So can pitch undergo chemical changes which make it start to melt at room temperatures?
Leaking sealant around cutout
- Thread starter Maxatoria
- Start date
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Chemical change is possible.
More likely the pitch initially in contact with warm conductors softened and expanded due to heat while the outer surface of the pitch in contact with the metal case remains cool and solid. Some of the warm and expanded pitch trapped by the rigid outler layers forces its way out. This could create a void between conductors and remaining pitch. The void reduces thermal conduction from warm ( hot ) conductor and remaining pitch. The rate of escape reduces even though the conductors are still when under high current getting warm / hot / overheating while the casing remains cool.
More likely the pitch initially in contact with warm conductors softened and expanded due to heat while the outer surface of the pitch in contact with the metal case remains cool and solid. Some of the warm and expanded pitch trapped by the rigid outler layers forces its way out. This could create a void between conductors and remaining pitch. The void reduces thermal conduction from warm ( hot ) conductor and remaining pitch. The rate of escape reduces even though the conductors are still when under high current getting warm / hot / overheating while the casing remains cool.
The stuff generally used has a low melting point and is a "soft" set so never gets really hard and brittle, it can then over the years start oozing out without there being any heat above ambient.
In some cases where the cable runs downhill to the cutout (cellars, houses on hillsides where the road is higher than the house) the oil in the paper insulation can migrate under gravity and start to run out of cut-outs, often melting the compound so a sticky mess ensues
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It won't actually be PME as the cable will be a two core paper insulated lead type which is what we call SNE (seperate neutral earth) and the system is designed in such a way that the lead provides the earth and is earthed at the substation and the neutral conductor is just that, neutral. On modern systems, there is three core cables with a combined earth neutral conductor which is earthed in multiple places hence PME.
This doesn't mean that you can't have an earth, it just means that the EFLI will need testing and if in limits, they will provide you with an earth off the lead sheath.
Since my mum doesn't care about what particular type of earthing it is so long as it works and doesn't fancy paying for someone to come and fix the board from TT to a DNO supplied earth as she had the enture house rewired about 5 years ago so everything should be fine
obviosly if the DNO wants to move her off TT and onto their earth and are willing to pay for it she'll have it but she can't be bothered to fix what isn't broke
obviosly if the DNO wants to move her off TT and onto their earth and are willing to pay for it she'll have it but she can't be bothered to fix what isn't broke
Only if the individual DNO allows it, we don't
It's not up to the DNO but is the customer's resposibility[/b]
As a kid (some 50 odd years ago) I remember seeing in the Science museum a large glass conical funnel into which a cube of tar had been placed, presumably some time before I was born. When I visited it the tar had started to 'dribble' down the neck of the funnel, so I think that under the force of gravity it will eventually flow albeit slowly even at room temperatures.
It's still there (well,was pretty recently), and continues to 'dribble'.
ISTR that glass theoretically also 'flows' under gravity in a similar manner, but one might need longer observation periods than a human lifetime to see it flow very far!
Kind Regards, John
It would seem that glass 'flowing' is just folklore
http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass
http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass
How come old telescopes still work? If the glass had flowed even the tinyest amount, they would stop working.
That's one of the examples quoted in the wikipedia, but telescopes have only been around for a few hundred years. The suggestions I've seen are in relation to very small amounts of flow over tens of thousands or hundreds of thosands of years!
Kind Regards, John.
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