Can Surge Protective Devices (or the MOVs) work without shunting to ground?

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181204-1210 EST

Besoeker:

Not harsh. How do you communicate with someone if you don't know what their background is.

I can tell someone that e = N*dPhi/dt and if they never studied calculus, then they won't have the foggiest idea what I am talking about. So possibly I tell them that the induced voltage in the card reader is a function of how fast I move the card thru the read. Still it possibly means nothing to the typical person. I have seen typical customers move their card more slowly thru a reader when it does not respond, and in almost all cases this is the wrong thing to do. I have only seen one reader where they obviously had a low pass filter in the circuit and a fast swipe failed to work.

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Gar is right to ask for background. remember electricity is a matter of life and death.

While I was into electronics and electrical in college, my interest was really medical.. and halfway I couldn't transfer to medicine anymore so got stuck with it jus to graduate, and slept through the subjects. Hence I forgot many critical things.

Back to MOVs.

So MOV lifetime is the same when connected pure line to line, or line to ground (provided there was no common mode voltage Golddigger was mentioning)? Many people avoid line to line MOV (without ground in between), because they reasoned line to ground can have pathways to clear the surge current. 80% say this. Their reasoning was not because pure line to line can't clear common mode voltage but because line to ground has something to dump the current. So is it just a misconception just like Mike Holt emphasizing in his lectures that the electricity doesn't go or stay at ground but back to source? Please say yes or no so I can be sure. Without a definite answer, I'm not sure. Thanks.
 
tersh said:
Gar is right to ask for background. remember electricity is a matter of life and death.

While I was into electronics and electrical in college, my interest was really medical.. and halfway I couldn't transfer to medicine anymore so got stuck with it jus to graduate, and slept through the subjects. Hence I forgot many critical things.

Back to MOVs.

So MOV lifetime is the same when connected pure line to line, or line to ground (provided there was no common mode voltage Golddigger was mentioning)? Many people avoid line to line MOV (without ground in between), because they reasoned line to ground can have pathways to clear the surge current. 80% say this. Their reasoning was not because pure line to line can't clear common mode voltage but because line to ground has something to dump the current. So is it just a misconception just like Mike Holt emphasizing in his lectures that the electricity doesn't go or stay at ground but back to source? Please say yes or no so I can be sure. Without a definite answer, I'm not sure. Thanks.
Click to expand...
MOV lifetime is dependent on how much energy is passed through the MOV and how many joules it can take before destruction occurs. With grounded neutral systems where all ungrounded are equal voltage to neutral - an MOV connected to ground will have about half the voltage rating as one connected line to line. Some cases you have MOV's connected both line to line as well as line to ground and/or to neutral.
 
tersh said:
So Surge Protective Devices can be connected directly between line to line right? and if there are surges, it just heats up (and degrades a bit). But compared to having access to ground. How good can it still dissipate the energy by heating up (without any access to ground)?

What do you think?
Click to expand...

The SPD triggers on the voltage delta. It will do this whether a path to ground exists or not. However, if you cut all the grounds (as you stated), the potential of the entire system can be raised to a level that overcomes the system's dielectrics (air or whatever) resulting arcing/flashing across those dialectics (along with any fire or explosions so induced) to get to ground. Remember, there is always a potential that will eventually find a path to ground. In fact, that's the very essence of a lightning strike. A big potential violently finding a path to ground. Well, technically, a path to equalization...but for sake of discussion, we'll use the colloquial path to ground.

That's why we ground our systems. To AVOID (as best we can) situations where a potential is induced to the point things blow up or catch fire as the electrons find their way to ground through whatever path they can find. A grounded system...where we have a DESIGNED path to ground goes a long way toward avoiding mother nature finding its own (sometimes explosive) path to ground.

In short, if you don't give an overvoltage a path to ground, it will try to find one. And in so doing, might damage the equipment and/or cause a fire or an explosion. In the case of the SPD, it might clamp in a manner to protect the load from a voltage delta, but the SPD can't eliminate the overvoltage condition impressed on the system...only a path to ground (designed or brute forced by mother nature) can do that.
 
