UL 551-2018 pdf free download

UL 551-2018 pdf free download.Transformer-Type Arc-Welding Machines.
24.5 For the purpose of this standard, duty cycle is defined as the ratio of arc time to total time, that is,
the time the secondary is to be loaded in a 10-minute cycle,
25 Leakage Current Test
25.1 When tested as described in 25.2 — 25.11, the leakage current of a cord-connected product with a
20-percent duty-cycle rating and rated for a nominal 250-volt or less supply shall not be more than 0.75
milliamperes.
25.2 Leakage current refers to all currents, including capacitively coupled currents, that may be conveyed between exposed conductive surfaces of a product and ground or other exposed conductive surfaces of the product.
25.3 All exposed conductive surfaces are to be tested for leakage currents. The leakage currents from these surfaces are to be measured to the grounded supply conductor individually as well as collectively where simultaneously accessible, and from one surface to another where simultaneously accessible. Parts are considered to be exposed surfaces unless guarded by an enclosure that has been investigated and found to be acceptable to reduce the risk of electric shock — see Frame and Enclosure. Section 7. Surfaces are considered to be simultaneously accessible if they can be readily contacted by one or both hands of a person at the same time. These measurements do not apply to terminals operating at voltages that are not considered to involve a risk of electric shock.
25.4 If a conductive surface other than metal is used for the enclosure or part of the enclosure, the leakage current is to be measured using metal foil with an area of 10 by 20 centimeters in contact with the surface. Where the surface is less than 10 by 20 centimeters, the metal foil is to be the same size as the surface. The metal foil is not to remain in place long enough to affect the temperature of the product.
25.5 The measurement Circuit for leakage current shall be as illustrated in Figure 25.1. The measurement instrument is defined in (a) — (C). The meter that is used for a measurement need only indicate the same numerical value for a particular measurement as would the defined instrument. The meter used need not have all of the attributes of the defined instrument.
a) The meter is to have an input impedance of 1500 ohms resistive shunted by a capacitance
of 0.15 microfarad.
b) The meter is to indicate 1.11 times the average of the full-wave rectified composite waveform of voltage across the resistor or current through the resistor.
c) Over a frequency range of 0 — 100 kilohertz, the measurement circuitry is to have a
frequency response — ratio of indicated to actual value of current — that is equal to the ratio of
the impedance of a 1500-ohm resistor shunted by a 0.15-microfarad capacitor to 1500 ohms. At an indication of 0.75 milliamperes, the measurement is not to have an error of more than 5
percent at 60 hertz.UL 551-2018 pdf free download.