Electrical Outlets / New apartment

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alexdingley
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Electrical Outlets / New apartment

Post by alexdingley » Tue Jul 09, 2013 2:14 pm

So, I'm moving into a new place in 10 days... and the landlord told me yesterday "oh, and the tenant before you had their father upgrade all my outlets to 3-prong instead of 2-prong"....

...and my heart dropped. So, I ran over there with a radioshack outlet tester...

Thankfully almost all of the outlets tested "proper" on the tester. A couple of them showed up as "hot & neutral reversed" on the tester...

Now, I've wired outlets before, and I know where the breaker panels are... So, I'm comfortable swapping the legs on those. My question; Will hot & neutral being reversed pose problems for my gear? I feel like I'm remembering that anything with the fat-blade / skinny-glad power cables is particular about power.

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Nick Sevilla
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Post by Nick Sevilla » Wed Jul 10, 2013 10:55 pm

You are correct.

But, most electrical stuff use DC for their internal guts, and have good power corrections built in, so they get the right DC voltage.

It still is a good idea though to have all the outlets be wired the same.

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Snarl 12/8
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Post by Snarl 12/8 » Wed Jul 10, 2013 11:18 pm

My understanding is that most (all?) AC devices aren't actually picky about polarity individually, but in combination (two devices wired together) having them be different polarities could be potentially lethal.

When you think about it, AC is wiggling up and down (or is it side to side? or is it positive to negative?) constantly. If devices were picky about whether it started off up or down (the difference between the two prongs) then you'd have to flip them on or plug them in at the exactly correct time in relation to the 60Hz cycle for them to function properly. But, two devices that are tied together might be expecting to be in sync with respect to each other, if one is up while the other is down, that is potentially 240 volts between them (the plugs are on different rails of your service), rather than the zero that is expected. When you start having big voltage differentials where there shouldn't be any, trouble can happen. Like between the ground on a guitar amp and the ground on a microphone. They better both be ground when you touch your lips to that mic while you're hitting a power chord.

I dunno, I could be way off on that, but that's how I've always thought about it. I believe, as Nick says, that most well designed devices will protect against even that situation, but who's to say how well designed, maintained, modded, built, etc. all the devices you're gonna plug in are?
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Post by The Scum » Thu Jul 11, 2013 10:46 am

Well designed gear doesn't care about the polarity of the two prongs relative to each other. The wires go to opposite ends of the power transformer primary, and it all gets rectified to DC.

There are a few things to consider, though:

Not all gear is well designed, and the standard has changed over the years (google for discussions about "death caps" if you need an example). Best practice for a modern designer is to anticipate that the ground and neutral might be swapped, and accomodate either.

But the opposite was true at one time - there are some old, cheap tube amps with no power transformer. They're a serious safety hazard in general. In particular, if the outlet is wired backwards, the chassis is live with 120VAC right off the wall.

And the poor-mans 2-prong to 3-prong conversion uses the existing 2 strand wiring, and drops in 3 prong outlets. The ground gets jumpered to the neutral line. This doesn't meet code, and poses a number of risks. The 3-light tester doesn't catch it, either...it takes a more sophisticated device.

The easy way to tell is to flip off the breaker, pull an outlet off the wall, and see how it's wired. Ideally, there is 3-wire cable coming into the j-box, with the bare wire going to the ground on the outlet, and the black and white wires going to the prong connections. If there's a wire jumper from the prong connections to the ground screw, you've got a cheater ground.
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Post by kevin206 » Fri Jul 12, 2013 2:41 pm

The Scum wrote: And the poor-mans 2-prong to 3-prong conversion uses the existing 2 strand wiring, and drops in 3 prong outlets. The ground gets jumpered to the neutral line. This doesn't meet code, and poses a number of risks. The 3-light tester doesn't catch it, either...it takes a more sophisticated device.
I've done this before and you DON'T want this! I did it to get my microwave to work...it wouldn't work with a lifted ground. For musical stuff, some of the old equipment had a "polarity" switch, Peavey amps in particular. You would flip the switch to which ever position gave the quietest operation. I had an incident with an outlet with a jumpered neutral in which I ended up with voltage between my guitar strings and a metal HVAC floor vent.

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alexdingley
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Just to be safe

Post by alexdingley » Fri Jul 12, 2013 6:54 pm

I'm definitely going to fix the couple of outlets that are hot/neutral reversed... but thanks, everyone for the input.

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Post by goose134 » Sun Jul 21, 2013 11:06 pm

Most gear that is DC supplied does not, in fact, care whether it is polarity correct. Some things are very important to get polarity correct like refrigerators. Occasionally, the improper polarity on a metal appliance will cause the casing to become electrified. And some light fixtures will become electrified. So because it's an easy fix, swap the wires and be done with it.
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Post by jhbrandt » Wed Jul 24, 2013 10:13 pm

goose134 wrote:Most gear that is DC supplied does not, in fact, care whether it is polarity correct. Some things are very important to get polarity correct like refrigerators. Occasionally, the improper polarity on a metal appliance will cause the casing to become electrified. And some light fixtures will become electrified. So because it's an easy fix, swap the wires and be done with it.
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