Help me to build a Surge Protector

Thread Starter

drjackool

Joined May 23, 2021
34
Hi
Currently I use a Digital Voltage protector for entire home (below picture), but problem is the response time of these type protectors is low, and for example take 1 second to cut the circuit when voltage goes high so it could not protect against the lightning and spikes so I decide to use a surge protector. But SPD devices class C or type 2 (If I not mistake types) in my country is very expensive Now I want build my own surge protector. By searching Internet I found an element widely used in surge protectors, MOV. My question is can I simply place a MOV in the main power entry (220V, 25A) or needs a complex circuit?
Also MOV types are vary (GAS, ...) Which combinations are needed?
Also our hose does not have earth wire! For devices need it I use metal door frame.
Please guide me
Thanks
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MisterBill2

Joined Jan 23, 2018
19,471
The wired connection of a surge protector device is at least as important as the device performance itself. That statement was from a surge protector company I dealt with a while back.
Consider that the way the protector does it's protecting is to conduct the surge through itself instead of it hitting the protected device.

Now consider also that some very good gas tube surge protectors protect by short circuiting the transient. But after being triggered, they stay conducting. So they MUST have a series circuit breaker to allow them to reset. So every transient defeated will mean a short power outage as well. Just a few seconds, but definitely an outage. That is the downside. The upside is that they are good.
 

Thread Starter

drjackool

Joined May 23, 2021
34
hi







I bought some varistors 20D471K and 20D431K. I wanted to know if one of these can be paralleled with phase and natural after the power (230v 25A) meter to protect the entire home appliances from transient surges. Or not, it should be placed separately for each device (for example, inside a power strip) with a fuse, for example, 10 amps! If it should be like this, should it be after the power strip key or is it effective before the key? (to repel the spark flow that is the result of the tee key)







If I put it after the meter, when the resistance of the varistor becomes zero, will the fuse of the meter, which is 25 amps, work or will the varistor catch fire?







Of course, I also have a digital voltage protector with a contactor, but these protectors, well, their response speed is at least 1 second, and it does not work for lightning and such!







Thanks.
 
Last edited:

sagor

Joined Mar 10, 2019
927
Get a proper surge suppressor power bar. Most "better" power bars have built in protection with MOVs already, and some have other devices in the power bar to further protect everything.
Another option is to install a "whole house surge protector", a device that connects directly to the house power panel and protects the entire house circuit.
 

sagor

Joined Mar 10, 2019
927
I think the 431K is a bit too low in rating. It is rated 275VAC (RMS) +/- 10%, a bit too close to your 230V. If you have a noisy powerline, it is possible it has small, short spikes over that value, and that will destroy the MOV is a short period of time.
The 471K is a bit higher, 300VAC RMS. The +/- 10% tolerance of that value may still make it too low a safe value as well.
Proper power bar protection may include the GDT as well as the MOV and inductors.
I would not recommend you simply install MOV at your power panel without checking how clean the power is to start with. Even then, installing such a thing yourself can cause a fire or arc if not properly safeguarded against failure. You would need fuses and/or breakers to safeguard the circuit if the MOV conducts too much (or blows up).
Bottom line, don't do it yourself, it is not safe to do so.
 

Thread Starter

drjackool

Joined May 23, 2021
34
I think the 431K is a bit too low in rating. It is rated 275VAC (RMS) +/- 10%, a bit too close to your 230V. If you have a noisy powerline, it is possible it has small, short spikes over that value, and that will destroy the MOV is a short period of time.
The 471K is a bit higher, 300VAC RMS. The +/- 10% tolerance of that value may still make it too low a safe value as well.
Proper power bar protection may include the GDT as well as the MOV and inductors.
I would not recommend you simply install MOV at your power panel without checking how clean the power is to start with. Even then, installing such a thing yourself can cause a fire or arc if not properly safeguarded against failure. You would need fuses and/or breakers to safeguard the circuit if the MOV conducts too much (or blows up).
Bottom line, don't do it yourself, it is not safe to do so.
I think the 431K is a bit too low in rating. It is rated 275VAC (RMS) +/- 10%, a bit too close to your 230V. If you have a noisy powerline, it is possible it has small, short spikes over that value, and that will destroy the MOV is a short period of time.
The 471K is a bit higher, 300VAC RMS. The +/- 10% tolerance of that value may still make it too low a safe value as well.
Proper power bar protection may include the GDT as well as the MOV and inductors.
I would not recommend you simply install MOV at your power panel without checking how clean the power is to start with. Even then, installing such a thing yourself can cause a fire or arc if not properly safeguarded against failure. You would need fuses and/or breakers to safeguard the circuit if the MOV conducts too much (or blows up).
Bottom line, don't do it yourself, it is not safe to do so.
thank you
I want use 471 between L and N and 431 between L and E (ground) and N and E, I want use metal door frame as ground connection. (Unfortunately my country is in Paleolithic age) . so voltage probably is lower than between L and N
Also I use 10Amp Thermal Fuse to protect varistor from blows up
I want use that circuit to connect to a conductor so 10amp TF is enough
 

