Single conductor wire requirement and ?

[JimWoo50]

I am installing a Flight Data Systems tachometer which requires 24 ga. shielded single conductor wire. I ordered it from Spruce and was surprised to find after I peeled the shielding back there was a inner insulated core of braided wire. I was expecting a single solid core hence the single conductor designation. What am I missing here? I'm sure Spruce sent me the correct wire.

Also installing a pmag on the other end of the aforementioned wire. Should I ground the shielding on one end or both ends or neither?

I am using the existing shielded p lead from my mag for the new pmag. The shielding is grounded at the switch does it have to be grounded at the mag too?
In the case of both wires if the shielding is grounded at the pmag it will require a length of at least 4" of shield to be pulled back to the nearest ground point. Is this excessive? Thanks in advance for helping me to learn new stuff.

[cfiidon]

Originally Posted by JimWoo50

I ordered it from Spruce and was surprised to find after I peeled the shielding back there was a inner insulated core of braided wire. I was expecting a single solid core hence the single conductor designation.

Should I ground the shielding on one end or both ends or neither?

The shielding is grounded at the switch does it have to be grounded at the mag too?
.... it will require a length of at least 4" of shield to be pulled back to the nearest ground point. Is this excessive? Thanks in advance for helping me to learn new stuff.

Single conductor does not mean solid conductor. The braided wire is preferable for its flexibility.

If I recall, shields should be grounded at one end only. I'm not sure it matters which you choose if you have no interference. I seem to recall that grounding at the mag was preferable so that induced currents coupled to the shield would not travel the length of the shield to return to ground. My internal logic; however, says that if the mag switch is open (Mag=on) there is no current flow to ground and therefore no magnetic field induced, therefore... nothing to couple. Others more knowledgeable with practical experience may chime in.

You shouldn't have to peel back four inches of shielding. Stein sells ring terminals with a coaxial lead to another ring terminal for grounding. Consider those. Here's the link http://www.steinair.com/storedetail.cfm?productid=397


Don

[WingsOnWheels]

On the topic of grounding the shield for P-Leads:

Most everything I have seen or read from A&P books to Kitpanes articles say to only ground the P-lead at one end.

That said, in Aero-electric connection his schematics show the P-lead shield connected at both ends. The shield is connected to the Ground terminal on the ignition switch and then to the magneto ground lug/case. This is how I wired my P-lead and it makes perfect sense to me. There is no separate airframe ground at the ignition switch in this arrangement.

1) There is no separate ground connection to the ignition switch, so if the engine ground fails, it won't toast your P-leads. Also, if the engine ground fails, the P-Leads would still have a way to ground the mag coil. (not really an issue with all the braided hoses and such, but doesn't hurt).

2) Both ends of the shield are only grounded when the P-lead is grounded and the ignition off. At that point electrical noise is not an issue.