Surge protector is a lie?

[Commander Kinsey]

I have a Micromark surge protector. Just a plug (not as in to connect an appliance, it just plugs into a socket to absorb surges, no cable comes out of it). I was interested in the LED on the front which says "protection active", so I opened it to look inside to see how it knew if it had expired. What do I find? An array of varistors as expected, but the only connection to live was through a clumsily soldered on piece of fusewire about 1-2 amps thickness. So.... it blows the fusewire as soon as there's an infinitely tiny surge, so therefore can't absorb much of it anyway? What's the point in that?

[Slevin]

Simple. When the light goes out you give Micromark more of your money...but I think you knew that.

[Brian Gaff]

Well, it is probably only meant for spikes caused by things switching on and off. I did, some years ago buy a packet of Surge protection vdr devices from RS and fitted them inside plugs where there was room. One day there apparently was a lightening strike nearby, and my stuff was fine except for

1 blown 5 amp fuse on a lamp. Interestingly these vdrs specs had an amazingly small reaction time and could for a split second dump many amps, but only over around 360v ish. So it was what one might call a limiter, I suppose. Many appliances have something like this inside, I'm told but never looked. Incidentally, I had a Samsung Fax machine, many years back trashed by a lightening strike to the public telephone wires about a mile away. It just rolled out black paper, It was under warranty, and the bloke who fixed it changed the pcb saying its a common fault, now fixed by a surge suppressor on the board.

Of course if you do really get a very local strike, I have seen the result in a local factory. Every bit of electronics had its mains input circuit trashed and nearly all the internal wiring had to be replaced and the sockets were in fact blown off the wall and melted. Really a sobering thought. Brian

[dyno dan]

I had a ground strike near me a few years ago. Apparently the surge of electricity in the ground was picked up by my satellite TV antenna's underground wire. The satellite receiver was fried AND SO WAS the UPS

• surge control unit that the satellite receiver was plugged into. Nothing else in the house was affected.

When lightning is real close, I now unscrew the dish antenna from the receiver and just watch things that I had previously recorded.

-dan z-

[trader_4]

A surge protector doesn't absorb surges, it shunts over voltage conditions. Ideally that's to a good earth ground, but with the plug-in type, earth ground is typically a long way away through a path that has impedance. The surge protector still shunts the hot, neutral and ground together, which limits the voltage difference between them. So if you have an appliance plugged in, while all the lines could go significantly higher, the difference between them will be limited, preventing damage. In the case of devices that have other connections, eg modem, TV, any phone, cable etc lines also need to pass through the surge protector for this to work. A

If the fuse is 2A, that does seem light, but it depends on what the surge protector was designed and specd for. Like the other poster said, it would still work with smaller transients, though modern appliances already have protection for that. Also, a fuse doesn't have to be able to carry a huge current to work with a surge protector. For example, the whole house surge protectors that can shunt 50K Amps just use a 20A breaker in the panel. That's because the surge is so fast, it's over before the breaker can open.

[Ed Pawlowski]

I live near the lightning capital of the US so I have whole house protection. I don't know what protection appliances have, but they all have some form of electronics today so I figure is is cheap insurance.

I also have a few thins on UPS but more for the interruption than the surge protection. Only takes a blink for the cable box to go out and they a long reboot time.

[trader_4]

Appliances have MOVs like what Commander found inside his surge protector. A tiered approach is ideal, with a whole house protector at the panel and plug-ins for important appliances, especially any that also connect to communication lines. I agree with you, I'd rather have a $15 plug-in surge protector deal with the surge instead of the $500 appliance.

[John Larkin]

Cheap chinese appliances with fake UL and CE labels need fake chinese surge protectors with fake UL and CE labels.

Micromark seems to be sold in the UK but not in the US.

[invalid unparseable]

Surge protectors are a lot cheaper than appliances like microwave, TV or computer. I had problems with all before using surge protectors. Living in a treed area, high tension line would fall onto low tension line to houses causing the voltage surge.

[Clare Snyder]

Up here in Ontario's "thunder alley" I have whole House Surge Protection and my main computer is on a full time online UPS and all of my internet - router, modems, etc are also on UPS / surge protection. All services are underground including the cable internet.

[Carlos E.R.]

Guessing, the varistors absorb a quick surge, and the "fuse" doesn't blow. If the surge is enough to blow the electronics and cause them to short circuit, the "fuse" blows and avoids the gadget to cause damage to the rest of the house. Of course, the spike could still blow the house, but you will not be able to sue Micromark for it.

[Paul]

Obviously, there is some complicated rationale for what was done.

If you look at a proper design, the protective components have barriers placed next to them, to contain shrapnel. And this is to prevent the protection block from becoming a flame thrower or punching holes in adjacent components.

The components are also placed in a metallic housing (for fun).

So it is possible to make a surge arrestor with some useful properties. Not all of these things need to be a joke.

There is a single-plug entrant there, but the physical properties aren't quite as good.

Paul

[The Natural Philosopher]

In general if you have SMPS on the rings, you have what amounts to an 8 amp + capacitor surge limiter right there and short transients wont get through the mains filters anyway.

In short if you get a surge big enough to be a problem it will take out the surge arrestors only anyway.

My time in S Africa taught me that nothing is proof against near wire strikes except physical isolation - transformer or opto coupler.

And if you get a full wire strike, all bets are off. You will be jumping across any short gap anywhere nearby.

Full carnage.

[trader_4]

Varistors don't absorb a surge, they just shunt it.

[trader_4]

Funny then that telecom companies and similar around the world have deployed a tiered surge protection strategy that has effectively protected their equipment, eg central office switches, cell phone sites, etc. Whole house surge protectors that can handle a 50K amp surge are readily available.

[Jasen Betts]

Varistors usually fail short-circuit, hence the fuse. There's no point wasting money on a breaker in that position.

[Andrew]

HT lines generally do not cross over LV lines for this reason.

All the places where I have seen this happens there is always an additional bare copper earth line above the 3 phases and neutral, and this extra earth is connected to earth at each of the supporting poles.

These days the LV stuff is being replaced with twisted bundles of insulated aluminium cable anyway which should minimise the problem.

[invalid unparseable]

I do not know about their wiring here. Service to my street is underground but above ground leads to it. In the past I recall wet branches falling causing the short between HT and LT.

[Vir Campestris]

The way this is done may vary between the US and UK. This is cross-posted to international groups.

Andy

[Commander Kinsey]

Trouble is any decent surge would blow its internal fuse, which stops it protecting, and the surge then carries on to the equipment. A better way would for the fuse to also stop power to the device it's protecting. Then if the surge is too much for the surge protector, you've stopped the power to the device.

I'm going make my own, with varistors big enough to blow a 30A fuse for the whole ring main.