JPinVA said:
The SPD triggers on the voltage delta. It will do this whether a path to ground exists or not. However, if you cut all the grounds (as you stated), the potential of the entire system can be raised to a level that overcomes the system's dielectrics (air or whatever) resulting arcing/flashing across those dialectics (along with any fire or explosions so induced) to get to ground. Remember, there is always a potential that will eventually find a path to ground. In fact, that's the very essence of a lightning strike. A big potential violently finding a path to ground. Well, technically, a path to equalization...but for sake of discussion, we'll use the colloquial path to ground.

That's why we ground our systems. To AVOID (as best we can) situations where a potential is induced to the point things blow up or catch fire as the electrons find their way to ground through whatever path they can find. A grounded system...where we have a DESIGNED path to ground goes a long way toward avoiding mother nature finding its own (sometimes explosive) path to ground.

In short, if you don't give an overvoltage a path to ground, it will try to find one. And in so doing, might damage the equipment and/or cause a fire or an explosion. In the case of the SPD, it might clamp in a manner to protect the load from a voltage delta, but the SPD can't eliminate the overvoltage condition impressed on the system...only a path to ground (designed or brute forced by mother nature) can do that.
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Just “NO”.
 
GoldDigger said:
A surge suppressor can do just as good a job at suppressing line to line transients when connected directly from line to line as it can with two devices each connected from one line to ground.
What it cannot do is provide any protection against common mode voltage (an abnormal transient voltage which affects both lines equally with the same polarity.)

To restate that, if the fault or transient condition applied +1000VDC to L1 with respect to ground and -1000VDC to L2, then a suppressor from L1 to L2 will see and excess voltage of 2000VDC and will conduct.
But if it applies +1000VDC to L1 and also +1000VDC to L2 a suppressor from L1 to L2 will not see any abnormal voltage and will provide no protection. In both cases two suppressors from L1 and L2 to ground (not neutral!!) would provide protection.

Another aspect to consider is whether a common mode transient will in fact do any damage to a connected load. The answer to that depends entirely on the details of the load and its insulation. 3
Click to expand...

In SPD world. They used the term "Common-mode voltage" to refer to phase to ground surges, but Golddigger used it to refer to Phase to phase surge with same polarity. For those familiar with SPDs. What are the equivalent jardons? Let's use standard terms so it's not confusing.
Si1O39.jpg


Ok. For practical SPD use, what is the most common transients that you need to protect against? How about from other equipments (such as motors opening and closing, etc.). Do they affect line to line or line to ground mostly (Let's assume for sake of discussions that all equipments used are 240v AC. I'd like to know how best to protect those equipments that only use the black and red hot lines in US 120/240v split phase system (meaning those that don't use phase to neutral or 120v).
 
GoldDigger said:
A surge suppressor can do just as good a job at suppressing line to line transients when connected directly from line to line as it can with two devices each connected from one line to ground.
What it cannot do is provide any protection against common mode voltage (an abnormal transient voltage which affects both lines equally with the same polarity.)

To restate that, if the fault or transient condition applied +1000VDC to L1 with respect to ground and -1000VDC to L2, then a suppressor from L1 to L2 will see and excess voltage of 2000VDC and will conduct.
But if it applies +1000VDC to L1 and also +1000VDC to L2 a suppressor from L1 to L2 will not see any abnormal voltage and will provide no protection. In both cases two suppressors from L1 and L2 to ground (not neutral!!) would provide protection.
Click to expand...


I've been analyzing this single paragraph for hours and thinking of it from time to time. So an MOV can only conduct when there is a potential difference, right. This is why when both +1000VCD is applied to both L1 and L2, it won't conduct.. simply because there is no potential difference, right?

