Series and parallel connection: the most important at a glance

Lamps can be connected in series or parallel, with tandem or duo connection. A series circuit means that the lamps are connected in series. Here, there is only one circuit. Parallel connection, on the other hand, results in several circuits, since each lamp has its own circuit.

Series and parallel connection as panel picture

The most important at a glance:

  • Series connection: lamps are connected in series in one circuit
  • Tandem circuit: Subtype of series circuit; two lamps are operated on one ballast
  • Parallel circuit: lamps each have their own circuit
  • Duo circuit: subform of parallel circuit; parallel circuit of two fluorescent lamp branches (inductive and capacitive)

What is a series circuit?

In a series circuit, lamps are connected in series. There is no branching during connection, as is the case with parallel connection, for example. This also means that all lamps operate in a single circuit.The series connection can also be found Series connection. As many lamps can be connected in series as the voltage of the power supply permits.

A commonly known example of lamps connected in series is the string of lights. If you connect the chain to 230 volts from the wall outlet and it has, for example, 10 lamps, each of them will receive 23 volts. The voltage is therefore distributed evenly across all electrical consumers, as electrical components are called. The partial voltage of all consumers added together results in the total voltage. If a lamp burns out, the entire light chain is no longer illuminated. This effect can be avoided by using a so-called current bridge.

A series circuit is when two lamps, each with a starter, are connected to a ballast.

Above: series connection with two resistors;
below: Parallel circuit with two resistors
By Saure – Own work , CC0, Link

Series connection for gas discharge lamps

If gas discharge lamps have the same rated current, they can be connected in series. Use a suitable ballast to obtain the required current limitation.

LED series connection – also applies to incandescent lamps

The same applies to LED lamps as well as incandescent lamps: the rated current must be the same for them to be connected in series. If you decide to use the inefficient incandescent lamps, you should still consider the following: make sure that the values match exactly, otherwise the product with the thinnest filament will burn out directly.

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What is a tandem circuit?

A tandem circuit is a form of series connection. In this case, two lamps, such as fluorescent tubes, are operated on a single ballast. How to save an additional ballast. Please note that a separate starter is still required for each lamp. This must be aligned for tandem operation. You can recognize this by the fact that the starter is marked with the term "series" or engl. "series" is marked.

Tandem circuit.png

By The authorship was not given in a machine-readable form. It is assumed>Journey234 is the author (based on the rights holder information). – Authorship was not given in a machine-readable form. It is assumed that this is an own work (based on the rights holder information)., Public domain>Link

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Starters for single operation are not suitable, as they do not ignite due to the divided mains voltage. Furthermore, the same applies here: If one of the two lamps fails, the second one will also no longer light up.

Tandem circuit for LEDs: is it possible?

If you want to change from conventional fluorescent tubes to LED tubes, it is absolutely necessary to rewire them. Please consult a qualified person for this purpose.

What is a parallel circuit?

In a parallel circuit, also known as a shunt circuit, two or more two-pole components are connected together. It is important that the poles with the same name are always connected to each other.

Each lamp connected in parallel has its own circuit (see diagram above). The individual currents add up to a total current. The electrical voltage is the same for each lamp you connect. This also means that if one light source fails, all the others do not automatically fail as well. So the intact loads continue to light.

Parallel circuit for gas discharge lamps

Gas discharge lamps can only be connected indirectly in parallel. Due to the principle of operation of the gas discharge, several lamps of this type can not be operated directly in a parallel circuit. Gas discharge lamps need a ballast to limit current. which is connected in series. Lamp and ballast together can now be connected in parallel.

What is a duo circuit?

A duo circuit is the parallel connection of two fluorescent lamp branches. One branch is inductive and consists of the conventional ballast (CCG) and the fluorescent lamp. The second branch is capacitive and also includes lamp and KVG, plus an additional compensation capacitor. This is connected in series with the ballast.

Fluorescent tube duo circuit compact.PNG

From Udm in Wikipedia in German – File:Leuchtstoffroehre Duoschaltung.PNG by User:Journey234, public domain, link

Explanation of terms: What is a capacitor?

A capacitor is an electronic component that can store energy. How to keep a lamp lit for a short time after it is turned off.

By the duo circuit it is possible to avoid a too high lamp current. Another advantage is that by the different branches, also the light-dark phases take place differently.

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