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Miswired Lights

When we moved into our new house we noticed that one of the light switches would sometimes shock you, and sometimes wouldn't turn on at all. When we got someone to look at it they discovered it was badly miswired.

There are two switches that each let you toggle a light on and off, one switch at the top of the stairs and one at the bottom. This should look like this:

Those switches are "three-way", and toggling either switch toggles the light. The diagram above shows a completed circuit and the light would be on, the diagram below shows turning off the light by turning off the switch on the right.

This was all working fine until one of the switches broke. The person doing the work, who apparently had no idea what they were doing, bought an ordinary "two-way" light switch and not seeing what to do with the extra wire connected it to the switch's ground terminal:

This is very wrong, but as drawn above they would have quickly noticed the problem because it's shorting to ground and would trip the circuit breaker. But this is old conduit (BX) wiring without a separate ground conductor, so the ground connection is just through the armored cable jacket. This is an unreliable ground because a poor connection at any joint along the conduit breaks the connection, and that seems to be what happened here:

Which explains why the light would shock people: the faceplate screws connect to the body of the switch, the body of the switch is connected to its the ground terminal, and in this setup the ground terminal has wall current.

This is fixed now, but it does make me worry what else the previous owners did wrong.

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When to Buy Insurance?

You can get insurance for cars, phones, vacations, health, houses, ... —pretty much anything that can accidentally fail you. When is it a rip-off and when is it worth it?

The big thing to keep in mind about insurance is that the insurance company makes money by charging people more than they pay out. If the chance of your house burning down is 0.1%/year then to get insurance to pay out the value of your house if this happens you should expect to pay a bit more than 0.1% of the value of your house every year. Insurance, considered strictly on expected value terms, is a losing bet. So when should you go ahead and buy it anyway? Where does this simple theory fail to apply? more...

The Counterfactual Validity of Donation Matching

"All donations will be matched, up to $1M!"
A foundation finds an organization doing good work with a funding gap of about $5M. They could just give the organization $5M, but instead they decide to try and help the organization find some small donors to spread its reach. The foundation offers to match donations up to $2.5M. This is a real match: they will give $1 for every $1 anyone else gives, up to their limit. When the match is over, however, if the funding gap still hasn't been met they plan to make up the difference.

Let's consider some possiblities:
Amount Raised Match Given Makeup Contribution Total Received
If the organization raises less than $2.5M from small donors they end up with a total of $5M regardless of the amount the small donors give. This is described as a 1:1 match, but because their "makeup contribution" acts as a 1:-2 match the overall effect on the charity is actually a 1:-1 match: for every dollar you give they'll give one fewer! By donating to the organization you're effectively donating to the foundation, by leaving them with more money to do other things. [1]

Most donation matching isn't this extreme, but this example shows the main consideration in donation matching: how is the world different if you do donate versus if you don't? more...

Even More on Lead-Follow

There are a bunch of ways contra dance can work with different amounts of leading and following:

  1. None of the dancers have "lead" or "follow" as part of their role. Everyone does what the caller says, but sometimes you'll help out someone who's newer or confused by increasing pressure a little bit at some connection to hint to them where they're supposed to go.

  2. Anyone can "lead". When experienced dancers are dancing together, either one can think of an interesting variation and signal it to the other by the same sort of connected pressure.

  3. The jet/port/gent/lark role "leads" and the ruby/starboard/lady/raven role "follows". When experienced dancers are dancing together, the lead can indicate variations to the follow. In general the follow doesn't lead, but if they do want to then first they lead a role swap to put themself into the leader role and lead stuff from there.

Lightweight Bus Map

If I'm running for the bus or trying to figure out when to leave the house then I want to be able to look up stop predictions as quickly and simply as possible. But sometimes I'm waiting at a stop and trying to understand predictions that don't make much sense. I'd still like to interact with something that's as fast as possible, but now instead of just predictions I'd like to see the reports from the buses that the predictions are based off of. Is there a bus waiting at the terminal, or making its way from the bus lot to the terminal? Is there a bus coming that just needs to turn around and go back the other way? So I made a map:


House Buying Timeline

Julia and I just bought a house, which is really exciting. It took a very long time, however, and was a giant mess. Now, I believe this is not typical, with most house sales either going much more smoothly or being called off entirely, but this was our experience: more...

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