MOVs in an outdoor outlet

[longball53098]

I am posting this question here in the electrical forum for anyone with the expertise to guide me to installing surge protection on a specific outlet in my outdoor area to protect a IP camera that has a transformer plugged in to it. My idea is to install MOVs in the outlet to protect the outlet and whatever is plugged to it. I have the ability to install the MOVs needed but my main question is what size MOVs and should I install on all 3 lines to cover the hot/neutral and earth. The feed cable to the outlet is coming from a breaker about 30 meters distant and is 2.5 sqm  THW cable. If possible give me a diagram of the correct connections for the MOVs

[Crossy]

I bought a bag of these chaps http://www.mynpe.com/mynpe/more.php?data=116450101007

 

 

8kA rating, 12 Baht a pop from NPE.

 

Datasheet S20K275.pdf

 

In your outlet connect three, L-N, L-E, N-E. Sleeve the exposed leads.

 

Since you have a long run it may be a good idea to bash in a local ground rod and not use the ground in the cable (if there is one).

 

This is what I did when our gate controller got fried by a surge. The supply run is about 60m, easily enough to pick up nasties on it's way from the house.

 

[longball53098]

Crossy, I new you had the answer. Easy to do. I may add to my power for the gate controller too.

 

THX

[maprao]

Is it as simple as insulating the legs and connecting it in parallel (across) the AC mains input to the PSU After selecting the correct value MOV.

Sent from my SM-N960F using Thailand Forum - Thaivisa mobile app

[Crossy]

1 hour ago, maprao said:

Is it as simple as insulating the legs and connecting it in parallel (across) the AC mains input to the PSU After selecting the correct value MOV.

Pretty much. 

 

As I noted earlier the 8kA beasties are cheap enough to do a full 3-leg job although most "surge supressors" do only have one (tiny) MOV L-N.

 

[maxpower]

Unprotected MOV across 220V supplies.

 

Take care when locating metal oxide varistors near to combustible materials and expensive electronic circuit boards because they can fail in spectacular fashion.

In risky areas, best to add a one shot thermal fuse in series or create a thermal fuse sandwich to break the live of L-N L-E protection.

 

 

 

 

 

[Crossy]

54 minutes ago, maxpower said:

Unprotected MOV across 220V supplies.

 

Take care when locating metal oxide varistors near to combustible materials and expensive electronic circuit boards because they can fail in spectacular fashion.

In risky areas, best to add a one shot thermal fuse in series or create a thermal fuse sandwich to break the live of L-N L-E protection.

Fun eh?

 

It is most definitely true that prolonged over-voltage does cause MOVs to overheat and potentially catch fire. It is also important to understand that these devices do wear out if subjected to many (should be thousands) surges and the wear out mechanism is a progressive reduction of the trigger voltage. So the scenario could indeed occur. At least in theory they are supposed to pop apart and go open circuit.

 

If you are going to put these chaps behind outlets, make sure there are metal back boxes and I would avoid wooden walls.

 

That said, these things are all over the place including in "surge arresting" power boards and plug-in arrestors. None of these that I've seen have any form of protection against the MOV going short, so one assumes they just catch fire ???? (I've never seen one go like that).

 

Of course, if you do add a fuse, you don't know if the protection has failed unless the fuse also cuts the power to the outlet.

 

For our OPs application behind an outdoor outlet I would just do it. If you're building your own extension boards add a 5A fuse to the inlet side (before the MOV), that should open if the MOV fails and still let you have a kW of connected load.

 

[longball53098]

Thanks for all added info.

[maxpower]

19 hours ago, Crossy said:

That said, these things are all over the place including in "surge arresting" power boards and plug-in arrestors. None of these that I've seen have any form of protection against the MOV going short, so one assumes they just catch fire ???? (I've never seen one go like that).

Self extinguishing materials and thermal fuse protection with indication are common in devices that employ MOV's. Din rail style surge modules usually include a spring loaded thermal safety link that disconnects the device.
UL1449 sets a safety and performance standard that many manufacturers follow.

 

19 hours ago, Crossy said:

Of course, if you do add a fuse, you don't know if the protection has failed unless the fuse also cuts the power to the outlet.

Fuse or no fuse how would you know if a MOV hidden inside an enclosure has failed. If the thermal fuse has activated there is usually signs of burning around the MOV. But of course you could just leave it to the smoke and flames to provide fail indication.

[Crossy]

33 minutes ago, maxpower said:

But of course you could just leave it to the smoke and flames to provide fail indication.

I'm persuaded ????

 

Since we probably don't want to do this, do you have a recommendation for a suitable thermal fuse that can be sandwiched between two 20mm MOVs? 

 

Ideally readily available here, if not then AliExpress or the like.

 

EDIT Something like this? https://www.aliexpress.com/item/TF-Thermal-Fuse-10A-250V-Temperature-65C-85C-100C-105C-100C-113C-120C-130C-152C-165C/32893092186.html

 

 

The 65C units would likely do the trick if the enclosure isn't getting too warm in operation. At 14 cents a pop we probably should be doing this.

 

Is it worth glueing the fuse to the MOV? 

 

 

[maxpower]

36 minutes ago, Crossy said:

I'm persuaded ????

