MOV's and Transient Surge Supression

[Doug Fraser]

I am in the process of collecting the parts for a power line conditioner project. The other threads on this forum have been very helpful. Thanks guys!

I am now turning my attention to transient surge protection for the conditioner. I understand that there is several types of suppression technology. One that uses a shunt inductor to limit surges (www.zerosurge.com) and (of interest to me) MOV's. In addition there are some other technologies that I am not considering at this point.

I have several questions that I hope someone can answer:

1.0 What is an optimal voltage rating for MOV's? I understand that the closer one specs MOV's to the line voltage the more often they will conduct and therefore a higher probability that they will have their energy rating exceeded and be fried.

2.0 Are the voltage specs for MOV a RMS or a peak spec?

3.0 Does it make sense to parallel MOV's to get a higher energy handling capacity or is there suffient variance in the specs of the MOV's so that it is probable that only one of a parallel set of MOV's conduct and effectively the other MOV's do not conduct in a transient spike situation?

4.0 I see that some transient suppressors have a light that indicates that the MOV's are still alive and well (ie. not blown apart by a surge beyond the spec of the device). Does anyone know what a circuit is that does that?

Thanks
Doug

[ThomasW]

Questions like this are why FAE (field application engineers) exist.

Pick the brand of MOV you want to use, and call up the company. It's their job to have the answers to your questions.

All the companies that make MOV's will have complete technical specs, usually in .pdf files you can download.

[Doug Fraser]

Thomas

Thanks for the info. Given there seem to be weath of knowledge on this forum wrt power conditioning I was hoping that someone had gone through most of this and was willing to share their experience.

I will follow up as you suggest.

regards,
Doug

[Dennis H]

FWIW, here is what Jon Risch says about the varistors used in his DIY power conditioner.

http://www.geocities.com/jonrisch/surge.htm

-Varistors-
For US AC lines :Harris V150LA20A,B or C from $.78 to $1.02

This is a 150 VAC rated part, capable of over 80 joules of transient
energy absorption, and peak currents over 6500 amps. The maximum
rated clamping voltage is 390V vs. 340V for a 130VAC rated part.
This is a minor difference, and the higher voltage point keeps the
MOV from conducting regularly on high line peak voltages, avoiding
the worst of the wearout mechanism that MOV's are prone to, and
preventing the degradation of the sound.

For 240 VAC use, I recommend the V275LA40A,B or C from $.97 to $1.85
which is capable of over 140 joules of transient energy absorption,
and peak currents over 6500 amps. Maximum rated clamping voltage is
710 volts @ 100 amps.

Both are available from Allied or Newark, and the manufacturers part
# is also the stock number.

Siemens and Panasonic also make excellent and reliable varistors,
but beware other brands! There are many cheap and unreliable MOV's
being offered, that can barely take rated surges once! The Harris
and other two recommended brands can take repeated overloads and
abuse and still keep functioning. MOV's generally either fail by
permanently short circuiting or exploding! In severe overload tests,
some brands other than GE/Harris, Siemens or Panasonic tended to explode.
Once a MOV fails in the short circuit mode, the circuit breaker will
trip, and will not reset. This indicates the need for replacement
of the device.

[ThomasW]

Doug,

I use a whole house surge unit and isolation transformers. I know that Jon doesn't use MOV's in any of his designs.

[Doug Fraser]

Guys, thanks for the replies. I have seen Jon Risch web site and it is very helpful. I especially like his comment to use resetable thermal circuit breakers (on another one of his web pages). I find it curious that he explains how to implement MOV's but does not employ them himself. Does any one know what surge suppression mechanism Jon uses, if any at all?

ThomasW, with your whole house surge unit does it use MOV's as the suppression mechanism? The reason that I ask is that I understand the MOV's deteriorate as they conduct surges. Has your whole house unit ever indicated there is a problem with MOV's due to degradation? Do you think you would replace just the MOV's if they did fail or replace the whole unit. Clearly there is a significant difference in cost, a few dollars vs approx $125 depending on the unit.

Regards,
Doug Fraser

[Dennis H]

Doug, I think Thomas was referring to our own resident poobah, JonMarsh, not Jon Risch.

[Doug Fraser]

Thanks Dennis, I guess the question is if no MOV's are used then what is the protection of choice? I believe that most of the whole house protectors use MOV's?

Regards,
Doug

[ThomasW]

Yes the whole house units use MOV's. GE Power Surge Mine's bigger than the one shown here. Rating is 68,000V.

It's been sometime since it was installed (atleast 3 yrs). Seems like the price was less than $100 for a unit that just snaps into the breaker panel. It has a green LED that dies when the unit needs replacement.

Since the area of Colo I live in is one of the highest lightning strike areas in the country, it seemed like a wise investment

[Hank]

Not many people know of ZeroSurge. I like their theory and applied engineering. You may have heard of Brick Wall, who actually licensed the technology from ZeroSurge. I have it protecting my gear and RPTV. About MOV's - remember they degrade with every surge spike and will eventually fail. MOV's are cheap protection, but the don't last forever.

