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Shunt Mounting Considerations

There are a number of considerations that should be taken into account when deciding on how and where to mount a shunt.  Electrically, it is common practice to place the shunt on the ground or return line in close proximity to the power source.  This practice minimizes the voltage potential between the shunt and the mounting location.  In addition, the close proximity helps to ensure that all of the loads are accounted for and the true total current measurement is being performed. 

Physically, the shunt should be mounted such that the manganin resistive elements are oriented vertically to ensure proper cooling.  In the case of our base mounted models, a good way to remember this is that the shunt should be mounted to a wall or panel and not the floor or ceiling. Another physical consideration, especially when working with busbar mounted shunts is to make sure that thermal expansion has been considered.  Wire termination may be necessary in application involving high pulse loads, or high heat in order to protect the shunt from physical damage.  In addition, it is good practice to ensure that there is good air flow, either through forced air, or providing plenty of fresh air. If neither of these are practical, it is possible to add heatsinks to the current carrying terminals or even use a heavier gauge wire or larger bus bar, as at currents above 100 amps a vast majority of the heat is transferred into the current carrying components.

Shunt Mounting Orientation

 

Shunts operate most accurately at temperatures between 30°C and 60°C but will perform quite well at temperatures below that level, although with overall accuracy somewhat compromised.  The upper temperature limit should not exceed 140°C, as at temperatures above this level the manganin resistance element will be permanently altered and the shunt will no longer perform as intended. In order to provide a good margin of safety we strongly recommend that the manganin element be kept below 125°C. 

Shunts should not be subject to continuous currents greater than 2/3 the rated current of the shunt. This is also a thermal consideration and is suggested to ensure that the upper temperature limit is not exceeded. Shunts are very well suited to measuring short duration pulse loads and can be used to monitor currents above their rating so long as there is sufficient time in between pulses for the shunt to adequately cool.  There are too many variable such as ambient temperature, airflow, size of the current carrying conductors and pulse duration and duty cycle to offer any specific data regarding how much the shunt can be over driven, and as such those application will require verification at the installation location.