Discrepancy on electrical theory between credible sources. Especially surge arrestors

[Jpflex]

In Mike Holts video regarding theory and operation of surge arrestors, it is stated by Mr. Holt that surge arrestors protect load devices downstream by clamping or limiting voltage potential level.

He states, these surge protectors contain a semiconductor in parallel path to the circuit being protected under cases of excessive voltage or lighting induction (mutual or direct contact). When exposed to high levels of voltage (300 volts or more?), the semiconductor in the surge protector connected in parallel to the circuit changes from an insulator to conductor and allows this excessive voltage to take this path and return on return path, neutral load leg.

Apparently, this causes such a high current that voltage is lowered or limited or “clamped” shunted on the circuit to loads to protect them.



However, in another credible source on electrical theory in the form of a text book (siting of source available upon request), it is stated that rules of parallel circuits follow that VOLTAGE IS CONSTANT, while amperes very per leg in parallel.

This I have also tested back in my old days as an ASE L1 Advanced level automotive electrician with a 94 Ford F-150 4.9L motor having 3 fuel injectors wired in parallel. When one injector went bad, the voltage remained constant BUT it’s individual AMPERE draw varied from the rest of the injectors.


Therefore, the old saying was that current travels ate the point of least resistance, but modern saying is that current takes ALL PATHS. Additionally, if we are following the rules of parallel circuits, how then can voltage be shunted or reduced to protect loads downstream from surge protectors since voltage remains constant in parallel circuits? Thanks

 

[ron]

The magical component is called a metal oxide varistor (MOV). Google it associated with the word "surge protection device" and you will have hours of reading from actual technical resources.

 

[retirede]

The textbook is using the theory of a pure parallel circuit. In reality, every circuit has series elements.
In the surge suppression scenario, the impedance of the suppressor path decreases as the voltage surges ( research MOVs as Ron suggested), resulting in a spike in current through its path. The source of the surge has some finite level of impedance (this is not considered in the textbook example), so the voltage across the suppressor and connected load is limited by the amount of the IZ drop across this source impedance.

I’ve over-simplified some aspects of this, but hopefully it helps!

 

[GoldDigger]

Equipment connected to our electrical system is designed to withstand nominal line voltages (peak as well as RMS) with a safety factor of 50% or more depending on the equipment. With the possible exception of resistance heating, their most likely sources of damage from surges or transients will be the permanent breakdown of something that should be an insulator or change in resistance of a normally current carrying element.
The damage will be done because the applied voltage is too high, not because more current than usual is available from the source.

The current divider effect described in the text book would not offer any protection from damage when the applied voltage is allowed to rise!

 

[jaggedben]

In Mike Holts video regarding theory and operation of surge arrestors, it is stated by Mr. Holt that surge arrestors protect load devices downstream by clamping or limiting voltage potential level.

He states, these surge protectors contain a semiconductor in parallel path to the circuit being protected under cases of excessive voltage or lighting induction (mutual or direct contact). When exposed to high levels of voltage (300 volts or more?), the semiconductor in the surge protector connected in parallel to the circuit changes from an insulator to conductor and allows this excessive voltage to take this path and return on return path, neutral load leg.

Apparently, this causes such a high current that voltage is lowered or limited or “clamped” shunted on the circuit to loads to protect them.



However, in another credible source on electrical theory in the form of a text book (siting of source available upon request), it is stated that rules of parallel circuits follow that VOLTAGE IS CONSTANT, while amperes very per leg in parallel.

This I have also tested back in my old days as an ASE L1 Advanced level automotive electrician with a 94 Ford F-150 4.9L motor having 3 fuel injectors wired in parallel. When one injector went bad, the voltage remained constant BUT it’s individual AMPERE draw varied from the rest of the injectors.


Therefore, the old saying was that current travels ate the point of least resistance, but modern saying is that current takes ALL PATHS. Additionally, if we are following the rules of parallel circuits, how then can voltage be shunted or reduced to protect loads downstream from surge protectors since voltage remains constant in parallel circuits? Thanks

I think you need to understand the difference between an ideal voltage source and voltage sources in the real world. The Wikipedia page on this is decent enough for starters. (Also check out current source, to understand that not all sources behave like voltage sources.)
Also study voltage drop, which is consistently a consideration in the theory of all electrical circuits.

In your case of the fuel injectors, having 2 instead of 3 did not noticeably affect the ability of the source to maintain the voltage. But it probably did make a difference, just too tiny for you to measure. And if you were to put 100 or 1000 fuel injectors on the same source, at some point you would see the voltage drop, and at some point the injectors simply wouldn't work anymore.

