Household Surge Protection

Introduction: Household Surge Protection

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first to…

The photo shows a lowly metal oxide varistor, or MOV. These cost less than a dollar and are the main component of a surge protector. They are effective, even though a high quality surge protector also includes other things, like coils of wire known as inductances or chokes. Back about 30 years our church lost some telephone equipment due to surges from nearby lightning strikes. I added an MOV between the green telephone wire and ground, and another between the red telephone wire and ground. We had more lightning strikes in the area, but never lost telephone equipment after I installed the MOVs.
An MOV normally does not conduct (presents an open circuit). In the presence of a voltage spike that could damage electronics, it suddenly conducts and shunts the spike safely to ground. An MOV does not last forever, but can become spent, like a match that has been struck, after a really heavy spike. If you know you had a strong lightning strike and neighbors lost electronic equipment, it might be good to replace MOVs you are using for surge protection.

Once MOVs were available in stores like Radio Shack. I bought this one on-line from an electronics parts supplier.

Step 1: What Do You Want to Protect?

The photo shows the MIG welder I won in a metalworking contest at Instructables four years ago. It has an electronic circuit board inside it, like many other modern devices do. Its warranty began the day the welder was made, even though it sat in a warehouse for a number of months before I came to have it. Now that it is out of warranty, I want to install surge protection. I could add the surge protection to the electrical wiring in my workshop, I want to add it to the welder in case I take the welder to a job site away from my workshop.
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Step 2: A Suitable Location

I want to install my MOV as near the entrance of the power cable into the machine as possible. The blue connector in my hand is from the power cable and connects to a circuit breaker that protects the welder from current overloads. The white wire carries power to the electronic circuit board. I am mounting one wire from an MOV as close to the body of the circuit breaker as possible so the blue connector attaches as securely as if the MOV were not there. I soldered the lead from the MOV to the metal spade, but avoided using excess solder.

Step 3: A Connection to Ground

The ground connection for the green wire in the welder power cable bolts to the metal frame of the welder. That is a good place for me to attach the other leg of the MOV. I am using a large closed crimp connector on some monster speaker cable.
The white wire from a 120 volt power cable and the green ground wire connect to the same strip in the circuit breaker panel and both are grounded. If your power cable does not have a third green wire, use a connection to the white wire to ground the MOV. I did that once with a Sangean solid state shortwave radio.
The grounding bolt is common 1/4 inch x 20 thread. I added a nut to secure the connection. I decided not to disturb the factory connection by using its nut.
The second photo shows the lead from the MOV wrapped around the end of the monster cable and ready to solder.
The third photo shows the finished solder connections. The spade connector from the power cord fits nicely where it belongs, even though it shares the connection with an MOV.
The MOV and the wire to the grounding connection are neatly out of the way. Nothing is in danger of shorting to anything. It is time to put the welder case back together.
You may not need to protect the circuit board in a MIG welder, but your stove or refrigerator or washing machine or microwave oven likely has an electronic circuit board vulnerable if lightning comes near. Those circuit boards can be expensive to replace, and as time passes they are sometimes difficult to find. What I did by adding an MOV to a welder is a sort of paradigm for what is possible for unrelated equipment you have. The more MOVs as surge protectors on your system, the better your whole house is protected. MOVs act together like a team. See the fourth photo. When it is not feasible to open a device and install an MOV inside it an MOV can be mounted in a male wall plug. The plug can be located in an unused outlet very near the device to be protected. This is an inexpensive male plug. I used a burr bit on a Dremel tool to make a slot that fits the MOV.

Step 4: Flat Screen TVs

Our 12-year old granddaughter is doing her schooling on-line from our house this year. I showed her an electronics experimenter‘s kit and she got excited about a couple of projects. A few days later she had managed to drag home someone’s 70 inch LED TV that went completely dead after a nearby lightning strike. (It is not the one in the photo.)

See the second photo. This is the power board from that defunct 70 inch TV. The green disc is marked on the circuit board as a resistor. Next to the green disc to the right is a honey colored MOV. Next to it on the right is a fuse. It is good to know this brand (VIZIO with parts made by Sharp) includes not only a fuse, but also an MOV for surge protection. An Ohmmeter should show no circuit through the MOV, but a circuit pathway through the fuse. But, lightning strikes do not always enter a TV through the power board. In the end, it appears the lightning strike near this TV sent a surge in through auxiliary components, like a DVR or an HDMI connection, Things connected to a TV also need surge protection.

Step 5: Undoing the Damage

There are numerous videos on the Internet for troubleshooting and restoring a flat screen TV. If you watch one such video you think it will be easy. Watch a few more videos and you begin to realize it could be more complex than you expected. The testing procedure is mostly a matter of checking for correct output voltages at various pins. There is supposed to be a table of voltages expected at particular pins imprinted on the power board. This VIZIO TV did not have that table. In the end, I strongly suspected the main board was faulty, not the power board and not the T-conn board. Auxiliary equipment connects to the main board. If a surge from lightning entered through an HDMI cable, and the main board likely failed, the MOV and the fuse on the power board would still be good. I found a set of the three primary boards for $112 US (delivered) at ShopJimmy (dot) com. (I have no connection to them other than satisfied customer.) After installing the three primary boards, the TV worked like new. I had my granddaughter do the work to give her a sense of fulfillment and confidence. All we needed to do was mount boards with screws and connect ribbon connectors. ShopJimmy will answer your questions and help you get your TV working again.