Second. What kind of fault or transient condition can apply +1000VCD to L1 with respect to ground and -1000VCD to L2 with respect to ground? Is this a very rare event. I'm trying to imagine the scenario it can happen. If you let a surge flows in the line to line (from motor starting).. it is still +1000VCD with respect to ground. Here can the MOV conduct? I've been reading this thread over and over again and I can't find specific answer to these questions. Thanks for any clarifications. If others would reply. Please address just these issues so it won't confuse me further (because there seems to be many misconception out there).

Another aspect to consider is whether a common mode transient will in fact do any damage to a connected load. The answer to that depends entirely on the details of the load and its insulation. 3
Click to expand...
 
tersh said:
I've been analyzing this single paragraph for hours and thinking of it from time to time. So an MOV can only conduct when there is a potential difference, right. This is why when both +1000VCD is applied to both L1 and L2, it won't conduct.. simply because there is no potential difference, right?

Second. What kind of fault or transient condition can apply +1000VCD to L1 with respect to ground and -1000VCD to L2 with respect to ground? Is this a very rare event. I'm trying to imagine the scenario it can happen. If you let a surge flows in the line to line (from motor starting).. it is still +1000VCD with respect to ground. Here can the MOV conduct? I've been reading this thread over and over again and I can't find specific answer to these questions. Thanks for any clarifications. If others would reply. Please address just these issues so it won't confuse me further (because there seems to be many misconception out there).
Click to expand...

Correct. An SPD is looking for a potential difference. Look at each SPD. One will be L1-N. One will be L2-N. One will be L1-L2. If L1 is +1000 and L2 is +1000, then the L1-N and L2-N will trigger, but the L1-L2 will not. If L1 is +1000 and L2 is -1000, then they all could trigger.
 
tersh said:
In SPD world. They used the term "Common-mode voltage" to refer to phase to ground surges, but Golddigger used it to refer to Phase to phase surge with same polarity. For those familiar with SPDs. What are the equivalent jardons? Let's use standard terms so it's not confusing.

Ok. For practical SPD use, what is the most common transients that you need to protect against? How about from other equipments (such as motors opening and closing, etc.). Do they affect line to line or line to ground mostly (Let's assume for sake of discussions that all equipments used are 240v AC. I'd like to know how best to protect those equipments that only use the black and red hot lines in US 120/240v split phase system (meaning those that don't use phase to neutral or 120v).
Click to expand...

1. I am using standard terminology and doing my best to avoid jargon. By definition a common mode transient affects both (or all) phase conductors equally. The transient (with unchanged polarity) is common to both phase lines. There is absolutely no difference between saying that there is a common mode transient of (for example) 1000V and saying that there is a 1000V transient from L1 to ground and from L2 to ground. Otherwise there would be a 1000V L1-L2 transient.

2. Depending on the nature of the cause of the transient it may be common mode or it may be differential (line to line.) Motors starting and stopping are not going to generate transients large enough to trigger SPDs! They may cause noise that an RF filter can reject, but not SPD level transients.

3. In a US 240/120 system the neutral is almost invariably grounded at the transformer secondary tap. That means that to best protect the load and wiring from transients you could just run SPDs from L1-N and from L2-N. But if there is no neutral present at the point you are installing the SPDs you are left with only the possibility of L1-L2, or you can do what is often done in built-in protection in equipment, L1-G and L2-G. This can cause other interesting problems, of course.
 
tersh said:
I've been analyzing this single paragraph for hours and thinking of it from time to time. So an MOV can only conduct when there is a potential difference, right. This is why when both +1000VCD is applied to both L1 and L2, it won't conduct.. simply because there is no potential difference, right?

Second. What kind of fault or transient condition can apply +1000VCD to L1 with respect to ground and -1000VCD to L2 with respect to ground? Is this a very rare event. I'm trying to imagine the scenario it can happen. If you let a surge flows in the line to line (from motor starting).. it is still +1000VCD with respect to ground. Here can the MOV conduct? I've been reading this thread over and over again and I can't find specific answer to these questions. Thanks for any clarifications. If others would reply. Please address just these issues so it won't confuse me further (because there seems to be many misconception out there).
Click to expand...

First: Right. It would not conduct, and so would not offer any protection against insulation breakdown to ground inside the equipment.

