Is this a separatley derived system

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sceepe

sceepe

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Is the secondary of a 240/480 to 120/240 single phase dry type considered a separatly derived system. I'm not familiar with the internal windings enough to know if there is a direct electrical connection to the primary system.

Second question. Why are single phase dry types listed for 240/480 primaries? I would think 277/480 would be much more common?
 
Re: Is this a separatley derived system

It is SDS.

480/277 is poly-phase.

[ January 31, 2006, 09:03 AM: Message edited by: dereckbc ]
 
Re: Is this a separatley derived system

The nameplate wiring diagram of the transformer would show if there were any internal connections. 99.99% of the time the transformer you described willl be an isolating transformer whioch is an SDS (the other times you may have an autotransformer which is not an SDS).

The two predominant nominal line to line voltages (without a 120V connection) for power systems in the US have been 240V and 480V. This is why the common single phase transformers (with a 120/240V output) are reconnectable for either voltage.
 
Re: Is this a separatley derived system

Originally posted by sceepe: Is the secondary of a 240/480 to 120/240 single phase dry type considered a separately derived system?
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My answer is "No," but I am just being picky. Look at the Article 100 definition of SDS. The transformer is not an SDS. Rather, the transformer is the source of an SDS. The second "S" stands for "system." The transformer is not the entire system. Rather, the system comprises the transformer, the secondary conductors, the overcurrent protection, and the entire distribution network that is powered from the transformer.
 
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