By Rogelio Castaneda, Design Engineer, Sensata Technologies, and Oscar Rivera, Engineering Director, Sensata Technologies
How to Prevent Electrical
Motors from Over-Heating
with Thermally Protected
Next-generation solid-state power relays with thermal protection can prevent expensive and hard to repair damage caused by
misuse, over use, and even cyberattacks.
What do conveyor belts, assembly lines, medical, energy, industrial/commercial HVAC and
refrigeration systems, heavy-duty transport and
construction vehicles, and other complex manufacturing
systems all have in common? Electrical Motors.
Big and expensive electrical motors that (if they overheat)
can be damaged or destroyed. Motors can overheat from a
variety of different causes—too much weight being moved,
jams in a conveyor belt, working in high temperature
environments, and fluctuations in supply voltage—all can
contribute to the possibility of overheating. Thermally
protected solid-state relays (SSRs) can also help protect
against cyberattacks by preventing rogue instructions
from forcing a machine to run extra fast, stressing its
components, and causing serious damage from overheating.
Many of these large machines require a system attached
to the motor’s power supply that can sense overheating and
will turn off the power to the motor, thus preventing this
damage. In many cases, this device is an electrical relay that
turns the power on and off. There are two main types of
these relays—electro-mechanical (EMRs) and SSRs.
What Is the Difference Between an EMR and SSR?
For more than 150 years, electro-mechanical relays were
the standard solution for managing these load circuits
providing power to big machines. However, in the last 30
years or so, SSRs have captured a great deal of market
share because of increased operational life, reliability, and
There are significant differences between EMRs and
SSRs, especially in terms of life span and performance.
EMRs are mechanical based and have moving parts,
making them highly susceptible to magnetic noise,
The average life span of EMRs is in the range of
hundreds of thousands of cycles compared to five million
hours for three-phase SSRs. With such maintenance-free
durability, SSRs can often outlast the equipment in which
they are installed.
In addition to a longer life span that provides greater
reliability and replacement cost savings, SSRs provide faster
switching than EMRs, making them adaptable to a wider
range of high power load applications.
SSRs operate silently (without the undesirable
clicking sound emitted by EMRs) with low input power
consumption and produce little electrical interference.
Both shock and vibration resistant, SSRs can withstand
harsh environments and continue to operate accurately and
reliably, whereas EMRs need frequent replacement, making
them very undesirable in harsh conditions.
SSRs Excel Over EMRs in Other Areas as Well
They are compatible with control systems, immune
to magnetic noise, and encapsulated to protect critical
components. Their solid-state design enables them to be
position insensitive and provides design engineers more
flexibility to mount SSRs anywhere within an application—
whether sideways or upside down.
Because they are solid-state without any moving
parts, SSRs can be safely used in industrial locations
where there is heavy vibration with no interference in
performance, whereas mechanical-based EMRs are very
sensitive to positioning, shock, and vibration, thereby
restricting design options.
With all the advantages SSRs provide, it is understandable
that they are more expensive than EMRs. Though significant,
this price point disparity becomes a non-issue when factored
in over the five million hours of life SSRs provide.