To eliminate this buzz, and to increase the solenoid hold- ing power, Decco adds two copper loops, called shad- ing coils, to the top of the "C" stack. Current is gen- erated in each of these shad- ing coils, and, most important, this generated current lags be- hind the applied current.	When the applied current is passing through zero, the shading coil current is at its maximum. This low shading coil current provides just enough magnetism to hold the plunger closed when ap- plied current magnetism is at zero, thus eliminating the buzz.	A.C. magnetic fluctuations also cause small stray currents, known as "eddy currents", to move in tiny circular paths within the "C" stack and plun- ger. Eddy currents consume power and cause a heat build-up which reduces sole- noid force. We must minimize them.
Decco makes the "C" stack and plunger of many thin sheets, or laminations, and coats each lamination with insulation. This contains the eddy currents within each lamination.	Magnetism can easily flow in its usual path around the coil, but the eddy currents cannot flow from one lamination to another. By containing the eddy currents within each lam- ination, (limiting their paths), we reduce heating and in- crease solenoid force.	Here's another important fact about solenoid operation. In- creased current in a solenoid coil produces increased mag- netism which increases sole- noid force. So...why don't we rig up a deal to ram all the cur- rent we can into a solenoid?
Because current generates heat, and generates it fast. If you double the current you increase the heat four fold. A small increase in current causes a great rise in tem- perature, which can burn out a coil.	As a solenoid closes, the flow of current decreases. The peak INRUSH CUR- RENT in the coil when the solenoid is open is several times greater than the "sole- noid closed" HOLDING CURRENT due to A.C. resistance (or IMPEDANCE) which increases as the sole- noid closes.	Here is an analogy to help you fix this situation in your mind. Visualize current flow- ing to the coil through a rub- ber tube. This tube runs under the solenoid plunger. As the solenoid closes, it pinches the tube, reducing the flow of cur- rent to the coil.
Remember--when a solenoid is open, it draws a high inrush current, which decreases as the solenoid closes. Now... suppose we energize a solenoid, but mechanically block it open. The high in- rush current will continue to flow in the coil.	This high current will gen- erate more heat than the solenoid can dissipate. The coil wire insulation burns, the bobbin melts, and the coil shorts out--all in a min- ute or two. Applying too heavy a load to a solenoid will hold the plunger open in the same way.	A CONTINUOUS DUTY SOLENOID is one that can be held energized indefinitely without overheating. The heat dissipating ability of this sole- noid is great enough to get rid of all the heat generated by the coil's lower holding current.