The idea behind the surge protector is when a high voltage spike occurs it momentarily puts such a high loads on the source that it keeps the voltage down to a level where it is less damaging to the other loads.

 

[Jpflex]

The textbook is using the theory of a pure parallel circuit. In reality, every circuit has series elements.
In the surge suppression scenario, the impedance of the suppressor path decreases as the voltage surges ( research MOVs as Ron suggested), resulting in a spike in current through its path. The source of the surge has some finite level of impedance (this is not considered in the textbook example), so the voltage across the suppressor and connected load is limited by the amount of the IZ drop across this source impedance.

I’ve over-simplified some aspects of this, but hopefully it helps!

If the surge protector is connected in parallel and this is merely a series circuit by itself connected in parallel With the entire downstream circuit then when the semiconductor conducts shouldn’t all voltage be dropped after the last load in this one circuit (surge protector leg) but also see the 300 volts or more on parallel lines downstream and parallel to this portion of circuit containing surge protector?

 

[Jpflex]

The textbook is using the theory of a pure parallel circuit. In reality, every circuit has series elements.
In the surge suppression scenario, the impedance of the suppressor path decreases as the voltage surges ( research MOVs as Ron suggested), resulting in a spike in current through its path. The source of the surge has some finite level of impedance (this is not considered in the textbook example), so the voltage across the suppressor and connected load is limited by the amount of the IZ drop across this source impedance.

I’ve over-simplified some aspects of this, but hopefully it helps!

Yes I see some of what you are saying. Batteries as a source have some internal resistance or impedance even if you directly short B+ and - post directly so current E/R would be limited to the minuscule internal resistance within the battery.

When you say the source (lightning) has some level of INFINITE? resistance don’t you mean definite Resistance while semiconductor is conducting? infinite resistance sounds like an open circuit or open circuit voltage path and current would not travel unless it arcs the gap (semiconductor not in conductive state)

Assume semiconductor changes states would you either have all resistance drop after semiconductor impedance as I was taught all voltage is consumed after the last load in a circuit or would voltage of near same potential be applied to both line and return load leg thus lowering the voltage potential between line and load return legs and therefore lowering entire circuit voltage? Thanks

 

[retirede]

If the surge protector is connected in parallel and this is merely a series circuit by itself connected in parallel With the entire downstream circuit then when the semiconductor conducts shouldn’t all voltage be dropped after the last load in this one circuit (surge protector leg) but also see the 300 volts or more on parallel lines downstream and parallel to this portion of circuit containing surge protector?

No. Voltage drop occurs where ever current flows through resistance (impedance). The source of the surge has significant impedance.

 

[Jpflex]

I think you need to understand the difference between an ideal voltage source and voltage sources in the real world. The Wikipedia page on this is decent enough for starters. (Also check out current source, to understand that not all sources behave like voltage sources.)
Also study voltage drop, which is consistently a consideration in the theory of all electrical circuits.

In your case of the fuel injectors, having 2 instead of 3 did not noticeably affect the ability of the source to maintain the voltage. But it probably did make a difference, just too tiny for you to measure. And if you were to put 100 or 1000 fuel injectors on the same source, at some point you would see the voltage drop, and at some point the injectors simply wouldn't work anymore.

The idea behind the surge protector is when a high voltage spike occurs it momentarily puts such a high loads on the source that it keeps the voltage down to a level where it is less damaging to the other loads.

You do obtain voltage spikes when injectors circuit opens however I do not know how this could put a high load on source to keep voltage down to other loads unless the voltage were in opposite direction to source as in series additive? Voltages equal but in opposite polarity do not add to increase but oppose each other?

 

[Jpflex]

No. Voltage drop occurs where ever current flows through resistance (impedance). The source of the surge has significant impedance.

Yes in this case lightning has its own internal impedance. So assume semiconductor has little impedance while conducting then the Source such as voltage of lighting drops More within itself and remaining minuscule drop between conductor lengths and semiconductor? So is this how entire circuit line sees less voltage?

 

[don_resqcapt19]

In Mike Holts video regarding theory and operation of surge arrestors, it is stated by Mr. Holt that surge arrestors protect load devices downstream by clamping or limiting voltage potential level.

He states, these surge protectors contain a semiconductor in parallel path to the circuit being protected under cases of excessive voltage or lighting induction (mutual or direct contact). When exposed to high levels of voltage (300 volts or more?), the semiconductor in the surge protector connected in parallel to the circuit changes from an insulator to conductor and allows this excessive voltage to take this path and return on return path, neutral load leg.

Apparently, this causes such a high current that voltage is lowered or limited or “clamped” shunted on the circuit to loads to protect them.



However, in another credible source on electrical theory in the form of a text book (siting of source available upon request), it is stated that rules of parallel circuits follow that VOLTAGE IS CONSTANT, while amperes very per leg in parallel.

