appliance safety - Appliance Design

APPLIANCE SAFETY
This is a right angle
user replaceable
GFCI. Source: Tower
Manufacturing
APPLIANCE SAFETY
Ways to avoid recalls,
fires, and electrocution
in white goods.
by paul piekarski
and vlad konopelko
Paul Piekarski is the director of engineering
and Vlad Konopelko is the director of product
management and business development at
Tower Manufacturing. For more information,
visit www.towermfg.com.
Tower Whitepaper.indd 30
I
oT, smart appliances, the latest energy-saving technologies and great
industrial design are all things appliance engineers like to think about every
day. For them, it is exciting and cool. It’s
more interesting to showcase and the value easier to explain to potential customers. However, there is another aspect of
appliances that is not so cool and sexy,
but is nevertheless just as important—if
not more so—to consider, engineer, and
talk about. I am talking about safety. The
risk of electrocution and fire are just two
amongst a plethora of safety concerns
every appliance engineer must consider
when designing a product. It is amazing
to see that there are so many different
products being recalled every year for reasons that could’ve been easily prevented
or quickly solved. So, why is it happening
when the costs are so high for both the
victim and manufacturers alike? Perhaps
it is because appliance technologies are
somewhat “boring” or commoditized, and
do not necessarily have any cutting edge
appeal. And so vendors might be losing
focus on what’s important in their desperation to make their products stand out
amongst a sea of mediocre, boring products. Or perhaps it just a matter of confusion. The few technologies that can help
protect customers are GFCI, ELCI, ALCI,
and LCDI. However for the majority of
engineers this is just an alphabet soup.
Although these technologies will not safeguard against every possible failure, they
have been proven to make appliances
much safer and predictable.
Leakage Current
Detection Devices
The first class of devices is leakage
current detection devices. The following
types of leakage current detection devices sense fault currents and trip to avoid
potentially hazardous safety conditions.
These include GFCI, ELCI, ALCI, IDCI,
and LCDI. Here is a brief overview of each
device type.
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APPLIANCE SAFETY
Here is an internal enclosure
mounted GFCI. Source: Tower
Manufacturing
GFCI:
ALCI:
Out of all of these
technologies the most
familiar one is a GFCI
or a ground fault circuit
interrupter. It is designed
to protect against shock
hazards and fires. GFCIs
come in different forms
and we see them all
around our everyday environments—kitchens, bathrooms and garages to name a
few. Although they come in different form factors, they all work the same
way. They measure the difference between
outgoing load current and incoming load
current and ensure there is no difference.
If there is a current difference of more
than 6 milliamps (mA), the GFCI unit
will disconnect power to the load. This
means that a GFCI will only allow 6mA
to flow through the wrong path—a failed
motor circuit that would create a fire, or
a wiring problem presenting a potentially lethal electrocution situation could be
mitigated if a GFCI is in use.
There are certain circumstances when a
GFCI might not prevent a shock, such as
when a person touches both electric wires
at the same time, offering a path from one
wire in through one hand, through the
body and out on the other hand to the
other electric wire. In this situation the
GFCI will not sense a current imbalance
and will not trip. This is a very important
point to consider when training personnel working on equipment with GFCIs. It
should also be noted that there are several
types of GFCIs with different attributes,
ALCI is an appliance leakage current interrupter. The main difference
between GFCI and ALCI is that GFCI
not only senses current imbalance, but
it also has an ability to identify improper
wiring. ALCI does not have that feature.
Having either an open neutral or a neutral-ground short will trip GFCI right
away, whereas ALCI will not detect these
hazards. ALCIs are used as components
on appliances, where these wiring conditions can be guaranteed. Not having circuitries dedicated to verifying the wiring
makes the ALCI unit smaller in size and
lower cost than a GFCI. Typical applications for ALCI are portable appliances
such as bathroom heaters, carpet cleaners
and hair dryers. ALCI devices are used to
protect customers from immersion electrocution. The ALCI will trip if the portable appliance is immersed in grounded
water (i.e., sink, tub, etc.).
Tower Whitepaper.indd 31
but we will be discussing it in future articles dedicated to GFCI protectors. GFCIs
also come in a variety of form factors that
have their own pros and cons that we will
also be discussing in future publications.
