Surge Protector "Discussion"

[SteveFury]

Hi Daverob.

The general public in the US don't usually concern themselves with electric codes and regulations. If they need an extension or power strip they just go get one.
The US has Underwriters Laboratories which is trusted to test consumer products to be safe before they go to market. I think most of us understand that if it didn't pass UL then the safety is questionable.

I still don't understand why a 9ft extension would be said to be unsafe when a 30ft cord made of the same materials would be tested in a laboratory to be safe for consumer use.

Here's a calculator:
http://www.powerstream.com/Wire_Size.htm

It calculates a 3 foot 14gauge wire drawing 15a will have only have a 0.2v drop, and a 9 foot cord of the same length will have 0.7v drop. 30 feet would be only 2.3v.
I haven't heard of anyone being electrocuted with less power than a common flashlight battery.

The only possible safety issue I can see with daisy chaining power strips is (1) overloading them or (2) using damaged ones in which the plugs and sockets have became dirty or corroded and cause heat under a high load. (Such as using strips that had been forgotten and left outside in the elements)

On the lighter side,
I understand your passion about the spread of misinformation and false claims about surge protection. For example, I learned a lot about solar power a few years ago. I learned its capabilities and limitations, and the limitations are most important. I built a small scale 240ah solar power backup system which also run back yard security lights. I firmly believe the solar power industry is involved in crooked trickery scams and false claims.

We've seen crooked, misleading scam advertisements like these:
http://www.homemadeenergy.org/specia...d1cf7cda210e4=
(Link deleted, see below)
Worse is that more scams keep appearing.

Also suppliers making wild unrealistic claims like these:
http://www.greenearth4energy.com/
http://www.freesunpower.com/

Someone made this comical parity website:
http://www.diysolar.com/

If you're interested, this is a thread to my own project:
http://www.solarpaneltalk.com/showth...ll-scale/page3

Anyway, I get just as aggressive to people making false claims about solar as some do here about surge protection. Maybe I get more aggressive about it.

[daverob]

The general public in the US don't usually concern themselves with electric codes and regulations. If they need an extension or power strip they just go get one.

It's the same here, want stuff - buy stuff - use stuff. The only thought given to safety is 'they wouldn't sell it if it wasn't safe'. In the UK we used to have the 'British Standards Institute' which allowed it's 'Kite Mark' to be put on products that had been tested for safety (In the same way as the UL mark is recognised in the US), but that's disappeared and been replaced by the 'CE' mark in the interests of European harmonisation. But seeing as the 'CE' mark is compulsory for pretty much everything nowadays, there's no longer a recognised mark of quality over here.

I still don't understand why a 9ft extension would be said to be unsafe when a 30ft cord made of the same materials would be tested in a laboratory to be safe for consumer use.

To be honest, I don't think there's anything fundamentally unsafe about your example of 3 3ft extension leads. But I'd still recommend not daisy chaining extension leads on principle, as an average person is only going to hear that there's nothing wrong with daisy chaining 3 extension leads, and then go on to connect 3 30ft extension leads together, which is likely to present a significant risk.

It calculates a 3 foot 14gauge wire drawing 15a will have only have a 0.2v drop, and a 9 foot cord of the same length will have 0.7v drop. 30 feet would be only 2.3v.
I haven't heard of anyone being electrocuted with less power than a common flashlight battery.

Ok, I must admit that I'm not familiar enough with AWG and imperial measurements used on that site to know if we are actually talking about the same thing here, even the metric equivalents shown are the wrong ones for me (we use cross sectional area to measure cable gauge rather than the diameter). The way I understand it is that voltage drop is not relevant to the safety of an electrical system. Voltage drop only tells you how much power is lost within the cable itself, and allows you to see if there's enough getting through to operate whatever is connected at the other end.

I don't understand the relevance of the flashlight battery remark. This may be a cultural difference in the way electrical systems are specified. Even with a 2.3v voltage drop, you still have the other 117.7v waiting to shock you at the end of cable.


In the UK the way electrical systems are specified and tested for safety is based on loop impedance and disconnection times. A rather simplified explanation follows...

