Power Source/Earth Connections; Dielectric Strength Test - NEC MultiSync LCD1550ME Service Manual

1.7.2. Power source/earth connections

a. Checks on the power source/earth connections
The earth side of the cord or the earth wire of the inlet filter for the cord set shall be visually checked to
see that it is connected to the chassis block of the unit as specified below.
1) The earth wire color shall be spiral of green and yellow.
[Units applicable to UL1950 or IEC60950 (EN60950)]
2) The earth wire shall be firmly connected to the chassis block by the use of a screw (See Note) of
3.5mm∅ in diameter.
Note: Spring washers or star washers shall be used, without fail.
b. Earth resistance testing
This testing shall be carried out prior to the dielectric strength test.
The earth resistance shall be 0.1Ω or less when a current of 25A AC is carried between the earth side of
the cord (the plug block or the section closest to the plug where no plug is provided) and the metallic
block (the DVI connector) that is used as a safety earth for the unit.
Where the earth resistance exceeds 0.1Ω, the condition shall be still acceptable if the earth resistance is
0.1Ω or less when the resistance of the power cord is excepted.

1.7.3. Dielectric strength test

To confirm the freedom from insulation breakdown, testing shall be carried out under the conditions
specified below.
1) Measuring conditions
•
Measuring instrument : Dielectric strength tester (The specified voltage shall be maintained in the
•
Testing point
Note: The electrical circuit block shall mean the power input block (primary side). Testing shall be carried
out under the condition that both poles of the power plug are short-circuited. (Where a 3-core cord is
used, the two poles other than the earth terminal shall be short-circuited.)
2) Judgment standard
The freedom from insulation breakdown shall be confirmed under the condition that the applied voltage is
maintained at 1500V AC (+0 to 50V) for one minute.
Even though the result of this testing is OK, such a condition shall be regarded as unacceptable if there is
a leakage (flashing) around the section where the test voltage has been applied.
If the result of insulation resistance test is found unacceptable, to be carried out after this testing, such a
condition shall be regarded as that an insulation breakdown has occurred.
state that a current of 10mA is carried.)
: Between the electrical circuit block and the exposed metallic block (D-SUB
connector)
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