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Loading Dimmers to Full Capacity

Bulletin Number: 145
Released By: dhs
Product Family: VX,ULD,LDS,LWD
Date: 8/26/2004

There is a lot of confusion regarding the acceptable load that can be connected to Leprecon installation dimmers. The dimmers are generally rated at 20 amps per channel, but often electricians are reluctant to load the dimmer to that level.

NEC established that breakers must be derated to 80% of their marked value if the load current is considered continuous. NEC defines continuous operation as three hours or longer.

However, the NEC does have an exception for complete assemblies (including the breakers) that are listed for operation at 100% of their rating for continuous loads. This means that the equipment has undergone additional testing to verify that it can handle the additional temperature rise associated with this level of operation.

In NEC 1993, the statement regarding continuous operation was in section 384-1699 (C). In the 2005 update, it can be found in section 210.20, which refers to 210.19 (A) (3). In both cases, the statement and the exception are basically the same. The following is a paraphrased summary:

...where a branch circuit supplies a continuous load, the overcurrent protection must be 125% of the load current EXCEPT where the assembly (including overcurrent devices) is listed for operation at 100 percent of it's rating.

Leprecon dimmers include the branch circuit breakers, and were tested under UL Standard 508, which specifies full load testing. The UL or ETL mark on each pack is proof that our gear was tested for continuous operation at full rated load.

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