The important thing to consider is that if an electrical fault happens, the source of power should be removed as soon as possible. As the longer the power is connected, the longer it has to hurt someone or cause additional damage (fires etc). This is why we have fuses and circuit breakers.

In the UK the regulations say that for equipment that may be hand held (which includes all electrical outlets and extension leads as you don't know what may be plugged into them), when an earth fault occurs the power should be disconnected within 0.4 seconds, any longer than this presents an unacceptable risk to the health of the person holding the equipment. I'm not certain why they specify this figure, I'm only really comfortable with my knowledge of the electrical theory side of things, the squidgy stuff between our head and toes is still a bit of a mystery to me.

To disconnect the power we use a fuse or a circuit breaker. These work by letting a safe amount of power through, with an unsafe amount of power causing it to blow or trip. Due to the way they work a 15 amp fuse will not blow immediately you pass more than 15 amps through it, it's quite likely that it will allow a 25 amp overload current to pass without ever blowing. It will still take about a minute to blow at 40 amps, and you'll need to pass over 70 amps through it to make it blow in under a second. To get this fuse to blow in less than the required 0.4 second disconnection time will need a fault current of around 90 amps.

Now 90 amps is quite a large amount of current, you're going to need decent wires and some nice solid connections for a current that high. Knowing this, would you still be comfortable that your three daisy chained extension leads are up to the job.

The loop impedance is also an important factor. If the resistance of the circuit is too high (mostly due to wires being too long or their gauge being to thin, or in the case of installations unsuitable earthing methods), then it would be impossible for a current of 90 amps to pass. This is a simple ohms law calculation and for a 240v circuit this resistance is 2.6 ohms (it would be 1.3 ohms for a 120v circuit). This seems like quite a high resistance value when you're talking about the sort of wire commonly used in electrical installations, but you've got to remember that this includes all the wiring in the circuit, the line/live conductor from the origin of the electrical supply all the way through to the electrical equipment in use and the neutral/return or earth conductor all the way back to the origin (hence the term 'loop' impedance).

In the UK we have specifications that need to be complied with to ensure that this loop impedance is always low enough. This includes measuring the external loop impedance where the supply enters the house, calculating the wire sizes used in the the homes fixed installation so that their contribution to the resistance is low enough, and ensuring that there's a suitable margin remaining for the power cables (and extension leads) leading to the electrical equipment itself. If the customer uses underspecified extension leads, or daisy chains too many of them together, then this margin is lost, and you have an installation that cannot comply to the disconnection time requirement.

On the lighter side,
I understand your passion about the spread of misinformation and false claims about surge protection. For example, I learned a lot about solar power a few years ago. I learned its capabilities and limitations, and the limitations are most important. I built a small scale 240ah solar power backup system which also run back yard security lights. I firmly believe the solar power industry is involved in crooked trickery scams and false claims.

I know exactly what you're talking about here, although my personal experience is on a smaller scale (just 12v yard lights and electric fencing at the stables when there was no grid power available). As the stables are shared, we got a few quotes from salesmen before I decided that I could it alone and make my own system from surplus/scavenged parts for less than my own contribution towards the cheapest quote. The price and specification differences were enormous, with some wanting to install huge panels, inverters and floodlights, and some with barely more than the LED garden lights you find in DIY stores.

We're not at those stables any more, and so I now have all the bits sitting in the workshop waiting for me to find a good use for them again.

If you're interested, this is a thread to my own project:
http://www.solarpaneltalk.com/showth...ll-scale/page3

Looks like an interesting project, your mount/frames look a lot better than my attempt. I don't think I'd ever go as far as making my own panels, I'd always be worried about water penetration, and seeing as we seem to get more rain than sun over here...

[SteveFury]

Hi Daverob,

That's a lot different than it is here in the U.S. A fuse here in the US is designed to open at its rated current, so a 15 amp fuse must open when 15 amps flows through it. The only exception is the slow-blow type which allow the temporary surge of a starting motor. Also, our grounds and returns are created close as possible to the individual power distribution boxes (Breaker boxes) so we won't have to figure tens of miles or kilometers of loop back to the power station. Does the UK really run a ground and/or return back to the station? Wow.

