Bundling PMag Leads

Mark Dickens · #1 08-25-2014, 07:50 AM

I have a dual PMag installation. Is it ok to bundle spark plug leads together or should they be kept separated?

Ironflight · #2 08-25-2014, 08:18 AM

If I recall, when I installed ours, the manual clearly said that they should be separated with little spacers or combs - not bundled right next to each other. I don't know the "why", but since they called it out, that's what we did....

Mark Dickens · #3 08-25-2014, 08:52 AM

Quote:

Originally Posted by Ironflight

If I recall, when I installed ours, the manual clearly said that they should be separated with little spacers or combs - not bundled right next to each other. I don't know the "why", but since they called it out, that's what we did....

This is the confusing part. They state on page 9 of the install manual that "Aircraft and auto style leads should be kept separated. Do NOT bundle them together as is common with shielded aircraft wires, as this can cause them to be inductively coupled.". So, does this mean just the case where auto AND aircraft leads are used together or is this also inclusive of the dual PMag case with all auto leads?

jjconstant · #4 08-25-2014, 09:15 AM

My understanding and practice is to keep the PMag high voltage leads away from each other AND away from any other metal. This is to prevent the very high voltage being contained inside the insulation from escaping by arcing through the insulation to adjacent wires or structures. I have a friend who was chasing an ignition miss with another Electronic ignition and found a spot where there was a tiny black mark on the ignition lead where it was in contact with the engine mount. Arced throught the insulation. Moved it away and no more miss.

I think that the spark plugs work by having a high resistance in the plug that forces a spark to jump at high voltage. With EI, the voltage is so high that you can't use aircraft style leads with metal sheilding because the voltage will simply arc to the sheilding because it is an easier path to ground than the spark plug. Bundling the leads together will put them so close that arcing through the insulation is still an easier path than through the plug.

Mark Dickens · #5 08-25-2014, 10:03 AM

I emailed Emagair and they said to separate them. They need to re-word their instructions to be clearer

Mark Dickens · #6 08-25-2014, 10:04 AM

Quote:

Originally Posted by jjconstant

My understanding and practice is to keep the PMag high voltage leads away from each other AND away from any other metal. This is to prevent the very high voltage being contained inside the insulation from escaping by arcing through the insulation to adjacent wires or structures. I have a friend who was chasing an ignition miss with another Electronic ignition and found a spot where there was a tiny black mark on the ignition lead where it was in contact with the engine mount. Arced throught the insulation. Moved it away and no more miss.

I think that the spark plugs work by having a high resistance in the plug that forces a spark to jump at high voltage. With EI, the voltage is so high that you can't use aircraft style leads with metal sheilding because the voltage will simply arc to the sheilding because it is an easier path to ground than the spark plug. Bundling the leads together will put them so close that arcing through the insulation is still an easier path than through the plug.

Excellent points. Thanks!

RVDan · #7 08-25-2014, 10:12 AM

If the leads are bundled closely together for enough length, they can inductively couple to the point of "cross firing" the other cylinder. Not sure if the Pmag has enough energy to do this or not, but that is the thought process.

N941WR · #8 08-25-2014, 01:20 PM

We had an EICommander customer who felt a stumble and noticed the coil pack graph was showing a shorted plug. When he decowled he found a plug wire laying against his engine mount. After moving and securing the wire, his problem went away.

Try using some of these to keep your wires separated.

Mark Dickens · #9 08-25-2014, 01:28 PM

Quote:

Originally Posted by N941WR

We had an EICommander customer who felt a stumble and noticed the coil pack graph was showing a shorted plug. When he decowled he found a plug wire laying against his engine mount. After moving and securing the wire, his problem went away.

Try using some of these to keep your wires separated.

Nice! I was planning to use the old zip ties with tube separator method, but these look cleaner

mburch · #10 08-25-2014, 01:45 PM

I'd be interested in knowing just how much bundling of wires is allowed and how much is too much. For instance, is it acceptable to pass two ignition wires through a single adel clamp (thus causing them to be bundled for a few inches) or must you use one clamp per wire so they remain entirely separated?

I ask because I was confused by the ambiguous wording in the installation manual, so I unknowingly ended up bundling all my ignition wires together. So now I have to go back yet again and address this. It would be nice if I could avoid reworking the whole thing from end to end.

I have to say, between the uneven track record, the non-aviation-grade electrical connections, and now this, I'm sorely tempted to swap my P-mag for a good old Slick magneto.

- Matt