and bringing up this and all the other stuff that we have been haranguing over for the past two pages and being told to sit down and shut up because I have been that nerd. :D
 
Maybe I’m dense or I’ve spent too much time on the excavator, but nowhere in the OP does it say anything about 120V lighting, and I’m puzzled as to the purpose of all the math.

The question asked “how would you accomplish this?”

My answer would be “install 4ea 240V luminaires fed by a 2P switch”. Period.

👍👍
 
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