ELCI:
The second most common safety protection device is an ELCI or equipment
leakage circuit interrupter. ELCI works
similar to GFCI, but has a higher “trip”
level, and is designed to avoid electrical
fires; an ELCI offers no protection to
personal electrocution. Whereas GFCI
trips at up to 6 mA, ELCI trips between 6
mA and 30 mA. Anything above 6 mA is
considered by Underwriters Laboratories
(UL) to be too high for personal protection. An ELCI will sense electrical breakdown from increased leakage current
within an appliance’s wiring, and will
turn the power off to the appliance when
the ELCI trip level is reached. ELCIs provide a cost effective fire protection level
in environments with low probability for
contact by personnel.
IDCI:
IDCI is an immersion detection circuit interrupter. This type of device will
sense that an appliance is immersed in a
conductive liquid. It can work in either
grounded or ungrounded conductive liquids. IDCI will not sense a current imbalance. An IDCI, like an ALCI, would be
used as a component for an end product
appliance, such as a hair dryer.
LCDI:
LCDI or leakage current detection
interrupter is a very different technology compared to GFCI and ELCI. LCDI’s
use shielded power conductor to sense
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APPLIANCE SAFETY
A corded inline GFCI
with flying leads is shown
here. Source: Tower
Manufacturing
any breakage in the cord. If a
break is detected, the LCDI
trips, interrupting the flow
of electricity. This is a power cord technology that
ensures there is no personal electrocution or fire
due to power cord damage.
Certain products are prone
to power cord damage. These
products would greatly benefit
from LCDI. In some cases certain
products are required by UL to have
LCDI power cords such as portable ACs,
window ACs and PTACs. There are a variety of ways that power cords can be damaged. A common way damage happens to
power cords is from a house pet chewing
on the cord. Unfortunately once the LCDI
protection is engaged the cable cannot be
fixed and needs to be replaced. In some
cases these cords are not field replaceable
and as such the whole appliance needs to
be replaced. Although replacing the appliance or the cable might be undesirable it is
a much better option than having a fire or
a dead pet.
Arc Detection Devices
The second class of safety devices are
arc detection devices. The following
devices sense series and parallel arc currents to avoid fire ignition. The Arc detection devices include AFCI. Here is a brief
overview of AFCI devices.
AFCI:
Arc fault circuit interrupters, or AFCI.
Like GFCIs, these devices are available
in breaker panel, outlet and cord connected versions. AFCIs are now required
by the National Electric Code (NEC) in
Tower Whitepaper.indd 32
circuit breakers for new construction in
bedrooms and living areas. These devices
sense arcing above a 5 Amp level. If such
an arc is sensed, the power to the load
is interrupted. These devices are more
expensive than the leakage current devices due to the complexity level required
to accurately detect when arcing occurs.
AFCIs are an alternative to LDCIs for
window and portable air conditioners
and PTACS, but are seldom used due to
cost vs. an LCDI.
Heat
Detection Devices
The third class of appliance is the heat
detection devices. The following devices
sense overheating to avoid fire ignition.
The heat detection devices include HDCI.
Here is a brief overview of HDCI devices.
HDCI:
HDCI, or heat detecting circuit interrupter, is a new, up-and-coming technology that has been in the development
stage for quite a while. These devices
sense heat level within an appliance component to shut the
appliance down should a component or system failure occur and
lead to overheating. These devices also include LCDI cord protection functionality. The HDCI
technology is a direct response to
the compressor overheating issues
that have been known to happen in
products like dehumidifiers. There are
other possible ways to detect overheating
of the compressor, however HDCI does
it in a cost effective and easy to integrate
way that is not currently available on the
market.
So far we touched on three different
technologies and discussed seven different types of products that can help avoid
electrocution and fire. These technologies have been around for a while and
have been proven to be an effective way
to protect humans and assets. Although
they might not be required by UL in a lot
of circumstances we see companies who
want to promote safety in their appliances
voluntarily including these technologies
into their products even when it is not
required by code. There are few companies in the market that offer custom products that would fit your particular application and help you integrate that device
into your appliance. The incremental cost
of the components is negligible compared
to costs of litigation, bad publicity and
recalls. In addition a lot of engineers we
work with have identified as their desire
to ensure that customer’s safety is their
number one priority and knowing they
did everything they could to ensure safety
of the user is what makes them sleep well
at night. <
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