3. October 2011 18:36
Bursting a Bubble
Frankest of Frogs,
I need a written response to my inquiry. I will use your response as a basis to NOT inject #2 copper cable that was installed prior to 1970. My stance is that there has been an instance where this older cable has burst during injection due to loading and geometry changes and should be replaced. Your comments would help substantiate this claim.
Figure 9. Enlarged cross section of a cable, which burst at its tailored injection pressure (TIP). The cable was eccentric along a significant length. This photograph was taken 72 cm from the burst point. The minimum insulation thickness is less than the 4.19 mm minimum insulation thickness required by Table 4-7 of ICEA S-97-682-2004. Note that the strand-shield remains in intimate contact with the strands.
I’m not sure you will be able to use my comments to substantiate your claim. While you are exactly right that “… there has been an instance where this older cable burst during injection,” it is also true that about 9,999 cable segments of similar vintage have not burst during injection. Put another way, bursting cable has historically occurred in just 0.01% of injection cases – success is realized 99.99% of the time! There aren’t many things with that level of performance. And even for that single case, the burst occurred, because the cable was eccentric and did not meet the minimum insulation thickness requirements of Table 4-7 of ICEA S-97-682-2004 of 4.19 mm. This lonely case was described in some detail on Page 5 of ...
“Silicone Injection: Better with Pressure”
... presented in Subcommittee A of the Insulated Conductors Committee (ICC) on May 19, 2009. I have reproduced Figure 9 from that paper above.
Reliably yours (at least with four nines),
T. B. Frog