Rewind electricians must be familiar with the types of insulating materials utilized in motor rewind. In addition, they must know how to properly fabricate and install the insulating components where required.

Types of insulation

The type of insulation used is related to its function.

MAGNET WIRE FILM protects individual coil turns from voltage stress and environmental factors.

SLOT CELL INSULATION provides protection between the magnet wire and the stator core.

COIL SEPARATORS provide separation between coil sides in the same slot.

SLOT WEDGES provide tight packing of magnet wire in slots and keeps slot cell insulation in place.

PHASE MATERIAL provides separation of magnet wire end turns into phase groups of approximately the same potential.

SLEEVING provides insulation over soldered connections, to separate connections from end turns.

VARNISH bonds magnet wires to prevent motion (vibration between the wires) and also provides environmental protection.

Preparation of slot cell insulation

Measure length and depth of stator slots. Record measurements.

Procure a sufficient amount of 0.007-inch thick NOMEX paper to fabricate slot cell insulation for the total number of stator slots.

Since the tear strength of NOMEX is greater in one direction than the other, cut the pieces so that the higher tear strength is at right angles to the slot length to prevent tears in the edges of the material. This is usually indicated by marks or a line printed on the paper.

Slot Cell Insulation

Cuffing Machine

Cut another piece of NOMEX paper ¾ inch longer than the length of the stator iron, and 1½ inches wider than double the length of the slots. This piece is also called the outside piece.

Click on image to enlarge.

Cutting Slot Cell Material

Slot Depth Cut on Precuffed Paper

Join the two pieces of NOMEX paper by fitting the smaller (outside) piece inside the cuff of the larger (inside) piece.

Roll the two pieces around your index finger with the edge of the cuff away from your finger.

Insert the slot cell insulation into a stator slot to ensure it fits properly.

Fabricate additional required cell insulation the same way, then lay the slot cell insulation aside until actual coil insertion takes place.

Preparation of coil separators and slot wedges

Measure the width of the stator slots.

Select this material in widths that will fit snugly against the sides of the slot.

Procure enough of the silicone glass coil separator and NOMEX slot wedge material to fabricate the number required.

Cut the silicone glass coil separators ½ inch longer than the slot cell insulation after cuffing. This is equal to core length plus 2 inches. It is the longest piece. In motors with less than 2 inches of end room, you may have to adjust this slightly smaller to allow enough space for the second coil half.

Cut the NOMEX slot wedges the same length as the slot cell insulation after cuffing.

Preparation of phase material and protective paper liner

Procure a sufficient amount of   0.007-inch NOMEX paper to fabricate phase material and protective paper liner.

Cut phase material pieces in the form of a triangle. Cut triangles larger than necessary to butt against the slot cell insulation to completely separate the coils of adjacent groups against the slot cell. Excess insulation will be trimmed after installation.

The protective paper liner will lay in the stator bore and protect the uninstalled coil sides from rubbing and chafing on the stator iron.

Cut a protective paper liner ¾ inch wider than the stator iron and approximately a the length of the stator inner bore circumference.

Click on image to enlarge.

Fitting the Pieces of a Slot Cell Insulator