Confused by graphic

mbrooke

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Alright- forgive me but I'm genuinely curious. Why is 1000 volt being measured at the service but 330 volts at the load? Wouldn't it also be 330 volts at the service once the MOV starts conducting? And why is it being shunted to the neutral bus when its coming from the primary and the load is L-L connected?


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infinity

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I'm guessing that the 1000 volts is the surge volts (the spike in the black line) and the 330 volts is what the device is letting through. The blue wording stated that it "shunts most of the voltage to the neutral bus" which is why it's depicted a let through of 330 volts.
 

mbrooke

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At the high frequencies usually associated with transient voltages (surges), the wiring between the POCO secondary and the load side of the main panel is high enough to drop the applied voltage as a result of operation of the downstream SPDs.

I had not though of that! Thank you :)
 

mbrooke

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I'm guessing that the 1000 volts is the surge volts (the spike in the black line) and the 330 volts is what the device is letting through. The blue wording stated that it "shunts most of the voltage to the neutral bus" which is why it's depicted a let through of 330 volts.

But why would it shunt to the neutral when the spike would be 180* out of phase with the other hot?
 

infinity

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But why would it shunt to the neutral when the spike would be 180* out of phase with the other hot?
I have no idea, I was just commenting on what I believe Mike was trying to convey with the graphic, he's showing that some but not all of the transient voltage is being limited.
 

mbrooke

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I have no idea, I was just commenting on what I believe Mike was trying to convey with the graphic, he's showing that some but not all of the transient voltage is being limited.
I agree, but in this case I can't see the neutral being involved but I am just assuming that on my part.
 

PaulMmn

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The Zero Surge web site says about their series-mode surge protectors "The current is then slowly released to the neutral wire (5), avoiding any ground wire contamination. "
 

mbrooke

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Are you saying surge protectors don't involve the neutral?

My understanding is that they are semi conductors and kick in when voltage gets high enough.
They do involve the noodle. Although this graphic leaves that out.

But I can't see it producing current on the neutral much the same way two balanced 120 volt loads don't.
 

hbiss

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Should have been shown as two surge protection devices, one from each phase to neutral or ground which is how surge suppressors work. That's the only way that blue wording would make sense.

As for the 330V, the surge suppressor was probably designed that way and Mike only used 330 as an example. I think 330V is what is most common. The SPDs inside are designed with a minimum clamping voltage. Over 330 and it starts clamping. We can get communications circuit protectors with SPDs that will clamp down to around 10 volts.

-Hal
 

synchro

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Chicago, IL
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This document on surge protection and associated grounding/earthing might be of interest:

In particular, on page 5 (page 7 of the pdf document) they distinguish two components of a surge:
1.) The common mode component where the voltages on the conductors move together relative to a local ground, and
2.) The difference mode (aka differential mode) component where the voltages on the conductors move relative to each other
Both components can be present during a surge.
As the document mentions a surge protector should reduce the level of both types of surge.

The surge protector that Hal mentions with a clamping device on each line to ground/neutral will protect against both common and differential mode components. For electronics or other loads that are more sensitive to differential mode surges, additional protection with a lower clamping voltage can be placed across twisted pairs, etc.
 

PaulMmn

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Don't forget-- MOVs are sacrificial devices-- every overload it prevents eats away at its protection!

I searched for >failed mov power strip< and found a lot of interesting links!
 
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