Shop Wall and Electric

[krw]

Why would you do that? BTW, bad choice of terminology. All loads are wired in parallel.

[Robert Bonomi]

Clarification -- this *is* somewhat unconventional, I realize it needs more explanation.

A standard GFI outlet has two pairs of isolated wiring points. One (hot and neutral) for upstream ['line'], the other (ISOLATED hot / ISOLATED neutral) for additional outlet(s) [load] to be protected.

Typical ("series") wiring is hot/neutral from panel to GFI 'line', GFI 'load' (isolated) hot/neutral to next outlet and on to next (repeating as needed) making sure that the isolated neutral is 'continuous' from GFI to end of run.

NEC has specified that neutral must be a continuous conductor back to the panel.

*PRESUMABLY* there's an exception to this for 'downstream' GFI protection, as the downstream outlet (isolated) neutral has to be wired to the GFI load neutral, *NOT* to the panel neutral bus.

What _I_ first did, motivated by the fact that (1) I was putting only 2 duplex outlets on a breaker, (2) the 2 duplex outlets were located 'distant' from each other (idea being to have 'as many as practical' different circuits 'within reach' at any given point), _and_ (3) as a result of (2), the outlets were usually in _opposite_directions_ from the panel. Each hot came out of the panel and into an immediately adjacent 'distribution box' where it was joined to a _separate_ wire going to each outlet (shorter to do 2 runs, then out to one outlet, back, and out to 2nd outlet.) (3 conductors in the wire-nut -- one to each outlet, and the 'common' back to the breaker) -- one to each outlet, and the 'common' back to the breaker) Neutral from each outlet was run all the way back to the panel. no breaks, no splices. This called for a GFI breaker at _each_ location. since neither 'downstream' of, or protected by the other. (Note: electrical inspector _did_ wonder at, and question, *all* those neutrals at the panel. more neutrals than circuits! :)

Subsequently, I've been able to find GFI receptacles for _not_ much more money than a quality duplex outlet. So, I treat the in wall wiring (hot/neutral) like a 'buss'. and pigtail off a tap on -each- one at each outlet. which connects to the _line_ side of a GFI outlet at each location. 'load' side goes unused. Each GFI can see only it's own pigtail and trips only if a device plugged into it fails. When it trips, it kills only the pigtail, and any other independently protected outlets on the 'buss' are still active.

There is an additional, but subtle, advantage to this set-up, _if_ there is a possibility of (young) children around. Since you've got a _separate_ GFI at

-each- outlet position, you can disable the outlets, by hitting the 'test' button on all of them, and only resetting when actually needed for use.

Outlets with switches 'built in' are *handy*. Especially when it's not particularly obvious that they _are_ switches. *GRIN*

[Robert Bonomi]

"because". See my self-follow-up article where I clarified everything.

You demonstrate you don't know what you don't know.

'protected' outlets downstream from a GFI outlet are wired in _series_ with the GFI device. (This doesn't mean that the loads are in series, they're not, but current-sensing _requires_ a sensor in series with the load.) Even a 'clamp-on' ammeter uses a sensor in series with the load. *grin*

You have a pair (hot/neutral) of 'line' terminals for the feed from the panel, and an _isolated_ pair of terminals for feeding the protected outlets. If you use _either_ the hot or neutral from the panel to the downstream outlets rather than the isolated ones from the GFI, there is *no* protection.

[Doug Miller]

Does using your compressor cause it to kick on at some random time *later* that day, after you're finished using it? If so, then it's time to check your air piping for leaks.

[Doug Miller]

I'm shocked that I didn't see that coming.

[Doug Miller]

Cite, please. I'm not aware of that one.

[Mike Marlow]

Not really. It will only come on if the pressure drops below the cut in pressure. Quite predictable actually.

No, but his point is valid. The compressor is not going to come on just because it's sitting there. If you're not using it to drain down the pressure, it's not going to come on unless you have a leak. Best to fix the leak.

[Scott Lurndal]

As I understand it, the grounded conductor may not be interrupted by a device; in other words, you must pigtail the grounded conductor rather than pass it through the receptacle or use the receptacle as a terminal strip to join the upstream and downstream grounded conductor. I wonder if there is an exception here for a GFCI device when protecting the downstream devices, tho.

scott

[Puckdropper]

"Mike Marlow" wrote in news:29f20$4c0b0bbe$adbc2859$ [e-mail]:

*snip*

I don't have a big compressor, so I've got to ask... Is it probable that the drop in temperature (say of 20-30F) and resulting drop in pressure could cause the compressor to kick on?

