Conv to 220?

[Duane Bozarth]

...

Probably not in this case...the particular saw in question is a convertible 110/220V model, not a stationary. It has double-pole mechanical switch.

[Doug Miller]

Ummmm... why could it not be more than 20A @ 120V ?

[Wes Stewart]

Not taking sides in this tar baby punching contest, but you're now worried about connecting "ground" to "neutral"? [g]

How come when I suggest this is something best avoided, I'm excessively cautious? Maybe so... I wouldn't rely on a Sawstop either.

[Duane Bozarth]

Actually, it was supposition that it would be highly unlikely...poor choice, probably to say "can't".

[Doug Miller]

Two separate issues.

In the stove-cum-tablesaw circuit thread, we are discussing connecting a pure

240V device (two hots and a ground, no neutral) to a circuit that has three conductors. You claim, utterly without foundation, that to do so is incorrect.

In the other case, someone was asking how to properly connect his stove, or range hood, I forget which - and toller told him to connect the green wire from the appliance (i.e. the equipment ground) to the circuit *neutral* _despite_ the OP having quoted the manufacturer's instructions saying to connect it to *ground*.

If you don't see that these are two separate issues - and *why* - you probably shouldn't be giving out electrical advice *either*.

In the first case, there is no neutral in the proposed circuit; in the second case, there *is* a neutral *and* an equipment ground, and we have an ignoramus who says it's ok to interconnect them.

[LRod]

Dear god, tell me he didn't. And here I thought (for a picosecond) that maybe I was being a little insensitive to him.

For those who don't know, the multiwire branch circuit is like a 240V circuit with a neutral which functions as two 120V circuits with a common neutral. A duplex 240V breaker is required since the concept of the common neutral is that the return currents of the two circuits being fed 180° out of phase (by virtue of the duplex 240V breaker) are in turn 180° out of phase and thus cancel. They can never sum to more than the capacity of one leg of the breaker, regardless of any imbalance of loads on the two branches, consequently the neutral is safe insofar as its current carrying is concerned.

To attempt to wire that circuit from a duplex 120V breaker means that both hots are of the same phase, and thus the return currents are additive, equalling as much as TWICE the breaker current (depending on the total load), and obviously much greater than the ampacity of the neutral wire.

And you guys think we're bitchslapping him just for amusement.

[LRod]

It probably isn't any bigger than, say 2½ HP (since it's a convertible motor). Are there any convertible motors bigger than that? Are there any that big? That would definitely max out a 20A/120V circuit. I think that's what he was getting at. We already know it's a convertible motor and we can thus speculate with some authority from there, can't we?

[toller]

No, just about 4 morons. If I was in step with them I would really worry.

Damn, you are incredibly stupid. Why would you make such silly assumptions otherwise?

[Doug Miller]

Yes, he did - because he thought that the "1 pole duplex" breaker that the OP in the thread referred to, was a 240V breaker. Whether the mistake was due to inattention, ignorance, malice, stupidity, or a combination thereof is impossible to tell, but there it is.

Google alt.home.repair for the phrase "duplex breaker" on 14 May 2005 for all the gory details.

[Doug Miller]

This, coming from the guy who, just in the last month, has: a) claimed that it was nearly impossible to get a fatal shock from 60Hz 120VAC b) admitted to working on branch circuits without verifying that power was off c) advised connecting an appliance equipment ground conductor to the *neutral* of the circuit supplying it d) advised connecting both legs of a multiwire circuit to a single pole duplex breaker.

[Duane Bozarth]

That was basis of my conjecture, yes...what is largest convertible available I don't know.

[Wes Stewart]

Sorry. My tongue-in-cheek eluded you.

*If* the OP is absolutely, positively sure that the line in question travels unbroken back to the service panel with no other loads attached, then he can wrap some green tape around the white wire at both ends and call it equipment ground. If I had personally wired this circuit and knew this to be the case, that's what I would do. Otherwise, I would make no such assumption without further detective work. That was the point I was trying to make in the first place; until you know for sure, it's a "neutral."

But since neither of us has provided our credentials that denote expertise in the field, I submit that our advice is equally suspect.

I have had my say and will sign off now and go back to the shop and see if my shellac flakes have dissolved.

[very_dirty_dave]

The Dewalt has a 1-3/4 HP TEFC induction motor convertible to 220. So the 20A socket/plug with 12 gauge wire should work.

I am absolutely sure the circuit comes directly from the service panel. One thing I did notice was the outlet is says 50A, but the breaker is definitely 40A. One of the posts mentioned subpanels. This circuit is in a subpanel technically. By subpanel I mean that the circuit is in the original main panel. The house service was upgraded for an addition prior to me owning the house. A new panel was installed and the original main panel became a subpanel (I think I as saying that right). Anyway the 40A breaker supplies the outlet approximately 8 ft away from the panel. There is nothing else connected to this circuit. I don't know the gauge of the wire, but it if a fat sucker. Since I installed the gas line 20 years ago, the prior owner could have only used electric. So the circuit was installed in the early 60's.

Thanks for all the responses. I think I know what to do now.

[Doug Miller]

That being the case - in order to do this safely: a) the subpanel must have a separate grounding bus bar... b) ... which must be connected to the ground or neutral bus in the main panel c) ... and must NOT be connected to the neutral bus in the subpanel d) and the grounding conductor of the circuit must be connected to the

*ground* bus in the subpanel.

[very_dirty_dave]

Two questions:

Can I check by removing the panel covers and checking that the connections match your above safety list?

Is your list the proper way it should have been done when the service was upgraded? (I have no reason to believe it wasn't)

Thanks for your help.

Dave

[Duane Bozarth]

...

Yes (to both).

[toller]

That you alpha-turd?

"Here are the instructions from Jennair:

'The neutral of this unit is grounded to the frame through the green grounding wire.'"

So exactly how did I contradict the instructions?

[Wes Stewart]

My code book is kind of old; however, it states:

"NEC Article 210-10: Ungrounded Conductors Tapped from Grounded Systems.

Two-wire dc and ac circuits of two or more ungrounded conductors shall be permitted to be tapped from the ungrounded conductors of circuits having a grounded neutral conductor. Switching devices in each tapped circuit shall have a pole in *each* (emphasis added) ungrounded conductor."

[Wes Stewart]

Okay. If this retrofit was done correctly, the neutral and ground bus bars in the "old" (now sub) panel were separated. Your (saw circuit) neutral wire connects to the now separate neutral bus bar and that bus in turn is wired to the common neutral-ground bus in the new service panel. This point is the earth ground reference.

*All* of the neutral currents from the "old" panel are now conducted by the one neutral wire back to the new panel where the wire connects to earth. So your circuit *is not* the only thing on this neutral conductor. Much of the rest of your house is a common load.

Now I don't know how far apart these panels are. They might be bolted together for all I know, in which case there is essentially no issue. However, if they are separated some distance then there will be some I^2 * R voltage drop in the neutral wire connecting the panels. If the loads on the two phases are split reasonably well, then the neutral current should be small. However, a major fault on some circuit can drive the current very high until a breaker opens. This will yank the neutral to some potential further above ground. If you are clamped onto your saw at the time with your feet on damp concrete, who knows what will happen.

[Doug Miller]

Yep.

Yep.