On Sat, 13 Dec 2003 1:22:28 -0400, Checkmate wrote
Yes, it is an apatment building...thanks, I now understand why (2 legs of a)
3-phase service registers 208VAC. The motor is 5hp nominal,an Emerson motor,
rated @ 22FLA.
What spec Buck-boost transformer should I be shopping for?
Any good online sources for the above?
Thanks again guys for the electricity lesson.
I assume you meant to say "usual" there?
I used to live in a 55 unit apartment building, and the wiring was done
exactly that way. Each apartment had a washer/dryer, with a "220"
outlet for the dryer. The dryer motor ran on 110 and the "220" was just
for the electric heating element, so I imagine all that happened is it
didn't get as hot as it should have.
On Sat, 13 Dec 2003 00:49:19 GMT, -n. put forth the notion that...
If you have a 120/208 volt single phase service, it's derived from two
legs and a neutral from a three phase service somewhere along the line.
If your motor has a thermal overload switch, it should shut off if it's
working properly, however this isn't going to solve your problem.
You are nuts to get your electrical wiring information from this
group. In the past some of the information I've seen posted is
downright dangerous, a lot is just plain wrong, some misguided, some
pertains to other jurisdictions or situations or is out of date, some
makes no economic sense. A small part is good sound advice from
knowledgable professionals who are up on current code. So how do you
sort it out? Hire an electrician.
On Sun, 07 Dec 2003 05:57:31 GMT, Ted Edwards put forth the notion
From my observations, that's usually because the guy with the license
isn't actually doing the work... he's hiring a bunch of twenty-something
year old's who think they're electricians, and he's not supervising the
job properly. Sometimes incompetence is actually profitable. A good
example is the electrical repair business. The guys that do
troubleshooting and repair usually charge by the hour. Who makes more
money, the guy who knows what he's doing and can find a problem in under
half an hour, or the guy who hasn't got a clue, and spends the whole day
pulling every outlet in the building apart until he stumbles upon the
I know what you're saying... the advice you get on Usenet is often worth
exactly what you paid for it. On the other hand, there are people out
there who know what they're talking about and don't mind helping people.
If you get enough answers from enough people, you can get a pretty good
idea as to who knows what they're talking about and who's full of shit.
I appreciate your admonition: with enough input I think the resolution(s)
rise to the top of the heap eventually. It may take a little debate to get
there, but often a few heads are better than one, and there are many
knowledgeble folks on these newsgroups. In fact, a few years ago when I was
first exploring electronics and wanted to design a digitalyl controlled
circuit, an electrical engineer emailed me and it started a very intense
email education...the man is brilliant and knew his stuff....one of the
greatest learning experiences of my life.
What you say can be true, but there are also some smart, informed , and
experienced folks on here. I'll wait till I get the doubts ironed out and
get consensus, then go forward.
If the panel you refer to is your service entrance, you *SHOULD* have a
bare #6 min/#4 preferred BARE ground wire running from the terminal block
which the white wire connects to a ground rod outside your building. This
provides the earth ground. As for your installation:
Typically, you will use a double breaker, 30A for #10 wire.
Pull 3 wires, 1 red, 1 black and 1 bare from your panel to the disconnect
box, and the same to your compressor.
Red to one hot side, black to the other and ground to the ground lug on
The ground must also attach via screw, to the disconnect box (if using
metal box) This bare ground should connect to the neutral/ground terminal
strip in the service panel.
In combination with the ground rod/#6/4 wire this provides a direct earth
ground for the compressor.
You can't 'idiot proof' anything....every time you try, they just make
The breaker panel in my residence does have a terminal block that the white
nuetral wire connects to (the largest white wire that comes from the main
service panel in the building's basement), and is also where all the white
neutral wires for the various circuits in my residence also terminate (but no
bare wires connect to it...indeed, there are no bare wires in my breaker
panel). Are you suggesting that this terminal block is where I should connect
the bare ground wire to (instead of just connecting to the panel itself)?
Obviously this system is grounded through the conduit (not my preference,
In this case, the metal flex conduit from the breaker panel to the
disconnect box obviously serves as ground path. You will probably need a
bonding wire (bare or green) from the ground lug on the compressor to the
ground lug on the disconnect box (the actual box itself).
You can't 'idiot proof' anything....every time you try, they just make
I am clear on this above wiring scheme except for one detail. The panel I am
starting from is a subpanel and it does not contain any grounding bar or
grounding terminal. In this case, does my ground wire need to be bare, or
will green insulated work just as well?
I pull red, black, and green insulated ground (all 10awg). Red goes to one
pole of 30A dual breaker, black goes to other pole of breaker, for ground I
drill a hole into the subpanel box itself then scrape some paint away and
screw in a copper grounding lug. I run these three wires through BX cable to
a 30AMP rated disconnect box, making certain to affix the ground to the
disconnect box via a screw and to acheive good continuity. THese 3 wires exit
the disconnect box and are encased in liquid tite flexible metal conduit
which goes to the compressor motor/switch. Again, black and red connect to
respective lugs on the motor and the ground goes to ground lug on motor.
[If I find out a boost transformer is absolutely needed to boost my 208VAC
service to run the 230VAC motor, I will research that and add it t the
If I wish to install a 120VAC recep box in the same room as the compressor,
it must be on a seperate ciruit with a dedicated breaker, NOT off the hot
wires used in the compressor circuit.
The only other modification I can forsee doing to this compressor circuit
would be to install a 230VAC receptacle in the wall and a mating 230VAC
plug/cordset [10awg, 3 wire: red, black, green] on the compressor .... and
run that downstream from the disconnect box as an option instead of the
hardwired liquid tite flexible metal conduit.
What do you think guys, does that sound like it confirms to code?
On Thu, 11 Dec 2003 09:22:04 GMT, -n. put forth the notion that...
You've got the right idea, and that's how I'd do it. Whether it
conforms to code is another issue. Offhand, I'd say yes, but every
jurisdiction has their own little quirks... what kind of conduit they
want you to use, etc. I've seen some weird demands from even weirder
inspectors. If you're going to get it permitted, it's best to run your
plans by an inspector first and get his blessings, so to speak.
According to Ingersoll Rand (I am a dealer) you CANNOT run a compressor with
a motor designed for 230v AC on a 208v circuit. IR sells a special 208v
motor for those installations. You have to order it with the correct motor
We've tried using the standard 230v motor and had problems with them
overheating and shorting out. It will run for a while, but eventually the
motor will fail.
We are seeing more and more 208v in our area instead of 230v. I'm not sure
of the reason, but most newly constructed areas are being serviced with
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