What is this 1960's cable insulation made of?

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ces

ces

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This aluminum cable is one of many we will be insulation-testing next week in a 5 story office building built in 1969. If any cables fail we will have to replace the cable, we are already replacing the main switchboard, all panelboards and 480-120/208V transformers.
The building has 3 dual cable-risers (480 and 208V) using these ancient conductors with numerous splices/kerneys on each floor. When we test I expect to leave all conductors in place unless we have to disconnect -for example the transformer secondaries which have no disconnects.
I should add that the intent is for the building to last another 25 years, not 50, and our budget for the replacement of the electrical distribution system is already committed to. Whether or not these cables hold up is a BIG DEAL.

My question is - what is this cable? The AL is very light weight the conductors flex/bounce a lot more than modern AL conductors.

My first concern is whether it will pass or fail insulation testing. I've been reading about this all day on this Great Forum and so far conclude that I should test the 480V at 500V and the 208V at 250V and not double these voltages which could reduce readings, and take 30sec and 60sec readings. There have been a number of faults in transformer and distribution boards leaving carbon dust in this equipment. Should we attempt to clean this (vacuum, compressed air etc?) if we get low readings? I assume the carbon could be a contaminant effecting readings.

My next concern is that if we pull these conductors out of switchboards & panelboards and replace the switchboards and panels by the time we re-terminate will this insulation be compromised, or with proper care will we be able to reterminate? Perhaps we tape or cables before touching them?

I should add I don't pull wires for a living I just size them on paper ... but I do have some responsibility for making sure we get this building tested in a one-day shutdown, for establishing test parameters and interpreting the test results, and for designing a new distribution system to cost effectively reuse existing wiring.

Any and all comments appreciated -Gary
 
They have the appearance of craft-paper, rubber, cloth and cambric, an may not be listed in the insulation tables of the NEC any longer. As far as testing them there a few megger aficionados to you may get more accurate responses from here on the forum, that often frequent other rooms like say the NEC forum - title it "megger this..." and I'm sure they will be drawn like cats to a fish shack.
 
I'm surprised to hear that it's actually aluminum. It looks like old tinned copper RH or RHW conductors not aluminum.
 
infinity said:
I'm surprised to hear that it's actually aluminum. It looks like old tinned copper RH or RHW conductors not aluminum.
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I'm pretty sure it is RH, but the aluminum thing does have me puzzled too. During that time period, I've never seen aluminum nor have I seen tinned copper in that big of a gauge during that time. I guess it is aluminum, but a few years before I'd expect to see it. I guess this was a cutting-edge install during its time
 
Per ANSI and NETA standars 600V rated (What you are caling 480V) should be tested at a minimum of 1000VDC for 60 seconds and should be at least 100M (Temperature corrected of course). Based on your pics I dont think you are going to have a big problem.

P.S. I stock those same breakers you are replacing.
 
I'm sure I've seen tinned copper that big and with that type of insulation, but, I can't

recall seeing alum. with that insulation.
 
If it is aluminum I think a thermal scan under full load would be more usefull than a megger of old varnished cambric insulation. I also suspect it is really tinned copper . Brian feel free to chime in any time now. It is much more likely that a termination point will fail than for a cable to have an insulation failure probably 1000 to 1 ratio or higher
 
quogueelectric said:
If it is aluminum I think a thermal scan under full load would be more usefull than a megger of old varnished cambric insulation. I also suspect it is really tinned copper . Brian feel free to chime in any time now. It is much more likely that a termination point will fail than for a cable to have an insulation failure probably 1000 to 1 ratio or higher
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Although I welcome Brian's response, you just spoke his words for him, and never gave hime the chance:grin:
 
Stitch in Time pg16 indicates 500V DC test voltage on 480V is 'commonly used ...for routine maintenance' You are saying to go 1000V. In another post someone quoted 2007 NETA 7.3.2 that says 1000VDC also. This is a US Govt. building I then expect NETA will apply. Thanks for pointing this out as it has taken a lot to just get a one-day saturday shutdown it appears a 500VDC would be have been voidable test.
I understand NETA 7.3.2.2 says. "Perform insulation-resistance test on each conductor with respect to ground and adjacent conductors. Applied potential shall be 500 volts dc for 300 volt rated cable and 1000 volts dc for 600 volt rated cable. Test duration shall be one minute."
About the adjacent conductors ... does this mean test each phase to each other phase plus neutral and ground -all individually or combined? I ask because Stitch in Time pg.31 fig.17 shows one of 3 current carrying conductors being tested against one other plus to ground suggesting that the conductor under test is being tested against multiple conductors. Page 51 fig.25b goes as far as to state "other conductors connected together and to sheath" but same as fig.17 in the picture it omits one conductor from the combining.
Combining phases B, C plus neutral and ground to test phase A would be tricky using test probes (does Fluke make a 4/0 aligator clip?) especially as we plan to isolate cables only by operating circuit breakers at the source and panelboards where the taps land on panelboard main breakers.
I know of one large electrical contracting firm that only tests one cable against one other conductor or ground at a time, but I have seen this combing requirement elesewhere in this Forum.
 
This has been a long running debate. It makes no difference on the working voltage of the wiring. Insulation testing is done and compared to the insulation value of the cable itself. It doesn't matter what voltage the wiring is used at, it matters what the cable/wiring is rated at.
 
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quogueelectric said:
If it is aluminum I think a thermal scan under full load would be more usefull than a megger of old varnished cambric insulation. I also suspect it is really tinned copper . Brian feel free to chime in any time now. It is much more likely that a termination point will fail than for a cable to have an insulation failure probably 1000 to 1 ratio or higher
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Completely agreed. In this case we are replacing all breakers/terminations and are instructed to megger cables and replace if any conductor fails.
 
I have seen a lot of tinned copper of that size and insulation. My area had a building boom in the '60's due to the space program and a lot of our schools were either built or renovated at that time, and almost all of them are wired with RHH tinned copper. The only problem I have ever had were under ground or under slab runs, that stuff doesn't like moisture.
 
mdshunk said:
I have too, but this is 1969. You ever seen tinned copper from that late?
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i was working in the technicolor processing facility in hollywood before
they outsourced film processing to china, and there's a ton of tinned copper
up to 500 mcm in that place, with braided covering....with thermoplastic
insulation under it... call it type TW, but the braided cover, some of it was
cotton, and some of it was asbestos.... :-((( (we had it tested)

it was circa late 1960's.

i'd be careful about disturbing it... :smile:

as for meggering it, zog is of course correct on voltage, duration, and
resistance, but i think i'd try a test or two at closer to the working voltage
before i gave it the big zot!... no reason to create a short that leaves the
system unuseable.... if i got good readings on the lower voltage, then i'd
give the full voltage test.... if i got iffy readings..... well, time to reconsider.

like zog says, you're prolly gonna be fine.... i've seen 34.5 kv stuff with
carbon tracks all over the bus, and it meggered fine at 5 kv, and hipotted
fine at 50 kv, carbon tracks and all....


randy
 
76nemo said:
Although I welcome Brian's response, you just spoke his words for him, and never gave hime the chance:grin:
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I never speak for Brian or anybody else here. I was just looking for a little backup in case of any cow clubbling that might ensue from my most thickheaded opinions. As I THINK Brian is a big fan of the thermal imaging as preventative measures to protect the insulation from catastrophic failure. He is much more the expert on the subject than I am and I would also welcome any responses as such.
 
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