skywagon8a
MEMBER
SE Mass MA6
Except that the P-lead shield is not airframe grounded at the switch end. Only at one end, the mag. Therefor would not "ground" the starter.
P Lead Wire Gauge
- Thread starter Eddie Foy
- Start date
cubdriver2
FRIEND
upstate NY
wireweinie
FOUNDER
Palmer, AK
Test them out before you use them on a harness for install. Sometimes you get the quality that you paid for. So be cautious.
Web
Web
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
In Mike's post it sounded like he was referring to the braid grounding to the airframe through the switch (specifically a mag switch, not toggles). Maybe I misinterpreted that. Again, if I read his post correctly, I think the hazard he was referring to would not be mitigated by grounding the shielding to the airframe (which would require bonding the ground post on the switch to the airframe).
Oh wait - Maybe he meant bond the switch ground post to the airframe and leave the braid connected ONLY at the mag, then the potential hazard of overcurrent in the braid is eliminated. I think maybe that's what I did on my 12 - gotta go look. Interesting discussion.
Eddie Foy
MEMBER
South Florida
I assume you mean the solder sleeves. Steinair dot com has them for sure. Spruce probably does too.
The Ebay listing that Glenn posted is for butt splices. The ones for adding pigtails are a little different.
Last edited:
cubdriver2
FRIEND
upstate NY
Sorry, I couldn't copy the link on my pad
www.ebay.com/sch/i.html?_nkw=solder+sleeve
Glenn
Frinkin windows 10
texmex
MEMBER
Hanging Rock, Australia.
Not sure why it's copying in bold.
But, if in normal operation, with the mag switch in the 'ON' position, the path between the wire from the primary coil, near the points to the mag switch, returning to the mag case is OPEN, how would the pulse travel along the P lead wire?
Wouldn't current only flow along the P lead if the mag switch was 'OFF'?
Thanks for the post Skywagon8a and wireweinie. I'm just trying to get it straight in my head. I've had that annoying tick before but was lead to believe it was an alternator noise not being suppressed. I'd love a separate thread on that please. :smile:
Due to age, alcohol and or jet lag, the electrical currents in my head are not the sharpest. Could someone explain Mike's comments a little more? Is it if the engine earth straps are failed there will be significant current from the alternator looking for a pathway? One possible pathway is from the engine, mag case, P lead shield and an arch on the mag switch to the P lead?? This still would not complete the alternator circuit would it. I'm missing something.
Also regarding the contecting of the P lead shield to the airframe. How would that complete the circuit of the P lead. That is from the Primary coil, out to the switch via the P lead core wire and back to the case via the mag case via the P lead wire shield. Wouldn't that circuit always be open, and therefore the mag 'HOT'??
Electricity!!! What fun.
mike mcs repair
Registered User
chugiak AK
thats called an antenna
wireweinie
FOUNDER
Palmer, AK
Not sure why it's copying in bold.
But, if in normal operation, with the mag switch in the 'ON' position, the path between the wire from the primary coil, near the points to the mag switch, returning to the mag case is OPEN, how would the pulse travel along the P lead wire?
Wouldn't current only flow along the P lead if the mag switch was 'OFF'?
Thanks for the post Skywagon8a and wireweinie. I'm just trying to get it straight in my head. I've had that annoying tick before but was lead to believe it was an alternator noise not being suppressed. I'd love a separate thread on that please. :smile:
Due to age, alcohol and or jet lag, the electrical currents in my head are not the sharpest. Could someone explain Mike's comments a little more? Is it if the engine earth straps are failed there will be significant current from the alternator looking for a pathway? One possible pathway is from the engine, mag case, P lead shield and an arch on the mag switch to the P lead?? This still would not complete the alternator circuit would it. I'm missing something.
Also regarding the contecting of the P lead shield to the airframe. How would that complete the circuit of the P lead. That is from the Primary coil, out to the switch via the P lead core wire and back to the case via the mag case via the P lead wire shield. Wouldn't that circuit always be open, and therefore the mag 'HOT'??
Electricity!!! What fun.
For alternators, other than a diode failure, noise is mainly a whine that varies with engine RPM. Verify it by pulling the field breaker and then the output breaker. If the noise stops with one or the other, the charging system is the source. Mag noise, too, usually shows as a whine, except at low RPMs. Unless it's caused by both mags, you should be able to verify the source by doing your mag drop check. A 'tick, tick, tick...' is most likely a spark plug or lead. Check the plugs on a spark tester and inspect the leads. If you can get ahold of one, use an old school lead tester. It works kind of like a megger by putting a high voltage on the center conductor and seeing if it jumps to the shielding. Another common source of that ticking is the little pin/spring terminal end coming loose. Process of elimination.
