Sequencers

Heating · Electric Furnaces · printed page 202 (PDF page 203)

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Electric Furnace – Sequencers Sequencers for Electric Furnaces Electric Heating Systems

Text in the illustration

hot air plenum
heating elements (typically 5 kw each)
elements turned on
25 kw electric furnace
electrical supply
blower
cold air return
5
4
3
2
1
120 to 360 seconds later
90 to 270 seconds later
60 to 180 seconds later
30 to 90 seconds later
thermostat calls for heat
the sequencers control when the heating elements come on
the elements are activated at 30 - 90 second intervals to avoid demand surges on the electrical system
in a staged furnace, the heating elements come on in sequence as long as the temperature at the thermostat continues to drop
once the temperature starts to rise, no more elements are turned on
when there is minimal demand for heat, the furnace may be utilizing only one or two heating elements

Generated explanation

A cutaway illustration of a 25 kW electric furnace shows a lower blower and cold-air return beneath an array of resistance heating elements and a hot-air plenum. Electrical supply conduit and internal wiring connect to the heating assembly and its sequencers. Five numbered heating stages illustrate the first element turning on when the thermostat calls for heat, with subsequent elements activated at cumulative delays of 30–90, 60–180, 90–270, and 120–360 seconds. The annotations explain that sequencers stagger element activation to avoid electrical demand surges. In a staged furnace, additional elements turn on while thermostat temperature continues to drop, but no additional elements turn on once temperature starts rising; minimal demand may require only one or two elements.

Components

electric furnace electric resistance heating elements sequencers blower hot-air plenum cold-air return electrical supply conduit electrical wiring furnace cabinet

Materials

sheet metal metal heating coils electrical wire

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