gfci

[LarryFine]

Re: gfci

Originally posted by charlie b:

Originally posted by triphase:What is MOV?

From littlefuse.com:

A metal oxide varistor, or MOV, is a voltage dependent, nonlinear device that provides excellent transient voltage suppression. When exposed to high transient voltage, the metal oxide varistor clamps voltage to a safe level. A metal oxide varistor absorbs potentially destructive energy and dissipates it as heat, thus protecting vulnerable circuit components and preventing system damage.

I'd like to add that MOV's are sacrificial devices, and do not last forever. Every time they clamp a surge, their life is shortened somewhat.

 

[jim dungar]

Re: gfci

Ramsy,

A check??? Wow, do you mean there is a way to get paid for advice?

To steal from Scott Adams and Dilbert:
I like to con people.
I like to insult people.
I think I will become a consultant.

 

[physis]

Re: gfci

I'm going to take Jim's side regarding the current leaking through capacitance. It's the only postulate that makes sense.

By Larry:

I'd like to add that MOV's are sacrificial devices, and do not last forever. Every time they clamp a surge, their life is shortened somewhat.

Sort of, but mostly they just have voltage limit and when that's exceeded they get pretty unhappy.

The reason they last at all I think is because they don't react immediately and the really high part of the spike (having little energy anyway) isn't shunted.

Don't quote me though because I really should look up the response characteristics before commenting, but I didn't.

[ January 12, 2006, 06:05 PM: Message edited by: physis ]

 

[LarryFine]

Re: gfci

Originally posted by physis:
Don't quote me though . . .

Oops! To late!

 

[hurk27]

Re: gfci

Sam I have seen this spike on a oscilloscope but only line to neutral I never looked line to ground. I wonder if like Jim mention about the capacitance of the windings to ground with the higher voltage spike, the current to ground would be increased and the leak to ground?
Could be what causes it?

I do know that an MOV will subdue it when placed across the line to neutral.

[ January 12, 2006, 11:53 PM: Message edited by: hurk27 ]

 

[physis]

Re: gfci

By Wayne:

Sam I have seen this spike on a oscilloscope but only line to neutral I never looked line to ground. I wonder if like Jim mention about the capacitance of the windings to ground with the higher voltage spike, the current to ground would be increased and the leak to ground?
Could be what causes it?

I do know that an MOV will subdue it when placed across the line to neutral.

Wayne, a MOV has no idea what it's placed across, of course you know that.

I'd have to guess that you might find more capacitance to ground than you would to neutral though just due to surface area. What are your thoughts?

___________________________________________________________

Edited to add Wayne's comments because of the new page.

Edited again: Hi Larry,

Oops! To late!

I figured there'd be a journalist in the crowd somewhere.

[ January 16, 2006, 01:58 AM: Message edited by: physis ]

 

[hurk27]

Re: gfci

Well Sam At first I was thinking along the lines of timing and phase shift to account for the imbalance, But Jim has now got me thinking

 

[physis]

Re: gfci

Hi wayne,

I used to figure it must be a phase shift phenominon too, but after thinking about it, like Jim says, there are still only two wires, can't gat a phase shift from that.

 

[romeo]

Re: gfci

6ft. or closer from sink gfci protected there is no exception.

romeo

 

[LarryFine]

Re: gfci

Originally posted by hurk27:
The problem I have is that some of the loads that caused the older GFCI's to trip didn't have a grounding conductor, I.E. two wire vacuum cleaner.

A vacuum cleaner, especially one with high hours (i.e., worn brushes), is a perfect example of a motor that produce a lot of arcing, as well as video noise on nearby TV screens.

 

[physis]

Re: gfci

By Wayne:

I'm now wanting to set up my quad trace to capture each line, neutral and ground with current transformers to see where this imbalance is occurring? I wish I had another OS to set up to see the voltage spike at the same time. I would probably find that current of a spike will be lagging voltage thus proving capacitance to ground.
I could run three channel and just capture each line to neutral and line to ground, Channel 1 would monitor line to neutral, channel 2 would monitor current on line, channel 3 would monitor current on neutral. Then same for L to G and N to G but each test would have different event as the trigger which could result in a tanted out come.

Wayne, I apologize, I don't always have the time to thoroughly read a thread or post now-a-days.

Your experiment sounds like a good one.

The problem I have is that some of the loads that caused the older GFCI's to trip didn't have a grounding conductor, I.E. two wire vacuum cleaner.
This then still leads me to go back to the timing/phase shift theroy

You might also want to prove that this difference in older and newer GFI's actually exists.

I'm not saying that they do or don't behave differently. Just that it should be measured or accounted for too.