Surge protector

This morning we had a power surge.  First one I ever experienced.  It knocked out the sub woofer components of my GoldenEar Triton one speakers. In my ignorance I had them plugged into the wall rather than a surge protector. Soooo it blew the amplifiers in the sub woofers. It’s going to be a costly proposition: $500 for the amplifiers plus God knows how much the dealer is going to charge for coming to my house. (He’s very reluctant to do it, wants me to lug the 80 lbs speakers to the store.   
Meanwhile, I’m having to listen to bass-less  speakers for the foreseeable future.
So, the moral of the story is plug everything into a surge protector.



Thermo-Fuse Varistor (TVZ)

Our Thermo-Fuse Varistor (TVZ) is a family of Transient Voltage Surge Suppression products. TVZ is a three-lead Thermally Protected Metal Oxide Varistor. One lead of the TVZ varistor is connected to a thermal fuse, it will automatically open-circuit when the varistor is under sustained abnormal over-voltage condition. The TVZ series is designed to meet the abnormal over-voltage requirements of UL 1449, Section 37.

Traditional Metal Oxide Varistor (MOV) withstands 150% of its rated voltage for a given duration.
But MOV may fail to a short-circuit condition or fail open when subjected to sustained steady-state over-voltage above its rated specifications.

Our TVZ has a thermal fuse incorporated with its MOV disk that responds to the MOV temperature and disconnects the MOV from power should the temperature exceed a certain level.

Our TVZ provides a real “Fail Safe” protection to sensitive downstream electric components.


UL1449 3rd Edition



As for this from a post of mine above on 05-13-2024 at 10:55am

jea48 Said:

For those with Sub panels for the audio equipment where the branch circuit wiring is less than 30ft from the wall outlet to the sub panel.

Type 3 - Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of conductors provided with or used to attach SPDs.

At the very least a good quality type 2 SPD should be installed, connected, to the sub panel.

Sounds like a cord and plug Type 3 SPD will do little, if anything, for protecting audio equipment from a high voltage transient event if the branch circuit wiring is less than 30ft long.


Type 3 - Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical SERVICE PANEL to the point of utilization,


"electrical service panel". UL1449 (3rd Edition) Type 3 SPD says nothing about a sub panel. Because it says nothing about a sub panel then the minimum 10meters, 30ft branch circuit conductor length does not apply. Sounds nuts to me but that’s the way I understand it.

In my search I looked in the 2020 NEC for anything that would shed some light on the subject. Why was a sub panel not in the language of the UL1449 rule for a Type 3 SPD?

I am pretty sure the reason for the minimum 30ft length of the branch circuit wiring has to do with the impedance/resistance of the conductor. ( It works as current limiter.)


Fault current:

2020 NEC 110.9 Interrupting Rating.

Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that must be interrupted.
110.10 Circuit Impedance, Short-Circuit Current Ratings, And Other Characteristics.
The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118. Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.
Impedance. The impedance of the minimum length of 30ft for a branch circuit wiring works as a current limiter? So a longer branch circuit wiring, just a guess, would be better. More impedance...
Just a guess ANSI / IEEE / UL used the impedance of #14AWG or #12AWG in their calculation. Wonder what happens when the branch circuit conductors are #10AWG. ??? Nothing, no difference???
Still doesn’t answer the question about a sub panel.


2020 NEC 230.67 Surge Protection. ( N = New for the 2020 Code edition.)

N 230.67 Surge Protection.

N (A) Surge-Protective Device. All services supplying dwelling units shall be provided with a surge-protective device (SPD).

N (B) Location. The SPD shall be an integral part of the service equipment or shall be located immediately adjacent thereto.

Exception: The SPD shall not be required to be located in the service equipment as required in (B) if located at each next level distribution equipment downstream toward the load.

N (C) Type. The SPD shall be a Type 1 or Type 2 SPD.


The Exception tells us it doesn’t have to be installed at the service equipment if it is installed at the sub panel(s).

Nothing here as for the UL1449 3rd Edition Type 3 SPD minimum 30ft branch circuit length for the conductors. You are required to have a type 1 or type 2 at the main electrical service equipment/panel or down stream sub panel(s).


Impedance. A Type 3 SPD is not capable of absorbing, clamping, or diverting to ground a large surge of energy as the bigger Type 1 or Type 2 SPD. Thus the above 30ft minimum length rule when the branch circuit is feed from the main electrical service panel. The further away from the main service electrical panel the Type 3 SPD is the higher the impedance of the conductors the Type 3 SPD will be plugged into.

Even the feeder that feeds a sub panel will add impedance. Maybe that’s why a sub panel is not mentioned in the UL1449 3rd Edition for a Type 3 SPD. ANSI / IEEE / UL took into account the total length of the sub panel feeder plus the branch circuit wiring. Don’t know...

One thing for sure, at least the way I see it, If the sub panel is within a few feet of the main service equipment panel I would treat the sub panel as a main electrical service panel. YMMV.


@jea48  , sorry if it seems as if I am beating this circuit breaker thing to death, but am I correct in assuming that the type of surge that the OP of this thread probably experienced would NOT have been one that would have jumped across a tripped breaker?  (As it stands, I unplugged my system after I finished up with it this evening.)

@immatthewj You are correct. and most surges capable of damaging electronics are invisible.

For some reason some people equate a power surge only with visible near by lightning strikes which cause visible arcing and sparks inside the home. The theory goes, well, if that’s what will damage my gear then there’s nothing I can do.

I wrote more about this here: