I am so bad about long posts and I know it, but I have to do this after what happened today.
By now, you all probably know that I am a real stickler about doing outside cabling correctly. Much of it is kind of a no-brainer, but the protector is the most important part of the equation.
There are lots of manufacturers that make 66 or 110 block "protectors". They are less-expensive, involve little knowledge other than color code, and they are generally easy to install.
Typically, they involve a split block, where the input pairs are on the left side and the output pairs are on the right side. Makes perfect sense, but they aren't TRUE protection. Here are a few issues:
1. Many "icky-pic" cable compounds are flammable and therefore their terminations must be either outdoors or contained within a fire-retardant splice case. In the latter, the "icky-pic" is spliced to an air-core cable feeding into the protector. To simply punch down "icky-pick" cable on a block indoors is in a word dangerous. If something goes wrong and there is heat, spark or flame, the block could catch fire. Not to mention that once "icky-pic" is on a block, it's there forever. It will be a mess, no matter how good of a job you do cleaning it.
2. Simple "punch-down" 66 block protectors do not provide nearly the protection levels that are required in the real world. Think about it; you have a split block where the input cable comes in, goes through the protectors, then leaves on the right side. On a typical split block, the clips are less than 1/4" apart. 1/4" separation during a lightning surge? Since lightning takes the path of least resistance, why would it choose to go up, through protector modules, then back down to the output side of the block? Of course it's not going to do that. It's going to jump across to the adjacent pins on the block. Kind of common sense when you think about it.
3. Let's face it: Most interconnect companies are not equipped properly to install and support outside plant installations. If a protector module fails on one of these blocks, will they have replacements on the truck? NO. Will they go to the supply house and buy a replacement module? NO. Will the local supply house (if there is one) have them on the shelf for purchase? Probably not.
What will happen? The technician will bridge the input and output pairs across the block. If it's a block that doesn't permit this by using bridge clips, they will pull and splice the pairs to restore service.
NOW, here's what "real" protectors are and why:
1. There's always a chance that an aerial or underground cable can be crossed with high-voltage power. This usually happens when someone digs without having cables located. Basic protectors are designed to protect against surges or lightning, something that occurs within a fraction of a second. Anything more than that and the basic protector doesn't do much of anything except burst into flames or blow apart.
2. "REAL" protectors include an intentional "weak link" to protect against maintained faults (contact with high voltage).
Imagine that I am using a backhoe to trench a pipe line. In one dig, I cut through a 7,200 volt power line and a telephone cable at the same time with my bucket. I see sparks and immediately shut down the machine. Even if I am 100% alert and able to react, it still took me 10 seconds (at best) to remove the bucket causing the cables to be crossed. In that ten seconds, the telephone cable, possibly all pairs, were energized at 7,200 volts.
Protector modules shunt excessive voltage to ground, they aren't designed to do this for more than a few seconds. That's were the design of the protector (building entrance terminal "BET" or protected entrance termial "PET") comes into play.
Real BET/PET's include a typical 26 gauge stub cable that intentionally reduces the size of the underound cable pairs. This must be at least two feet in length to have any effect. BET/PET's with stub cable entries have a mark on the jacket warning that the cable not be cut shorter that two feet. The "real" protectors that have punch-down or spliced input connections have this two feet of smaller-gauge wire built inside the unit.
True, if a maintained fault as mentioned here happens, the reduced-guage pair(s) will burn out and the entire protector will require replacement. Still, at least the building didn't burn down. The pair(s) simply burn "open".
3. Plug-in protector modules, regardless of the type, are only as good as the mounting assembly itself. Lightning and power crosses don't follow any rules or wiring diagrams. They get to ground as quickly as possible.
In summary:
Cheaper protectors are like buying used cars. They won't do the job as well as a new one might. Expect the customer to pay about $600.00 per 25 pair terminal for it to be done correctly. Remember that you have to provide the protected entrance terminal PLUS the plug-in modules, since the modules usually aren't included with the termial.
A #6 AWG grounding conductor must always be used for any protector over 25 pairs. In general, up to two pairs can be grounded with a #12, and up to six pairs can be grounded with a #10. Imagine twisting all of the individual stripped wires together; their combined total diameter should match or be smaller than the ground conductor.
There are a lot of items in our industry designed to make our job easier. With protection, if it's really easy, it is not right. If you don't truly understand this part of the industry, you are risking liability as a contractor. When in doubt, sub out the work to an outside plant contractor, they will work with you. If there are none listed in the local phone book, ask any electric, telephone or cable TV employee you see on the side of the road. Just about all utility companies use sub-contractors who don't need to advertise. They know how to do it correctly.
In closing, don't risk having a cheapo "protected" 66 block being blown off the wall. Do it right or don't do it at all.
We restored service to a site (at a state prison) recently where this occurred due to our competition (the low bidder) beating us out on a buried cable installation.
Glad to collect the money for the repair/replacement, but we lost the original installation job due to price. We were doing it right and what we replaced was done wrong.
Things that make you say HMMMMMMMMM.
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Ed
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How come there's always enough time to go back and fix it a second time?