About your statment:

Now 90 amps is quite a large amount of current, you're going to need decent wires and some nice solid connections for a current that high. Knowing this, would you still be comfortable that your three daisy chained extension leads are up to the job.

As I've just posted, the circuit would open at 15a not 90, and if the hot side met ground or return with a person touching it, the bulk majority of current would flow to ground (not the person) as its supposed to until the fuse or breaker opened. Based on the calculations of 9 feet of 14 gauge wire and 120v, 119.3v would safely pass to ground and 0.7v goes to the person holding the metal case of the appliance.

Would I be comfortable holding that 0.7v on a daisy chained strip? Hmm. It depends. Of course the situation is to be avoided if possible... and I'd feel better about it if they weren't cheap $4 Walmart strips with crappy sockets and connections, drawing the entire +15a from the furthest strip on the end... and operating an inductive load.
I admit that worse case scenario sounds kinda scary.

Looks like an interesting project, your mount/frames look a lot better than my attempt. I don't think I'd ever go as far as making my own panels, I'd always be worried about water penetration, and seeing as we seem to get more rain than sun over here...

Yes, exactly.

My panels have been outside now since August 2010 with no sign of moisture penetration. It's because I used thick tempered glass on both sides and had them hermetically sealed. But that's an unusually long time for DIY solar panels to last outside. It's anyone's guess how long they will endure.

My charge controller can handle an array input of 30a and my two panels provide only 6-7a on a clear and bright sunny day. I got the larger controller so I can expand in the future without having to buy another.
I won't be building any more DIY panels. They cost around $0.34 per watt to build, not including around 70 hours of labor. They're not UL listed so I can't use them for anything attached to the home and have no warranty. It was a fun and educational project, but no more DIY panels. I can purchase a very good quality commercial panel that is UL listed, comes with a 25yr warranty for around $0.24/w. I still can't attach them to the home without permits and licensed installers, but I'd surely use them to power outside lights and an out building. I'd also have around 500-600ah of renewable power backup in case of a grid failure.

[daverob]

That's a lot different than it is here in the U.S. A fuse here in the US is designed to open at its rated current, so a 15 amp fuse must open when 15 amps flows through it.

I didn't realise that there was that significant a difference. With an IEC specified fuse (which I had assumed was used the world over, as the 'I' in IEC does stand for 'international' !), the current rating of the fuse is the amount of current that can be passed through the fuse continuously without it rupturing, and each type of fuse is specified with disconnection time information, saying how long it will take to blow at different levels of overload. We then use this information to design our electrical installation so that the fuse does provide suitable protection.

Also, our grounds and returns are created close as possible to the individual power distribution boxes (Breaker boxes) so we won't have to figure tens of miles or kilometers of loop back to the power station. Does the UK really run a ground and/or return back to the station? Wow.

Not exactly, the origin of supply will usually be the substation or pole mounted transformer, the supply circuit will include the secondary winding of this transformer, but ignores any of the grid side network, as this won't have any significant effect on the calculations. There's a lot of different styles of earthing used over here, from an earth rod sunk into the ground nearby the house, an supply side earth bonded to neutral at the substation/transformer, or bonding to neutral where the supply enters the house. Each of these different methods needs to be taken into account when designing an electrical installation, hence the importance given to loop impedance over here.

As I've just posted, the circuit would open at 15a not 90, and if the hot side met ground or return with a person touching it, the bulk majority of current would flow to ground (not the person) as its supposed to until the fuse or breaker opened. Based on the calculations of 9 feet of 14 gauge wire and 120v, 119.3v would safely pass to ground and 0.7v goes to the person holding the metal case of the appliance.

If I understand you correctly, in the states the electrical safety is determined by the contact voltage available under fault conditions (ie the voltage that will give the person a shock). I guess this is easier to comply with given a 120v supply, with the higher 240v supply over here, I don't think it's practical to ensure that the contact voltage is always safe under fault conditions, so we rely on disconnection time and need to calculate fuse rupture currents and supply impedances as a result.

Still we calculate the contact voltage using a potential divider model. The supply voltage is present at the origin of supply, there's a certain amount of resistance in the live/line cable to the place the fault occurs, and a certain resistance in the ground/neutral path back to the origin. The contact voltage available at the fault location is a ratio of these resistances. You'd need an impossibly good earthing system to get a 0.7v contact voltage out of these calculations (even with the lower 120v supply voltage).

