Ac Power Supplies and Use

[Charles Caillouet]

George,
Thanks for that complete report.
Here is a related event that i can offer…

I was on a job a few weeks ago and we were using four Tripp-Lite power strips, two of which were plugged into a third one and the fourth one straight into another outlet. Both strings were apparently on the same circuit. After checking out the temporary installation, we went home for the day, but a couple of hours later we got a call from someone in the office near the installation that she smelled something burning, saw some smoke coming from one of the strips and unplugged the whole thing. Post mortem showed that filter caps in all four strips were blown out; the strips were still working, but presumably the surge protection function was gone. Nothing else in the office was damaged, even a printer and phone plugged into one of the strips.

I suspect that the failure of these surge protectors was related to some interaction among the components but it is still not clear to me what really went on. We did not have power monitoring so we don’t know if there was a surge but all indications are that there was not. We were on shore power and apparently nothing changed. There were no known thunder storms in the area.

This brings up a couple of issues:

First, the safety office at the large facility where this event occurred recommended that power strips not be cascaded, even if the total load is well under the breaker ratings in the strips. They were a bit vague about the reasoning but were adamant that it was against their policies. After some discussion, we found that they had experienced a similar unsolved event some time prior to ours, so they didn’t give us a hard time; they just recommended that we don’t do that. Kind of “If it hurts when you laugh, don’t laugh.” advice.

Second, in the past, i have found that surge protectors often are the source of ground current leakage, which is a big pain in analog video systems. It is second only to neutral/ground reversals in causing ground loops and audio hum. So i would leave your surge protectors at home and get some good quad boxes with no electronics in them; you can cascade those till the breaker blows. Of course, don’t overload the circuits and don’t use underrated wire or receptacles when you draw heavy loads.

Anyone else have experience on this subject?

cheers,
C. R. Caillouet

C. R. Caillouet
Vision Unlimited/LA
HD Production Technical Support since 1987
…searching for the right tool for the job…

[George Griswold]

Charles,

Thanks for those observations– You are right never to cascade the surge devices– adds no benefit, causes odd behaviors and in fact invalidates the warranty/ guarantee that come with them. As far as not using them– that remains to be seen in my case; my application is Camera and a monitor with no other ties to a ground other than earth (wireless mics,no switcher or remote devices). I have never used nor recommended using a QUALITY surge device in 27 years, but have not had problems when used in a simple EFP setup over the last 40 days. The Ground leg feeds right through the box as I recall (popped one Iso open of just to see) so chassis downstream are brought to that potential.

At this point I think it better to use one unless it creates a problem. As it stands I will be lucky if they don’t cancel my insurance after my whopper claim– not to mention the cardiac stress, tears and gnashing of teeth. In the end a surge event did not kill the camera, but it has created a culture of extra caution in me and my freelancers.

Hope to see you soon…
George

George Griswold
http://www.videonow.info
New Orleans, Louisiana