Protective Wire Coating

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DBoone

DBoone

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General Contractor
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The outer martial is Nylon which gives THHN its gasoline and oil resistance. Technically outside of that it makes no difference from an insulation stand point if the nylon is damaged but the PVC is undamaged.
 
It doesn't appear to me that the equipment grounds are spliced with a device identified for the use. Also I don't see EGC pigtails for the switches.

How many wires are installed in the wire nuts? They appear to be Ideal Tan wirenuts.

Chris
 
raider1 said:
It doesn't appear to me that the equipment grounds are spliced with a device identified for the use. Also I don't see EGC pigtails for the switches.

How many wires are installed in the wire nuts? They appear to be Ideal Tan wirenuts.

Chris
Click to expand...

You're right. Not my work. Gray wirenuts. No listed connector on EGCs and no pigtails for devices. Honestly it's a common install around here though. Even in town where it's inspected I see the grounds twisted together and some long tails left for devices. No connector.
 
171229-2429 EST

If you compare an insulator of thickness T that is composed of one solid layer vs the same material applied in many thinner layers, then you will find the long term voltage breakdown to be better with the multilayer construction.

.
 
gar said:
171229-2429 EST

If you compare an insulator of thickness T that is composed of one solid layer vs the same material applied in many thinner layers, then you will find the long term voltage breakdown to be better with the multilayer construction.

.
Click to expand...

Does that result require semiconductive layer with each layer to equalize voltage or is it just the termination of stress cracks etc. at the surface of each layer?
 
171230-1225 EST

GoldDigger:

When insulators are produced, like enameled wire, there are very small imperfections existent or produced that have a different dielectric constants than the insulating material itself. When a voltage is applied to the insulator these imperfections may have a resulting higher field intensity resulting in an electrical discharge, heat, and destruction of adjacent insulating material. These pockets tend to grow.

By applying the insulation in layers the interface between layers tends to reduce the propagation of these breakdown spots. These breakdow pockets can be seen with a microscope. There is no semiconductor layer applied. But it does bring up the point that if conductive layers were at these interface layers could there be a further improvement.

I believe that thinner sections of insulating material have a greater breakdown voltage gradient.

Wire insulation for electric or hybrid car motors is being made with about 10 to 15 very thin enamel layers.

At the old GMI, now Kettering University, they are performming tests on various insulators in their high voltage lab.

.
 
Last edited:
gar said:
171230-1225 EST

GoldDigger:

When insulators are produced, like enameled wire, there are very small imperfections existent or produced that have a different dielectric constants than the insulating material itself. When a voltage is applied to the insulator these imperfections may have a resulting higher field intensity resulting in an electrical discharge, heat, and destruction of adjacent insulating material. These pockets tend to grow.

By applying the insulation in layers the interface between layers tends to reduce the propagation of these breakdown spots. These breakdow pockets can be seen with a microscope. There is no semiconductor layer applied. But it does bring up the point that if conductive layers were at these interface layers could there be a further improvement.

I believe that thinner sections of insulating material have a greater breakdown voltage gradient.

Wire insulation for electric or hybrid car motors is being made with about 10 to 15 very thin enamel layers.

At the old GMI, now Kettering University, they are performming tests on various insulators in their high voltage lab.

.
Click to expand...




You must be talking spacer cable here! :D Putting covered wire on porcelain insulators- only to track decades down the road. Always use the insulators and spacers intended by the manufacture, its not a conspiracy to get them to buy their stuff! :rant:
 
171230-1437 EST

mbrooke:

If you place a 1 micron, about 0.000,04", layer of enamel on a wire, and continue to add 15 similar layers, then total thickness is about 0.000,6".

At 2000 V/mil the breakdown would be about 1200 V.

.
 
gar said:
171230-1437 EST

mbrooke:

If you place a 1 micron, about 0.000,04", layer of enamel on a wire, and continue to add 15 similar layers, then total thickness is about 0.000,6".

At 2000 V/mil the breakdown would be about 1200 V.

.
Click to expand...

Confused- explain. :?
 
171230-1930 EST

mbrooke:

If you had used one single layer of enamel 0.000,6" thick the breakdown might have been only 1500 V/mil or about 900 V for the total thickness of 0.000,6".

This general concept is from reading and presentations. I have not directly run the experiments.

General Motors is using magnet wire with layered enamel in production electric vehicles to improve motor power to weight ratio, and improve reliability. I suspect everyone is doing the same.

In general an insulator has a higher breakdown voltage for a short duration, but there will be a gradual decline in breakdown as exposures increase in duration, and/or total exposure time increases.

.
 
gar said:
171230-1930 EST

mbrooke:

If you had used one single layer of enamel 0.000,6" thick the breakdown might have been only 1500 V/mil or about 900 V for the total thickness of 0.000,6".

This general concept is from reading and presentations. I have not directly run the experiments.

General Motors is using magnet wire with layered enamel in production electric vehicles to improve motor power to weight ratio, and improve reliability. I suspect everyone is doing the same.

In general an insulator has a higher breakdown voltage for a short duration, but there will be a gradual decline in breakdown as exposures increase in duration, and/or total exposure time increases.

.
Click to expand...


In other words more layers mean a higher break down voltage?
 
My AHJ would have had something to say


But i digress, the painters that spray will usually get anything exposed

So i've adopted another strategy

I don't make my box conductors up anymore. I'll use the spent sheathing to cover and mark what they are with a sharpie

Then i'll roll them up sharpie print in

That seems to work ,at least for me

~RJ~
 
171231-0951 EST

mbrooke:

If you take a fixed space (thickness) and fill it solid with an insulating material and measure the breakdown voltage, then change to filling this same space with multiple layers of the same material the breakdown voltage will increase. The increase in breakdown over a short time, or in the lifetime of adequate breakdown is apparently worth the extra work in some applications. Ordinary electrical work probably not.

The tensile strength, #/sq-in, of glass increases as the diameter is reduced. A similar characteristic.

.
 
gar said:
171231-0951 EST

mbrooke:

If you take a fixed space (thickness) and fill it solid with an insulating material and measure the breakdown voltage, then change to filling this same space with multiple layers of the same material the breakdown voltage will increase. The increase in breakdown over a short time, or in the lifetime of adequate breakdown is apparently worth the extra work in some applications. Ordinary electrical work probably not.

The tensile strength, #/sq-in, of glass increases as the diameter is reduced. A similar characteristic.

.
Click to expand...


Is this why insulator on power lines are all wavy and saucer like?
 
171231-1159 EST

mbrooke:

Power line insulators are wavy or saucer like to increase the over the surface distance. Breakdown over a surface is usually lower than within air, and air breakdown is generally lower than within an insulator.

Breakdown in air is greatly dependent upon air pressure, and ionizing radiation.

.
 
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