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Shunt Tap Procedures

A shunt-type furnace is a tubular furnace which has a number of external "taps" or "shunts" incorporated into the element windings in addition to the normal power feed taps.  (The furnace can be either single or multi zone.)

These shunts are a means of influencing the thermal characteristics of an axial region within the furnace bore (to create a more uniform flat zone) by a method known as "shunting".

What are the benefits to shunts in my furnace?

The procedure for furnace shunting involves the physical placement of an external resistor across the external "taps" in parallel with the element windings.  The external resistor effectively lowers the temperature of the region which has been shunted by reducing the current flow in two parallel paths, resulting in a lower temperature in the area where the shunt resistor is placed.

The use of shunt(s) decreases the resistance of the region(s) that were shunted and at the same time, reduces the resistance of the entire furnace.   This reduction in resistance causes the shunted regions to run cooler, while the un-shunted regions will run somewhat hotter. The current drawn by the furnace will increase with the use of shunts.  The current drawn must not exceed the capacity of the power supply unit or the furnace windings.  With proper shunt selection and placement, a more uniform and longer flat zone can be achieved.

--excerpts taken from a paper written by Robert Mellen, Jr. 2000

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