Insulating Material Property Question

[Rileyesi]

First, thanks to all who replied to my request for sources for insulating
washers.

One vendor quoted me PVC washers as opposed to the linen based phenolic washers
that we have used in the past, but they could not tell me the difference it
would make in the insulating properties. I hope someone can shed some light on
this for me.

The application is in an office environment, so no temperature or humidity
extremes. The signal that will be insulated is a variable 0-15 VDC at 100 mA
max. This will be used on the back of an analog panel meter and the function
of the washers is to isolate the signal from the metal meter case.

I think the PVC will do just fine, but would like any thoughts the group may
have.

Thanks.

 

[Tim Wescott]

First, thanks to all who replied to my request for sources for insulating
washers.

One vendor quoted me PVC washers as opposed to the linen based phenolic washers
that we have used in the past, but they could not tell me the difference it
would make in the insulating properties. I hope someone can shed some light on
this for me.

The application is in an office environment, so no temperature or humidity
extremes. The signal that will be insulated is a variable 0-15 VDC at 100 mA
max. This will be used on the back of an analog panel meter and the function
of the washers is to isolate the signal from the metal meter case.

I think the PVC will do just fine, but would like any thoughts the group may
have.

Thanks.

Electrically it probably won't make a difference, but there may be
mechanical issues. I know that nylon hardware has a reputation of
creeping under temperature and vibration, but even there a washer was
considered OK.

 

[John Larkin]

First, thanks to all who replied to my request for sources for insulating
washers.

One vendor quoted me PVC washers as opposed to the linen based phenolic washers
that we have used in the past, but they could not tell me the difference it
would make in the insulating properties. I hope someone can shed some light on
this for me.

The application is in an office environment, so no temperature or humidity
extremes. The signal that will be insulated is a variable 0-15 VDC at 100 mA
max. This will be used on the back of an analog panel meter and the function
of the washers is to isolate the signal from the metal meter case.

I think the PVC will do just fine, but would like any thoughts the group may
have.

Thanks.

PVC is not generally used as an insulator under pressure. It's soft,
melts easily, makes toxics when it burns, and may cold-flow. The
cheapest insulator is probably "fish paper", a phenolic or something
laminated fabric that punches well. You can buy sheets of it at most
auto-parts stores to see what it's like.

Have you looked for a standard part, Keystone or somebody?

John

 

[Active8]

humidity

are you sure? Inside a PC chassis in an office can be pretty hot for
example, especially when the chassis is in a cupboard - 70 degrees!
(cupboard to prevent idiots from physically switching server off.
ventilation added later)


well put. Not only does it outgas toxic things, but corrosive ones too - I
used to work for an AC drive manufacturer that made large drives (400kW+)
with many crimped connections, and they found that crimp reliability was
greatly improved by changing away from PVC insulation - warming the
insulation to 60-70 degrees C softens it and increases outgassing of
chlorine compounds (dont know exact chemistry)

I think it's HCl

 

[R.Legg]

First, thanks to all who replied to my request for sources for insulating
washers.

One vendor quoted me PVC washers as opposed to the linen based phenolic washers
that we have used in the past, but they could not tell me the difference it
would make in the insulating properties. I hope someone can shed some light on
this for me.

The application is in an office environment, so no temperature or humidity
extremes. The signal that will be insulated is a variable 0-15 VDC at 100 mA
max. This will be used on the back of an analog panel meter and the function
of the washers is to isolate the signal from the metal meter case.

I think the PVC will do just fine, but would like any thoughts the group may
have.

Normally you'd want something with a recognized temperature or
flamability index. PVC is for low temperatures.

Normal plastics query at UL seems to be unavailable through the normal
web link;
http://data.ul.com/ULiQ_Link/index.asp

RL

 

[Terry Given]

humidity

are you sure? Inside a PC chassis in an office can be pretty hot for
example, especially when the chassis is in a cupboard - 70 degrees!
(cupboard to prevent idiots from physically switching server off.
ventilation added later)

PVC is not generally used as an insulator under pressure. It's soft,
melts easily, makes toxics when it burns, and may cold-flow. The
cheapest insulator is probably "fish paper", a phenolic or something
laminated fabric that punches well. You can buy sheets of it at most
auto-parts stores to see what it's like.

well put. Not only does it outgas toxic things, but corrosive ones too - I
used to work for an AC drive manufacturer that made large drives (400kW+)
with many crimped connections, and they found that crimp reliability was
greatly improved by changing away from PVC insulation - warming the
insulation to 60-70 degrees C softens it and increases outgassing of
chlorine compounds (dont know exact chemistry) which attack the exposed
copper in the crimp joint, increasing resistance and hence
temperature.....changed cable to RADOX (x-linked polymer sheathing) which is
rated at 125C and joint reliability increased significantly (calibrating
crimpers daily, too)

(Ultimately this was all replaced with large aluminium plates and a 1mm
nomex spacer, greatly reducing ESR and ESL, and eliminating almost all
crimped connections)

 

[Terry Given]

I think it's HCl

probably. It certainly eats copper!