Hardwiring 230VAC Compressor Question

Page 1 of 3  
Finally (!) after a two year wait, my building received hookup of the second leg of an electrical service upgrade (delay was due to asbestos contamination issues)...I now have 220VAC availible. Time to hookup my 5HP/80 gallon IR compressor!
I have a question regarding grounding that I need to be clear on before proceeding. *[I have copy of the NEC 2002 Codebook in case anyone needs to reference it].
Here's the hardware configuration: -Compressor Motor: 5HP/230VAC/ 1 Phase/ 22.5 FLA -Electrical Service Panel: We have BX metal cable in this building which is the local NYC code. The breaker panel in my place has as the main feed a metal Greenfield conduit entering it: the Greenfield carries three wires, white/red/blk. There is NO green ground wire anywhere in this panel. Red connects to one side of the breaker terminal. Black connects to the other side of the breaker terminal. White goes to a seperate non-breaker terminal, and I am assuming the white is thus neutral.
Here are the voltage meter readings I get when testing at the breaker panel: Blk/Red 9VAC Blk/Wht 0VAC Red/Wht 0VAC Wht/Service Panel = 0.29 VAC Blk/ Service Panel = 120VAC Red/ Service Panel = 120VAC
------------------------ I intend to run BX cable from the service panel to an enclosed metal switchbox: and then a short length of Liquid Tite Flexible Metal Conduit from the switchbox to the compressor motor. I am using 10guage wire for the circuit. Total length of the circuit from panel to motor is approx. 20'.
Questions: 1) Will a 230VAC single phase motor run OK on 210VAC service? 2) I need either a Duplex Breaker, or 2 Single Breakers to control the circuit. What should each pole of the breaker be rated at? Is 25 or 30amps correct? Do I need any special 'motor type breaker'? 3)The motor has terminals for 2 wires and 1 ground wire. From my understanding I can run the Red (120VAC) & Blk (120VAC) from the breaker panel to the switchbox, and then from the switchbox onto the motor to their respective terminals. However, what do I use as a ground wire??? Can I put a copper grounding screw/lug into the service panel box and run a green ground wire off of that and use it as my ground? 4) There is no need to utilize the white wire in this circuit, correct (unless I decide to place a 120VAC outlet somewhere on the circuit?
Thanks a bunch. -N.
I have the current NEC codebook but am still perplexed. Thanks for any clarification.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 2 Dec 2003 10:10:12 -0800, N. wrote

I have no knowledge of NYC local codes, but as far as the national code goes:
1. Yes 2. A double breaker is required. 30 Amp would be correct for #10 wire. 3. The ground is through the shell of the BX cable. If your flex does not complete the grounding path a bonding wire must be installed. A copper lug in the panel is not necessary, I am unclear as to if the panel is your "Service entrance" or a subpanel. If a subpanel a lug is NOT allowed. 4. Correct.
Roger in Vegas Worlds Greatest Impulse Buyer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Not quite. If it is a subpanel, bonding the grounded conductor and the grounding conductor is not allowed. It is common for a subpanel to have a ground bar bonded to the panel (the panel is required to be bonded to the grounding conductor, but that happens through the BX shell as pointed out in this case).
The NEC no longer allows the armor on some armored cables to be used as the grounding conductor. This typically applies to flexible metal conduit, but may also apply to BX armored cable. Check the book.

scott
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 2 Dec 2003 18:08:53 -0400, Scott Lurndal wrote

