Lumps, Blisters, and Neck

Good day!

I would like to ask if any lumps, blisters, and neck (downs) can cause any problems on the cable's electrical properties? This problem in regards to building wires.

Hello again,

In general, a country's specifications are very clear in regards to both the minimum thickness of the insulation and the jacket or sheath. Thus neck downs, blisters and lumps are not allowed.

This typically is to protect people from electrocution and/ or fires.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212

Now sir, these reasons are for building wires or also for LV and MV cables?

Currently we have a neck and lump detector in our spooler machines. We are debating if we should turn off this detector or not because we have too much lumps and neck. We are using pressure toolings and I think by using this kind of tooling the lumps will be very less, right?

Can you tell me what is the difference of neck and lumps and their reasons?

Thanks and More Power to you and to WAI!!!

Hello,

A "neck down" is generally a short term reduction in the diameter of the cable because the cable was jerked suddenly forward while the plastic was being applied at constant speed. Often this is because the capstan was overhauled by the pull of the take up. (Again often because of a very bad wind on the take up reel.) It can also be the result of momentary starvation of the extruder or other short term loss of plastic pressure for some reason.

Lumps on the other hand are bumps on the surface of the cable and they may be the result of die rings (The build up of hot plastic around the die which occasionally lets go. This is the result of damaged dies.) It could also be the result of pay off jerking or bumpy cores, especially if you are tubing instead of using a pressure set up at extrusion. In tubing, the outside diameter reflects the surface of the core at any particular point.

As far as turning off your detection instruments for lumps and neck downs, it is very difficult to advise because you may have the sensitivity or the control limits set too fine. The instrument is there as a tool for you to use to confirm conformance to the specification as interpreted by your product engineers. If the instrument is set up correctly, cleaned properly, has been calibrated properly, is working properly and is on an electrical feed that is not affecting the performance of the instrument, then it is a tool that should be properly used by the plant operations people.

We of course cannot see what you are seeing so it is impossible for us to assess and correct your company's present situation from so far away. All we can do is give you some typical areas to look at and the rest is really up to you people.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212

Hello Good day!!

Military Gauge wire ( 22 AWG ) was damaged after final automated electrical testing of cable harness.
Wire insulation blister were found in some locations, on further investigation, we found conductor is burnt and cut under these insulation blister.

Automatic Test parameters : Continuity test ( low voltage, current = 0.5A, time = 0.1s, Resistance > 5 Ohms )
Insulation resistance test ( Voltage = 500 VDC, time = 4 second, IR > 1MOhms)

Can you kindly tell us the possible reason of blister formation in the wire during testing .

Regards,
Rakshith Radhakrishna