View pricing, availability, product information and place orders online 24/7 at singlesource.mingledorffs.com

Troubleshooting Electrical Problems: Voltage and Current

Bubba Moore

Bubba Moore

Technical Services Manager
Southeast District

Troubleshooting Electrical Problems: Voltage and Current

Troubleshooting electrical problems in an HVAC system can feel complicated. Sometimes the problem is overlooked as a faulty part. How often do we look beyond the obvious after the motors or compressors fail electrically?

Let’s first look at the incoming voltage. If the voltage is too high or too low, it can cause the motor to fail due to overheating. The voltage should fall between a minimum and a maximum limit that is listed on the data plate of the components. The voltage that is going to a motor or compressor should be within plus or minus 10% of the voltage listed on the data plate. For example, a 208/230-volt motor voltage range would be between 187 volts (208 – 10%) and 253 volts (230 +10%). On 3-phase units, voltages between phases must be balanced within 2%, or we have what is called phase imbalance. For example, if there was a 5% imbalance on the three- phase voltage, it could cause the motor winding temperature to increase 50% over a safe level.  If the voltages are outside of this plus or minus 10% range, or there is more than 2% phase imbalance on three phase components, then it will have to be determined if the problem is from the electrical panel or the incoming power supplied to the building that will have to be corrected. If it is not corrected, motors and compressors will continue to fail.

You can use this formula below to determine the percentage of voltage imbalance coming to a unit, or the voltage going to the motor or compressor.

As we discuss current imbalance, keep in mind that voltage imbalance will cause current imbalance. However, current imbalance will happen without a voltage imbalance. Current imbalance between any two legs of a three phase system should never be above 10%. What can cause the current imbalance? When there is a current imbalance, look for poor points on a contactor, loose crimp connectors, lugs on disconnects or corrosion. All this can cause high resistance on one leg of power in a three-phase unit. Current, like most things, will follow the path of least resistance. When this happens, the current will increase in the other two legs of power, causing the other two windings in the motor to generate more heat and eventually damaging the motor or compressor.

You can use this formula below to determine the percentage of current imbalance on the load side going to the equipment, motor or compressor.

Always keep in mind that the voltage to compressor terminals or motor connections during operation must be within voltage range indicated on unit nameplate. On three-phase units, voltages between phases must be balanced within 2%, and the current within 10%. Use the formulas above to determine the percent of voltage or current imbalance if there have been motor or compressor failures in a unit.

The voltage imbalance formula is in most three-phase installation instructions.

Sources:

48HC07-12 Installation Instructions

48TJ004-014 Product Data

HVAC SERVICING PROCEDURES

More to explore

soldering

Soldering, Brazing, and Welding

In this article, we will go over a few differences between the types of metal-joining processes used to connect pipes together. Without

The Infamous E1: Part 1

First, what is an E1 fault code?  E1 is a ductless system communication fault between the indoor and outdoor units. Are you

Alabama Locations

Anniston (256) 241-3026 105 E D St, Anniston, AL 36201
Auburn (334) 734-8011 2295 1st Ave, Opelika, AL 36801
Birmingham (205) 250-7714 516 31st St N, Birmingham, AL 35203
Dothan (334) 836-1035 205 Wedgewood Dr, Dothan, AL 36303
Gulf Shores (251) 968-2660 820 Commerce Dr, Gulf Shores, AL 36542
Huntsville (256) 859-2691 391 Nick Fitcheard Rd NW, Huntsville, AL 35806
Loxley (251) 964-2707 30020 Co Rd 49, Loxley, AL 36551
Mobile (251) 476-2220 5522 W Commerce Blvd West, Mobile, AL 36619
Montgomery (334) 262-4855 861 Plantation Way, Montgomery, AL 36117
Muscle Shoals (256) 383-6904 107 Commerce St, Muscle Shoals, AL 35661

