what is this wire type?

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frank112

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I have been working in an old building, I'm guessing maybe 50 or 60 years old, but that is just a guess. I came across a wire type that I'm not familiar with. The conductor itself appears to be copper with a tin or lead coating, but is clearly copper inside when cut. The insulation is a layer of rubber(?) , then a fabric layer which covered by what feels like tar(?), I'm not sure exactly what it is. Anyone know what this is? I need to determine it's ampacity. There are no markings and looks like #6
 
These conductors are in a raceway, feeding a subpanel, they are not weathered, as they are in good condition. I have seen this wire before so it's fairly common in old commercial buildings, I just don't know how to rate it. I thought it might be copper clad, but its definitely copper when scraped with a knife
 
old Copper wire was tinned when it came with cotton coated rubber insulation.

the copper would draw the moisture from the rubber and dry it out. creating a brittle material and reducing the insulation value. .



It is very common in old rubber covered conductors.

Charlie
 
Tinned copper conductors used to be common. I guess it goes back to when connections were soldered and the tinning helped make a better joint. I remember Anacondas "durasheath" brand had tinned conductors and the RHW insulation was so thick you could only get 4 No. 12's in a 3/4" RMC
 
electricman2 said:
Tinned copper conductors used to be common. I guess it goes back to when connections were soldered and the tinning helped make a better joint. I remember Anacondas "durasheath" brand had tinned conductors and the RHW insulation was so thick you could only get 4 No. 12's in a 3/4" RMC
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Well now that you mention it most of the original installs were soldered but believe it or not the solder technique was before my time.

there still a lot of it in Boston.

The tinning was applied mostly to prevent the degradation of the rubber. There was a lot of stuff applied to the cotton braid, asphalt or tar and sometimes wax.

edit for spelling

Charlie
 
I agree with Charlie, we still have a lot of old rubber insulated wire around here. The purpose of the tin was to keep the rubber from reacting with the copper. However, I find it hard to believe that this old stuff was ever rated for 75 degrees C.
 
infinity said:
I find it hard to believe that this old stuff was ever rated for 75 degrees C.
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RHW is still in the tables in the 75?C column.:)
 
al hildenbrand said:
RHW is still in the tables in the 75?C column.:)
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I was just looking at that. I'm still kind of shocked that 75 degree C wire was around 50-75 years ago. Could the old stuff be a different insulation type? Maybe RW if there ever was such a thing?
 
From the 1959 NEC Table 310-2(a). Conductor Applications.

Code Rubber R 60?C Dry locations
Heat Resistant Rubber RH 75?C Dry locations
Heat Resistant Rubber RHH 90?C Dry locations
Moisture Resistant Rubber RW 60?C Dry and wet locations
Moisture and Heat Resistant Rubber RH-RW 60?C Dry and wet locations
Moisture and Heat Resistant Rubber RH-RW 75?C Dry locations
Moisture and Heat Resistant Rubber RHW 75?C Dry and wet locations.
 
I was pulling this stuff of my house , yes its 60C core rubber. beleive or not that same core rubber compound was also used on wood floors in the 1940's and of couse for wiring. they would lay this core rubber down by the bucket on the cement floors then brush this stuff on it too hold the floor down. its was used for lots of other applications also. sewer pipe, floors. wiringing, and get this. also used for runway drain pipes in WW2. when they had to build a runway very fast. they would make the pipe of of a cardboard type material. the apply this compound over it. and presto. drain pipe.
It was a do all compound for every thing. now we have plastic.
 
iwire said:
Regardless of what it may have been rated for if I was considering reusing it I would treat it as 60 C.
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A safe bet. Most of the time it is hard to expose an undisturbed, ledgible portion of the insulation to be able to read the marking.
 
Doesn't the NEC require you to default to 60 deg C, unless you know for sure it's something else?

I know FPN (1) of 310.15(B) talks about temperature compatability, with equipment and connections.

I would think that at that age, the equipment connected are probably not rated for anytinh higher then 60 deg c.
 
al hildenbrand said:
From the 1959 NEC Table 310-2(a). Conductor Applications.

Code Rubber R 60?C Dry locations
Heat Resistant Rubber RH 75?C Dry locations
Heat Resistant Rubber RHH 90?C Dry locations
Moisture Resistant Rubber RW 60?C Dry and wet locations
Moisture and Heat Resistant Rubber RH-RW 60?C Dry and wet locations
Moisture and Heat Resistant Rubber RH-RW 75?C Dry locations
Moisture and Heat Resistant Rubber RHW 75?C Dry and wet locations.
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Thanks for posting that Al. I thought that the old stuff I ripped out on occasion over the years was RW.
 
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