Second: This was just a made up example to put some numbers in to look at. In practice anything that is connected between L1 and L2 can generate a differential transient. Voltage produced by a nearby lighting strike is most likely to generate a common mode voltage, even if it just comes from offsetting the neutral point from ground. One thing that can generate opposite polarity transient voltages on L1 and L2 is anything that affects the primary of the service transformer. (Such as a higher voltage wire momentarily touching a wire at transformer primary voltage.)
 
GoldDigger said:
1. I am using standard terminology and doing my best to avoid jargon. By definition a common mode transient affects both (or all) phase conductors equally. The transient (with unchanged polarity) is common to both phase lines. There is absolutely no difference between saying that there is a common mode transient of (for example) 1000V and saying that there is a 1000V transient from L1 to ground and from L2 to ground. Otherwise there would be a 1000V L1-L2 transient.

2. Depending on the nature of the cause of the transient it may be common mode or it may be differential (line to line.) Motors starting and stopping are not going to generate transients large enough to trigger SPDs! They may cause noise that an RF filter can reject, but not SPD level transients.
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But SPDs are designed to handle internal surges. I read in NEMA that "
60-80% of surges are created within a facility" https://www.nemasurge.org/history/​

Internal Sources:
​
  • Switching of Electrical Loads
    ​
    ​
    The switching (on and off) and operation of certain electrical loads – whether due to intentional or unintentional operations – can be a source of surges in the electrical system. Switching surges are not always immediately recognized or disruptive as larger externally generated surges but they occur far more frequently. These switching surges can be disruptive and damaging to equipment over time. They occur as part of every day operations.Sources of switching and oscillatory surges include:
    • Contactor, relay and breaker operations
    • Switching of capacitor banks and loads (such as power factor correction)
    • Discharge of inductive devices (motors, transformers, etc.)
    • Starting and stopping of loads
    • Fault or arc initiation
    • Arcing (ground) faults
    • Fault clearing or interruption
    • Power system recovery (from outage)
    • Loose connections
  • Magnetic and Inductive coupling
    ​
    ​
    Whenever electric current flows, a magnetic field is created. If this magnetic field extends to a second wire, it will induce a voltage in that wire. This is the basic principle by which transformers work. A magnetic field in the primary induces a voltage in the secondary. In the case of adjacent or nearby building wiring, this voltage is undesirable and can be transient in nature.Examples of equipment that can cause inductive coupling include: Elevators, heating ventilation and air conditioning systems (HVAC with variable frequency drives), and fluorescent light ballasts, copy machines, and computers.


SPDs can handle these, no?

3. In a US 240/120 system the neutral is almost invariably grounded at the transformer secondary tap. That means that to best protect the load and wiring from transients you could just run SPDs from L1-N and from L2-N. But if there is no neutral present at the point you are installing the SPDs you are left with only the possibility of L1-L2, or you can do what is often done in built-in protection in equipment, L1-G and L2-G. This can cause other interesting problems, of course.
Click to expand...
 
Yes. But only if the transient voltages are enough higher than the nominal voltage that they can trigger the SPD. Various types of SPD will have different voltage threshold characteristics.
 
GoldDigger said:
Yes. But only if the transient voltages are enough higher than the nominal voltage that they can trigger the SPD. Various types of SPD will have different voltage threshold characteristics.
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My questions were not just theoretical, because I actually bought two 240v SPDs and installed these line to line for 240v equipments (without connecting it L1 to ground or L2 to ground.. Didn't use 150v MCOV... these are more effective isn't it?):

oWh4BU.jpg



G4sP6W.jpg


So for lightning strikes that can cause common mode voltages. These are useless. The EE who taught me about SPDs only mentioned that common mode voltages or line to ground are only to protect against surges reaching the metal enclosures. He never explained that they can hit the load. But then.. if there is no potential differences between them.. how could the common mode surge even affect the load??

