GFCI breaker with built in TVSS question

[SPERRY-1]

I was watching the webinar that mike did a week or so back and saw a gfci breaker with what looked like TVSS built into it. There was actually just a MOV inside of it and that lead me to believe it had TVSS. Does anyone know if these are available and if so, what would be the utility of having suppression in a single breaker as opposed to clamping the whole panel?
By the way I am Master licensed and also a senior in architectural engineering, so you know I am not trying to waste someones time.

Thanks guys!

 

[gar]

130511-2120 EDT

SPERRY-1:

Look at my Photo 5 (P5 - Moving Breaker Contact Buttons and Other Components) (sorry there are several P5s) at http://beta-a2.com/GFCI.html for a photo of a GFCI receptacle circuit board. You will see an MOV at the right.

An MOV as contrasted to a Zener diode does not have a very sharp characteristic curve, and its threshold voltage is not as well controlled or stable.

Why is one used in the GFCI? Because it is closer to the item to be protected. There is more impedance before the MOV in the GFCI than before a whole house MOV. However, when the breaker is in the main panel that added impedance is minute. The MOV in the GFCI may reduce transient triggering of the GFCI. I have not run any tests with and without the GFCI MOV, just with the MOV.

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[hurk27]

I would be willing to bet that the MOV is there more to protect the electronics in the breaker or as Gar said to lower the tripping from transients then it is to provide TVSS protection for that circuit, while installing TVSS at the panel can provide some limited protection from surges coning in from the power lines, because of the high frequency nature of transient surges they will provide very little to no protection to event that happen closer to the load, this is why providing surge protection at the load is so important, any manufacture claiming other wise if just selling snake oil, some surge events such as near field lightning strikes that induce voltages into house wiring as well as networks and phone and cable will not be protected by any TVSS on the power lines even if they are at the load end. which also goes for TVSS installed on phone and cable lines, this is because this type of induced surge will treat all the conductors of a cable pathway as one conductor and the loop that can include the cable network and phone lines will develop a voltage difference of potential across the electronics within the equipment, so protection between the line neutral and EGC is no longer effective as all three will be effectively as one pathway for this induced current, also since it will also act like the secondaries of a transformer this current is no longer seeking to return to Earth so even Earth grounding has no effect, do a search on LEMP or lightning electro magnetic pulse.

 

[SPERRY-1]

130511-2120 EDT

The MOV in the GFCI may reduce transient triggering of the GFCI.

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Gar,

So it is primarily nuisance tripping that this MOV resolves? Not actual clamping protection?

Thank you for a speedy reply!

 

[gar]

130511-2345 EDT

SPERRY-1:

The MOV in the GFCI is there to minimize false triggering of the GFCI and to protect the GFCI components. It may provide some down stream protection of loads on the GFCI.

Note: the MOV in the GFCI is tiny and thus energy limited compared to a whole house MOV. But pay close attention to what hurk27 described.

MOVs are useful, but better for certain purpose when combined with filtering, and gaseous discharge devices.

Simple MOVs and Zener diodes are quite often used to prevent excessive PIV (Peak Inverse Voltage) from damaging semiconductors resulting from inductive kick switching transients.

MOVs and Zener diodes are voltage clamping devices, but must be preceded by current limiting impedance or the clamping device will be destroyed.

GFCI breakers are not always located in main panels, and main panels don't always have an MOV or equivalent. Thus, it makes sense to include an MOV in the GFCI breaker.

.

 

[SPERRY-1]

GFCI breakers are not always located in main panels, and main panels don't always have an MOV or equivalent. Thus, it makes sense to include an MOV in the GFCI breaker

Gar,

This leads me back to my original question that i wasn't sure how to ask. The MOV in a gfci breaker is surge protection for the breaker or just helps stop nuisance tripping?

To wrap things up:

1) TVSS needs to be as close as possible to the load it protects?

2) Cascading the SPD such that you limit the transient voltage in tiers so to speak is best practice?

3) Utilizing a MOV based SPD alone offers only limited clamping? (this opens 20 more questions that I will research on my own time haha.)

4) Is there a rule of thumb or hard science to sizing them? (I guess it seems like one should be able to select for the same size TVSS regardless of a 200a service panel or a 4000a switchgear).

 

[gar]

130512-0639 EDT

SPERRY-1:

An MOV or Zener diode is a constant voltage device when sufficient current is applied and not too much current. A Zener diode is much more constant in its voltage vs current than an MOV. A typical MOV is really quite poor.

See: http://en.wikipedia.org/wiki/Varistor for a good overall discussion. Also see
http://www.cliftonlaboratories.com/metal_oxide_varistor_(mov).htm . The author uses the word power in some spots where energy should have been used. You can search the Internet for other useful discussions.

Answers to your questions:

1, Yes.

2. Can be useful.

3. Yes. The MOV is a voltage limiting device, requires series impedance to limit current, and does not change dv/dt. Does not lower the peak voltage, whereas a filter following the MOV will lower the peak voltage but extend its duration. dv/dt and peak voltage can be a factor in transient triggering of an SCR for example. Breakdown because of excessive voltage to a semiconductor is mostly a voltage problem, and less of a dv/dt problem.

4. Maximum expected energy pulse. This is a function of the origin of the problem and the current limiting impedance.

.