Insulation breakdown of a Conduit?

[FaradayFF]

Hi Guys,
Are the non-conductive conduits, such as PVC, need to have a stated rating for maximum voltage withstand? I know they are not typically Meggered, just an application came up where this spec may be necessary.
Regards,
EE

 

[ActionDave]

PVC is being used to protect conductors not insulate them so I don't think there is any voltage rating on it.

 

[paulengr]

Hi Guys,
Are the non-conductive conduits, such as PVC, need to have a stated rating for maximum voltage withstand? I know they are not typically Meggered, just an application came up where this spec may be necessary.
Regards,
EE

I don’t recall any insulation rating so depending on fillers used insulation resistance can vary. When building some home made moisture sensors years ago (home made Megger) I found a log of so-called insulators weren’t very insulative. Unless it was say rubber blankets most weren’t very insulating.

 

[roger]

I agree with Dave and I know POCO's use PVC for MV cables quite often.

Roger

 

[drcampbell]

... [A lot] of so-called insulators weren’t very insulative. ...

Many plastics, rubbers and other polymers are conductive, often deliberately so.
There are conductive shoes available for static-sensitive environments, and tires are conductive to drain away any static charge that might be on the vehicle body when you pull up to a filling station. (I can't think of a much worse place for a static-electricity spark than between an open filler neck and a gasoline-dispenser nozzle)

 

[ramsy]

Now I see why gas stations post signs prohibiting cellphone use, and pipe everything in GRC. Perhaps a properly bonded metallic conduit conducts static charge buildup before a critical mass charge can develop lighting strikes.

Static discharge in this dry California climate destroyed my phone chargers, until the carpet, polyester sheets, blankets, & bath robe was removed & replaced with natural fibers.

Nose bleeds also stopped shortly after removing most static sources, albeit a coincidence.

 

[drcampbell]

Could have been allergens and not a coincidence.

 

[Jraef]

Dielectric strength is a way of measuring the ability of a material to insulate (block conduction) and is usually measured in kV per mm of thickness.

PVC, with added "plasticizers to make it flexible, is the insulation material used on a lot of LV building wire like THHN, and is also used in some MV wire. The minimum dielectric strength of PVC wire insulation is 10kV/mm, the maximum is 30kV/mm. Hard PVC (no plasticizers) as is used in conduit has the same minimum, but a higher maximum, 40kV/mm.

Dielectric Strength: Unit, Formula & Test Methods of Materials

Learn what is dielectric strength? Understand its various testing methods, units, formula and factors affecting strength & dielectric breakdown voltage.

omnexus.specialchem.com