How the right choice of
circuit breaker can open up
new opportunities for savings
witch-mode power supplies
(SMPS) have come a long
way in recent years, and for
many are now preferred
in industry to their linear
predecessors. Advantages include greater
efficiency, smaller size and lower heat
generation, making them ideal for use in
densely populated cabinets.
S
It’s important to choose a circuit breaker
that will work in tandem with the power
supply in order to extract the best
reliability and productivity performance
with minimal down-time. Specifying the
right circuit breaker and power supply
early on in the design process can greatly
reduce development costs later on.
Whilst a modern SMPS is far more efficient
than its linear counterparts, it is also far
more complex. Despite recent advances,
an SMPS supplying a 24 VDC system is not
considered to be properly protected when
employing thermomagnetic miniature
circuit breakers (MCBs) as their reaction
time can cause modern SMPSs to quickly
go into overload, causing other branches
and networks to experience a dip.
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PECM Issue 29
However this can be mitigated with the
use of an electronic circuit breaker (ECB),
which constantly monitors current and
reacts quickly to faults as a Z curve MCB
would, while still allowing high inrush
loads during start-up.
This allows companies to save money by
using a lower end power supply whilst
pairing it with an ECB for enhanced
overload protection. Modern ECBs are
also very thin, which saves cabinet space
and can allow a larger power supply to be
accommodated.
In an MCB circuit a low overcurrent
can result in a slow trip, which can be
exacerbated further by the use of long
wires which create increased resistance.
This can prevent the overload current
from ever being reached, delaying the trip
and preventing the circuit breaker from
performing its job. An ECB continuously
monitors the current, and switches off the
circuit quickly in the event of a fault, even
in low overcurrent conditions.
Some engineers may prefer to stick with
older MCBs, perhaps due to familiarity
or cost reasons, and there are solutions
available for these configurations too.
In such cases the reduced functionality
of an MCB compared to an ECB can be
offset up to a point by specifying a higher
end SMPS and built-in overload features
such as WAGO’s TopBoost function, which
provides sufficient power with a multiple
of the rated current for up to 50ms. The
added functionality of a newer SMPS
makes it more suitable with older MCBs,
which means that companies can save
time and money by only uprating the
devices that they need to for the required
level of protection.
For more information about WAGO’s
EPSITRON range of power supplies and
ECBs, contact Product Specialist Phil
Thompson at WAGO on 01788 568008.
WAGO Limited
Visit: http://global.wago.com/uk
Telephone: 01788 568008
Email: [email protected]