UL often receives questions on compliance to the requirements on input current. One of the most common questions is whether supply voltage tolerances (e.g. +6, -10%) is considered when determining compliance of Information Technology Equipment (ITE) with power rating marking requirements, in particular input current.

The answer is No. When you check the compliance to the requirements on marking of power rating, you do not have to consider supply voltage tolerances.

The Sub-clause 1.6.2 of UL 60950-1 clarifies that the input current is measured at each RATED VOLTAGE or at each RATED VOLTAGE RANGE. Therefore supply tolerances shall not be considered when determining compliance with power rating marking requirements.

Reference
The above-mentioned guideline is stated in the Practical Application Guidelines (PAG) for sub-clause 1.6.2-1 of IEC/ UL 60950-1. PAGs provide formal, documented clarification of key Standard clauses that have historically been subject to varied interpretations.

As of September 2005, UL had issued 216 PAGs for IEC/ UL 60950-1 and new guidelines are frequently included. You will find the guidelines very useful for not only increasing your understanding of how UL applies IEC/ UL 60950-1 requirements but also for increasing your awareness of the underlying principles for product safety.

PAG Online Service (PAGOS) gives you a source of reference for understanding and applying the requirements of IEC/ UL 60950-1 through the Internet. For a yearly subscription fee, you will be able to access the guidelines anytime you need.

For subscription, please check at http://data.ul.com/pagos