This I have also tested back in my old days as an ASE L1 Advanced level automotive electrician with a 94 Ford F-150 4.9L motor having 3 fuel injectors wired in parallel. When one injector went bad, the voltage remained constant BUT it’s individual AMPERE draw varied from the rest of the injectors.


Therefore, the old saying was that current travels ate the point of least resistance, but modern saying is that current takes ALL PATHS. Additionally, if we are following the rules of parallel circuits, how then can voltage be shunted or reduced to protect loads downstream from surge protectors since voltage remains constant in parallel circuits? Thanks

Another way of saying this is that the SPD is connected in parallel with the loads being protected....that is the loads and the SPD are both connected line to line, or line to neutral.

 

[retirede]

Yes in this case lightning has its own internal impedance. So assume semiconductor has little impedance while conducting then the Source such as voltage of lighting drops More within itself and remaining minuscule drop between conductor lengths and semiconductor? So is this how entire circuit line sees less voltage?

In the case of Lightning, a direct strike to the system renders surge suppressors useless. They become victims just like the loads. A nearby strike can induce voltage transients inductively. The imperfect inductive coupling has (may have) a high enough source impedance that the current drawn by the suppressor limits the voltage rise at the protected load.

 

[__dan]

Yes, if the connection is made on a large bus, the bus itself does not drop Voltage. Voltage is the same at every point on the bus. And at the connection point itself, each leg sees the same Voltage always.

The type of surge for the MOV is fast transient Voltage. That would come from nearby lightning strikes, strike to ground induces Voltage in the line, and power switching events. Very fast lower total energy induced noise, not something that will persist much more than 1/4 cycle.

Over the threshold Voltage, the MOV conducts, shorted to neutral or EGC (probably Y connected for 3 phase). Anything more than a low energy fast transient Voltage and the MOV's are sacrificial elements and can fail catastrophically. Big ones should be in a separate can (imo). They're probably mated with sacrificial fuses for the ones that mount in panels and control cabinets. Then you see them with 'failed' indicator lights (blown fuse indicator).

The IR drop over the line between the source and the MOV changes a lot with the MOV shunting current to ground. The original circuit could be high impedance front, transistor rectifiers are exposed to the hazard. The MOV adds a low impedance load above the threshold value and the IR drop over the source line is where the excess Voltage transient is taken up. They're made for fast transient noise with the MOV conducting during that time.

 

[ggunn]

The Delta Labs "lightning arrestors" are just a couple of hemispherical contacts in a container of sand.

 

[synchro]

The Delta Labs "lightning arrestors" are just a couple of hemispherical contacts in a container of sand.

And the sand acts to quench the arc after the surge so that it does not become sustained. Similar to what's done in some fuses.

 

[petersonra]

There isn't much that can protect you from a direct strike other than a highly engineered lightning protection system that nobody can afford.

You can do things that will protect you to some extent from momentary voltage excursions coming into your house by installing surge protection devices. My personal opinion is that the idea of layering them is probably not something that works all that well in reality. I think your best bang for the buck is something close to the device that needs protection.

If you want to do it as cheap as possible and as simple as possible, putting one at the service point, and maybe every panel is about as simple as you're going to get and probably as cheap. But I'm not completely convinced that this really gives you as much protection as some people think.

These kinds of momentary voltage surges are difficult to model under the best of circumstances and all but impossible in a typical real-world example. So, you do what you can and hope for the best.

 

[rambojoe]

You can always set up a rig of meters and just test that dang thing....

 

[Sea Nile]

Usually text books have a disclaimer that says something like "because the resistance of the conductors are so low, we are not factoring it in in the calculations"
So voltage is essentially constant in a series circuit, but in reality copper is not a perfect conductor.

But disregarding the resistance of copper, voltage is constant in a series circuit at any specific point in time. Much the same way that the speed the wheels of a motorcycle are always spinning at the same speed to each other even if the motorcycle is traveling at variable speeds.

 

[rambojoe]

Much the same way that the speed the wheels of a motorcycle are always spinning at the same speed to each other even if the motorcycle is traveling at variable speeds.

Well that aint true...once again, variables, disclaimers and paradoxes...
Saying always will always get you some trouble...
This is something ive tested. Alot.

 

[winnie]

The point here is important and generalizable

Whenever someone tells you 'In theory TTTT', the little voice in your head should hear 'In theory _approximately_ TTTT'.

The few times that something is _exact_ are because they are taken as definitions, and everything else is approximate around them.

For example the speed of light is exactly 299,792,458 metres per second, by definition, not just in theory. But this means that we only approximately know the length of the meter.

Jon