Regarding service panels: The basement houses the 'Main Service Feed Panel' for the building. I live on the 4th floor, and I have a 'Breaker Panel' that is fed from that main panel: a Greenfield cable rises 4 floors and enters my 'Breaker Panel'...it is the ONLY panel in my living space. Nomenclature: does this 'Breaker Panel' generally qualify as a 'subpanel', or conversely, would a 'subpanel' be the nomenclature for any additional breaker panel installed along a new circuit I run downstream from my 'Breaker Panel'?
Yes, I had assumed the ground to be the shell of the BX cable...there is no 'ground bar' in my breaker panel. In my space, none of the receptacles have a ground wire .... I assume the BX cable itself to be the ground.
Regarding grounding the motor to the 'Breaker Panel': I was thinking the BX/Flexible Metal Conduit would suffice, but I had purchased a little copper screw/terminal to screw to the 'Breaker Panel" (refering to it as a 'lug' in my initial post). I'm still a little unclear as to general grounding/bonding practices, and was wondering if the BX was sufficient for the ground in my circuit, or if I would need to install a seperate green ground wire off the 'lug' from the 'Breaker Panel' and connect that to the motor.
When the electrical upgrade was made, the contractor installed a new receptacle and ran BX back to the 'Breaker Panel"...there is no seperate ground wire in this circuit, so, yes, I'm assuming the BX is functioning as the ground. What are the views on the best way for me to execute the ground for this motor circuit?
Thanks again. -N.
--
Swap out the air for lovegasoline to make contact.


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Any breaker panel that is fed from another breaker panel is a subpanel. There is only one "Service entrance" panel and it is fed from the power company lines. The panel in your living quarters sounds like a subpanel and is fed from the service entrance somewhere else in the building. As to running an additional green wire from the motor to the panel, it is not necessary by code but will do no harm (Except to confuse the next occupant :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
N. wrote:

BX is a lot different than Flexible Metal Conduit. Run the separate ground. When you install the lug in the subpanel scrape the paint off the back of the subpanel behind the lug.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 2 Dec 2003 22:16:38 -0400, ATP wrote

Good idea. Thanks to all for the assistance.
I have one last question. As long as I'm running the circuit into the room the compressor is in, I figure I might as well throw in an additional 120VAC recep while I'm at it. This would be for running other shop stuff, likely when the compressor ISN'T running. What would be the simplest method? Can I branch off one of the 120VAC wires going to the compressor (either the red or black) either before or after it enters the compressor's switchbox, and then run it down to a standard dual 120VAC three prong wall receptacle Of course I would have to run a white neutral wire off the subpanel to complete the wiring to the recep.
I could always just run a completely seperate 120VAC wire and a white nuetral wire from the subpanel and put them on a dedicated breaker to provide juice to the recep. I just figure it would be easier to run both the 120VAC recep and the compressor motor off the same circuit.
Is that kosher? Thanks. -N.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
-n. wrote:

No. You could accomplish the same thing by running a small feeder to a subpanel, but you cannot piggyback a receptacle load on a hot leg running to a piece of equipment. BTW, the hot legs are not really 120 VAC, that is the phase to neutral potential but you are using phase to phase and the phase to phase potential is what is important here. If you have 210V between phases you may have a 120/208 three phase service to the building, a single phase service would give you approximately 240 hot leg to hot leg, yet the legs would still be 120V to neutral. Calling them 120 V legs implies an additive relationship when you put them together which does not really exist, it only appears to exist in center tapped single phase systems because of the symmetry involved.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
ATP wrote:

Especially because the wires going to the compressor will be protected by a 25 or 30 amp breaker. You want the 120 receptacle to be on a 15 or 20 amp breaker.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
RE: Subject
Some where in this thread, 209V was noted as a measured voltage.
If that data is in fact true, you may be getting two legs and a neutral of a 208Y/120V, 3 phase service.
If that is true, you will almost certainly burn up a 240V motor unless you also install a buck-boost transformer for the 240V motor.
BTW, 208Y/120V is quite common in commercial buildings.
Be a good idea to reconfirm your supply voltage.
--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lew Hodgett wrote:

Although 208/230 motors are pretty common, he should check the nameplate.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 3 Dec 2003 23:40:33 -0500, ATP wrote

UPDATE: I spoke by phone with the electrical contractor who did the install and asked him exactly what kind of service I now have. He responded that I have two lines at 115VAC with a common nuetral. It is single phase 208VAC service. He mentioned that for 230VAC motor, I should do the install for a 220VAC line, with double breaker. I asked his opinion about running a 230 VAC 1-phase motor on 208 service...he said it wouldn't be a problem, at the very worst the motor may run a little slow.
-N.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
[snip]

This is extremely doubtful. 208V is THREE-phase, not single-phase. You might have two legs of a three-phase service. What voltage do you measure between the two 115V legs?

You need to get a _competent_ electrician, ASAP. This guy doesn't have a clue. Unless the motor was designed to be run on 208 3-phase, you'll burn it up in a hurry.
-- Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Doug Miller wrote:

He said 210 in a previous post.

His "electrician" is definitely clueless. There are plenty of 208/230 single phase motors however. Otherwise the vast number of commercial and institutional customers with 208Y service would not be able to use them.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"ATPwrites:

Typically motors that will operate at either 208V or 240V are more expensive than the equivalent motor wound to operate at 230V.
Over the years, have sold a lot of buck-boost transformers to solve this problem.
Get one, install it, then get a beer, and enjoy life.
--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Dec 2003 08:41:49 GMT, -n. put forth the notion that...

What he should have said, is at the worst it may run a little HOT. AC induction motors turn at a certain speed because of the frequency of the sine wave, not the amount of voltage. If you give the motor less voltage than it was designed for, it won't slow down initially, it'll draw more current, and current equals heat. You really have to lower the voltage significantly to see a drop in speed, but you don't have to lower it a whole lot to see an increase in amperage and heat buildup. Some motors are designed to run on anything between 208 and 230, but not all of them. If the manufacturer says the motor is okay to run at 208, that's fine, but don't go by what the contractor is telling you.
--
Checkmate
Copyright 2003
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Dec 2003 11:58:40 -0500, Checkmate wrote

To reiterate, the supply voltage I measured is 209VAC between the two hots. The motor states 230VAC single phase, 1.25 service factor, and is thermally proteted with a reset button. Again, the electrical contractor who owns the bizz that did the install states I have single phase service @ 208VAC....although many of you are claiming that this latter data must be incorrect. I will need to bug that contractor again and discuss the doubts expressed here. I haven't spoken with the motor manufacturer to check if the motor can run on 208-230VAC, although it most certainly does not list 208-230VAC on the nameplate. Is there a way for me to check and confirm the phase of the service I have (1 or 3 phase) with only a voltage/amp meter? Lastly, going with only the data I now have, many of you have expressed concern that the motor would run HOT and possibly burn out, short, or experience a reduced servie life if it were connected as is without a boost transformer. Hypothetically, wouldn't the thermal protection/reset circuit in the motor protect it before damage was done by shutting off the motor in the event that it did experience an increase in temp?
Thanks again.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You almost certainly don't have three phase service unless you live in some space that used to be industrial.
I don't think that reset button will protect you from chronic undervoltage. How big a motor is this? If it's just a horse or two, then your solution is really simple - buy a cheap buck/boost transformer, hook it up, and have a nice cup of coffee!
Grant Erwin
-n. wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    What about a large apartment building? Those are probably fed three phase, since all totaled, there is a *lot* of load, and this will distribute it fairly evenly.
    Anyway -- if you are measuring 120V from neutral to both hots, but 209 between them, you *are* getting two phases of a 208V three phase feed.

    Agreed -- that is the safest thing to do.
    Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 13 Dec 2003 01:09:00 -0500, DoN. Nichols put forth the notion that...

Most likely they're feeding the building with three phase, but splitting it up to the individual apartments with approximately 1/3 of the units on AB, BC, and CA. That's pretty unusual in residential buildings. Too bad he can't pull the third leg up to his unit, but he's most likely on a single phase meter unless there's just one meter for everybody.

--
Checkmate
Copyright 2003
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.