Some items may have multiple voltages and current ratings listed in the datasheet due to testing procedures from the approval agencies like UL, VDE, or IEC. There is a common confusion about these ratings because it can make it unclear what to go by. This article aims to help understand how to interpret these ratings.
Example Part Number: 4008-XACA881-ND (XACA881)
XACA881 is a pendant control with seven push buttons for industrial settings. The following approval agencies and standards apply:
- IEC 60947-5-1
- UL 508
- CSA C22.2 No. 14
- IEC 60204-32
Page 2 of the datasheet gives context on how the contacts of the switch are rated. See a snapshot of the relevant data below.
IEC Standard Overview
If you look at the brief review for IEC60947-5-1, you can get some idea of what is going on. This particular standard is specifically for “Low-voltage switchgear and control gear.” They define “low voltage” as “not exceeding 1000VAC [not exceeding 1000Hz] or 600VDC.” Commission groups and approval agencies all have their own testing methods which then establish applicable standards. Many engineering applications are required to meet these particular standards. These ratings are supposed to streamline the compliance process. However, not all end users necessarily have to comply with these standards.
Generic Design Guidelines
For this particular part, if you don’t care about compliance, you can consider the contact code designation as the best guideline for current rating. The current rating depends on what target voltage you are aiming for. Note that you can go between the 240V rating for AC and the 600V rating, if you wish. An estimate on current rating would have to be extrapolated from the available data. If you assume a linear change, the equation below is a model for estimating the current rating at a specific voltage in the range.
Insulation Voltage Note
Note that the datasheet does call out that the maximum insulation voltage is 600V. This happens to coincide with the maximum rating for the contacts. There is a possibility where the insulation rating may be higher than the contact rating because these are different tests.
Multiple Ratings
Other products may show multiple ratings because multiple agencies tested the device. The din rail terminal block category is a good example of this. The filters distinguish between IEC current/voltage and UL current/voltage. In this case, I usually advise to go by the higher rating of the two if the standard isn’t applicable.
Conclusion
The main takeaway is that the standards are there for the purpose of compliance. If there are no other ratings listed, it is best to use the standard specific ratings as a reference for design. Some types of components may have multiple ratings that refer to specific standards.