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I got this photo only for reference, and have no idea about the circuit:enter image description here

but why in this surge protector too many MOVs are used, I mean normally the lowest impedance MOV would take the most surge current so what are the others used for? I know some of them are tied with Live and Neutral or Live and Ground or Ground and Neutral and so on...

But why using the others?

EDIT:

I had re uploaded a better photo to represent my question in a better manner this is an APC surge protector it can be shown here it has two MOVs at least in parallel

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    \$\begingroup\$ Your picture confuses the issue. MOVs in parallel should share the transient. MOVs from different points are to limit the voltage between those points - the transient might manifest itself in different ways. Lightning might be from L or N to earth. A switching transient might be L to N. \$\endgroup\$
    – Kartman
    Commented Jul 20 at 4:14
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    \$\begingroup\$ I don't think anything's in parallel. There's 8 tracks,8 MOVs, 8 pins on that connector. Each pin probably supplies a different circuit. Each circuit has individual protection. \$\endgroup\$
    – hobbs
    Commented Jul 20 at 4:29
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    \$\begingroup\$ MOVs have finite impedance - they are not off or on. Think of two springs in parallel - even if one is slightly longer, if the applied force is enough, the shorter spring will eventually share the load. Also, given enough energy, MOVs explode. They normally don’t fail short circuit - if anything, they tend to degrade with each transient. \$\endgroup\$
    – Kartman
    Commented Jul 20 at 4:34
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    \$\begingroup\$ Sure, MOVs don't have perfect current sharing, but paralleling similar MOVs (with the same brand and model) in practice is still okay, and it can somewhat increase their current rating to a certain extent, just not as high as their sums. Furthermore, each MOV is connected in series with a resistor, which acts as a ballast resistor thus forcing current sharing in case the MOVs are mismatched. Furthermore, the PCB you've showed is a multi-channel PCB, there's only one MOV at each channel, so they're not actually in parallel in your particular example... \$\endgroup\$
    – 比尔盖子
    Commented Jul 20 at 4:47
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    \$\begingroup\$ How do you know that it’s “too many” when you admit to not knowing what the circuit is for? \$\endgroup\$
    – Kuba hasn't forgotten Monica
    Commented Jul 20 at 4:47

1 Answer 1

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Typical application of MOV looks like this:

MOV circuit

(image credit and more about the topic here)

The image that you have shared seems like eight copies of this circuit, supposed to be wired with eight separate circuit loops for protection.

Once the MOV has reached end of life, it will short and the fuse will open to prevent a fire.

Your question is also about MOVs in parallel. Shown circuit doesn't seem like this case but one potential use of parallel MOV circuits could be redundancy. The circuit with least resistance is likely to trigger first, get damaged, lead to open fuse and end up as on open circuit. In such a case, parallel paths will continue to provide power to the load. In next surge event, the next least resistance circuit will trigger and so on. If the surge spike is powerful enough, there is a chance all MOVs will get damaged in one shot.

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  • \$\begingroup\$ So just to make sure I understood: now we say hypothetically, you mean every time will be a spark there one of the fuses will burn because the MOV got burned and went short circuit, and another spark comes another MOV burn and short circuit so the fuse would blow and so on, right? \$\endgroup\$
    – Hazardous Voltage
    Commented Jul 20 at 4:46
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    \$\begingroup\$ Yes, your train of thought is correct for parallel MOVs. That's how it will work. However, there are alternative outcomes as well. If the spark/surge energy is low, it might not be strong enough to damage the first MOV. So first MOV will continue to handle multiple spikes before it dies. Once it is dead, second MOV will take over. If multiple MOVs are close in resistance or surge is powerful enough, they might get triggered together. In such a case, more than one fuse can open in a single event. \$\endgroup\$
    – Whiskeyjack
    Commented Jul 20 at 4:52
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    \$\begingroup\$ I can also think of a case where multiple MOVs are cascaded together to handle a wide range of surges and reducing the let through voltage (the remaining voltage after MOV has done its job, that goes downstream). This is also a common practice when it comes to complete protection for a site. Typically, a larger MOV at the distribution panel, then a lower voltage rated one at sub distribution panel and then even a further lower voltage rated one near the appliance to be protected. It goes on :) \$\endgroup\$
    – Whiskeyjack
    Commented Jul 20 at 4:58
  • \$\begingroup\$ Thanks, you got a big question of my brain, you and the good comments guys<3 \$\endgroup\$
    – Hazardous Voltage
    Commented Jul 20 at 4:59

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