You are correct in pointing out that when the mags are 'on', the mag switch is in the open position and current will not be flowing. But it's trying hard, lol. Think of it like a water pipe when the pressure pulses for some reason. You can hear the pipe do the 'water hammer' thing. If you bundle P-leads with other wires, especially anything with audio signals, you can inject this electrical noise into your intercom or radios. Be aware than many systems now have audio lines that can be hooked up to your audio system. Think of the alarms built into some instruments. Your P-leads can be bundled with these and inject noise without you being aware of the source. Just play it safe and don't bundle them with anything else.
I think skywagon expanded on Mike's comment pretty well in #25. If you ground the mag body directly to the switch, you are now dealing with two separate ground paths. One is for the mag only and the other is for the battery/charging system only. As long as they are not physically connected the current from one system cannot travel through the ground path of the other. Think about the current to drive the starter motor. It goes out through the starter cable, through the starter motor, and enters the ground path of the crank case. From the crank case it travels through the ground strap, to the fuselage frame, and back to the battery through the battery ground cable. If the engine/firewall ground strap is broken or never reinstalled (ahem) the current is going to attempt to return to the battery through any available means. And I mean any. Any conductive item attached, both to the engine and the fuselage will now become part of the ground path. Control cables, primer lines, etc. Now, if you have attached the shield of each P-lead to airframe ground, say up near the key switch, you'll have 100+ amps flowing through them from the engine to the airframe. For about three seconds. By the time you smell smoke, it's to late. But if the shields are only run from the mag body to the switch, it will be isolated from airframe ground, at the switch, and have no path to the airframe. The same explanation goes for the charging circuit. The alternator will seek a ground path just like the starter motor, just not quite as impressive as you're usually dealing with around 20 to 30 amps.
Welcome to my world. How's the winter treating you?
Web
texmex
MEMBER
Hanging Rock, Australia.
1) Thanks for the noise elimination process there Wireweinie. I've copied that paragraph into some notes I keep. When you say
2) I can wrap my head around this. Even though there is no current flowing through the P leads when the mag switches are on (switch open) it's acting as antenna, effected by the primary coils creating and collapsing magnetic field as the points open and close. Hence we need Faraday's cage, or shielding around that wire. (who ever created electricity????)
3) Done correctly, taking the shielding to the other pole in the mag switch, and assuming the switch is insulated/isolated from the frame, there is no path for the separate electrical or starter systems to use the p-lead path.
If you where to join the p-lead shield to the earthed airframe, and not to the switch at all, obviously this would make the disable the switch, creating hot mags.
Ok. The penny has dropped. What Mikes saying is if the shielded braid is joined to the switch pole, AND then to the ground it would operate normally BUT in this case if there was an engine ground wire issue a lot of current could flow down the shielded braid, causing it to get hot and melt the inner wirer insulation. The same as switching the mags off.
I get it now. Crazy stuff.
No winter for me. I'm in China and flying around the wrong hemisphere, east west daily. The 78 flies far too far. No Cub flying for the next six weeks also as a result!
Thanks.
, you mean the cigarette ends of the leads? Do you use DC4 on these?
2) I can wrap my head around this. Even though there is no current flowing through the P leads when the mag switches are on (switch open) it's acting as antenna, effected by the primary coils creating and collapsing magnetic field as the points open and close. Hence we need Faraday's cage, or shielding around that wire. (who ever created electricity????)
3) Done correctly, taking the shielding to the other pole in the mag switch, and assuming the switch is insulated/isolated from the frame, there is no path for the separate electrical or starter systems to use the p-lead path.
If you where to join the p-lead shield to the earthed airframe, and not to the switch at all, obviously this would make the disable the switch, creating hot mags.
Ok. The penny has dropped. What Mikes saying is if the shielded braid is joined to the switch pole, AND then to the ground it would operate normally BUT in this case if there was an engine ground wire issue a lot of current could flow down the shielded braid, causing it to get hot and melt the inner wirer insulation. The same as switching the mags off.
I get it now. Crazy stuff.
No winter for me. I'm in China and flying around the wrong hemisphere, east west daily. The 78 flies far too far. No Cub flying for the next six weeks also as a result!
Thanks.
wireweinie
FOUNDER
Palmer, AK
Yes, the terminal end that ends up inside the top of the spark plug. They get handled a lot which loosens them up and they usually don't get cleaned. If you have one that comes apart, down load the service bulletin from the harness manufacturer and it will instruct you on how to re terminate the lead. I never put anything on these ends. I was taught to assemble them with the contacts clean and dry. I swab the inside of the spark plug barrel with a Q tip and MEK and wipe the spring/pin on the lead, also with MEK. If needed, a TINY bit of DC4 can be wiped on the rubber plug gasket, but keep it off the surfaces you just cleaned.
By the time you get home, you'll be looking for spring! Enjoy.
Web
