47 year feeders

[mshields]

Would be very interested in your collective opinion on this:

I am replacing a 47 year old indoor unit substation with a new outdoor pad mounted transformer AND new indoor main switchboard albeit in a different location for a 90,000 square foot, 4 story college dormitory. So in a not entirely atypical fashion, we will install the new switchboard, run new conduit to the old switchboard. When everything is ready to go with the new, the contractor will de-energize and gut the old switchboard leaving the shell as a junction point.

Now here's my question. I have two options at that point. 1. pull all of the feeders some of which must run hundreds of feet to the various panelboards in this facility and replace them with new in the same conduits OR 2. Splice new conductors to these 47 year old circuits within the shell of the old switchboard.

On the one hand, I am terrified at the unknown factor of directing the contractor to pull these out. What if there is rusting of the conduit and they're stuck. What if he damages them in the process and then we need to run an entirely new feeder and because of the construction, the new feeder would have to be exposed making the people in charge of the dormitories very unhappy.

I lean towards leaving the 47 year old conductors. Do you agree that this is the best of my two options here?

Thanks,

Mike

 

[jumper]

Hire a contractor qualified to test them and if okay, leave them and splice. If bad then replace.

 

[infinity]

I wonder how testing them today is going to ensure that they last another 20 years. If the conduits are in such poor condition that the feeders may not come out then it's possible that the feeders will fail sooner than later. I would pull them out.

 

[Coppersmith]

Yellow 77 injected in the pipes. Lots of it.

 

[GoldDigger]

If you suspect that there may be hardened waxy lube in the conduits, Polywater (TM) Cable Free (TM) dissolves that stuff and lubricates too.

 

[zbang]

I wonder how testing them today is going to ensure that they last another 20 years.

It won't, but neither will new wire guarantee that (it is likely that new wire will last a long time).

If the conduits are in such poor condition that the feeders may not come out then it's possible that the feeders will fail sooner than later. I would pull them out.

Nothing says they are in bad condition, they could be fine. And we've probably all seen 10 year old wire almost glued in place.

It's kind of a tossup to me-
Maybe you pull out good wire but mess up the pipes.
Maybe you leave tested-good wire and something fails in a year.

What's the cost to replace all the feeders? That's likely the determining factor.

 

[ramsy]

Hire a contractor qualified to test them and if okay, leave them and splice. If bad then replace.

Perhaps submit test report with indemnity notice of "No Warranty", stating failure of existing equip. can't be warranted.

Then attach 2 estimates to replace feeder & raceways:
1) Most efficiently designed cost, during remodel, and before feeder terminations.
2) Least efficient method of emergency repairs, after unforeseeable failures.

 

[Tony S]

Test the feeders first and then decide. I’ve put feeders from the 19940’s back in service with no problem, they are still in service.

 

[drktmplr12]

Hire a contractor qualified to test them and if okay, leave them and splice. If bad then replace.

My opinion:
Let the owner decide the acceptable level risk they want to take and advise them of the relative cost of both scenarios, as Tony S suggested.

I would at least have a third party do non destructive tests on the conductors and generate a report stating they can be reused. Test them before you do anything else to establish a baseline. Then test them when you are done. Submit both reports and let the design engineer determine that they are acceptable. Explicitly do not warranty the existing feeder conductors.

How much copper (or aluminum) to replace are we talking, relative to the entire project?

 

[Fulthrotl]

I lean towards leaving the 47 year old conductors. Do you agree that this is the best of my two options here?

Thanks,

Mike

i'd megger all the old feeders AT THEIR WORKING VOLTAGE FIRST,
to see what kind of resistances you are getting, phase to phase, and
phase to ground.

if it all looks good, megger at 1,000 volts. if it still looks good,
i'd hypress butt splices and cold shrink. and reuse them.

pulling them out, in my experience, isn't going to go well. IF you
can get them out at all. polywater makes a lube you pour into the
pipe WELL BEFORE attempting the removal. it'll soften up old wax
lube, etc. like a couple weeks or more before attempting.

something to consider is polywater will migrate thru the entire conduit system.
wonderful if it's an underground run. if it is overhead, expect a pail of the
crap draining into the gear. that doesn't always turn out well, either.

your big downside is damaging the existing stuff in place, rendering it
unusable, and irreplaceable if you can't pull it out. then you have an
exended interruption of service, while stuff is repiped.

 

[ramsy]

..if it all looks good, megger at 1,000 volts. ..

Who's responsible for destructive testing of 40yr old wire @ 1k volts if it was only listed for 600 volts.

 

[jumper]

Who's responsible for destructive testing of 40yr old wire @ 1k volts if it was only listed for 600 volts.

I thought insulation resting, megging, of LV cables was considered non-destructive.

Hi-potting of MV cables was the destructive test IIRC. IDK, MV cables and such are not in my scope of experience.

 

[ramsy]

I thought insulation resting, megging, of LV cables was considered non-destructive...

Ok, so would accidentally destructive be considered discovering a Potential Failure?

 

[Fulthrotl]

Who's responsible for destructive testing of 40yr old wire @ 1k volts if it was only listed for 600 volts.

600 volt insulation is commonly meggered at 1kv dc.

you can also set it for 500 volts. or anything else you like.