Is 62 - Year Old Building Wire Still Good?

Ravenvalor

Senior Member
Hello,

I have a customer who has a house built in 1959. The original meterbase/panel combo is about 25' away from the basement where the original fuse panel is. The meterbase/panel combo feeds the fuse panel with a 100-amp circuit composed of building wire pulled in EMT. The total run is about about 60'. Does anyone have an idea as to what condition this wire might be in? I would like to replace the fuse panel with a breaker panel and use this existing feeder.

Thank you,
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Is the wire type TW which is insulated with PVC or does it use a rubber compound? If it's TW then I'd leave it in place unless it shows signs of leaching out an oily plasticizer. Of course this is just my opinion.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I have had experiences where it was impossible to pull the conductors out of the conduit because they were the rubber with a cloth jacket. I guess it depends on whether they push the wire thru each section of conduit as they installed it or if they did it as a complete run as they should have. The wire is probably fine unless there was too much heat on the service but I would change it if possible
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
If it's in EMT likely sources of damage (rodents) probably didn't happen. I would though look for any obvious signs of heating of conductors.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Engineering
Is there even 100 amps of load there?
I'd use it back and put a 70 amp feeder breaker in the meter base/panel combo or is it fused too?
 

Russs57

Senior Member
Why guess when you can do a visual inspection and take megger readings.

If the wire isn't dripping stuff and copper turning green, if the terminations show no signs of overheating, and if the megs fine I wouldn't think twice about reusing it. In fact I might even feel it was better quality copper than what I can buy today.

What "megs fine" means is open for debate. I often see the plastic/phenolic parts of the panel/switch gear meg worse than the wire but usally those parts aren't checked. I'll also admit to running a 750KW, 480 volt generator for years after a hurricane when it megged as low as 1 meg. We solvent washed it and baked it out, kept a heater jacket on it, etc. After about five years it finally stayed at acceptable values.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I think you need to do a good visual inspection of the wiring and possibly megger it and see what happens. However if you can pull it through the EMT it might be more cost effective not to bother to megger it and just replace it if you can. A 60-ft run would be about 200-ft of conductor and I'll bet that will cost you less than the time it would take you to properly do an insulation resistance test.

I Don't see any real use to reducing the overcurrent protection device rating. Either the wiring is good or it doesn't. I don't see that reducing the OCPD rating changes that any.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
I have had experiences where it was impossible to pull the conductors out of the conduit because they were the rubber with a cloth jacket. I guess it depends on whether they push the wire thru each section of conduit as they installed it or if they did it as a complete run as they should have. The wire is probably fine unless there was too much heat on the service but I would change it if possible
Same. Sometimes the rubber literally melts to the conduit walls.

Sent from my BE2028 using Tapatalk
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
I'll bet that will cost you less than the time it would take you to properly do an insulation resistance test..
The 500-1kv industry standard Megger test may not be appropriate here, just to check for dielectric loss from condensation accumulation in the raceway.

Can anyone advise why not just a 60-second Megger at operating voltage, where equipment was not subject to thermal limits & continuous use? Its quick & easy with OCP open and terminations kept in place.

..I would like to replace the fuse panel with a breaker panel and use this existing feeder.

I believe the issue is some remodel contractors & panel flippers don't have any use for fancy testers like a Megger.

Much less Meter spots & inspectors that red tag 100A service / feeders on 200A upgrades.
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
60-second Megger at operating voltage
LOL, that is not a megger test btw...
That would be ok if tested immersed in salt water -- mom's 109 YO linen wiring had cracked insulation in numerous places. Would pass a dry 120 Vac operating voltage /megger/. If dry and you want a decent test for dry conditions, , do it at 1500 Vac.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
..If dry and you want a decent test for dry conditions, , do it at 1500 Vac.
I'm having visions of a 1500vac destructive-test weapon, blasting existing rubber cheese cloth or other 600vac wire, to prove new work is needed.

Yes, I see the business argument for captivating clients, if you arrived in the nick of time to prevent a fire.

If they refuse to sign your contract, or attempt competitive bids, they're left with blasted wire & bolted faults where an old, but working service used to be.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
60-second Megger at operating voltage
LOL, that is not a megger test btw...
That would be ok if tested immersed in salt water

Would you agree, a 1-second 100v Megger reading shows bolted faults where continuity testers do not?
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I know prices are high right now, but I would never consider looking for reasons to leave 60+ year old wiring and conduit in place on a service change.

I have some in my scrap pile that's about the same age. The insulation on the conductors has swelled so much, they are impossible to pull out. The scary part is that everything in my scrap pile was in service and conducting electricity 'just fine' when it was pulled out.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Same. Sometimes the rubber literally melts to the conduit walls.

Sent from my BE2028 using Tapatalk
Yep, or it’s just that it grabs the walls enough that the force of puling it snaps the wire somewhere deep in the conduit run, then you end up ripping open walls to find it and have to do a lot of drywall repairs... Been there.

I vote for doing a megger test on it and if it’s good, leave it alone.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
No. You should be able to find a bolted fault with about anything. The constant fuse clearing would be the first indication.

While line-voltage, or dry Megger readings may not check most insulation integrity, much less help existing conductors too small for upgraded services, sometimes a diagnostic service call only needs Ohms law.

Using Ohms law to solve for current V/R, with 100v Megger readings <= 17kOhm is within 6mA trip range of GFCI's. Except for surge protectors shunting to EGC, I usually remove appliances <=1 megaohm H-G, before resetting the GFCI.

Brief 100v Megger readings H-G can see end-of-service life for equipment that continuity testers can not.
 
Last edited:

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
While line-voltage, or dry Megger readings may not check most insulation integrity, much less help existing conductors too small for upgraded services, sometimes a diagnostic service call only needs Ohms law.

Using Ohms law to solve for current V/R, with 100v Megger readings <= 17kOhm is within 6mA trip range of GFCI's. Except for surge protectors shunting to EGC, I usually remove appliances <=1 megaohm H-G, before resetting the GFCI.

Brief 100v Megger readings H-G can see end-of-service life for equipment that continuity testers can not.
A bolted fault is just that. Bolted.
 
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