Motor Connections

Posted on: June 17th, 2014 by admin No Comments

One of the most important, yet most frequently misunderstood, parts of placing an electric motor in service is connecting the motor leads correctly. One would think it would be easy, but in fact it can be easy to get it wrong. Over the last 45 years I have seen literally scores of different connections used in electric motors. Let me say up front that, if you have any question about how to properly connect your motor, give the motor experts at Gem State Electric a call. We’ve gotten pretty good at figuring these things out over the phone. The major challenge in figuring out the proper connection for a given motor is the shear variety and the (sometimes) lack of standards. Color coding, NEMA numbering, IEC numbering and non-standard systems exist in both single phase and three phase motors. Single voltage, dual voltage, tri-voltage, wye-delta start, part winding start, two speed single winding, two speed two winding , constant torque, variable torque, constant horsepower, even two phase – we’ve seen just about everything. Then there is the occasional 18 lead motor with no markings on the leads! The point is – if you can’t figure it out don’t feel bad. Just give us a call at 208-344-5461. Some standards, of course, do exist. It’s just that some standards are more standard than other standards. So let’s look at some of the more common connections, keeping in mind that there can be variations on all of these diagrams.

SINGLE PHASE: It would be nice if all single phase motors could be reduced to two leads but that will never happen. We can however reduce the noise to a few groups that will handle most motors – single voltage, multi-voltage, set rotation and reversible. The single voltage and set rotation connections are typically a simplification of the multi-voltage reversible connections with some of the connections made internally, leaving fewer choices for the installer. Take a look at a few sample wiring diagrams, (right click on the link below to open in a new tab.)

NA Single-Phase1 connections

Some common modifications to this connection scheme: The use of colors instead of numbers (no standard between manufacturers is known to exist for colors) Some manufacturers interchange leads 2 and 3 GE made some larger single phase motors in the 1970s that used a 10 lead connection Some manufacturers use four leads for the start winding, adding lead numbers 6 and 7

THREE PHASE: Most three phase connections are either a “wye” (sometimes referred to as a “Y” or “star” connection) or Delta. There are a number of combinations that utilize both a wye and a delta connection but these connections are best left for another discussion. Let’s take a look at some of the more common three phase connections. You should note when comparing the wye and delta dual voltage (nine lead) connections that the external high voltage connections are identical. This means that when connecting a nine lead three phase dual voltage motor for 460 volts it is not necessary to know the internal configuration of the winding. However, if it is 230 volts that you wish to connect to your three phase motor you must first determine what the internal connection was used. The easiest way to do this is to look at the low voltage wiring diagram. If there is no diagram, you must take continuity readings. In order to do this you must disconnect any leads that are already connected. Caution: It is always best, before disconnecting an existing connection, to notice two things: 1) Are the leads identified (alpha numeric or color coded) 2) What leads are currently connected to each other? If the leads are not identified in any manner, stop before it is too late and call the motor experts at Gem State Electric. We can help you figure out what steps to take before it is too late! If you don’t stop at this point you may be taking a minor challenge into a major project (also spelled m-a-j-o-r-e-x-p-e-n-s-e). If the leads are identified and currently connected together in some configuration right down which leads are connected before disconnecting anything. This way, if you get in over your head you can still go back to the start instead of launching that major project to which we were just referring. With all leads disconnected and not touching each other, check for continuity (a circuit) between leads 7, 8 and 9 with your ohm meter or continuity tester. If a circuit exists between all three leads, you have an internal wye connected motor. If no circuit exists, and you know the winding to be good, you have a delta connected motor. Using the appropriate connection diagram it is now an easy matter to reconnect your motor for the lower voltage.

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