Ivan
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| posted on 30/10/14 at 10:14 AM |
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Any electrical engineers out there to help me?
Hi
I am looking at a guideline that gives the expected useful lives municipal electrical reticulation as follows:
Lines
Underground 25 - 45yrs
Overhead 20 - 30 yrs
Cables 25 - 45 yrs
What I don't understand is the difference between overhead lines and cables - based on the EUL I would guess that cables are the same as
underground lines but then why have two categories - or would it be equally correct to say that cable are the same as overhead lines?
There is no explanation of the differences in the guidelines.
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nick205
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| posted on 30/10/14 at 11:10 AM |
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I would read that as the life expectancy of the physical cable itself is 25-45 years.
When used in underground applications the life expectancy is unchanged.
When used in overhead applications (subject to weathering) the life expectancy is reduced to 20-30 years.
Either way 10 years seems a big margin!
Just my interpretation and I'm not qualified.
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v8kid
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| posted on 30/10/14 at 11:15 AM |
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Not sure i understand your terminology so here goes generally.
underground cables are insulated and protected with a waterproof and armored sheath. Generally they have a 50 year lifespan and faults anr invariamly
due to damage caused by excavations. Ulser cables had paper and oil insulation and were moisture sensitive so covered with a continuous lead sheath
whilst modern cables are plastic and at 415v at least are capable of operating with water running out od the cores ( I have seen this!)
Overhead lines are uninsulated and rely on the insulating properties of air to prevent flashover. that is why they are high to prevent touching  As
they are exposed to the elements they deteriorate (oxidize) asnd are subject to weather damage. there are various standards with various lifetimes. as
access is easier it is cost effective to design a shorter lifetime.
Overhead cables are insulated lines run overhead. they do not have to be separated to insulate them and are subject to the same weather conditions but
are less liable to corrosion.
There is more - but do you rewally want to know!
What is the context of your question and I can be more specific - voltage, location, operating company all make a difference.
Cheers1
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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Sporty
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| posted on 30/10/14 at 11:16 AM |
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Its a bit out of context but I think when they say cables they are referring to the cables of the overhead lines as opposed to the wood poles and
fittings.
Generally with overhead lines you refurbish them piecemeal so for example after maybe twenty years you would go through replacing fittings and some
poles but leaving the cables and some poles in place. Then after 40 years you would go along and do a complete rebuild.
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Ivan
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| posted on 30/10/14 at 02:56 PM |
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OK - thanks for the feedback guys - I spoke to one of my contacts in the electricity distribution industry and he informs me that cables are insulated
overhead lines and lines are uninsulated. Hence the difference in EUL.
So V8kid wins first prize. You can move to the front of the class. 
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