Second. Based on the above specs. Were you referring to the MCOV of 320v or VPR of 1200v where only if they are above the nominal voltages that it can conduct? Is your nominal the MCOV or VPR? I'm very familiar what these two mean and the concept.. but just clarification which you meant by "nominal voltage".. the MCOV?
 
When I look at your picture, I see two 240V nominal (the normal operating line voltage of the circuit has to be well below the MCOV of the SPD so that the SPDs do not get destroyed by a continuous overvoltage caused by improper primary taps or other adverse conditions.

And these two (independent) SPDs are each connected from one of the L wires to GROUND. For that connection each SPD will normally be seeing only 120V applied, so they will not give nearly as much protection using 240V units.

I am having a real problem understanding how you can connect one end of an SPD to L1 and the other end to ground and still assert that it is wired only from L1 to L2.

Note that I did at one point make a distinction between an SPD connected L-N and one connected L-G. A pair of SPDs connected L-N will not do any better at clamping common mode transients than a single L-L connection.
 
GoldDigger said:
When I look at your picture, I see two 240V nominal (the normal operating line voltage of the circuit has to be well below the MCOV of the SPD so that the SPDs do not get destroyed by a continuous overvoltage caused by improper primary taps or other adverse conditions.

And these two (independent) SPDs are each connected from one of the L wires to GROUND. For that connection each SPD will normally be seeing only 120V applied, so they will not give nearly as much protection using 240V units.

I am having a real problem understanding how you can connect one end of an SPD to L1 and the other end to ground and still assert that it is wired only from L1 to L2.

Note that I did at one point make a distinction between an SPD connected L-N and one connected L-G. A pair of SPDs connected L-N will not do any better at clamping common mode transients than a single L-L connection.
Click to expand...

No. Each of the SPD is connected line to line (parallel to the load). I use 2 pcs so it's 2 line to line or 2 parallel line to line. The supplier initially installed them wrong.. by installing between line to ground. But he should use 150v MCOV instead of 320v MCOV. So instead I installed them parallel to the load. Since I have two pcs. then use the 2 pcs for line to line (not line to ground).
 
tersh said:
No. Each of the SPD is connected line to line (parallel to the load). I use 2 pcs so it's 2 line to line or 2 parallel line to line. The supplier initially installed them wrong.. by installing between line to ground. But he should use 150v MCOV instead of 320v MCOV. So instead I installed them parallel to the load. Since I have two pcs. then use the 2 pcs for line to line (not line to ground).
Click to expand...

Oh wait. It's wrong picture. It's the initial one showing connection of line to ground. I'll post the right picture showing line to line.. wait.
 
GoldDigger said:
When I look at your picture, I see two 240V nominal (the normal operating line voltage of the circuit has to be well below the MCOV of the SPD so that the SPDs do not get destroyed by a continuous overvoltage caused by improper primary taps or other adverse conditions.

And these two (independent) SPDs are each connected from one of the L wires to GROUND. For that connection each SPD will normally be seeing only 120V applied, so they will not give nearly as much protection using 240V units.

I am having a real problem understanding how you can connect one end of an SPD to L1 and the other end to ground and still assert that it is wired only from L1 to L2.

Note that I did at one point make a distinction between an SPD connected L-N and one connected L-G. A pair of SPDs connected L-N will not do any better at clamping common mode transients than a single L-L connection.
Click to expand...

Here's the right picture showing line to line connection:

IUcLMc.jpg


The earlier picture was showing line to ground connection near main panel (used as SPD type 2). But because the supplier sent me wrong 320v MCOV instead of 150m MCOV. I installed them instead line to line of 240v near equipment (became type 3). A few days after. I added another one line to line (no picture). The red conduit in loop with wire inside is to satisfy the 10 meters (30 feet) UL requirement. The above was connected near the load 10 meters away from main panel. It's just temporary connection anyway. I'll finalize connections after learning more. So I guess I need to get 150v MCOV instead (of 320v MCOV wrongly given to me) and install line to ground to take advantage of common mode voltage..

But then for common mode voltage.. how can it affect the load when there is no potential difference in the load at all?
 
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