Solid vs Stranded

mbrooke

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When it comes to lightning protection, and to a lesser degree 60Hz impedance, which is better when compared based on the same gauges?
 

jumper

Senior Member
Interesting for now.

Would not the evidence of a parallel conductor's ampacity of a single conductor over the equivilant of a single conductor lend a certain amount of credence.

After all is not a braided/stranded conductor a parallel application?
 
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user 100

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When it comes to lightning protection, and to a lesser degree 60Hz impedance, which is better when compared based on the same gauges?
Not an expert here, but iirc the skin effect/stranded is a better conductor etc,.. is a non issue at lower frequencies- so, no, stranded wire isn't going to provide a better path than solid of the same gauge per the lower frequencies associated with building wiring. It is an issue with higher frequencies- I don't know what the rough threshold is, but I do know it is higher than 60 hz for sure.
 

mbrooke

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Lightning is not a DC or 60 Hz event, it has components in the MHz so skin effect is a factor. I'll also suggest that the braided cable used for downcomers is much easier to install than the equivalent normally stranded copper.


But how can it be a MHz event when it is in fact a brief DC flow? (I have a theory {similar to a DC transmission displaying capacitance and inductance when first energized} , but want to hear an unbiased take)
 

GoldDigger

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But how can it be a MHz event when it is in fact a brief DC flow? (I have a theory {similar to a DC transmission displaying capacitance and inductance when first energized} , but want to hear an unbiased take)
There can actually be moments of reverse current flow in a strike, as well a "ripple" at very high frequency.
The driving voltage is DC, but the current is affected by sudden changed in path impdedance caused by ionization and the inductance of the "wire" when subject to sudden enormous currents.
 
It isn't the braiding that makes lightning protection conductors efficient, it's the flat shape. Flat copper strap is also used, but braided is easier to install.

The flat shape allows for the most surface area, and as mentioned, lightning acts like MHZ AC, so skin effect is a huge consideration when designing conductors.
 
But how can it be a MHz event when it is in fact a brief DC flow? (I have a theory {similar to a DC transmission displaying capacitance and inductance when first energized} , but want to hear an unbiased take)
It's pulsating DC and it pulsates at around 100 MHZ. The pulses are thought to be caused by the breakdown and re-establishment of ionized air in the strike path.
 

GoldDigger

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It's pulsating DC and it pulsates at around 100 MHZ. The pulses are thought to be caused by the breakdown and re-establishment of ionized air in the strike path.
It also has a very sharp leading edge, and if there is too much inductance in the wire a substantial enough voltage can be developed to cause arcs to other paths.
 

mbrooke

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There can actually be moments of reverse current flow in a strike, as well a "ripple" at very high frequency.
The driving voltage is DC, but the current is affected by sudden changed in path impdedance caused by ionization and the inductance of the "wire" when subject to sudden enormous currents.
A counter EMF like skin effect in a sense?
 
Like an HID lamp have a non sine wave arc?
I am not sure about that, but if you are asking how DC can behave like AC, the best example I can give is an automobile ignition system. The coil has pulsating 12 VDC on one side, and 10-30 kV coming out the other, but is also pulsating DC, but with a high enough voltage to make a spark. The frequency is dependent on the RPM of the engine.

Lighting is a bigger spark at hundreds of millions of volts, but still pulsating DC.
 

GoldDigger

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I am not sure about that, but if you are asking how DC can behave like AC, the best example I can give is an automobile ignition system. The coil has pulsating 12 VDC on one side, and 10-30 kV coming out the other, but is also pulsating DC, but with a high enough voltage to make a spark. The frequency is dependent on the RPM of the engine.

Lighting is a bigger spark at hundreds of millions of volts, but still pulsating DC.
The capacitor across the points insures that the spark is actually AC with a DC bias. The coil secondary is grounded at one end.
 
The capacitor across the points insures that the spark is actually AC with a DC bias. The coil secondary is grounded at one end.
Points? Capacitors? That's so last millennium.

No, the spark is not AC. If it were, we would not distinguish the anode from the electrode in a spark plug.

How can the spark plug, which is solidly grounded to the engine, change polarity? It can't, and one of the reasons we went from positive to negative ground on automobiles was to decrease spark plug wear.

I have looked at many a spark plug pattern on O scopes and I can assure you there is no AC. It's pulsating DC, no crossing of the zero line.

In a former life I worked on cars for a living.
 

GoldDigger

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Points? Capacitors? That's so last millennium.

No, the spark is not AC. If it were, we would not distinguish the anode from the electrode in a spark plug.
You can if the DC bias is close to 1/2 the peak to peak AC.
The dividing line between AC with a DC bias and DC with close to 100% ripple seems to be different depending on what field you are in. :happyyes:
I am also perfectly happy to call it pulsed DC with ringing as long as the order of magnitude of the pulse frequency and the ringing frequency is part of the discussion.
 
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