I've had my little one down to the threshold several times, where just plugging in a nailer (usually a big one) or shooting a couple of brads causes the compressor to come on.

Puckdropper

[krw]

It can. There are *always* leaks. The pressure switch can be right on the edge of tripping. It wouldn't be nice to have it go over the edge just as you're making a that cut in 2" maple.

[krw]

...sure, AFTER I posted. ;-)

Au contraire, I know what I know. ;-)

That is *not* a series connection. "Series" has a very specific meaning. I did understand what you were saying, though.

[krw]

The groundING conductor may not be interrupted, but it is my understanding that the GroundED conductor may. It's common practice to pigtail the GroundED conductor, as well.

groundING conductor == Safety Ground groundED conductor == Neutral

[Jack Stein]

Not at the exact same time, but unlike other tools, the compressor doesn't stop running when you stop sanding, or drilling or whatever.

What happens with a compressor is it doesn't run until you use a bunch of air, then it runs until the tank pressure maxes out. You can be using other tools while it is running and you are not using an air tool.

If it cycles on, when not in use, once a day,

I have significant air leaks then, but not enough for me to bother with. One thing that also happens is if a tool drops the tank pressure to just above the start up level, the thing will start up later on it's own. Even if you have no leaks, some tools if left connected can have bleed through.

At any rate, since the dust collector runs with all other tools, and the compressor starts up on it's own, sometimes when using other tools, it's good practice to have those two on their own circuit.

[Scott Lurndal]

I'm fully aware of the difference between a grounded conductor and a grounding conductor. I pulled out my NEC 1999 and see that my statement above applies only to multiwire branch circuits:

1999 NEC Section 300-13.

In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, recptacles, etc. where removal of such devices would interrupt the continuity.

This means that neutrals of branch circuits supplying receptacles are not permitted to depend on terminal connections for continuity between devices for a circuit with two or more ungrounded conductors that have a potential difference between them and a grounded conductor that has equal potential difference between it and each ungrounded conductor.

Section 300-13 doesn't apply to individual two-wire circuits or circuits without a grounded conductor.

It does apply to 240v circuits with a grounded conductor (such as 4-wire dryer or electric stove circuits with two ungrounded conductors, a grounded conductor and a grounding conductor).

Note that there must be at least 6" of conductor from the point at which it emerges from the sheath or raceway (e.g. conduit), and it must extend at least 3" outside the handy box.

[Doug Miller]

Dunno... let's do the math and find out. Suppose your pressure settings are on at 90psi, off at 120. Those pressures are psig, not psia -- absolute pressures are 1 atm higher, or on at 105psia, off at 135. When volume is constant, absolute pressure is directly proportional to absolute temperature (degrees Kelvin or Rankine). So a drop in temperature from, say, 90F = 549R to 60F =

519R reduces pressure by (549 - 519) / 549, or a little more than 5%. So if the pressure in the tank is below about 111psia = 96psig, then, yes, a drop in temperature from 90F to 60F *would* reduce the pressure enough to kick in the compressor. Above that, no.

[Doug Miller]

I haven't been able to find that in the Code either.

[Doug Miller]

FWIW, the same section in the 2008 NEC contains identical language.

True enough -- but such circuits generally supply only one outlet anyway, making 300.13 moot.

[Doug Miller]

And you can't wait to start the table saw til the compressor stops? :-)

How often, though, do you really switch back and forth that quickly?

No, it won't, unless there's a leak somewhere.

That's a leak.

I agree that it's good practice. I don't agree that it's mandatory. And it certainly isn't a Code violation, as one person appeared to suggest.

[Robert Bonomi]

"No mho" says Tom, without reluctance.

[Bill]

A few months ago, the idea of a "quad in a box" go-anywhere power source was brought up.

:: sheepishly he asked::

Is it okay to power this configuration by plugging it into a wall outlet???

Trying to answer the question myself, I'm pretty sure it's not even ok to be able to step on nm cable, so, at the very minimum, more durable insulation is required.

Swingman offered me a good piece of advice, which is never to do anything (electrical) that you don't feel confident about (and I'm following that).

I've learned even more since he mentioned that--learning to appreciate for instance the importance of being very careful not to even nick any of the conducting wires (which might result in a short for instance), and in installing a panel with a level. Attention to detail.

I was chopping up a few small logs today after the midwest storm lastnight.

7/8 of the way through one, I broke it across my thigh and as I did 14" extra broke off and swung swiftly within 2" of my throat, breaking off like if it was part of an overlapping joint. It occurred to me that I might have just as easily have butchered myself except for those few inches.

Anyway, the moral is: Woodworking, electrical, or anything else--think about what could go wrong before you do it.

Bill