SPD & Open neutral

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220613-1411 EDT

What is a surge protector? It is most likely a non-linear resistance, and of some limited power handling capability. A physically larger device may tolerate higher power dissipation levels. Also larger device means a lower resistance device when its goes into a lower resistance mode.

The device has to have some rather high resistance below a certain threshold voltage. Above the threshold it needs to become a lower resistance. The threshold voltage needs to be selected some distance above the peak applied voltage from normal expected peak voltage. For a nominal 120 V supply you probably need to select a threshold about 135 V RMS or a peak of 200 V is usually selected. But clamping of voltage vs current is not very sharp.

Will this do much to limit peak voltage on a lost neutral? Maybe and maybe not.

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Most common surge devices would have a clamping voltage that is too high. Or are you asking if there is a particular make & model number with added protection?

What about a phase monitor like ones used for motors? Motors don't use the neutral, but it seems like phase monitors would still have to detect and trip on an unbalanced voltage.
 
According to the document from NIST at the link below:

".. because of the common misuse of the word “surge,” some expectations linger that an SPD might also protect equipment against temporary overvoltages (TOVs). The reality is that because of their intended deliberate response to any overvoltage, SPDs are perhaps more likely to be victims rather than protectors in a TOV scenario."

https://www.nist.gov/system/files/documents/pml/div684/TOVs_on_SPDs.pdf


There is this, but I have no idea if it works or is bogus:

http://www.tvsssurgesuppressor.com/openneutral.html
 
steve66 said:
Most common surge devices would have a clamping voltage that is too high. Or are you asking if there is a particular make & model number with added protection?

What about a phase monitor like ones used for motors? Motors don't use the neutral, but it seems like phase monitors would still have to detect and trip on an unbalanced voltage.
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Phase monitors don’t measure phase to ground, only phase to phase voltages, so they wouldn’t detect it because phase to phase loads are unaffected by the neutral. It’s the phase to neutral voltage that changes when the neutral goes open.
 
ptonsparky said:
My question is more directed to a particular make model.

I read about an RVr 'expert' saying a SPD would protect the RV from bad neutrals. 200 to 400 dollar Range. None I've ever installed would, and most would likely die. Wondered if missed something.
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Those are totally different, they have a relay that doesn’t close if the voltage isn’t within specs, so technically, it’s not the surge suppression part that protects from an open neutral.
 
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