[personal profile] da
Dear Builders,

I'm ecstatic that yesterday's plumbing fix means our kitchen sink no longer makes a 'thunk' sound when we close the tap, and turning on the outside faucet no longer makes a machine-gun sound. Less ecstatic at the holes in our ceiling, and attendant remains of drywall dust, but I am still reassured you will actually fix these holes today. Actually get all the drywall dust, I'm less confident about, given the amount you left behind last night, but we can deal.

I am hopeful you'll finish patching the holes in the membrane outside, so we have a terrace again before the snow starts falling, and perhaps more importantly, our downstairs neighbours don't have a leak.

But this morning, that fire alarm just as I was waking up? Not so cool. Granted it's only the second (third?) one during sleeping hours, but if there are power issues causing the alarm system to flake out, can you please fix them?

While we're on power, I'm less than ecstatic that our new vacuum (12 amps) will trip the CFGI circuit-breaker (15 amps). But whatever; we can avoid using those outlets (or just one outlet; I'm a bit confused about why that would be).

The parking garage which was going to be weather-sealed last week, is less than half complete; the slalom to get in and park is sort of exciting. If it were me driving instead of dan, I might just decide to take the bus instead.

And finally, when I got into the shower after the fire alarm this morning, I didn't want to be right when I thought, "at this rate, I bet the hot water flakes out."

Someone who feels whiny this morning.

Date: Tuesday, 13 November 2012 05:27 pm (UTC)
From: [identity profile] psychedelicbike.livejournal.com

GFCI = ground fault circuit interrupter. It measures the difference in current on the "hot" and "neutral" wires. If there's a significant difference, the assumption is that current is going "somewhere else," and usually, "somewhere else" is not good, so it cuts the power. Called "Ground Fault" because normally the fault, the reason the currents don't match, is a leak to ground.

These are mandated by electrical code whenever there's an outlet within 6 feet of open water - sinks, bathtubs, etc. That's why you'll see them in bathrooms and near the kitchen sink.

Unfortunately, reactive electrical elements (capacitors and inductors) that can act as short-term energy storage devices, can cause momentary imbalances between the current into an appliance and the current out of an appliance, and trip a GFCI. It shouldn't happen, but sometimes it does. It's not because you're drawing too much current, but because in & out are not the same.

The motor in your vacuum is a giant inductor, when you look at it with only the elctrical components in mind.

Date: Wednesday, 14 November 2012 03:47 am (UTC)
From: [identity profile] da-lj.livejournal.com
Would it change much if I said I mis-spoke, and it's actually an arc fault circuit interrupter? (the breaker says AFCI, the hand-written label on the door says GFCI).

And would it change much if I said I haven't found another outlet on that circut that tripped it? I still have to try more of them, but I've tried a few and it didn't trip.


Thanks for the quite cogent description; I didn't consider that it might have been a design-property of the circuit...

Date: Wednesday, 14 November 2012 03:23 pm (UTC)
From: [identity profile] psychedelicbike.livejournal.com
Would it change much if I said I mis-spoke, and it's actually an arc fault circuit interrupter? (the breaker says AFCI, the hand-written label on the door says GFCI).


AFCI breakers are required by code for all circuits that service bedrooms. They are designed to detect electrical arcs, both parallel (hot to neutral or ground) and series (over a high-resistance contact). The idea there is that electrical arcs can cause fires, and fires that start in the bedroom are more likely to kill people before smoke alarms can wake them up, when compared to fires started outside of bedrooms.

AFCI's work by detecting current spikes, which are indicative of the electrical arcing (like when you shuffle your feet across the carpet and touch a doorknob).

So, why is this tripping for your vacuum? If it were a DC motor, that would be easy to answer. DC motors use slip-rings or brushes to conduct power to the rotating part of the motor. These connections open and close as the motor spins, and every time it opens or closes, there's the opportunity for a spark to happen. Unfortunately, I don't know enough about AC motors to answer the question, though :(

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