The distance between passage boxes or the rules for installation of conduit, corrugated conduit, a curve for the conduit is in the standard NBR 5410, where you will also find conduit tables that will facilitate the choice and installation of the passage box. In this article, we will talk not only about the rules of the box but also about the conduits, come on guys!
Passage box: NBR 5410 standard
As already said, all the rules on conduits or passage boxes are removed from NBR 5410, after all, it couldn’t be different, the standard says everything we need for low voltage electrical installation. In this standard, there is an entire part that deals exclusively with installation, with several specific points talking about the conduits and the passage boxes.
Passage box: Conduits
The conduits offer mechanical protection and contain the electrical cables and the passage boxes will be the points for inspection and where the splices and connections of the electrical cables will be accommodated. Generally, the 3/4 corrugated conduit is the most used in electrical installations, be it PVC or other material.
It is essential to pay attention to the occupation rate of the conduits, as this is one of the rules for installing conduits since all of them must guarantee the placement and removal of cables in an easy and safe way, and this is only possible if the due fees occupancy rates are maintained.
What should be the distance between the pass boxes?
The answer to this question is quite simple and we can find it by analyzing item 220.127.116.11.6, in letter b), which says that: the continuous sections of piping, without the interposition of boxes or equipment, must not exceed 15 meters in length for internal lines to buildings and 30 meters for lines outside the buildings, if the stretches are straight.
We can see that the rule was very clear, being 15 meters for the internal pipes and 30 meters for the external pipes in a straight line, but what if the sections include curves? Well, in these cases, the limit of 15 and 30 meters must be reduced by 3 meters for each 90 ° curve.
Continuing with the analysis of what the standard says, just below item 18.104.22.168.6 you will find a note that explains how to facilitate those cases where it is impossible to place a transit box for some reason. In these cases, the note says that: it is possible to increase the conduit or piping to the next gauge every 6 meters of additional pipe without a passage box. To facilitate your understanding, follow this example below.
- Suppose I have a 1/2 inch conduit, internal to a facility, and 27 meters long. In a traditional way I would have to put a passage box in the middle of this pipe due to the 15 meters that the rule of the rule stipulates, but if it is not possible to install this box after the 15 meters, I must increase the gauge of the conduit for every 6 meters.
- So, in this example, I have 15 meters plus 2 sections of 6 meters, totaling the 27 meters mentioned. Then the conduit becomes a 1-inch conduit because in the manufacture of conduits we have the measurement of 1/2 inch, 3/4 inch and the next is 1 inch.
With this increase in the conduit gauge, the installation of the passage box is eliminated and guarantees the ease of cable installation. Another important rule that must always be taken into account is that never use curves with a degree greater than 90 degrees and as already said, for each 90-degree curve the distance from the passage box must be reduced by 3 meters, observe the example below.
- Suppose I have a pipe with two 90 degree curves. In this case, the passage boxes, instead of 15 meters for indoor installations and 30 meters for outdoor installations, should actually be 9 meters for indoor installations and 24 meters for outdoor installations.
Still, on curves, the rule is also clear regarding the use of accessories to bend curves. The standard says that even with the use of accessories, the section of the conduit should not decrease. This is very clear in item 22.214.171.124.8 of the standard!
Passage box: Where is the use mandatory?
In addition to the use of pass boxes to facilitate the passage of cables, there are 3 other situations where the use of pass boxes is mandatory, as shown in item 126.96.36.199.9 of the standard, which says:
- At all points of the piping where conductors enter or exit, except at the transition points from an open line to the line in conduits, which, in these cases, must be finished off with dowels.
- At all points of splice or branch of conductors.
- Whenever it is necessary to segment the pipe.
Attention, the splices, and connections must never be inside the wall in the conduit, they must be in the boxes of passages to allow a better inspection and maintenance whenever necessary. This rule is also in the standard, in item 188.8.131.52.10 which says: the location of the boxes must be in order to ensure that they are easily accessible. They must be provided with covers or, if the house switches, power sockets, and the like, they must be closed with the mirrors that complete the installation of these devices.
And with that we conclude this article on the installation distance of the passage box and conduits, now there is no way to miss the distance of the passage boxes in electrical installations anymore! Reading, interpreting and following the standards is not just a luxury, in addition to ensuring safety, the standard aims to facilitate both the installation and possible future preventive and corrective actions.