Multiple surge strips, Why a bad idea?

[compudog]

I remember reading something about plugging a surge strip into another surge strip (you know the kind, with the MOVs across the line and load) or into a UPS device negates the spike and surge capability of the strip. Why would this be? I know how MOVs work (at least I think I do) and I don't know why they still wouldn't work. Any ideas?

BTW, it's not an amperage issue. I realize that if you have a 6 outlet surge strip and plug another 6 outlet strip into it (for a total of 11) and each is rated at 15 amps max doesn't get you 30 amps. The former IT provider at my company had UPS devices for each workstation and then plugged a surge strip into the UPS so all devices would have battery back-up. (UPSs had 2 battery receptacles and 4 non-battery) and he had the speakers and other peripherals plugged into the surge strip. I removed all the surge stips and just used the back up jacks fro the PC and monitor (as intended by APC.)

 

[dkozloski]

Plugging surge strips together in series will not hurt anything as long as the current capability is not exceeded and I see by your post that you understand this. In fact since most PC power supplies have surge protection built in you are probably already using two in series. Where the confusion comes from is that the first protector will affect the rise time of the surge spike and make the protection features of the second strip less effective so that it may not provide any additional protection beyond that of the first.

 

[compudog]

Thank you. It tends to clarify things. I wish I had saved the original article/post/thread.

 

[glugglug]

Don't know of any problems plugging a surge protector into a UPS or into another surge protector.

But there IS a problem plugging a UPS into either. The UPS draws much more current while the battery is being charged, which can blow the one its being plugged into.

 

[blahblah99]

Well, you don't cascade surge strips because the outlets are rated at 15A (for home). If your using low powered devices, then I don't see a problem with cascading strips, but if you're running a TV, two amplifiers, a computer, a monitor, and need more outlets for your vacuum cleaner, hairdryer, and laser printer, its going to be a problem

 

[ScottMac]

Cascading surge protectors and/or surge protectors into UPS is/can be a bad thing.

Every device you use to transport power affects the power: devices and circuits (at least less expensive ones) that are attached to the line will cause some deformation of the sine wave. All of the components / devices are generally capacitive or (more likely) inductive (versus pure resistance).

Most / all of the surge protectors are meant to be used standalone: the engineering analysis and testing says "we are changing the power to this degree, which is within acceptable limits." When you cascade surge protection systems, you compound those changes and in some cases, amplify the adverse effect.

In the case of using a surge protector behind a UPS, you are adding a load that the UPS feedback/control system may not able to compensate.

Some (most?) switching power supplies use a method of regulation that includes watching for the sine wave to cross the zero-reference. If the changes to the sine wave are extreme enough, the zero-crossing-reference may not provide accurate enough regulation or (in one case I know of) cause the power supply to eat itself.

A company named "Best" used to make a line of UPS with a regulation system that turned out to be incompatible with switching power supplies (Ferro-resonance something-or-other, "Ferrups" ...something like that). The regulation system caused the front-end of the power supply to burn out because the two systems (switched power supply and the UPS regulation system) conflicted.

IBM did a study ~15-20 years ago on the effects of huge quantities of switching power supplys on the power grid. Their concern was "What does the grid power look like after leaving a large building full of computers (switched power supplys)?" The extremely short version of their findings: "Pretty Damn Ugly!" The resultant actions taken, in part because of this study, include balancing the inductive/capacitive reactance more often along a span of shared power lines and changing the input side of a switched power supply to allow for crappier power.

The bottom line is that until you get to the higher-end power filter systems (or UPS), the filtering components or circuits cause some changes in the power waveform or L/C reactance relationships - cascading the systems cascades (multiplies) the effect - possibly to the detriment of the device being fed. Additionally, the effectiveness of some filter components (like MOVs) is reduced (I believe) because the "power event" is distributed and reduced to below the trigger threshold (but still high enough to adversely affect the "protected" device).

It's been a while, so some of the details may be missing or mutilated, but this is the way I remember it ...

FWIW

Scott

 

[compudog]

That's it ScottMac. It was the IBM thing, or something like it. Thanks. I know with the proliferation of AC-Vector drives and switching DC power supplies, the electrical power distribution system of a manufacturing facility can become quite "dirty" and no long resemble a true sine wave. We were having this sort of problem at my company. One of the solutions is to install a line reactor in front of the AC Inverter (or Variable Speed Drive) to prevent the rapid switching of the IGBT output stage from introducing all sorts of noise into the power grid. It was while I was researching a computer problem at the plant that I discovered some of this information and it laid dormant in the back of my thought-locker. What we finally did to stop the laser printer errors and spontaneous PC reboots/glitches was to install power conditioning transformers to provide clean, pure sine-wave power to our office area. Powersmiths transformers were what I found that solved our problem.

 

[compudog]

Here's a great FAQ on power and computers. FAQ Should prove to be interesting reading for those so inclined.