I wanted to try to apply the UK style thinking to an US installation, and run through our safety calculations on what would be a typical US circuit. But while I can find information about the wiring layout and earthing arrangements, I can't seem to find any information on US fuses or breakers apart from they are continuously rated at 80% and will blow at 100%. Without knowing the disconnection time parameters for the fuses or breakers used, I can't really achieve this.

I still think that the same fundamental principles apply, I just don't have the calculations to back myself up, and I think I might find that even when I run the calculations, that the disconnection time isn't really all that relevant, as the worst case contact voltage is going to be lower due to the lower supply voltage.


BTW, I still think surge protectors are a waste of time.

[westom]

That's a lot different than it is here in the U.S. A fuse here in the US is designed to open at its rated current, so a 15 amp fuse must open when 15 amps flows through it. The only exception is the slow-blow type which allow the temporary surge of a starting motor. Also, our grounds and returns are created close as possible to the individual power distribution boxes (Breaker boxes) so we won't have to figure tens of miles or kilometers of loop back to the power station.

First, a 15 amp fuse or breaker can conduct 20+ amps for up to two hours before it might trip. 30 amps can flow for 5 seconds without blowing a fuse. Rated current is only a ballpark trip number; a number that varies with a time constant.

daverob’s numbers for fuses are spot on.


So, how much surge current is necessary to blow a 10 amp fuse? According to a 1985 research paper, 9,000 amps. The I squared T law even applies to 10 microsecond currents. No fuse or circuit breaker does or claims to protect from surges. Fuses are only human safety devices.

Second, earth ground is as close as possible only for human safety. Often is too far for surge protection. Those contradictory statements are both true or false as long as numbers are ignored. A wire from the breaker box up over the foundation and down to earth electrodes is too long for surge protection. Creates excessive impedance. A term 'low impedance' means a distance typically less than 10 feet or 3 meters. And single point ground. Multiple grounds also makes surge damage easier.

Polyphaser makes a protector that has no earth ground connection. A connection to earth is so critical that their protector mounts ON earth ground. Zero feet to earth.

Third, a 30 foot (10 meter) extension cord is fine as a temporary device. But power strips are not temporary. Daisy chaining power strips is dangerous for the same reason a 30 foot extension cord to power a refrigerator is a major code violation and a serious human safety threat.

That danger is also why code calls for a wall receptacle located so appliances only need a six foot power cord. Why do so many appliances only have six foot power cords? Because six feet is long enough in a safely wired house. Longer wires decrease safety.

A dog kennel down the street killed over 20 dogs. They daisy chained power strips. All dogs were killed by the resulting fire.

Another example: how many watts does a 100 watt light bulb demand when powered on? About 960 watts. Power on times for electrical appliances is just another in a long list of reasons why power strips much not be daisy chained.

Many devices sold to Americans do not have a UL label. UL listing is not required. How many consumers bother to check for that UL label? Virtually none. A UL label on a 30 foot refrigerator power cord is still a serious human safety threat and a code violation.

Fourth, direct lightning strikes without damage is routine. Your telco CO suffers about 100 surges during each thunderstorm. How often is your town without phone service while they replace that $multi-million switching computer? Never? Exactly. Because when a direct lightning strike causes damage, then damage is traceable to human failure.

Why do homeowners earth a ‘whole house’ protector? Because lightning is typically 20,000 amps. A minimally sized ‘whole house’ protector starts at 50,000 amps. Even a protector must remain functional after each surge. Informed consumers earth a ‘whole house’ protector because a properly sized and installed protector makes surges that irrelevant.

What defines a good or bad protector? Quality of earth ground. That ‘less than 10 foot’ connection to earth is critical. Otherwise a protector is bad – has excessive impedance - cannot protect from typically destructive surges.

