NXT POWER 022-00104 Rev 6-Outlet Surge Protector Instructions
- June 13, 2024
- NXT POWER
Table of Contents
MOVs ARE SACRIFICIAL POWER PROTECTORS
022-00104 Rev 6-Outlet Surge Protector
A commonly used component is a surge protector (Surge Strip) is the MOV (Metal
Oxide Varistor).
MOV is also known as a “self-sacrificing” component, it will divert energy and
weaken over time, rather than letting voltage surges harm your devices. A
metal oxide varistor is a voltage dependent variable resistor. During normal
voltages the resistance is high but when voltage increases the resistance
lowers and excess voltage is diverted to ground. Below is a chart of voltage
vs current in the high and low resistance region. As noted in the chart below
the varistor will allow some of the surge through the protection device until
it reaches the shunt voltage (Varistor Voltage). When the clamping voltage is
reached the MOV has become a switch diverting the surge.
The concern is that 100’s of volts is allowed to pass through the MOV before
the varistor starts to divert the surge at. This typically happens above 300
Volts. This is called the ‘let though voltage’. This is the critical
specification for any power protection device for it details the true amount
of surge that load being protected receive.A MOV is made
up of zinc oxide or similar compound. When the voltage surges to a certain
point the zinc oxide particles begin conducting current internal to the MOV
essentially diverting the energy of the surge.
The main issue with MOVs is that there is a limit to the amount of energy they
can divert. The power diverting rating of an MOV is listed in joules. They
become ineffective and unable to provide any protection when the energy
diverter is greater than the MOV’s joule rating. Because the MOV is placed in
parallel to the load it is not readily apparent to the user that the MOV has
failed, and the electronic load is no longer protected. Sometimes circuitry is
added to notify the user that the MOV is no longer effective or damaged.
Another issue is the potential for catastrophic failure of the surge
protection device from the MOV diverting a very large surge of energy.
Designers will add fuses to protect the MOV and add MOVs in parallel to
distribute the surge to increase its joule rating. This is ok in theory but
not in practice. Not all MOVs are made the same so inevitably one MOV will
“turn on” before the other and a cascade failure of the MOVs will occur
causing a catastrophic failure of the surge protection device.
Surge protection devices that incorporate MOVs state the let through voltage
of the device on the unit.
They will also document joule rating of the unit. (One Joule is equal to 1
watt for 1 second) This is the amount of energy that the MOV will absorb
before it fails. Manufacturers of such equipment will recommend a rating of
1000 joules for small electronics up to 2000 joules for home theater
components, gaming consoles or computers that store data. Having 2000 joules
of protection may sound good but manufacturers will inflate such numbers by
providing the cumulative number of joules from all the MOVs in the surge
suppression device. As stated earlier no 2 MOVs are made the same so not all
MOVs will “turn on” at the same time. Inevitably one MOV will “turn on” first
and cause a cascade failure of the surge protection device provided the surge
energy and voltage is high enough.
The key in this discussion is that the joule rating itself for surge
suppression devices is not even recognized by surge suppression standards!
Surge suppression standards specify ‘let through voltage’.
UL 1449 is the primary spec for UPSs, and it calls for a let through of 330V.
IEEE 62.41 denotes surge protective categories and ratings for electrical
circuits. It specifies a let through 10 volts of AC surge (normal mode noise)
and ½ volt of ground noise (common mode noise) for a 6000V 100Khz ring wave.
So, rating in power protection in joules is not part of the standards for
power protection.
The goal is to provide power condition that is non-sacrificial protection and
can conform to the highest protection standards which is IEEE 62.41. The best
technology to meet this requirement is an isolation transformer-based
solution. A low impedance transformer matched with a low impendence bandpass
filter can surges, noise and strikes that cause so many problems with
electronic systems. The band pass filter filters any disturbances above 60Hz
to keep AC noise (Normal Mode) below 10 volts. In addition, neutral and ground
are bonded at the transformer so ground noise (Common Mode) is reduced to
under ½ volt.
The components are non-sacrificial so these devices will last for many years!
In conclusion, there is a power protection solution that can provide the clean
consistent power that your sensitive electronics demand and will work
flawlessly for many years.
‘NXT Power is a team of unparalleled experts dedicated to providing premium
power quality solutions for manufacturers of critical electronic equipment.
Our products help our customers receive cleaner, more reliable power; avoid
destruction, degradation, and disruption; and achieve long-term cost savings
through reduced service calls and costly downtime.
Visit www.nxtpower.com for more
information.
022-00104 Rev B (06/22)
References
- Next-Generation Power Conditioners & UPS Systems | NXT Power
- Next-Generation Power Conditioners & UPS Systems | NXT Power
Read User Manual Online (PDF format)
Read User Manual Online (PDF format) >>