Hardwiring 230VAC Compressor Question

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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.
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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.
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Roy Smith wrote:

I got this hilarious mental image of a home shop type with a Bridgeport in his bedroom and extension cords running to the apartments on either side of him to get the other two phases...
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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.
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Checkmate
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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dangerous, a lot is just plain wrong, some misguided, some pertains to other jurisdictions or situations or is out of date, some makes no economic sense.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.
mike
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On 6 Dec 2003 11:12:08 -0800, Mike put forth the notion that...

I've been a licensed electrical contractor for 29 years... does that count?

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Checkmate
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Checkmate wrote:

Nope. Considering some of the work I've seen that was done by "licensed electrical contractors", that alone doesn't mean much.
Ted
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On Sun, 07 Dec 2003 05:57:31 GMT, Ted Edwards put forth the notion that...

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 problem?
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.
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On Sat, 6 Dec 2003 15:12:08 -0500, Mike wrote

Mike, 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. Cheers, -N.
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On Tue, 2 Dec 2003 16:56:23 -0400, Roger Hull wrote

Roger, what sort of purchases are we talking about to have won the title? -N.
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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 compressor. 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.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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On Wed, 3 Dec 2003 1:27:37 -0500, Anthony wrote

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)?

Thanks. -N.
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Obviously this system is grounded through the conduit (not my preference, but ok) 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).
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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On Wed, 3 Dec 2003 11:27:06 -0500, Anthony wrote

To reiterate: 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 system]. 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? Thanks. -N.

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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.
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On Wed, 03 Dec 2003 10:06:45 GMT, -n. put forth the notion that...

Never connect a ground wire to the neutral bus bar in a subpanel. Your ground has to connect to the can, preferably by using a ground lug bolted to the back of the panel.

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Checkmate
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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 on it.
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 208v.
Rick

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@no.spam.please.bis.midco.net says...

Rick, do you know what RPM motor I should be using on an older Ingersoll-Rand Type 30 Model 234C4?
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Jim,
I honestly don't know the answer to that question, and I don't have my work resources available to me right now.
You may find an answer here:
http://air.irco.com/index.asp
Rick
says...

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On Sat, 6 Dec 2003 08:24:57 -0600, Rick put forth the notion that...

It's a simple matter to get a 240/24 volt transformer, and wire it up in a boost configuration. This will turn 208 volts into 230.

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Checkmate
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