Surge/noise filtering

[JHZR2]

Hello,

i have a situation where there is interest in adding surge and noise protection in a kitchen. The interest is in providing surge/noise filtering for the refrigerator and stove, since both have circuit boards and are big money to repair/replace. Notionally some protection and filtering could help ensure longevity.

The refrigerator has its own dedicated circuit, and the range is one of the two legs of a mwbc that has a microwave on the other.

Neither have good access without removing the appliances, so im not really keen on installing outlet type surge protection. I'd rather put the protection at/near the subpanel which feeds the kitchen - a 50A Eaton CH unit. Easier to see, easier to diagnose, easier to replace, and notionally, if the MOVs fail, could also be easier to keep cool and safe.

Im looking at using something like the leviton 51110, but would like to hear the pros/cons of a device like that versus some others option.

And assuming i ue I use something liked that, the instructions that come with those devices are not very clear, so I have a couple questions:

1) if they are designed for a "Line 1" and "Line 2" connection for a 120/240 split phase setup, can one use such a device with just a single 120v circuit connected?

2) can a mwbc be used as line 1 and 2 in one of these? I.e. Feed it off a two pole breaker and share the neutral conductor? It seems that two separate sets of conductors and breakers may be desired.

On a related note, if one put a surge suppressor outlet in the basement near the panel, and then used the load terminals to connect, any idea how the protection performs with distance from the device, and if there is any difference using the load terminals versus plugging a load into it? That could be smaller/cheaper/easier for at least the dedicated refrigerator circuit.

Thank!

 

[Dennis Alwon]

I believe all panel manufacturers make a DP breaker that will have surge protection for the entire panel. Probably at least as good as that Leviton unit. Here is a Seimens Whole House Surge Suppressor


[h=1]Siemens QSA2020SPD Whole House Surge Protection with Two 20-Amp Circuit Breakers[/h]

 

[JHZR2]

Thanks, yes I've seen those but my understanding is that they don to offer the filtering circuit, which can help remove harmful electric noise/harmonics/transient effects that can do funny things to circuit boards...

 

[Dennis Alwon]

Thanks, yes I've seen those but my understanding is that they don to offer the filtering circuit, which can help remove harmful electric noise/harmonics/transient effects that can do funny things to circuit boards...

I have never had an issue with the appliances you mentioned. Not sure what type of noise is harmful to them. I have never heard that was an issue.

 

[gar]

150104-1432 EST

A low pass inductance-capacitance filter consists of inductors and capacitors. This does not dissipate much energy. What it does is take the input transient energy and spread it out over a longer time period, but does not reduce energy at the output. Since the input pulse energy is spread out over a longer time period means the peak output voltage is reduced compared to the input transient voltage.

During WWII there were major vacuum tube failures resulting from the shock of firing guns on board ship. When our ship, BB64, fired 16" guns the ship moved many feet sideways. The ship was nominally rated at 45,000 tons.

Accelerometer measurements were made at the gun mounts of some test ships to determine the shock that vacuum tubes were encountering. 1000 Gs and short durations were measured. Tubes were designed to tolerate this shock level. but the failure rate on board was not changed. The shock measurements were made in the wrong place. The structure of the ship was actually a low pass filter. The tubes actually saw a lower shock level, but of much longer duration. The point here is that the circuit, mechanical in this case, must be correctly analyzed to to determine how to solve a problem.

The problem with solid-state circuits is that they are very intolerant of over voltage. Thus, it is important to keep peak voltage below an allowed value. If we keep the voltage at an acceptable level, then duration is not important. Low pass filtering is useful to accomplish this goal. The low pass filter should be close to the device being protected.

MOVs, Zener diodes, and other nonlinear impedances are devices that conduct little current up to a designed voltage level, then start to conduct. MOVs don't have a real sharp thrreshold, but are large area devices with considerable thermal mass, that can tolerate large currents for short durations. The clipping point has to be above the highest normal peak voltage. For a 120 V circuit this might mean clipping at a voltage about 140/0.707 = 200 V.

Current limiting impedance is needed before the clipping device. Thus, the transient limiter should be close to the load.

It is advantageous to also have a transient limiter at the main panel.

There is even more that can be done, but the above can be useful.

.

 

[GoldDigger]

Regarding low pass filters: in addition to spreading out the energy on the load side they can simply reflect the high frequency components of the surge back upstream, reducing the total energy going to the load. Not necessarily good for other circuits connected upstream.
MOVs, on the other hand, will absorb some of the incident energy and also potentially reflect high harmonics upstream.

 

[robbietan]

I generally recommend line reactors, as these printed circuit boards are more susceptible to current spikes than to harmonics. current spikes in electronics occur every time you switch the appliance on. sensitive hospital equipment that gets its fuses blown every month now has operated for more than 5 years without any problem