Moving 40 Year Old 480v Cables

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Ragin Cajun

Senior Member
Location
Upstate S.C.
Have another one for the forum.

Same client wants to move existing 40+ year old 3/C, 350 MCM power cables and re-route them to some new transfer switches.

I have serious concerns whether the cables will survive the physical bending, re-routing, moving around, etc. I fear the aged insulation will crack, etc. and fail upon re-energization.

Anyone on the forum have any hard experience here?

My experience has been such drastic movement cracks the insulation and we ran new cables to avoid the problems.

We are dealing with at least 18 cables with multiple moves. Critical process area that affects the whole plant and only a 6 day shutdown window. We're also looking at several hundred 480V terminations, splices, etc. all in the same electrical building!


Thanks!

RC
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am guessing that new cables would be somewhat expensive. The old cables have substantial salvage value which would tend tor educe the added cost to replace the cables.

Chances are that at least some of the cables will need repair or replacement anyway.

Is it possible to do some kind of survey in advance and make a guess as to what the extent of repair/replacement might need to be?

I have run into a fair number of 40+ year old wiring that were moved without being damaged so I am not convicted they all need replacement. Forty year old wiring is late 1960's era and the insulation on that vintage of wiring and cabling tends to be pretty modern.

If you were talking about 1940's and 1950's vintage wiring, I might be inclined to say it warrants ripping out, as the insulation on some of that stuff is pretty bad.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
More than anything else, it depends on the temperatures to which the cables were subjected during the past 40 years. You are in South Carolina, and it gets hot there. Heat will, in time, destroy a cable?s insulation system. 40 years is a reasonable lifetime. A cable should survive 40 years, provided that it was not overheated by excessive currents or by long periods of high ambient temperatures.

As a rule of thumb, if you increase the temperature of a conductor?s insulation system by 10 degrees Celsius, either by increasing ambient or by passing more current, and maintain that extra 10 degrees throughout the lifetime of the conductor, that change in temperature will reduce the useful lifetime by half. If on the other hand you reduce the temperature, and keep it lower, you will increase the useful lifetime. It is not a linear thing, so 10 degrees lower will not double the useful lifetime.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
As Charlie pointed out, life is very dependent on temperature. With that said, if this was my design, and my seal was going on it, the old cables are coming out and new ones are going in!

Our specifications do not even allow cable that has been pulled into a conduit, and then pulled out to be re-used, let alone after it's been used/abused for 40years.

As a minimum, the cables will need to be tested before moving, then after moving to compare test results. This if course does not guarantee long term use, only that the cable insulation was the same before and after.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The OP never said anything about pulling them out of an existing conduit and then into another conduit.

Why would they have pulled 3/C cables in a conduit in the first place??
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I think Kingpb was just giving a related example: No re-use of cables. If you pull cables out of a conduit, you replace them. I agree. The implication is that cables should not, in general, be re-used.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
I would also suggest replacement. I would tell the customer to use the old copper salvage to help offset the expense of the new conductors.

Roger
 

Ragin Cajun

Senior Member
Location
Upstate S.C.
petersonra said:
The OP never said anything about pulling them out of an existing conduit and then into another conduit.

Why would they have pulled 3/C cables in a conduit in the first place??

They went into an underground duct bank and on into cable trays! Couldn't see if they put both 3/C cables in one hole or two.

After 40+ years, I don't see pulling them out and reusing the same holes. They are likely glued in there! One thought was to install overhead cable trays. Many problems there, one was no time.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Ragin Cajun said:
They went into an underground duct bank and on into cable trays! Couldn't see if they put both 3/C cables in one hole or two.

After 40+ years, I don't see pulling them out and reusing the same holes. They are likely glued in there! One thought was to install overhead cable trays. Many problems there, one was no time.

I suspect you are right. Getting them out of the UG duct banks probably will cause significant insulation damage. I was thinking cable trays because your OP said cables. It may actually be more cost effective to abandon them in place, rather then try and yank them out, especially if the UG segment if relatively short.

You might be able to reuse the stuff that is in the cable trays though. In some ways it depends a lot on just how much cable you are talking about and how much fooling around it takes to get it out of the trays.
 

foqnc

Member
My 2 cents...
With such a small shut down window, do you want to take the chance on moving them, re-terminating only to find some are at fault, and you now have less time to replace them.
How much money will the plant lose if they are not up and running in 6 days? Surely this would justify paying for replacement, as a piece of mind.
Also, if you replace, is it possible to try and remove the old ones after the plant is up and running and salvage to re-coup some money?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
foqnc said:
My 2 cents...
With such a small shut down window, do you want to take the chance on moving them, re-terminating only to find some are at fault, and you now have less time to replace them.
How much money will the plant lose if they are not up and running in 6 days? Surely this would justify paying for replacement, as a piece of mind.
Also, if you replace, is it possible to try and remove the old ones after the plant is up and running and salvage to re-coup some money?

Good point about the shutdown window. Might be worthwhile from that perspective to run all new ahead of time and just do the terminations during the shutdown. Then pull out the old stuff if it is worth the effort after you are back up and running.
 
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