I found a few posts on this topic on Google Groups, but none of them
seem to have answered any of my current questions.
I need a switch for my soon-to-be-homebuilt Bill Pentz DC. It's going
to be based upon the Harbor Freight 220V "5HP" motor... which is
actually more like 3HP and draws something like 11-15 amps.
1 - I don't need remote control... and I also don't really need a
magnetic switch in this case, but I think I'd really like both of the
hot legs to be switched (ie, double-pole). Does anyone have any
inexpensive sources for this?
2 - Those Grizzly magnetic ones which go for about $60.... are those
On 2 Aug 2004 17:51:48 -0700, email@example.com (Joe Emenaker) wrote:
I've got a 220v Long Ranger remote. I know you said you don't need
it, but I find it very convenient. You should be able to find a
double-pole 20a switch at an electrical store for 15 bucks. A
magnetic switch is not really needed for a DC.
It doesn't "have" to be double pole as long as you can easily unplug it, but
it is certainly a good idea.
Anyhow, your hardware store should have a double pole switch for about $10;
my recollection is that they are good for 30a.
I was in my local Home Depot to pick up a commercial rated wall switch
the other day. They had double pole/single throw switches in both 15A
and 20A ratings. I don't recall the exact prices but they were around
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)
Read the fine print on those switches--you'll find that they also have a
horsepower rating that is surprisingly low. Motor loads put somewhat
different demands on the switch from lighting loads and so you can't go
entirely by the current capacity--what you want is a "motor starting
switch"--check the Leviton catalog, which you can find at their web site
<http://www.leviton.com> and you'll find several. If you use a switch not
rated for the horsepower, two things happen--first, it goes "pffft" a lot
sooner than it would otherwise and you have to replace it, second, in the
unlikely event that it sets the shop on fire your insurance company goes
"whaddaya say, ya say no, whaddaya do, deny the claim" as the local
ambulance chaser's ad used to say.
The purpose-made motor starting switches also break both phases.
Reply to jclarke at ae tee tee global dot net
I was aware of the HP ratings of switches. I understand this is because of
the high starting (& breaking) currents. After going to the Levitron site
you recommended I discovered that plugs also have HP ratings.
Does this mean that the 20A 230V plug outlet (feed with 12g) I use for a 3HP
table saw is a problem. That Levitron book rates it at 2HP. I would bet
that many of us have this situation.
I understand that the 12 gauge wire is OK if the motor full load current is
less than 80% of the wire rating. eg 12 guage (20amps) motor could be up to
16amps and that the wire will handle the start up currents. I had assumed
this also applied to the plugs. Guess not.
Is this correct?
I suspect that with the plugs it's a "make" current (a plug can weld itself
if something is plugged into it that draws more current than it can handle)
that's the limiting factor. Don't know for sure though--probably a good
idea to play safe though.
Reply to jclarke at ae tee tee global dot net
Partly because of starting current but more because a motor is an
inductive load. When you break the circuit to an inductor, it acts like
an electrical flywheel. I tends to keep the current flowing in the
direction it's been flowing. This will produce an arc (spark) accross
the contacts as they start to open that would not occur with a resistive
load (light bulbs) drawing the same amperage. Tends to burn the contacts.
I doubt the HP rating of the plug is that important unless you routinely
make and break the circuit with the plug. I think you're likely not
going to notice a temp rise in that plug and it isn't going to arc.
Unless you only have one machine hooked up and never vacumm the floor,
you want remote control on your dust collector. If you use a low
voltage magnetic contactor you can wire several small switches using
doorbell wire. I did that for a while, then hooked up an X-10 dry
contact with a clicker. Works pretty good.
How/where did you do the sheet metal work for the cyclone. I never
could get that done cheat enough to justify building one. The
motor-impeller part seems easy enough. I watch the guys on the chopper
garage show weld up a gas tank and just drool.
firstname.lastname@example.org (Joe Emenaker) wrote in message
No - you don't "want" both hot legs to be switched, you *must* switch both
legs. Any electrical supply center will carry 220v switches. Ace hardware
is likely nearby by you and they'll carry it as a regular stock item.
double pole relay. I used a low voltage (12vDC) so I could run microswitches
to each blast gate. Graingers is where I got mine (I think - might have been
one of the random electrical supply houses)....
Please, DO NOT switch only one line!
If you are using 220V (or 230/240) you MUST disconnect both wires to
be safe and to comply with the NEC (national Electric Code.)
Go to an electrical supply house and ask for a 2-pole disconnect for a
2 HP (or whatever you're using) motor. The guys there will be able to
help you to get the correct (and safe) switch.
=========================It's not the heat, it's the humidity!
=========================(..Think the humidity's bad?
You should watch us vote!)
I was hoping someone else would post this. I posted the same comment a
couple of days ago and have been somewhat surprised that yours and mine were
the only comments about switching just one leg of a 220 circuit.
Fortunately, the OP was intending to switch both legs, but I did not get the
impression he knew that he had to switch both legs.
Well, I didn't know that it was mandated in the electrical code, but I
do know enough about house wiring for the thought of an unswitched hot
line going to my motor to give me the serious creeps.
That said, I'll also mention that I've seen 220V single-pole switches
at the hardware store. In fact, that's the ONLY kind of 220V switches
I've seen locally. At the time, I was thinking "So... are these the
ones they sell to the people with lots of life insurance?". I was
beginning to think that my only option was to buy two of them, put
them in a two-gang box, and glue some bar to both of the toggles or
I ended up getting one of the 5HP Leviton ones.
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