Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Don't know......

Specific instructions for use as a balanced AC power unit:
Connect the AC input power to the primary windings. There are a set of two rows of four terminals, marked "0", "208", "220", and "240". Place the "0" terminals in parallel (connected together) and the "240" terminals in parallel. These are the input terminals for the AC power from the line cord, which should run through a safety device such as a fuse or circuit breaker. See the common section at the end for details. For the secondary, connect the AC outlet neutrals to one of the "0" terminals, then connect the "120" terminal of that row to the "0" terminal of the other secondary side row of terminals, and connect the AC outlet hot to the remaining "120" terminal.


*The two primary windings are connected in parallel. Fed by 120V....

*The two secondary windings are connected in series. The outer 2 leads will output 120V nominal. Each outer lead to center tap will output 60V.

Here the manufacture design and FLA data info must be used.
If the winding wire size is the same as the DU-2, (not knowing for sure), then each winding has a max rating of 9 amps each.

With the secondary windings in series, yes the voltage is doubled from 60V to 120V (nominal), but putting the two windings is series will not double the available output current rating. Current is the same in all parts of a series circuit.

I admit I could be missing something here with the Signal SU-2 isolation xfmr.....

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I did catch something Jon missed in his instruction wiring the DU-2 for use as a separately derived 120V isolation transformer. He forgot to mention one lead of the 120V secondary shall be intentionally connected to earth, thus becoming the Neutral, The Grounded Conductor....

The connection must be connected to the main electrical service grounding electrode system. In the case of a cord and plug fed iso xfrm the wall recept safety equipment ground can be used.

(There is a code change in the latest edition of NEC 2011 regarding using the safety equipment ground for the neutral earth connection of a separately derived power system.... Call me lazy I haven't read the change yet.)

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A comment on Technical Grounds.

(No separate isolated ground rods allowed.)

A technical ground does not mean the secondary neutral conductor of a transformer does not have to be connected to the main service grounding electrode system of the main electrical service. Per code the grounded center connection of a balanced AC grounded 60/120 system is called the neutral conductor. The two 120V leads of the secondary, that feed the two hots of the recept, are called the ungrounded conductors.

Yes you can drive a separate ground rod/s, (Technical ground / Aux Ground), but per NEC code the ground rod/s shall connect back to the main system ground with a minimum size #6 copper wire. (See link below.)









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  • Don't know...... - jea48 17:26:30 07/14/12 (0)

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