August 1955 Popular Electronics
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The Underwriter's Laboratory (UL) is an entity that seems to
have been around forever. A lot of people - maybe most people
- assume that it is a government entity. In fact, it is a non-profit
organization sponsored by the National Board of Fire Underwriters.
Its roots are traceable back to the Chicago World's Fair in
1893. Concern over the potential fire hazard of Edison's light
bulbs was the impetus for the effort. Another aspect of the
UL that a lot of people don't know is that the UL label of approval
is no guarantee that the device works properly, only that is
passes standards of safety as it relates to fire hazards. This
article in the August 1955 edition of Popular Electronics gives
a brief history.
Behind the U.L. Label
By E. D. MORGAN
Equipment is tested, dropped, pounded, and
before it is rated as safe and tagged
with the Underwriters'
A familiar sight on much electrical and electronic equipment
used today is an Underwriters' Laboratories label. Exactly what
is implied by the use of this label, however, is often misunderstood.
Underwriters' Laboratories, Inc. is a non-profit organization
sponsored by the National Board of Fire Underwriters. Its function
is to test and inspect materials and equipment to prevent loss
of life and property from fire, crime and casualty hazards.
To do this adequately, it subjects devices to grueling tests.
Only the hardiest designs survive and earn the right to the
coveted label of acceptance.
Television sets are subjected to a thorough
going-over by Underwriters' Laboratories. Inc. engineers. Special
attention is paid to shock hazards and to overheating problems.
Cabinets are pounded and safety glass hit with steel balls in
An enclosed heavy-duty switch is tested in
one of U.L.'s many laboratories. Equipment such as this is operated
repeatedly under excessive loads before it is approved and given
the U.L. label. It is important to point out that U. L. approval
does not guarantee quality of performance. The testing is concerned
primarily with the safety aspects of equipment. Thus, the label
on an approved radio receiver, for instance, does not imply
that it will perform better than one not so approved. It does
mean, though, that the chance of setting a house on fire is
negligible if the approved model is used.
No conceivable method of testing is overlooked. Much of the
test equipment is of U. L.'s own design and they dream up diabolical
plans to subject samples to the meanest treatment possible.
They try to anticipate all of the mistakes that could be made
by a consumer. Appliances are left on for weeks and electric
heater cords are twisted and untwisted thousands of times.
Automatic flatiron is dropped four times
during continuous operation test of 500 hours. Temperatures
of various parts as well as operation of the thermostat are
Television cabinets get a thorough pounding before they receive
U. L. approval. A large picture tube can be a deadly weapon
when broken, as it hurls tiny fragments of glass in all directions.
To insure against injury, the safety screen on the front must
be capable of withstanding such shattering. A pound-and-aquarter
steel ball is hurled at the set to determine its fitness for
These are only a few of the authorized labels
used by U.L. to designate approved equipment. An item bearing
such a label has met specifications and passed severe tests.
Electronic equipment is often used by U.L. technicians. Here,
the split-second operation of a burglary detection system is
photographed. Accuracy is assured by using a cathode-ray oscilloscope,
a beatfrequency generator, and various meters.
To determine whether a safe is fireproof and burglar-proof,
U. L. employs its own staff of "arsonists" and "safecrackers."
These men are masters at their trades and tackle a new item
with drills, sledges, torches, and explosives. Just to make
sure, the safes are dropped onto concrete from a second-story
level, then placed in a 2000° F furnace for an hour or so. If
the internal temperature goes high enough to turn valuable papers
brown, what is left of the safe is returned to the maker with
Fire doors are tested in large gas furnaces where flames
lick at them until they are red-hot. Then a fire hose is intermittently
played on the other side of the door. Acceptable fire barriers
must pass the fire endurance as well as the hose stream tests.
U. L.'s Growth
The organization had its unique
start when bulbs were installed at the first Chicago World's
Fair in 1893. These became the Fair's chief attraction - as
well as its greatest hazard. Fires, started by the not-yet-perfected
lamps and wiring, were commonplace. This led a group of New
England insurance interests to authorize William H. Merrill,
a young engineer, to investigate the situation. He responded
to each fire alarm at the fairgrounds. If the cause were electrical,
he would try to locate the defective device and determine why
Because of Merrill's insistence on thorough
testing before the lamps were installed, and correcting their
faults before offering them to the public, Underwriters' Laboratories,
Inc. was born the following year. Merrill was its first president.
Since then, U. L. has mushroomed. Over 375,000 products
have been found acceptable under its rigorous standards. Testing
laboratories are located in Chicago, New York and San Francisco,
with representatives in nearly 200 cities insuring that the
standards are upheld at the factories. The work is financed
solely by charges made to manufacturers for the inspection of
Annual lists are published giving the
manufacturers' names and their approved products. Four main
lists are prepared which cover: electrical equipment; fire protection
equipment; gas, oil and miscellaneous appliances; and accident
hazard, automotive equipment and burglary protection.
Good will and impeccable honesty is the main stock-in-trade
of this organization. U. L. never solicits business, but industry
has learned that it is well worth the effort to make sure its
products deserve the U. L. label.
Posted August 26, 2011