Cable Crossings and Ampacity
- Thread starter Joao
- Start date
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
This would typically not be done for most of the circuits that the electricians on this site deal with. We tend to deal with low voltage circuits in structures where ampacity is set by design tables. These design tables pretty much ignore crossing factors, but these tables are so conservative that this isn't a problem.
As the video describes, these are for utility distribution circuits buried in the ground. Such circuits tend to be much higher voltage, and the circuit ampacity is set by engineering calculations. These circuits are designed to be closer to the true thermal limits of the cables. In any such calculation you must evaluate every factor that could lead to any portion of the circuit overheating, and account for that.
As the video describes, these are for utility distribution circuits buried in the ground. Such circuits tend to be much higher voltage, and the circuit ampacity is set by engineering calculations. These circuits are designed to be closer to the true thermal limits of the cables. In any such calculation you must evaluate every factor that could lead to any portion of the circuit overheating, and account for that.
If are not used for most of cables in which situation shall we use that criteria? Only in special cases? Only in revampings? Only for HV cables?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
This is my opinion, not a detailed code analysis:
I believe that the issue of cable crossings should be considered whenever the ampacity of the circuit is determined by engineering calculation rather than the use of ampacity tables.
These would typically be underground duct banks and high current direct burial circuits.
-Jonathan
I believe that the issue of cable crossings should be considered whenever the ampacity of the circuit is determined by engineering calculation rather than the use of ampacity tables.
These would typically be underground duct banks and high current direct burial circuits.
-Jonathan
I agree with you. Thanks
Julius Right
Senior Member
- Location
- Israel
- Occupation
- Electrical Engineer Power Station Physical Design Retired
It is a very interesting item with economic aspect if we can increase the current capacity [ampacity] of the cable when we choose the right angle and distance at the intersection point.
However, if this environment is according IEC standard 60502-2 -single core cables in flat touching ducts, it will also be interesting for buried directly in the ground.
In the USA it is also practiced to use duct banks in concrete, where the angle can be 90 degrees from the start.
I wonder if the heat built up in the junction point can be vented through the conductor as well, since by reducing the current the temperature in the rest of the cable can be less than 90oC.
However, if this environment is according IEC standard 60502-2 -single core cables in flat touching ducts, it will also be interesting for buried directly in the ground.
In the USA it is also practiced to use duct banks in concrete, where the angle can be 90 degrees from the start.
I wonder if the heat built up in the junction point can be vented through the conductor as well, since by reducing the current the temperature in the rest of the cable can be less than 90oC.