Lesson plan
True DC
True DC is a type of switch disconnect (isolator) used in solar photovoltaic installations, in accordance with EN 60364–7–712. It was created by UK based IMO Precision Controls Ltd, and later adopted by other manufacturers such as Senton and ABB. The isolator design ensures a very fast break/make action by incorporating a user-independent switching action. As the handle is moved, it interacts with a spring mechanism causing the contacts to "snap" over upon reaching a set point. This mechanism means that the disconnection of the load circuits and the suppression of the electrical arc, produced by a constant DC load, is normally extinguished in a maximum of 5 milliseconds (MS), using the specific pole suppression chambers incorporated into the design. Many alternative solutions, particularly those based upon an AC Switch Disconnect design which use bridge contacts, have been modified and rated for DC operation. These types of products have a switching speed that is directly linked to the operator speed, therefore slow operation of the handle results in slow contact separation of the contacts which can produce arcing times of 100 MS or more.…
Article summary
True DC is a type of switch disconnect (isolator) used in solar photovoltaic installations, in accordance with EN 60364–7–712. It was created by UK based IMO Precision Controls Ltd, and later adopted by other manufacturers such as Senton and ABB. The isolator design ensures a very fast break/make action by incorporating a user-independent switching action. As the handle is moved, it interacts with a spring mechanism causing the contacts to "snap" over upon reaching a set point. This mechanism means that the disconnection of the load circuits and the suppression of the electrical arc, produced by a constant DC load, is normally extinguished in a maximum of 5 milliseconds (MS), using the specific pole suppression chambers incorporated into the design. Many alternative solutions, particularly those based upon an AC Switch Disconnect design which use bridge contacts, have been modified and rated for DC operation. These types of products have a switching speed that is directly linked to the operator speed, therefore slow operation of the handle results in slow contact separation of the contacts which can produce arcing times of 100 MS or more.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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