LESSON: My boss had a lightning strike on an upstairs dormer peak last Thursday. The energy concentrated at an outlet in that spare bedroom and blew a hole in the wall. Inside, drywall shot across the room, hitting the opposite wall. Outside, a few bricks blew out into the yard, almost to the street. He lost his big TV and HT gear. Next day, he bought some good protective power strips with the $$ equipment protection warranty. I told him to save the sales receipt and box UPC label.

[Doug Fraser]

Hank:

I know about their shunt mode surge protectors. In fact I have ordered 2 of their 20 amp models for a power conditioner(s) I am building. I too very much like their thinking and the analysis put forward in their papers. I got them from info@zerosurge.com

I was considering the use of MOV's after their surge protector.

Now you may ask why double up on surge protection? Well I have been accused of "if a little is good then allot is better" thinking. It would seem to me that if the zero surge didn't stop the surges then a MOV would. Given that MOV's are cheap it really isn't allot to pay for insurance. But then again, if the zero surge unit behaves as claimed, then the MOV's would never be used so why include them? The jury is still out.

The one concern that I did have was that zero surge does not protect against common mode surges. Line to ground and Neutral to ground. I got a paper from them titled "Common Mode Surges and Ground Contamination" written by Rudy their president.

The summary is as follows (directly from the paper)...

--------------
The building ground wire is very sensitive to surges and noise if audio, video or networked computers are in use, so diverting surges to the ground wire is very undesirable if such equipment is to be protected.

The building neutral wire is not sensitive to surge and noise voltage, so it is a good choice for returning surges back to the earth ground.

Modern electrical equipment is inherently immune to common mode (N-G) surges. Common mode surges are very weak, and UL mandates at least 2,000 volt common mode immunity, so a surge protector which offers common mode, or “all modes” protection offers no benefits, but has the liability of ground wire contamination.

If audio, video, or networked equipment is to be protected, avoid surge protection products which claim “all modes of protection” and seek “Mode 1” (line-neutral only) protection, otherwise excessive noise or damage to the respective equipment data ports may result.
---------

The paper explains that common mode surges will be very weak as the neutral and ground are by the electrical code connected together in the electrical panel. Therefore there should be no (or very little) voltage difference between the Neutral and Ground in a typical home as the runs of cable are relatively short.

It is highly improbable that any common mode surges will make it through this connection. If any do then they are generated locally in the home and they will not exceed the 2,000 volt common mode immunity that UL mandates for electrical equipment. The Hi Pot test.

Therefore, given that noise on a ground, even at very low levels, can affect equipment performance and given we don't ever expect to have any sizable common mode surge and if there is common mode surge, electrical equipment is mandated (by UL) to be immune to it, then there is no need to have common mode surge protection. The logic holds for me. While I am an EE my field of expertise is not surge protection, so I admit I may not even know what questions to ask.

I welcome any thoughts that people may have on this.

Regards,
Doug

[brucek]

UL mandates at least 2,000 volt common mode immunity, so a surge protector which offers common mode, or “all modes” protection offers no benefits, but has the liability of ground wire contamination.

I have to consider that anything posted on zerosurges website might be a little self serving... :roll:

Using the logic in the quote, could we not say that there would be no ground wire contamination unless a common mode spike or surge occurred since the L/G and N/G MOV's offer a high impedance path to safety ground during normal conditions.

In that case, why not have the MOV's in place to protect for this unusual but possible situation. If the common mode situation doesn't often occur (as he claims likely won't), then the common mode MOV's won't be dumping current to ground and effectively won't ever be noticed in the circuit and their lifespan would be infinite.

So by this reasoning, why not have the common mode protection using MOV's and then use the series mode protection with the zero surge choke system to shunt current to neutral for regular line surges.

Has your whole house unit ever indicated there is a problem with MOV's due to degradation? Do you think you would replace just the MOV's if they did fail or replace the whole unit.

I've had my whole house suppressor for about 4 years now and it still indicates good. In fact, one of my dedicated circuits is fed from one of the suppressors breakers, so if protection is lost, my stereo won't turn on. This helps, since I'm not likely to be checking the protection lights on the unit itself very often. The fact that my stereo won't turn on is a good tell-tale.
When the unit fails, it is completely replaced......small price to pay.. 8O

I feel the 'whole house' units are effective by the fact that they're so close to the service panel. This makes the shunt path impedance extremely low for diverting impulses to ground.
Since I've been playing with my picture files lately, here's one of my Siemans surge arrestor (from another thread). Love my digital camera......
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brucek

[Hank]

Bruce, you certainly can have MOV's as well as inductors. AAMOF, I have a good Trip-Lite conditioner (MOV's inside) plugged into my Zero-Surge unit and my gear is plugged into the Trip-Lite. As I said before, MOV's are fine, but the general public doesn't know that they degrade/fail over time, and that's a false sense of security. I think you and Thomas have the best setup: whole-house unit in the breaker panel, then extra protection/conditioning equipment of your choice located at your equipment location.