Step 6: Surge Protection for Auxiliary Components

These two photos show the main board (front and back sides) from the TV my granddaughter brought home. A surge that gets into an auxiliary component can enter an otherwise protected TV through the signal inputs to the TV’s main board. You might be able to attach MOVs to solder points on the backside of the main board, but space is very limited and it could be very tricky to do. If you want to add surge protection to a coaxial cable, it might be easier to buy a surge protection power strip with coaxial connectors attached. Those are widely available. Do add surge protection to auxiliary devices like VCRs and DVRs or DVD players.
Surges are not all caused by lightning. A few years ago I lost the keyboard on my PC when someone hit a power pole in a traffic accident and it caused a surge.
MOVs are not perfect surge protectors, but are a big help in limiting damage to your devices from surges, whether caused by lightning or some other cause. They are inexpensive and not difficult to add to your system. Just be careful not to cause any shock hazards.

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    8 Comments

    0
    shadders
    shadders

    10 months ago

    Normally when using varistors circuit designers consider a few things that haven't been mentioned here as far as I can see and these are worth thinking about:
    1) What voltage level do you want to protect? - MOVs come in different voltage ranges.
    2) How much energy does it need to handle before failure? - Every over voltage event it experiences degrades it and the severity has an effect on this too (as mentioned in the article) but you can buy ones with different ratings (mentioned in mscaldwell888 comment but left in for completeness).
    3) Sustained over voltage conditions can lead to them catching fire so you normally include thermal protection i.e. a fuse or circuit breaker to blow/trip on a fault
    4) Inherently MOVs have no over current protection so when designing circuits think of how to handle an over current condition if your load or power supply circuit fails.

    One last point to consider on protecting electronics (and motors) is an under voltage fault. MOVs will not operate here but more expensive surge protectors/UPS' can have monitoring for this and for more expensive or critical loads consider investing in something more robust than a simple MOV. Here in Africa we frequently experience these and most people buy "fridge guards" which have over voltage/under voltage and surge protection built in.

    Saying all this MOVs are a critical component in any AC powered circuit in my opinion so I am very happy to see this, thank you!

    0
    Phil B
    Phil B

    Reply 10 months ago

    Thank you for your detailed information. As best I can determine what you call an under-voltage event we in the USA call a “brownout.” I have never experienced one, but I have heard of them where power stations were unable to keep up with demand, as a hot summer day when many people run air conditioning in a high population area.
    I checked the on-line retailer where I purchased my MOVs. Most are rated at more than twice the voltage in our power outlets. They do have one style of MOV rated at different voltages below our standard power outlet voltage.
    When I first learned of MOVs the article I was reading mentioned the honey colored MOVs and said a turn to a darker color was a sign the MOV is no longer effective and needs replacement.
    If we have had a sustained over-voltage exposure anywhere in the USA, I am not aware of it.

    0
    mscaldwell888
    mscaldwell888

    11 months ago

    Interesting 'ible. I started looking at purchasing some MOV's and there seem to be various different ones (different ratings?). What do I look for in the rating or description that will help me find the right one for a particular application?

    0
    Phil B
    Phil B

    Reply 11 months ago

    Thank you for your comment and for looking at this. When I first learned about MOVs they were rated in Joules. Now a volt and Ampere rating is given. I do not know what changed. I have not been a constant observer. You want their capacity to be big enough to handle a surge. If there is information on how to determine that, I have not seen it. The MOVs I have used have been nearly 1 inch or 25 mm in diameter. I believe those were rated 1500 Joules. In the text of my ‘ible I mentioned successfully protecting telephone items from surges. I used two MOVs about 1 inch in diameter and those did the job. I would say a more important consideration than size is the number of them you are able to use. If you have them scattered throughout your home they will have a cumulative effect when a surge comes. Also, I remember reading about static discharges that ruin semiconductors. With those voltage seemed to be more important. Current was extremely low. By the time you put an MOV on each item in your house with an electronic circuit board inside, you will have quite a bit of cumulative protection.

    0
    john pedersen
    john pedersen

    12 months ago on Introduction

    I've been using MOV's since the mid 1970's, They really do save electronics from surges and lighting strikes. Good Instructable Phil B

    0
    Phil B
    Phil B

    Reply 12 months ago

    Thank you for looking and for commenting. I am hardly an expert on MOVs. I related most of my experiences with them. I thought someone who Is unfamiliar with them might benefit from what I have here, especially in these days of fairly expensive flat screen TVs. Thank you for not finding anything where I went far off of the rails.

    0
    john pedersen
    john pedersen

    Reply 12 months ago

    You're welcome Phil B, I'm no expert either, they were introduced to me by an electronics salesman when I was working as a Radio Technician. A MOV saved my B&W TV, from a lightning strike back in the 1980's, I had put the MOV across the antenna terminals. There was a bright flash, and the TV continued to work and did for several more years after that.

    0
    Phil B
    Phil B

    Reply 12 months ago

    It is fun to know some little thing, like how to use an MOV, to get around a big problem that leaves others standing on the platform after the train has left the station. It is also fun to share those things with any who are interested and will make use of them. Thank you for your story about your TV.