wire with the current coming out of the deive on another wire. If they don 't match, some current is finding another path back to the power supply, wh ich could pass through somebody. The RCD turns off the power to the device when this happens.
yep
the other end of the coil that doesn't pass through the two power leads, that could - if big enough, and sustained for long enough - trigger the RCD (also know as an earth leakage trip).
coil, and wouldn't necessarily degrade or wreck the insulation.
A deliberate spark gap might be incorporated, I've not opened it yet. Curre nt across it should not be noticed by the RCD.
Again no path to ground exists. There can be no ground current, other than a miniscule amount at rf due to stray capacitance to the nearest object. Tr y to understand, or I'm pretty sure I'm going to replonk you.
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It w orks flawlessly, but often trips the 30mA RCD when switched off. 500v inusl ation testing shows no problem. I assume it has no built in snubber. I'm no t working out why it trips the RCD. Any ideas?
The appliance has a built-in switch. Switching it off there trips the RCD a bout 50% of the time. It has a 2 contact BC plug which plugs into a lead wi th BC socket at one end & a 30mA trip threshold RCD mains plug.
ne wire with the current coming out of the deive on another wire. If they d on't match, some current is finding another path back to the power supply, which could pass through somebody. The RCD turns off the power to the devic e when this happens.
to the other end of the coil that doesn't pass through the two power leads , that could - if big enough, and sustained for long enough - trigger the R CD (also know as an earth leakage trip).
e coil, and wouldn't necessarily degrade or wreck the insulation.
rent across it should not be noticed by the RCD.
n a miniscule amount at rf due to stray capacitance to the nearest object. Try to understand, or I'm pretty sure I'm going to replonk you.
If its only function is as RCD then the trip may be legitimate. It could be there's embrittled wire insulation in there somewhere, not necessarily the vibrator, that's not withstanding the high voltage and arcing to case grou nd or worse another circuit in a wire bundle.
ng centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inu slation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas?
e
CD about 50% of the time. It has a 2 contact BC plug which plugs into a lea d with BC socket at one end & a 30mA trip threshold RCD mains plug.
Interesting idea. It would need to arc across the vibrator switch first, wh ereupon the low current spike would meet extremely low impedance mains, so I don't think it would cause a noticeable spike on the mains.
Vibrator is between L and N, so induced voltage jumps from L to GND back to N common at the service panel bypassing the N at the RCD, causing it to trip.
I have a memory of reading about this sort of problem, some years ago.
The explanation I read was this: the "balanced" current sensors (often toroids) used in GFCIs aren't perfectly balanced at all frequencies. There's enough asymmetry in their windings, and enough capacitive coupling between the windings, that the balance deteriorates at high (RF) frequencies.
Switch-off/inductive-kickback arcs have a lot of high-frequency content (up into upper HF and VHF). Even if the RF-kickback currents in the mains conductors do turn out to be perfectly balanced, there's often a spike of RF induced in the current-sense winding due to the imperfect balance of the sensor itself. If the imbalance-detection circuit doesn't low-pass-filter the sensed signal (and I gather this often isn't done) the spike can trigger the GFCI.
And, of course, if the GFCI incorporates an arc detector (as some of the modern ones do), it's even more likely to trigger in this case.
Well, to the atmosphere, by corona discharge, if there's enough voltage. Look for a pointy part that (sometimes) glows a little at turn-off, as seen in a dark room.
I've seen entire wire harnesses with St. Elmo's fire, by their own light.
ne wire with the current coming out of the deive on another wire. If they d on't match, some current is finding another path back to the power supply, which could pass through somebody. The RCD turns off the power to the devic e when this happens.
to the other end of the coil that doesn't pass through the two power leads , that could - if big enough, and sustained for long enough - trigger the R CD (also know as an earth leakage trip).
e coil, and wouldn't necessarily degrade or wreck the insulation.
rent across it should not be noticed by the RCD.
n a miniscule amount at rf due to stray capacitance to the nearest object. Try to understand, or I'm pretty sure I'm going to replonk you.
Whatever power source excites your vibrator is going to be grounded on one side to go to a safely ground, surrounding metalwork or whatever.
If the decaying current in the vibrator coil after you turn it off generate s a big enough voltage, it will find it own way back to that safety ground or the surrounding metalwork. The other end of the coil will be connected t o one of the wires going through the Residual Current Detector, and could w ell generated enough residual current difference to trigger it.
The point is that all current flows in a loop, and if the high voltage acro ss the coil at turn-off is high it will find it own way of completing the l oop, not neccessarily following the route that is follwed when the vibrator is running normally.
The proposition that "Again no path to ground exists. There can be no groun d current, other than a miniscule amount at rf due to stray capacitance to the nearest object" is invalidated by the observation that you are complai ning about, viz that the RCD trips.
It's probably easier to plonk me than carefully trace out possible current loops, but the latter exercise might prove more rewarding.
RCD's see a magnetic field. Normally it is generated by a current imbalance in the two wires running through it - if they are equal and opposite return currents they don't generate an external magnetic field.
In principle an EMP pulse could generate enough current in a nearby conductive loop to fool the RCD.
ving centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v i nuslation testing shows no problem. I assume it has no built in snubber. I' m not working out why it trips the RCD. Any ideas?
ice
RCD about 50% of the time. It has a 2 contact BC plug which plugs into a l ead with BC socket at one end & a 30mA trip threshold RCD mains plug.
whereupon the low current spike would meet extremely low impedance mains, s o I don't think it would cause a noticeable spike on the mains.
formatting link
Residual current devices don't react to "spikes on the mains". There look a t current flowing through one one and compare it with the current flowing b ack through another wire, and trip if they aren't equal and opposite.
Their sensitivity is finite, and they do take time to act, but they are loo king for a current imbalance, not a spike as such.
Corona discharge is a low current mechanism. With any significant current y ou get a rapid transition to an arc discharge.
Glow discharges work by positive ion bombardment of the negative electrode which knock off secondary electrons to provide more current carriers to car ry the current.
It doesn't take much current to get some point on the surface of the negati ve electrode hot enough to initiate an arc, where the surface has got hot e nough to be molten, which lets the electric field distort into atomically s harp spikes, which release lots of electrons by field emission.
You get a voltage drop of the order of 100v at the anode in a glow discharg e, perhap 20V in an arc discharge, and the anode hot-spot is a lot smaller.
Can you provide a real world example when this might happen? Not one associated with nuclear charged particle decay.
Kirchoff's laws are good to microwave frequencies and beyond. You seem to be saying that a node can disobey such laws? And generate current out of thin air?
--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.