How Deep Must An Electrical Cable or Conduit Be Buried
** originally posted on Linkedin Jan 9/17
If you ever have trouble falling asleep I have a sure fire remedy: the CEC or Canadian Electrical Code. After reading a few lines you should be fast asleep. I don’t have this luxury as I need to know the code and make sure it is implemented in all of the jobs we complete to make sure it passes inspection but more importantly, to make sure our customers homes and businesses are safe.
A question that often comes up is how deep must a trench be when burying an electrical cable or conduit. The CEC code is very specific on this and the answer to the question will have many variations depending on the situation.
To keep things simple let’s take an example of providing power to a baby barn in the back yard of a residential house. In this scenario the baby barn is about 50 feet from the house and the trench will run across the back yard. The type of cable will be 14/2 NMWU underground rated cable at 120V. According to Section 12-012 of the code and table 53 the minimum depth without any protection must be 600 mm (or 24 in.). You must also bury caution tape above the depth of the wire so that if someone digs in the future they won’t be shocked by their efforts.
You might ask if this depth can be less than 24 inches. Let’s say the digging is difficult. You can decrease the depth but you will have to take additional steps to protect the wire. For example, you could decrease the depth 150 mm (or 6 inches) if you use mechanical protection such as laying pressure treated planks (2 x 4) along the entire trench 3 inches above the wire. You could also use PVC conduit which table 53 indicates only 450 mm (or 18 inches) depth is required (vs. 24 inches for direct buried cable as in the case above). If you use planks above the conduit you could actually reduce the total depth of the trench to 300 mm (or 12 inches). This trick may come in handy. We did a job where the trench crossed a driveway (table 53 indicates you have to add an additional 150 mm depth for vehicular areas) and the digging was extremely difficult. We were able to decrease the depth of the trench under the driveway using conduit and mechanical protection. This saved time but also ensured the cable remained safe.
Keep in mind this is only one example of burying an electrical circuit. It can get more complicated on commercial jobs and NB Power may have other codes that will need to be considered over and above the CEC code.
Yes the code can be boring but it was written for a reason – to keep people and their property safe from shock hazards and other consequences such equipment damage or worse. Like most things, doing it right from the start may cost a few more dollars but the savings over the long run more than make up for it.