Advantages of a mechanical switch over semiconductor technologies

Even if semiconductor technologies are often the first choice nowadays, mechanical switches (electromechanical relays) still have numerous advantages that – depending on the requirements – are sometimes more convincing. The best choice should therefore be weighed up carefully.

Admittedly: Semiconductors are the perfect solution in many situations and with absolutely justified reasons. Thanks to their simple design, they make it possible to control the on/off status of another signal line without any electrical contact between the two. And even though millions of them are used for new designs every year, the proven and therefore well-known advantages will not be discussed further at this point. Instead, the focus will be on the mechanical switches, of which tens of millions are sold. And not only as replacements in existing applications, but a large proportion are also used for new designs.

The most obvious difference

While a mechanical relay requires a physically moving part to connect the contacts in the output components of the switch, a solid state relay does not need one at all. Instead, a low-power electrical signal is used to generate a semiconductor signal, which in turn transmits an output signal.

In addition to this one very obvious difference, both solutions have numerous other features that differentiate them in terms of design and functionality. But which of these sometimes make the mechanical switch the better solution?

Advantageous properties of the mechanical switch

A mechanical relay can be placed virtually anywhere in the circuit, as neither the contact closure nor the coil are connected to the ground of the circuit or earthed. With a semiconductor, this is not always possible with this degree of flexibility.

Flexibility is also the keyword when it comes to multiple contacts. These do not have to have the same nominal value and the same type of load. For example, some contacts can be designed for weak signals, others for current. On the solid state relay market, however, there are not many multi-pole variants to choose from. They are also very limited in terms of range and nominal values.

Mechanical switches are also very resistant to voltage and overcurrent peaks, as these can hardly cause any damage to the coil or contacts. In contrast, semiconductors tend to fail with a short circuit at their output, which can lead to critical situations.

The most important advantages at a glance:

– Can be used regardless of load: both AC and DC loads possible

– Wide switching range

– Contact resistance in the milliohm range (voltage drop is close to zero)

– Generate almost no leakage current (megaohm air gap)

– Resistant to spikes, transients and EMI

– Can be placed anywhere in a circuit (not exclusively as a low or high-side device)

– Provides a reliable, non-actuated (non-powered) state: N.O. or N.C.

– Can be biased to control the non-actuated state (N.O. <–> N.C.)

– Unlimited isolated poles (SPST, DPST, TPST, etc.)

– Own galvanic isolation

– No external circuitry required to switch a load

– No external power supply required to switch a load

– Not inherently polarity sensitive (but can be modified/biased for polarity sensitivity)

– Simple troubleshooting thanks to easy to understand technology

– Mature technology with a wide and immediate range of applications

Of course, the reasons mentioned above do not mean that a mechanical switch is “better” than a semiconductor. Both technologies have their strengths. What the numerous advantages do show, however, is that the next time you need a relay, you do not automatically have to fall back on a semiconductor. Rather, it is worth checking the individual requirements in each individual case and comparing them with the properties of both options. Only then can you be sure of finding the perfect solution.

If you have any application-specific questions, please contact our experts by phone or e-mail.