Georgia Locations

Albany(229) 432-5254205 Baldwin Dr, Albany, GA 31707
Athens(706) 548-2563105 Whitetail Way, Bogart, GA 30622
Atlanta(404) 875-77551290 Tacoma Dr NW, Atlanta, GA 30318
Augusta(706) 651-19503618 Wrightsboro Rd, Augusta, GA 30909
Brunswick(912) 265-5193275 Rose Dr, Brunswick, GA 31520
Columbus(706) 322-38706201 W Hamilton Park Rd, Columbus, GA 31909
Conyers(770) 918-9132335 Gees Mill Business Pkwy NE, Conyers, GA 30013
Forest Park(404) 361-24745158-C Kennedy Rd, Forest Park, GA 30297
Gainesville(770) 297-93352472 Hilton Dr, Gainesville, GA 30501
Lawrenceville(678) 442-10602111 Cedars Rd SE, Lawrenceville, GA 30043
Lithia Springs(770) 948-3451320 Thornton Rd #106, Lithia Springs, GA 30122
Macon(478) 474-85445527 Thomaston Rd, Macon, GA 31220
Marietta(770) 426-05511060 Triad Ct, Marietta, GA 30062
Newnan(770) 239-210570 Enterprise Ct, Newnan, GA 30265
Peachtree Corners(770) 239-21006675 Jones Mill Ct, Peachtree Corners, GA 30092
Savannah(912) 232-1228103 Central Jct Blvd, Savannah, GA 31405
Statesboro(912) 764-8841126 W Parrish St, Statesboro, GA 30458
Valdosta(229) 245-8200363 Connell Rd, Valdosta, GA 31602
Warner Robins(478) 953-3727110 Byrd Way, Warner Robins, GA 31088

South Carolina Locations

Hilton Head(843) 689-34043715, 21 Hunter Rd, Hilton Head Island, SC 29926

Florida Locations

Fort Walton Beach(850) 244-201776 Beal Pkwy SW, Fort Walton Beach, FL 32548
Panama City(850) 913-05853012 Lisenby Ave, Panama City, FL 32405
Pensacola(850) 438-10054405 N. Palafox Street, Pensacola FL 32505

Mississippi Locations

Hattiesburg(601) 579-96701851 Lincoln Rd, Hattiesburg, MS 39402
Ocean Springs(228) 497-5090Sunplex Industrial Park, 5717 Suntec Drive, Ocean Springs, MS 39564

Commercial Sales

Norcross – North Georgia Hub
(800) 282-4911

Birmingham – North Alabama Hub
(205) 250-7714

Macon – Southwest Hub
(800) 342-9250

Loxley – Gulf Coast Hub
(800) 239-7419

Savannah – Southeast Hub
(800) 822-7617

Commercial Parts

 CompanyWeb AddressDescription
Airzonewww.airzoneinc.comCustom and Underfloor Air Handlers
Aladdin Metal Productswww.aladdinmetalproducts.comCurb Adapters and Roof Curbs
Aprilairewww.aprilaire.comIndoor Air Quality Products
Autaniwww.autani.comBuilding Automation and Controls
Bardwww.bardhvac.comHeat Pumps,Gas/Electric, and Wall Mounted Air Conditioners
Bryantwww.bryant.comCommercial, Industrial, Residential Heating & A/C Products and Controls
Carrierwww.commercial.carrier.comCommercial and Residential Heating & A/C Products
Data Airewww.dataaire.comPrecision Air Control for Data Processing Centers
 DXairwww.dxair.comPool dehumidification systems
 First Companywww.firstco.comFan Coil Units
Global Plasma Solutionswww.gpshvac.comAir Purification and Bi-Polar Ionization
 Greewww.greeusa.comPTACs
 Hayes Fluid Controlswww.haysfluidcontrols.comHose Kits and Control Valves
 iAirewww.myiaire.comCommercial Air Purification using ionization with energy savings
 IslandAirewww.islandaire.comPTACs, Vertical Units, Water Source Heat Pumps
 i-Vuwww.commercial.carrier.comBuilding Automation and Controls
 Magic Airewww.magicaire.comFan Coil Units
 Micro Metlwww.micrometl.comRoof Curbs, RTU Accessories, & ERVs
 Modinewww.modine.comGas-Fired Unit Heaters, Duct, Furnaces, Hot Water Cabinet Unit Heaters, Makeup Air, and Dedicated Outdoor Air Systems
 Network Thermostatwww.networkthermostat.comInternet Thermostats, Wifi Themostats, Ethernet Thermostats
Paynewww.payne.comResidential Heating & A/C Products
Rawal Deviceswww.rawal.comContinuous Capacity Modulation and Dehumidification for DX Systems
Renew Airewww.renewaire.comFixed-Plate ERVs
Totalinewww.totaline.comCompressors, Parts, and Supplies
United CoolAirwww.unitedcoolair.comModular All-Indoor HVAC Systems
 Warren Technologywww.warrenhvac.comElectric Heaters
 Wilo Pumpswww.wilo-usa.comPump Systems for HVAC and Water Supply and Sewage