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When choosing replacement parts for customers boats it is often tempting to be the good
guy and save the customer some money by installing the price leader part. The conflict
usually stems from the price that the customer saw for an item in one of those discount
parts books and the one you would like to install. If it's the same identical part, that
can mean trouble, but, often it is not the same. One of the items that isn't often thought
about is the battery switch. They're all the same? Sorry, but they are not.
The following is a brief explanation of how a switch is rated. Often the price increases
as the load carrying capacity, case construction, and overall durability of the switch is
accounted for. ( Much like almost everything else in the world.) Before you buy,
take a closer look.
A battery switch amperage rating means nothing without also specifying time and
temperature, for the amperage rating is the current that the switch can conduct for a
specified time without exceeding a specified temperature.
To compare amperage ratings between various switches there must be a common standard of
time and temperature. That standard is underwriter's Laboratories (UL) Standard 1107 which
defines these two important amperage ratings:
Continuous Duty Rating:
Amperage that can be conducted for 1 hour without raising the terminal temperature
more than 100 degrees C or the housing temperature, more than 65 degrees C.
Intermittent Duty Rating:
Amperage that can be conducted for 5 minutes without raising the terminal
temperature more then 100 degrees C or the housing temperature more than 65 degrees
C.
Battery Switches which do not adhere to this standard or rate at very short time
periods such as 10 seconds cannot be compared to those of manufacturers adhering to UL
1107.
One other item to look at, is the battery switch casing, how it is
assembled and sealed. Since moisture corrodes the contacts of the switch, as the
switch gets older, the resistance at the contacts increases and the load carrying capacity
is reduced. So, a switch of sufficient capacity as listed, when new, could be undersized
as it ages.
Excerpted from: Blue Sea
Systems Marine Electrical parts catalogue.
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