Question is, why is the electrician there in the first place? All these solutions presume no wiring fault between the switches and the fans, right?
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We have to assume that, since you’ve been called out to fix the wiring/switches, the fans have not been in use.
- Turn on switch 1 and leave it on.
- Turn on switch 2 for 5 minutes, and turn off again.
- Leave switch 3 off.
- Take your single trip upstairs and check the rooms. Look for a running fan (s1), a stopped fan with clean blades (s2), and a stopped fan with dusty blades (s3).
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Turn first switch on.
Leave second switch off.
Reverse the polarity of the third switch.
When you get upstairs, one fan will be blowing, one fans will be still and one fan, like this answer, will suck.
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That says the leading edge of the blade is where static buildup occurs and causes the most accumulation, so I guess you could reverse it… Leave one running for a day, leave another running for an hour, and leave one alone, and then check for ‘dirty edges’ on the fans tomorrow. But that’d be pretty overwrought, right? Our electrician is a busy dude. Lots of electricianing to do in other hidden basements with different, exotic switches.
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Here’s a similar puzzle, in that it involves wiring and switches in the basement:
There is a light switch in my basement stairway. Nothing obvious happens when I frob it. On close (and careful) inspection, it is connected to 3 conductor + ground romex (indicating that it is a relatively recent addition as the house still has a lot of original 1926 wiring). The hot wire is live.
What is this switch?
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That won’t work. Remember, it will take an hour to climb the stairs, so any lightbulb would have cooled off by then. And any temporary change in temperature in a room would have reverted as well.
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Tell all the owners to a fix a piece of string on the ceiling above the fan going through the fan blades all the way down to the floor. Assuming all fans are off at the start press button a once and leave, press button b for 5 seconds and then press again, leave button c. Go to the top of the block look in the first apartment and if the string has not moved then the fan is attached to button c. If the string has left the floor but not fully wound round the fan it’s button b. If the fan is on, it’s button a’s attachment. Hey Ive had a smoke tonight so might be very wrong, lol.
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That’s for the Internet (the whole Internet, not just your access to it).
Do not turn it off.
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Yeah, I leave it on just in case. I apologize for any outages earlier today when I was poking at it.
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Assuming this is in the US with three-phase power:
- Leave button A off.
- Wire button B between one of the power lines and neutral. Turn it on.
- Wire button C between two power lines. Turn it on.
The voltage between a line and neutral is less than the voltage between lines (1:sqrt(3) ratio, so hopefully won’t burn the fan), so when the electrician goes upstairs:
Fan connected to button A: off
Fan connected to button B: spinning
Fan connected to button C: spinning faster than the one connected to button B.
Reference for the voltage thing: http://electronics.stackexchange.com/questions/92678/three-phase-power-supply-what-is-line-to-line-voltage
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Here’s mine:
The poor, lazy electrician needs to put in that extra effort to carry three nanny cams up the stairs. Point each one at a different fan, connect to power source and the Internet.
He can now walk down the stairs, and using the app he has installed that connects to the nanny cams, he can push each button and watch from the comfort of his mobile phone as the fans turn on.
…In my mind he is also sitting in a Lay-Z-Boy and sipping a beer while “working”, a football game playing in the background, but I digress.
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I don’t even care if any of these are right. They were fun to read.
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Give 5 bucks to a kid with a mobile phone. Let the kid go upstairs and text the electrician as fans go on and off. Electrician doesn’t need to go up even once.
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Also, the landlord will eat the electrician, the electrician will eat the cabbage, but the landlord won’t eat the cabbage…
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I think I almost have it. Not quite, but I’m going to go out on a limb and say the electrician starts on the top floor.
“the electrician is very lazy so he will only climb up the stairs to the top floor once”
**“up the stairs” **
So he can go down the stairs once too. If he starts on the top floor he knows the initial conditions. When he goes down stairs he can check the status of the buttons. (I just realized I contradicted myself when I was typing this post within the next two sentances, so edit) Then he can push some buttons and go up stairs because he still has a trip left. Then he can go down stairs again. (might be important but I don’t think so).
That’s three one way trips. Also the fact that this problem involves toggle buttons instead of the more familiar “flip switches” means he can’t just look at the switch to determine if the fan is on or off.
Things to keep in mind.
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Amusing replies, especially the ones that assume he starts at the top of the building (maybe it’s a converted missile silo, under ground!). The dust and heat approaches are quite clever.
I feel that this is meant to be a pure logic puzzle. This seems especially true from the statement “he refuses to use any assistance of any kind in order to complete this job”. I consider disassembly of the switches and/or the use of additional tools and components from a standard electrician’s supply to be in violation of this statement.
The puzzle specifically says that he will climb UP the stairs only once. It says nothing about going down, or modes of travel other than climbing. However, this seems like the wrong approach, especially because he’s supposed to be lazy.
From a logical point of view, the electrician could turn on one fan and climb the stairs. He would then know one pairing of fan and switch, and has a 50% chance of getting the other right through guessing. Maybe he’s lazy enough to take that risk?
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Well I’ll be darned, all this time I thought he was gesturing with a pipe, (bowl in hand, stem sticking out).
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Alright I have to make one minor and one major assumption. The electrician starts upstairs and all three fans are off. He marks one blade on each fan with a sharpie.
He then goes downstairs and pushes button 1, then he pushes button two rapidly twice, and he leaves button three alone.
The fan on button 1 will be running. The fan on button 2 will be stopped but rotated in a different direction (hence the sharpie). the fan on button 3 will be unrotated.
Again, a bit of a stretch to assume two things. First, all the fans are off to begin with. Second to assume the electrician starts up stairs.
Punchline…
The electrician lives in one of the apartments.
P.S. Remember, he is very lazy.
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Can we assume that Monty Hall is in one of the rooms upstairs?
Turn on switch A to figure which room it’s connected to, then run upstairs and ask Monty which fan is connected to switch B. Odds are that you should choose the room he suggests.
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