 

Since we probably don't want to do this, do you have a recommendation for a suitable thermal fuse that can be sandwiched between two 20mm MOVs? 

 

Ideally readily available here, if not then AliExpress or the like.

 

EDIT Something like this? https://www.aliexpress.com/item/TF-Thermal-Fuse-10A-250V-Temperature-65C-85C-100C-105C-100C-113C-120C-130C-152C-165C/32893092186.html

 

 

The 65C units would likely do the trick if the enclosure isn't getting too warm in operation. At 14 cents a pop we probably should be doing this.

 

Is it worth glueing the fuse to the MOV? 

 

 

I have custom MOV/GAS arrestor boards on my home electronics which have 80 deg C 10 Amp one shot thermal fuses near to the MOV's

These axial lead thermal fuses are assailable from Eleement14, RS, Ebay, Ali and good electronic component stores.

Best to crimp tails on thermal fuses as soldering requires heat sink on the leads. 

 

[Crossy]

4 minutes ago, maxpower said:

Best to crimp tails on thermal fuses as soldering requires heat sink on the leads.

Bloody good point ????

 

[maxpower]

Old photo from BKK workshops showing switched Thai sockets mounted on sealed metal box containing a bunch of L-N L-E N-E connected MOVS and mains filter. No thermal protection required in this metal enclosure.

 

[Crossy]

Taking on board @maxpower's much appreciated comments we have this:-

 

 

 

All the bits were "in stock" in the assorted stuff box (never throw anything away). The bolt next to the MOVs is blocking up a hole which I thought was a bit big to maintain integrity should the MOVs fail.

 

A few small holes wouldn't be a big issue, indeed they could serve to let the "magic smoke" (smell of frying MOVs) out to alert you to their failure.

 

Of course, this being Thailand the ground wire is brown (and bolted to the metal box) thus maintaining the black and white L and N convention.

 

In reality I wouldn't bother for an outdoor outlet in a block wall or inside a mostly metal and glass light fitting (all our circular "used to be fluorescent but now LED" fittings have these MOVs on the incoming choc-bloc). But if you're going to have it in your lounge or other valuable places go with the metal box. 

 

 

  

 

 

[maxpower]

1 hour ago, Crossy said:

All the bits were "in stock" in the assorted stuff box (never throw anything away). The bolt next to the MOVs is blocking up a hole which I thought was a bit big to maintain integrity should the MOVs fail.

You can use the same method to build a whole house protection box using higher rated MOVS. Maybe include gas arrestors and spark gaps to make a level one box.

[longball53098]

On 11/18/2018 at 10:04 AM, Crossy said:

I bought a bag of these chaps http://www.mynpe.com/mynpe/more.php?data=116450101007

 

 

8kA rating, 12 Baht a pop from NPE.

 

Datasheet S20K275.pdf

 

In your outlet connect three, L-N, L-E, N-E. Sleeve the exposed leads.

 

Since you have a long run it may be a good idea to bash in a local ground rod and not use the ground in the cable (if there is one).

 

This is what I did when our gate controller got fried by a surge. The supply run is about 60m, easily enough to pick up nasties on it's way from the house.

 

Crossy, seems NPE does not stock this animal any longer and will not re-stock it. I have not been able to locate a MOV with the same specs at my limited on line searching. Any ideas? Using NPE on line and chats via LINE they are very slow to respond to any questions or suggestions. Im my searches the 8000 A spec is hard to find around in my searches.

 

 

[Crossy]

20 minutes ago, longball53098 said:

Crossy, seems NPE does not stock this animal any longer and will not re-stock it. I have not been able to locate a MOV with the same specs at my limited on line searching. Any ideas? Using NPE on line and chats via LINE they are very slow to respond to any questions or suggestions. Im my searches the 8000 A spec is hard to find around in my searches.

AliExpress have them from various sellers @ USD 0.40 - 0.50 a pop (search for "varistor S20K275"). How many do you need (I still have a few left)?

 

Or the S20K250 should be fine. The S20K230 would likely be marginal on voltage rating.

 

[longball53098]

15 hours ago, Crossy said:

AliExpress have them from various sellers @ USD 0.40 - 0.50 a pop (search for "varistor S20K275"). How many do you need (I still have a few left)?

 

Or the S20K250 should be fine. The S20K230 would likely be marginal on voltage rating.

 

Thanks, don't need many but I will locate a source. You need yours for the next season of storms.

[longball53098]

2 hours ago, longball53098 said:

Thanks, don't need many but I will locate a source. You need yours for the next season of storms.

A little searching today proved good. Found the MOV here and already ordered and will ship today. Very easy to use this company and online ordering.

http://www.es.co.th/detail.asp?prod=022100121

[Crossy]

Only 36,000 in stock!

 

I've bought stuff from ES in the past, no issues whatever.

 

[MoD1977]

On 11/19/2018 at 7:34 PM, maxpower said:

You can use the same method to build a whole house protection box using higher rated MOVS. Maybe include gas arrestors and spark gaps to make a level one box.

I'm interested into building a whole house box for myself, what kind of MOV's would you recomend?

My house electrics are 3 Phase and i would like to protect all of them (of course ????)

How would this setup look like?