Surge Protectors
Daily HSE Note 17 January
2003: Surge Protectors
An employee arrived at the Greensport Yard in Houston this morning to find the
field office full of smoke. Investigation led him to a melted down surge
protector.
An office-by-office search
revealed another surge protector, of the same brand and model as above, that was
starting to melt down. IT WAS READY TO BLOW!
The manufacturer, Newpoint, was contacted to see if similar incidents have
occurred with this product. Newpoint stated that the surge protector had
absorbed all of the energy it was capable of absorbing and melted down as a
result. The surge protectors involved were not on a recall list.
IMPORTANT INFORMATION ABOUT SURGE PROTECTORS
Most modern businesses and
homes are supplied with 220-volt power systems. Heavy draw appliances such as
air conditioners, dryers, and electric stoves operate on 220-volts and are not
protected by surge protectors. Other appliances operate on 110-volts. These
include computers, microwaves, stereo equipment and TV sets. These items are
often used with surge protectors. The normal voltage flow will range from
110-117 volts. Surge Protectors are designed to trap the voltage that exceeds
those limits. Excessive voltage occurs due to power spikes. When these spikes
occur for a sufficient duration, this activates the trapping device, a Metal
Oxide Varistor MOV), located in the surge protector. The MOV is the heart of
surge
suppressors. The role of the MOV is to divert surge current. However, MOVs wear
out with use. As more surges are diverted, the MOVs life span shortens, and
failure becomes imminent. There is no forewarning or visual indications given -
just failure. And while failing, they can reach very high temperatures, and
actually start fires.
Most surge protectors will continue to function as a power strip, even though
the surge trap mechanism may have been destroyed by the power spike. This
presents two possible dangers: 1) If another power surge should occur, it can
damage the equipment or appliances that are plugged into this surge protector,
and 2) If sufficient voltage passes through the surge protector due to a second
power spike, a resistant short may have been formed, allowing heating to occur
and a fire to ignite.
When buying this equipment, look for a surge protector with an indicator light
that tells you if the protection components are functioning. All MOVs will burn
out after repeated power surges. Without an indicator light, you have no way of
knowing if your protector is still functioning properly. Unfortunately due to
manufacturing differences, the light may be "on" or "off"
during proper operation. It is important to review the operating instructions
provided with the surge protector.
Every year, thousands of fires result from surge protectors, power strips and
electrical cords. Listed below are some suggestions to help prevent a possible
fire from igniting.
*
USE ONLY SURGE PROTECTORS OR POWER STRIPS THAT HAVE AN INTERNAL CIRCUIT BREAKER.
These units will trip the breaker if the power strip is over loaded or shorted
to prevent overheating and fire.
* Any surge protector or power strip that
has frayed wires, or has a unit that is not working properly, replace them
immediately.
* Surge protectors, power strips, or
extension cords are not a substitute for permanent wiring.
* If at any time the surge protector or
power strip is hot to the touch remove and replace the unit. The electrical load
for this strip should be evaluated for overloading.
* Do not plug a surge protector or power
strip into an existing surge protector or power strip. This practice is called
"daisy chaining" or "piggy backing" and can lead to serious
problems.
* The Underwriters Laboratory (UL) label
must never be removed from the unit. On the underside of the casing, there
should be the manufacturer's name and the name of the testing lab where the unit
was tested.
* Do not locate a surge protector or power
strip in any area where the unit would be covered with carpet, furniture, or any
other item that will limit or prevent air circulation.
* Do not locate a surge protector in a moist
environment.
All surge protectors or power strips need to be UL approved. Be sure that the
product is listed as a TRANSIENT VOLTAGE SURGE SUPPRESSOR. This means that it
meets the criteria for UL 1449, UL's minimum performance standard for surge
suppressors. There are a lot of power strips listed by UL that have no surge
protection components at all. They are listed only for their performance as
extension cords. On a UL listed surge protectors, you will find a couple of
ratings. Look for:
* Clamping voltage. This tells you what
voltage will cause the MOVs to conduct electricity to the ground line. A lower
clamping voltage indicates better protection. There are three levels of
protection in the UL rating -- 330 V, 400 V and 500 V. Generally, a clamping
voltage more than 400V is too high.
* Energy absorption/dissipation. This
rating, given in joules, tells you how much energy the surge protector can
absorb before it fails. A higher number indicates greater protection. Look for a
protector that is at least rated at 200 to 400 joules. For better protection,
look for a rating of 600 joules or more.
* Response time. Surge protectors don't kick
in immediately; there is a very slight delay as they respond to the power surge.
A longer response time tells you that your computer (or other equipment) will be
exposed to the surge for a greater amount of time. Look for a surge protector
that responds in less than one nanosecond.
Visually inspect all surge protectors or power strips on a regular basis to
ensure that they are not damaged or showing signs of wear or damage. During the
visual inspection, ensure that the plug is fully engaged in their respective
outlets. The surge protector or power strips should always have either a
polarized plug with one of the blades being larger then the other one or a
three-prong grounded plug. Never use a three to two prong adapter to power the
unit. Surge protectors or power strips should have a cord of no more than 6 feet
in length. When the surge protector or plug strip is not in use, unplug the cord
from the power source.