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HVACR - Refrigeration

Series and Parallel Circuits

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Series Circuits

• A series circuit has one single path for current flow.

• The loads are arranged so current must flow through load #1, then load #2, then load #3.

• If the connection is broken anywhere, or if one load fails, current flow stops in the entire circuit.

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Series Circuits

• Voltage is divided by all of the loads in a series circuit.

• In a series circuit, as each load consumes power there will be a voltage drop.

• Switches and contacts are not power consuming devices and should not cause any voltage drop.

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Simple Series Circuit Diagram

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Series Circuits

• Total Resistance for Series Circuit− A series circuit has only one path

for current flow.− The total resistance is the sum of

all the resistances in the circuit.

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Series Circuits

• The resistances of a series circuit can be added for the sum of the resistances of the total circuit. For example:

R1 = 10 ohmsR2 = 10 ohmsR3 = 20 ohmsRT = 40 ohms

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Parallel Circuits

• A parallel circuit has more than one path for current to flow.

• Parallel circuits will connect several loads across the same voltage source.

• The current flows through each load, independent of the others.

• The current flow through each load is not always equal.

• The voltage across each load is always equal.

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Parallel Circuit Diagram

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Parallel Circuits

• Total resistance in a parallel circuit:− A series circuit has more than one

path for current flow.− Adding additional loads will

decrease the total resistance in the circuit.

− The total resistance is always less than the smallest resistance in the circuit.