Hacker News Reader

A bad neutral isn't going to trigger a brownout that reproduces reliably in some random gzip code when you're booting fully into Windows, on a modern CPU with fine grained frequency/voltage scaling, on a battery-powered laptop, powered by a switched-mode power supply with tons of capacitance in every single layer on the way to the CPU.

The most plausible explanation I can think of would be if the return current is flowing through the monitor and EMI from that is disturbing things, but 60Hz might as well be DC to modern signal rates, so that's tantamount to blaming witchcraft.

That is exactly what bad neutrals do (produce brown-outs). They produce brown-outs because the potential between the "hot" side and neutral is < 120 V, because the neutral is > 0 V.

Yes, it'll produce a brownout at the outlet, but it's highly unlikely that this will manifest as a brownout at any of the component voltages, because there are so many layers of filtering. That <120V goes through a switched-mode power supply which converts that down to 20ish V, which goes to a battery charger IC which charges the battery, which outputs a variable voltage that goes through multiple more layers of monitored DC/DC conversion to generate the power rails. Every one of these steps has circuitry that will panic and send a signal to the main PMIC if it sees a voltage that is out of spec.

My guess would be that the issue was not brownouts, but noise (which could even have peaks well above 230V). The air conditioner has a motor, and motors can be electrically noisy; it should have filtering, but with a broken neutral, that filtering might not have been as effective. Grounding the outlet with the computer (the solution at the end) would have allowed the filters at the computer and monitor power supply to filter out the noise (AFAIK these filters work mostly by shorting high-frequency components of the waveform to the other wire and/or to ground, so they need a good neutral and/or ground to work).

But yeah, these sorts of "bad wiring" situations can have baffling effects. I would love to see someone in one these situations actually manage to get a logic analyzer trace or similar to show what's actually going on with the power supply, together with an investigation (and fix) of its real cause.

Anyway, disgraceful that the electrician failed to diagnose Al or any of it on the first visit.

Most residential power is dirty to some extent, and AC/DC converters are supposed to be able to cope with a wide range of input distortions. For the problem to have worked its way through all of the safety components in both the laptops power brick and its internal electronics means that the distortions must have been particularly high amplitude, and at frequencies that couldn't be easily filtered out (very high, very low, or both).

Electricians that aren't particularly well trained, or particularly experienced are probably not going to be able to diagnose this kind of problem.

This is really a problem for an electrical engineer.

Unfortunately, in most jurisdictions, engineers aren't allowed to perform these kinds of repairs because they don't necessarily have the certifications to perform work on live wires.

Most electricians can only trace wires and identify visible faults, and replace things that aren't up to building codes.

You can buy a $10 tester[0] that will detect open grounds, open neutrals, and any other wiring fault you'd care to think of. It doesn't take an experienced electrician to use; you plug it in, and see which lights turn on.

What I think is more likely in this case is the A/C turning off. All electric motors induce a current whose direction is opposed to the originally applied current (Lenz's Law). This is called back-EMF or counter-EMF. It's also proportional to the rate of change of the magnetic flux. You can see this when you turn on a motor like a vacuum cleaner, and observe the lights briefly dim. The same thing happens when a motor turns off. Additionally, things like vacuum cleaners or fans have relatively little resistance to them, so when they turn off they can coast down - small rate of change, small impact to voltage levels. An A/C or refrigerator compressor presents a relatively large resistance to its driving motor, so when it shuts off, it shuts off HARD. Big rate of change, big induced voltage spike. I don't know about a small motor like you'd see in a household, but large industrial motors can generate hundreds of volts when turned off. This is usually handled with a circuit called a snubber, but it doesn't generally matter in residential applications so it's rare to be included, as a cost savings measure.

[0]: https://www.kleintools.com/catalog/electrical-testers/recept...

The author appears to be in Vancouver BC Canada.

In US/Canada, power supply is done via 240V split phase. Therefore, a broken neutral between service and home would have lead to a 120V outlet getting anywhere between 0 and 240V AC. That sure would have lead to something a lot less pleasant than just gzip errors.

Therefore, a broken neutral between service and home would have lead to a 120V outlet getting anywhere between 0 and 240V AC.

That is true, although loads are normally balanced between the two phases so that the extremes don't often appear, and the neutral could just be intermittent instead of fully broken. But a heavy load (such as the air conditioner in the article) would definitely cause the voltage to swing to one extreme.

To my understanding a ground isn't necessary for equipment to operate at all, however it sinks the EMI, reducing floating neutral voltage and noise.

PC equipment such as voltage regulators put out a lot of noise. The neutral is not bonded to the metal chassis when a ground is not present, meaning the difference in potential in the chassis cannot be synced with ground, causing various crazy issues. It's why cases still are overwhelmingly metal, steel mostly.

Ground is (ideally) a just in case safety measure. It catches voltage transients, shorts, etc. and routes them safely to ground via a (normally) non-current carrying conductor. This is also useful for EMI protection.

The neutral should also be bonded to ground at the panel in residential installations.

It used to be there was no ground, and neutral carried the ‘return’ load and was also used for equipment grounding and the like. It’s not as terrible an option as you’d think, if everything else is done correctly.

However, this can be dangerous as certain types of wiring setups (generally incorrect and non-code compliant) can produce voltages on other neutrals in the circuit, and if that is being used to ground a metal case (which there is no other alternative), zap to anyone who touches it.

Especially if someone wired something backwards and you get a hot neutral (aka now hot metal case). Especially if the badly wired thing is something sporadic, like a rarely used light switch or outlet. It turns it into a ticking time bomb.

It’s a somewhat common DIY error to create floating grounds (and floating neutrals), and a floating ground can still cause this even with modern wiring with the right kind of screw up.

It’s one of the most dangerous types of wiring problems.

I’ve run across it in two different houses I moved into after the fact. Also damaged conductors causing heat and sparking. Also damaged outlets that on closer inspection exposed current carrying parts of the sockets due to cracked and broken plastic.

It’s a jungle out there!

> Oof. A missing equipment ground (the third pin on your outlet or its wiring) will not cause these issues. In fact, it’s legal to have an ungrounded three pin outlet in a retrofit situation as long as it’s GFCI protected and labeled.

I’m pretty sure that this is location specific and I don’t think this was pass where I am. Even outlets which aren’t RCD protected get a fail now.

You must be somewhere that calls them GFCIs RCDs. :)

This particular rule in the NEC (the code for most US jurisdictions) only allows this as a retrofit:

https://www.electricallicenserenewal.com/Electrical-Continui...

Not going to lie, that's above me. But is that allowing outlets that aren't grounded? If so, yikes.

I'm in New Zealand and if you are touching your electrics when getting work done, you need to be installing RDCs on the circuit.

You can do all sorts of stupid things when you have an RCD on a circuit, and while I'm sure you could still get electrocuted, you'd have to try quite hard.

https://www.nhpnz.co.nz/en/News/Stay-safe-with-compliant-RCD...

GFCI is American for RCD, more or less. Except that our GFCIs are almost always 5mA, whereas yours seem to mostly be 30mA. And ours don’t generally live on DIN rails.

The rule here is that, if you replace an old ungrounded outlet, you ought to find a way to ground it and, if you can’t, you must add a GFCI.

(Sadly this often can’t be done in the breaker box, so it means a GFCI in the receptacle. The issue with adding GFCIs in the breaker box is that a lot of old knob and tube installations didn’t match up neutrals with their corresponding hots, so individual circuits don’t have circuit-specific neutrals to run through the GFCI.)

American GFCI breakers generally look like this:

https://www.homedepot.com/p/Square-D-Homeline-20-Amp-Single-...