Electrical current when circuit is off

[team karst]

Faraday cage requires no ground. Ie: airplanes/cars in lightning.

However, i do ground my stays to the waterline to provide a controlled strike path. Nothing to do with shielding.

[Dieseldude]

Originally Posted by GoodShipLolipop

The mast itself should act as a Faraday cage so long as it's grounded. Mesh is typically used because it's much cheaper than solid metal. Solid metal does the same thing, and works on a broader range of frequencies.

Oh, the wiring is inside of the aluminum mast, and not secured to the outside? I had been reasoning on the assumption that the wires are outside. If they are in fact inside, and the mast is grounded, this should substantially eliminate a lot of radio interference. Though the lights themselves and any wires that extend outside can receive radio signal. Replacing wires that are already shielded by the hollow metal mast with shielded wires may be unproductive. But then RF interference is often unpredictable. An experiment can be done to outfit one circuit with shielded cable. But probably best to watch if the problem returns. It may have been a unique situation of local interference that will not be seen again. One more idea is to quiz the manufacture of your lighting equipment if they have had to deal with this problem. They probably have an electrical engineer or technician who might be able to assist.



Solution could be as simple as putting a filter capacitor or choke coil in the each light circuit. This possibility had not been discussed. Choosing what value of capacitor will shunt RF signal to ground, or what value of coil will keep RF out requires some calculations. This is based upon the formula C = 1 / (2π f Xc) Of course, the interfering radio signal frequency(s) must be known. But generally, the value of Xc is kept low to present a low impedance path to ground for the undesired radio signal. The capacitor would be put in parallel with the light, or to simplify terminology, a capacitor would be connected between the light positive supply line and ground. Usually, capacitors are cheaper than copper wire coils.



Of course the wire gauge size of a choke coil must be large enough to conduct the current draw of the light, since it would be series connected. Selection of a choke coil or inductor is based upon L = XL / 2π fA. The value of XL is kept high to present a high impedance to the undesired RF signal.



One more point, this is a sort of grasping at straws idea. Does the mast have wire rope stays? If so, are they grounded or are they insulated? Could be some issues there. Wire rope stays can act as antennae and inducing interference into the lighting wires. If insulated, try temporarily grounding stays with test leads and see if the problem goes away.

[team karst]

On a built-up complex system as the mast example is; lossy inductors, such as ferrites of the correct mix, are very often employed. Bypass caps and multistage filters tend to be features on pc boards, and power inlets.

[Dieseldude]

Originally Posted by team karst

On a built-up complex system as the mast example is; lossy inductors, such as ferrites of the correct mix, are very often employed. Bypass caps and multistage filters tend to be features on pc boards, and power inlets.

Good idea. Ferrite doughnuts positioned on wiring can be easier to deal with and cheaper than capacitors and coils. Suppose good articles about this might be found on line.

[Wotname]

Originally Posted by team karst

Faraday cage requires no ground. Ie: airplanes/cars in lightning.

However, i do ground my stays to the waterline to provide a controlled strike path. Nothing to do with shielding.

Cars and aircraft are 'grounded'. Cars via the tyres, aircraft via static wicks. I agree that the grounding has little to do with lightning mitigation.

When aircraft are struck by lightning, the charge usually enters at one point and travels through / along the fuselage and then exists at another random point. The are many techniques employed in the wiring and components to minimise effects of the (sometimes large) lightning induced currents and they are not always successful.

[team karst]

Originally Posted by Wotname

Cars and aircraft are 'grounded'. Cars via the tyres, aircraft via static wicks. I agree that the grounding has little to do with lightning mitigation.



When aircraft are struck by lightning, the charge usually enters at one point and travels through / along the fuselage and then exists at another random point. The are many techniques employed in the wiring and components to minimise effects of the (sometimes large) lightning induced currents and they are not always successful.

Must be some very long ground wires out there [emoji848]

A metallic/ conductive closed body in space presents an excellent shield. And whether or not its grounded does not affect that property.

[Wotname]

Originally Posted by team karst

....

A metallic/ conductive closed body in space presents an excellent shield. And whether or not its grounded does not affect that property.

Yep this true and remains true until a huge current flows through the said closed body (e.g. when hit by lightning) - at which point the closed body is no longer acting as a Faraday cage, rather it becomes a source of EMI.

[RaymondR]

what is the mechanism whereby an electromagnetic field is excluded from a Faraday cage even though the cage material is not formed by a magnetic material: aluminium for instance?

[donradcliffe]

Originally Posted by PaulvR

What the hell it's all that is left :-)..

So what about the mast-head anamometer cable misbehaving in some way, leaking a little while bundled in the same harness or occasionally touching a conductive surface as it does the halyard dance?....only in the mast right? Minor wind generated currents?

I think I'm going to be flogged..SEND :-)

If its B&G the most common problem is the MHU electronics, not the cable.

[donradcliffe]

Originally Posted by RaymondR

what is the mechanism whereby an electromagnetic field is excluded from a Faraday cage even though the cage material is not formed by a magnetic material: aluminium for instance?

I'm brushing away some old cobwebs, but its not the magnetic property, its the conductivity.

[Dieseldude]

Originally Posted by RaymondR

what is the mechanism whereby an electromagnetic field is excluded from a Faraday cage even though the cage material is not formed by a magnetic material: aluminium for instance?

Good question. In electronics college we were just told that a metallic material acts as a shield. But considering the two components of electromagnetic fields, the mechanism can be deduced. By the word itself, there is an electrical component and there is a magnetic component. A conductive material intercepts the electrical component of the field. A hollow pipe for instance will be the path of least resistance to the the electrical field compared to the air, so it shunts it around the wire that is contained inside. It must dissipate the electrical component, so the whole field breaks down. This is certainly not a physicist's explanation. But maybe there is a forum member with some deeper electrical physics knowledge who can explain it in more detail.


Technicians and engineers just know that metal is a barrier to electromagnetic energy and do not delve into the deep theoretical physics of it. We just make electrical things work using that principle.

[team karst]

Originally Posted by donradcliffe

I'm brushing away some old cobwebs, but its not the magnetic property, its the conductivity.

Correct. An e-field cannot exist inside a conductor. The more conductive the shield, the better the shielding effectiveness.

[team karst]

Originally Posted by RaymondR

what is the mechanism whereby an electromagnetic field is excluded from a Faraday cage even though the cage material is not formed by a magnetic material: aluminium for instance?

A far field EM signal consists of two vector quantities 90 deg apart. E and H vectors. You kill one and the signal is killed.
Yes, Al does not have strong magnetic properties, and so will be a non effective mag shield. However, it is a vg current conductor, and therefore makes a good E field shield.
So, inside a Al shield, E fields are highly attenuated, but a mag field is mostly unaffected.
In a coax, with equal and opposite shield and center currents, the mag field is cancelled, not relying on the physical mag properties of the outer shield. I have worked with coax containing high permeable shields to increase low frequency rejection, but those are not common.

[mako]

Originally Posted by crayiii

We moved about 30 miles to a new Anchorage yesterday. The panel and all the lights are now working as they should.

Starting to think that those guys wearing the tin foil hats knew something we didn't

[paul2884]

Originally Posted by team karst

My SSB blinks the LED anchor light.
In your case, its possible a high powered pulsed radar could do the same.
OR, do you have a satellite tracker or AIS enabled?

If they blink together at 4 to 5 second interval, I'd be thinking airport surveillance radar.

I had this will a car radio speakers, the clicked each time the radar on a near by airport sweped past even with the radio turned off!