Where’s the CSA logo on my power supply?

As I sat here at the end of March pondering what my April blog article was going to be about, I had an email from one of our sales people.  Her customer had purchased one of our SWS series of power supplies based on our data sheet, and could not see the CSA certification mark on the product label, just the CE, TUV (the triangle) and the UL (recognized) marks.

Looking at our data sheet though, it clearly claimed the product had CSA 60950.

(Click to enlarge) You can see the safety approvals

This prompted the email to me!

In 2003, UL & CSA drafted a bi-national agreement to recognize each other’s testing and certifications.  UL can now cross certify to CSA 60950 and likewise CSA can certify to UL 60950.  This avoids manufacturers from having to pay and maintain two separate certifications.

If the product was certified by UL for both countries it would have this mark (often referred to as “cUL”.

If the product was certified by CSA for both countries it would have this mark  

As the SWS power supply has the “cUL” mark, it is certified to CSA 60950 (or to be fully correct CSA C22.2 No. 60950-1-07) and that is stated on the UL test report.

How does the new UL Mark affect me?

UL recently announced their first Transcontinental Mark which denotes product compliance with European EN safety standards as well as the CSA/UL/US Mark for the North American markets.  Basically, UL will be providing an “international safety certification”.  And, this may affect European safety houses like TUV and others.  Here is what the new international UL mark it looks like:

Although, at first glance, this mark looks like a “UL Listed” power supply certification with its encircled UL mark (as used for External Power Supplies), UL-EU confirmed that it also applies to stand-alone component power supplies like those installed in all electronic equipment.  Prior to this new mark, the standard “component power supply” UL mark for the US and Canada looked like this:

Some power supply manufacturers have been reviewing use of UL to display the existing C-UL-US mark along with the self-declared CE mark.  The CE mark would be backed up with an IEC60950-1 CB report as documented proof of compliance.

It will be interesting to see how the European test houses (e.g., TUV) react and if CSA responds with their own version of this new UL mark.

Why is my power supply input only rated from 100-240VAC?

Most power supplies have a rating label that looks something like this:


However, a close look at the power supply’s datasheet will usually show the absolute AC input voltage range, from minimum to maximum. This is usually 90-264VAC, or occasionally 85-264VAC if the power supply has been designed for Japanese use.

Japan uses the lowest AC mains voltage, which is 100VAC nominal; however, short duration AC line droops or brown-out conditions often mandate a rating down to 85VAC. The UK is among the countries that use the highest AC mains, with a nominal rating of 240VAC.

The safety certification bodies (UL, CSA, TUV, etc.) mandate that a rating of 100-240VAC be listed on the power supply’s label. However, they factor in a +/-10% tolerance for the power generation and transmission utilities. -10% of 100VAC is 90VAC, and +10% of 240VAC is 264VAC. All safety testing is performed at the high and low limits as listed on the power supply’s datasheet.

So, if the power supply label states 100-240VAC, it can usually operate over a wider AC operating input range. However, always check with the manufacturer’s datasheet to confirm this. Continuous operation of the power supply over the datasheet’s specified AC input range will not normally cause any problems. In some cases, however, the maximum output power (total watts) of the power supply may need to be derated if the supply is operating off an input voltage that is on the low-end of the specified range. Always check the power supply’s datasheet for the specified minimum AC input voltage with various output load levels. Deratings may also apply depending upon the power supply’s operating ambient temperatures.

Should a label state 100/240VAC (note the slash) it “may” indicate that there is a voltage select switch or jumper that is required to be set for the correct operating input voltage range. Newer products tend to not have an AC select switch or jumper.

Worldwide, the AC mains power has a nominal frequency of either 50 or 60 Hz (cycles per second). However, these frequencies are subject to variations by the power generators in different countries (especially third world) and so the typical AC frequency range for power supplies is 47-63Hz.