Trenching cable for surveillance is surprisingly complex. While using shovels, picks, and hoes is not advanced technology, the proper planning, construction, and execution of trenched cable runs is underestimated.
I am really glad that chart was referenced on burial depths. Everytime I have a conversation with someone about trenching, they always say it is low voltage, it doesn't have to be buried that deep. I always ask wherein the NEC does it say that and I get a shrug.
I know that chart well as we went over it a ton while prepping for the state test
This is a great article. However I have a different understanding for burying low voltage cable and fiber optics. I hope someone might be able to clarify. We have been involved in several projects with extensive trenching (several miles). My understanding is that the NEC doesn't even use the term low voltage anywhere. Instead, it uses the term limited energy. Limited Energy would fall under Article 725 class 2 circuit. My understanding is there is no depth requirement for these circuits. This is why if you do a lot of trenching you will often find utility companies like AT&T and Comcast have their cables buried without conduit at depths of only a few inches instead of 24 inches under cover.
First, the disclaimer: That particular objection gets well beyond installation work, and typically is for AHJs to define. I suspect many areas firmly define NEC as applicable to security work, but some areas may not. Our post covers typical interpretations in most areas.
Interestingly, NEC's Section 725 circuits does not generally apply to life/safety and security systems but other 'power limited' systems like landscaping lights and cable/satellite TV networks. (Section 725-1 further defines applicability for circuits where they "are not an integral part of a device or appliance" for safe operation). This is why ATT and Comcast do not consider the NEC applies to them.
I'm not sure how 'integral' is defined, but in as far as the expected life/safety function of the security system will be disrupted without them, cables should be protected as much as possible and buried to the full depths addressed elsewhere.
Historically, companies who are registered as regulated utilities have been exempt from many provisions of the NEC, and they can pretty much do whatever they want. This would include telephone companies, cable companies, etc.
As an interesting side note, when ADT first got started in the late 1800's/early 1900's, it was considered a utility in many jurisdictions because it strung its own cable on poles between its call boxes and its central stations. This "utility" status remained in effect for many years afterwards.
When I was a contractor for the cable company, we would drop our RG-6 service line on the ground between house and pedestal. Then we would spray paint it orange. A different contractor would come along and bury it. They were paid $18 to bury it regardless of length. I never witnessed it, but supposedly they just stomped a spade type shovel in the ground repeatedly across the yard to make a crack, dropped the line in, and kind of stomped it back together. Line would only end up 6" or so underground if they did a good job. They wouldn't tear up mulch or flower beds, so lot's of replacements from lines getting damaged near the house.
Guess they get pretty good at it because figuring in drive time and expenses, not sure how you could make a living that way.
I believe section 725 includes CAT5 when used for low voltage and I believe that last year there was a new section added to better define. Section 725.144 was added further clarify that POE cables are in fact included in this section. http://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/NEC-Content.php?sectionID=399.0
Wouldn't this then further contribute to the fact that Cat5 POE cables for CCTV would not fall under section 800 and therefore CAT5 direct burial cable or Fiber would not have to be buried at 24 inches below cover?
We recently finished a project for a community where we buried several miles of cat5 and fiber for a 100 camera system. We had to trench in very tight areas packed with utilities and the deeper we go the greater the chance of hitting something. Obviously we had locates done, but in many cases we had no other way. So with customer approval we would bury at 12 inches in some areas. During rough inspection, inspectors did question us about our trench depths but after we quoted them NEC 725 they passed us.
Now we have a new project with 5 miles of trenching for Fiber and Cat 5. There may be areas we will have to implement the same strategy. I would like to have the peace of mind to know that I am in fact using the correct code.
I have trenched many ditches in my time. Some by hand and some by machine. To me years ago this made sense but in this day and age is doing your own trenching really worth the liability. I guess if you trench on a regular basis I can see the advantage but how many integrators are really trenching that often.
I'm not saying do or don't trench either. For instance we have very knowledgeable IT folks here but we still hire this service out for our office. We aren't making money when we are fixing and installing IT issues in our own office. Same can be said with trenching. How much money are you making when you are trenching instead of installing the equipment that you are good at selling, installing and servicing. If you are trenching that much then probably a good idea to have your own trenching business as well.
I also see the point where you hire a contractor to do trenching for you and then the conduits are filled with water and debris, have come apart or didn't use ridged elbows and your pull string cuts right through the plastic 90. In that case you make the contractor fix the issues.
As far as the depth required for low voltage I have always buried whatever I am putting in the ground below the frost line. Believe you me if you don't whatever you put down there will eventually come out of the ground. I too have seen many times where the cable TV and phone lines were basically covered with a thin layer of dust and they were never held responsible. Several years ago my son wanted to put a horseshoe pit in our back yard so I agreed. Who doesn't like a good game of horseshoes. I didn't have the yard marked as we were only going to dig a few inches down. Low and behold on his first shovel in the ground no more internet. This wouldn't have happened if they would have buried the wire below the frost line.
@ Shannon Davis, whether we sub the trenching out or do it ourselves we are still liable as far as our customer is concerned. In this case we won this contract in part because they knew we handled all the electrical, trenching and poles ourselves. When they let us know we won the project they told us two reasons they liked us over much larger competitors. First was we had just recently finished a similar project in another community and we were able to demo that for them. Second was because we were willing to handle everything ourselves.
I trust my team to do the project right, including the trenching. Also, for a job like this, we cannot have a company just come in and trench the entire community at once. Then we will have open trenches for weeks while we pull all the cable and wait for our rough inspections. It is easier to trench small sections at a time, pull cable, call for inspection, backfill the trench then move on to the next section.
Frost line is a non issue in this area as we have tropical weather most of the year. I prefer to bury my cables 24" under cover just to help limit opportunity for someone to cut our lines, but there are times where we have to carefully hand trench areas that have been marked with utility lines, and we have nowhere else we can go. In these cases we need to trench must more shallow and by hand to make sure we don't hit anything. This is the reason I want to be able to prove to AHJ that these cables are considered Section 725 Class 2 which do not have a minimum depth requirement when using direct burial cable.
I see no other reason for the NEC to have added Section 725.144 in the 2017 edition if that were not the case. I am hoping someone in this forum can help me to support this assumption. Here is how it reads:
Tropical weather would be nice. Midwest living is really cold then really hot. Fortunately it sounds like you have the competent staff to accomplish the items you list above. Good for your company I must say. Now maybe as we don't do residential we don't come across this near as much. When we do the trenching needing done is usually really long and realistically out of our scope. Not that we couldn't get it done it's just not in our wheelhouse. We do lot's of crazy integrations with devices just not real good at trenching setting poles and such.
As far as the liability I agree the customer puts that on us. Where I am more concerned is the liability while doing the project.