[SteveFury]

First, a 15 amp fuse or breaker can conduct 20+ amps for up to two hours before it might trip. 30 amps can flow for 5 seconds without blowing a fuse. Rated current is only a ballpark trip number

I'm curious to see documentation on this. Nobody is disputing initial surges in fuses or breakers, or the existence of delay nor that they are any type of surge surpressors. Each fuse or breaker have two ratings: voltage and amperage. The fuse is designed to open at the rated amperage, given the voltage does not exceed or is less than its posted rating.

Third, a 30 foot (10 meter) extension cord is fine as a temporary device. But power strips are not temporary. Daisy chaining power strips is dangerous for the same reason a 30 foot extension cord to power a refrigerator is a major code violation and a serious human safety threat.

Power strips are portable and impermanent devices. I don't think anyone here is advocating placing a fridge on the end of a daisy chain or 30 foot extension cord.

Another example: how many watts does a 100 watt light bulb demand when powered on? About 960 watts. Power on times for electrical appliances is just another in a long list of reasons why power strips much not be daisy chained.

Your example is 8 amps, well within specifications of a 15 amp circuit.

A UL label on a 30 foot refrigerator power cord is still a serious human safety threat and a code violation.

Nobody here is advocating placing a refrigerator on the end of a 30 foot extension. I'm not sure where you got that.

Fourth, direct lightning strikes without damage is routine. Your telco CO suffers about 100 surges during each thunderstorm. How often is your town without phone service while they replace that $multi-million switching computer? Never? Exactly. Because when a direct lightning strike causes damage, then damage is traceable to human failure.

I've worked for BellSouth (Now AT&T) for 16 years. I started working in central offices and for the past 12 years been troubleshooting DSL networks between customers modems and ISP's NOC's. I can't tell you how many heat coils I've replaced in central offices after storms pass by, surely in the hundreds. It remains to be a common thing to replace by field technicians after storms at remote DSLAM sites.
Heat coils are carbon based protection devices which isolate the office equipment from the OSP.

[westom]

Power strips are portable and impermanent devices. I don't think anyone here is advocating placing a fridge on the end of a daisy chain or 30 foot extension cord. ...
Your example is 8 amps, well within specifications of a 15 amp circuit. ...
Nobody here is advocating placing a refrigerator on the end of a 30 foot extension. I'm not sure where you got that.

All those statement ignore context. The topic was powering appliances. The only reason you mentioned a 30 foot power cord is because you said that is safe enough to power a refrigerator and other appliances.

Do you daisy chain power strips? Do you use a 30 foot extension cord to power appliances? Both are not temporary and are major human safety threats.
The topic is not about using a 30 foot extension cord in its intended function - temporary power. The topic is about using 30 foot extension cords and daisy chained power strips for permanent appliances. Ie a game in the basement or a refrigerator in the kitchen.

Even the 960 watts consumed by one light bulb demonstrates why multiple devices from daisy chained power strips can create serious dangers. Nobody said anything about powering only one light bulb on daisy chained power strips. The threat is well defined also by the number of fires that resulted. Do not daisy chain power strips.

Also well defined for generations is an I2T rule for fuses. Curves are published for fuse families by fuse manufacturers. A one amp fuse does not trip at one amp. We imply that to make it easy for layman. Because how a fuse actually works is too complex. Same applies to 15 amp circuit breakers. And a complexity that says why daisy chaining power strips even killed all 20+ dogs in that dog kennel.

What is a fuse purpose? That is the emergency backup protection system. When a fuse trips, a human should immediate fix/change a major human safety threat. Not repeatedly depend on the emergency backup system. Next time, that fuse or breaker may not trip fast enough. The I2T curves also define tripping times as quite wide. An overloaded fuse may take 10 seconds to trip. Or may not trip for 2 hours.

[Forex]

I love my vintage machine

[SteveFury]

The only reason you mentioned a 30 foot power cord is because you said that is safe enough to power a refrigerator and other appliances.

No, the question was why a 9 foot cord is deemed dangerous while a 30 foot wire made of the same materials meet UL standards. It was you who mentioned the outrageous scenario of placing a refrigerator on the end of a 30 foot cord in post #45 not me. I said: "I don't think anyone here is advocating placing a fridge on the end of a daisy chain or 30 foot extension cord."

You don't have to misquote people.

This is a good community at PachiTalk which deserves a reasonable and civil conversation.