Ya’akov

Joined Jan 27, 2019
9,267
When I measuring voltage between L and the metal door frame voltage is 220V so I think it is better than nothing how ever I have no other cheap options. Do you?
A safety ground need to be certainly low impedance to earth. Since you have no idea what the door is attached to, it's very dodgy as a ground. You might as well use the neutral if you are doing that, and hope it is properly bonded.

I think I would make a real earth ground, either by a connection to a cold water pipe or better yet with two or three grounding rods and uninsulated copper cable.
 

sagor

Joined Mar 10, 2019
927
If you think a metal door frame is a valid "earth" ground, I would say you should not be doing any of this. You may in fact electrocute someone touching the door/frame.
I think this topic should be closed, as what you are thinking is very, very dangerous.
 

DickCappels

Joined Aug 21, 2008
10,247
On a personal note, years ago I rented a 15th floor apartment which had no grounded electrical outlets (in a developing country), so I had a real licensed electrician come out and provide a ground for the breaker panel and a grounded outlet for my computer and ‘scope.

He grounded everything via a wire fastened to the doorframe of the sliding glass door to the balcony.

As far as I could tell it worked fine.
 

Ya’akov

Joined Jan 27, 2019
9,267
On a personal note, years ago I rented a 15th floor apartment which had no grounded electrical outlets (in a developing country), so I had a real licensed electrician come out and provide a ground for the breaker panel and a grounded outlet for my computer and ‘scope.

He grounded everything via a wire fastened to the doorframe of the sliding glass door to the balcony.

As far as I could tell it worked fine.
It’s not that such an arrangement couldn’t serve, it’s that measuring 220V from L to the door doesn’t tell us why that potential exists. Safety grounds are bonded to the N at the panel, why is the door frame a low impedance path to the N?
 

DickCappels

Joined Aug 21, 2008
10,247
It’s not that such an arrangement couldn’t serve, it’s that measuring 220V from L to the door doesn’t tell us why that potential exists. Safety grounds are bonded to the N at the panel, why is the door frame a low impedance path to the N?
At my house (in S.E. Asia) all of the outlets are grounded by a long ground rod driven into the earth next to the house by the electrician who installed the wiring -or at least that's he told me. The Neutral is earthed at the pole supporting the distribution transformer about 100 meters away. At about 11:00 PM there is a 2.7 VAC difference between the two. Probably a little higher when the air conditioners are running : -)

With respect to thread starter's doorframe, there is a good chance that the doorframe is bonded to the other metal parts in that building, or at least that part of the building. Speaking (writing) from limited experience, such bonding is done to reduce the chance of electrolysis eating away at rebar embedded in concrete as well as providing a good path to earth.
 

MisterBill2

Joined Jan 23, 2018
19,471
The mechanism for protection by a varistor, gas tube device, or even a spark gap, from excess voltage, is to suddenly start conduction so that the surge power is conducted away from the protected device. The result is that the current flowing in the protective device will be large, and a great deal of power will be dissipated in that device. Therefore there must be some means of disconnecting the power to that protective device. That is commonly a fuse, although it may also be a circuit breaker.

What that means is that the protective device should be located electrically close to the protected device, and after a suitable excessive current device. The reason is that this tends to limit the current that flows when the protective device starts conducting.
What I have seen is that such protective devices installed on their own circuit in a standard circuit breaker panel only provide protection until the series circuit breaker trips and disconnects them. After that they provide no protection at all.
 
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