budding electricians, isolation transformer question

[bud--]

One of the plug-in protectors I am using has 3 MOVs with a rating of 590 joules each, 1770 joules total

Surge protector "energy" ratings are not additive. Only 1 surge diverter will ever fire at a time.

It doesn't matter whether you have 3 or 10 or 100 varistors built into a surge protection device. Only the most sensitive one will fire, and if the energy released by clamping the surge exceeds it's capacity, it will be incinerated. This is the case even when using "binned" varistors - the variation within a single bin will typically result in 1 varistor taking 99.9% of the surge energy, even when paralleled with multiple "matched" varistors.

MOVs are voltage limiters, and their current smoothly (but rapidly) rises when the voltage increases (they don't "fire"). They can conduct thousands of amps for a very short time. The voltage will then be significantly over the nominal clamp voltage.

If the MOVs are connected in parallel one is likely to conduct at a lower voltage. High current drives the voltage higher, which causes MOVs with close clamp voltage characteristics to conduct. If using MOVs from the same manufacturing lot the characteristics are pretty similar and I would expect the surge to be largely shared. If not from the same lot not likely. (Paralleling is a side issue.)

But a plug-in protector has separate MOVs connected L-N, L-G, N-G. This is detailed in the IEEE surge guide. That would be how my 590J MOVs are connected. If there was a strong surge entering on power service wires, the hot wire rises with respect to the neutral and ground (there is a N-G bond at US services). Both the L-N and L-G MOVs will conduct. The N-G MOV may conduct depending on its voltage rating.

Of course, the "surge energy" rating of a surge protector isn't really that useful a measure, as it is an aggregation of all the more important parameters of the protector: namely surge diversion current, maximum surge duration and clamping voltage.

MOVs accumulate damage and the joule rating is useful because it indicates how much damage they can withstand. (Cumulative ratings are likely much higher than the single event rating.)

Surge current ratings are equivalent to the joule rating. If you have a service protector rated 10,000 surge amps and there is a 10,000A surge the protector is likely at about end of life. The 590J MOVs in one of my protectors have an equivalent surge current rating of 30,000A. That is far more than you can get on a service wire.

The surge energy isn't actually dissipated by the protector - it is diverted away from the protected device. This means that the actual amount of surge energy that can be protected against is much higher than the rating of the protection device.

I don't think this is as much appreciated as it should be.

[Westom thinks plug-in protectors work by absorbing the surge.]

 

[bud--]

ok, now I am starting to get confused.
westoms posts are rambling on...

If you are confused by what westom says - some of his information is good, some not so good, and some is pure rubbish. All of what he says about plug-in protectors is rubbish.

bud's job and nasty posts are to keep you confused with lies, half truths, disparaging remarks, and no spec numbers.

My "lies, half truths" come from the IEEE and NIST surge guides. What I write is entirely consistent with them (and much of it comes directly from them). Read the sources.
I provided specs in this thread. Mark found them.

A lot of the IEEE surge guide is spent explaining how plug-in protectors work and how to connect them. The NIST surge guide does the same. Both say plug-in protectors are effective.

Westom says plug-in protectors are a scam. It is the basis of what he says about plug-in protectors.

Either westom is right or the IEEE and NIST are right - they can't both be right.

Westom compulsively posts his drivel about plug-in protectors. He has posted it here at least 3 times in the last 3 months. He says he has been posting it for 10 years. Westom is an internet nut.

 

[bud--]

A typical lightning strike consists of 20,000 to 100,000 amps at 30 million volts

I believe 20,000A is 'average' and a few are much larger than 100,000A.

Francois Martzloff, the author of the NIST surge guide, looked at the current that would come to a building from a lightning strike to utility wiring. He used a strike of 100,000A to the high voltage primary wire at a utility pole adjacent to a house in typical urban distribution. Only about 5% of lightning strikes are stronger, and this is a very near worst case. There are multiple paths to earth for the strike. About 30,000A goes to the house on the service neutral. Some of that energy transfers by inductive and capacitive coupling to the hot wires, which wind up with 10,000A each. That is for practical purposes the worst case, and is referred to in the IEEE surge guide.

Lightning isn't the only source of electrical surges. Many the Home devices that are sensitive to electrical surges also produce electrical surges. Motor driven equipment, such as garage door openers, refrigeration, and air conditioners are not the only sources of electrical surges within the home. Television,computers, microwave ovens, and modern gas ranges and furnaces that use electronic ignition can also cause line disturbances and surges.

I agree with Mark.

There is a common misperception that larger surge amplitudes deposit more energy into a SPD. IEEE research shows this is not the case. Energy deposited into MOVs actually decreases as surge intensity reaches certain levels.

Martzloff also looked at the amount of energy that can deposit in MOVs in a plug-in protector. He used power line surges up to 10,000A (as above the maximum likely), and branch circuits 10 meters and longer. The maximum energy was a surprisingly small 35 joules. In 13 of 15 cases it was 1 joule or less.

There are 2 reasons why the energies were so small. At about 6,000V there is arc-over from service panel busbars to the enclosure. After the arc is established the voltage is hundreds of volts. Since the enclosure is connected to the earthing electrodes, most of the surge energy is dumped to earth. And the N-G bond at the service further limits the exposure inside the building.
The second reason is that surges are a very short event. That means the surge currents are relatively high frequency. That means the inductance of the branch circuit wire is more important than the resistance. The impedance of the branch circuit greatly limits the current, and thus the energy that can reach the plug-in protector.

Just as surprising was, as you said, the highest energies were from some of the smallest surges. Large surges drove the voltage at the service to the 6,000V arc-over. For the smallest surges the MOV on the short branch circuits could limit the voltage at the service to less than 6,000V. But the voltage, higher than the stable voltage of an arc, caused higher current on the branch circuit.

Therefore, Joule ratings are misleading. The surge industry’s technical community avoids Joule ratings in this context

.

Joules are useful since MOVs have cumulative damage from surges. But there is no defined way to measure the joule rating. So some manufacturers use dishonest measurements. That puts honest manufacturers at a disadvantage and some have stopped providing joule ratings. Surge current is an equivalent rating. The IEEE surge guide suggests using surge current and cautions that joule ratings are not necessarily comparable.

Energy is defined as Power x Time. How are Power and Time defined and where are Watts actually going?

Another example, can the SPD sustain a Joule rating many times, one time, or does it define failure? At least one manufacturer uses a multiplier. For example, if an MOV is rated 1J, but can withstand 5,000 hits, the SPD is rated 1J x 5,000 = 5,000 Joules. In summary, Joule ratings are not recognized by surge suppression Standards.

The joule rating of a MOV is the single event energy that puts the MOV at the defined end of life but still functioning. If the energy hits are much smaller, the cumulative energy rating is much higher. For example a MOV might have a (single event) rating of 1,000J. If the individual hits are 14J the cumulative energy rating might be 13,000J.

I haven't seen a manufacturer using a cumulative rating, and I think it is particularly dishonest.

For a plug-in protector, the limited energy that can get to the protector along with high ratings along with the higher cumulative rating mean that plug-in protectors are not likely to fail from a surge. But they must be connected properly (as in my first post). The IEEE surge guide has 2 examples of protection. Both use plug-in protectors in relatively complicated setups with TV and computer and power with phone/cable wires.

Read this IEEE white paper titled, "No Joules for Surges: Relevant and Realistic Assessment of Surge Stress Threats"

Have a link by chance?

Read this as well
http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

Great source. I posted it earlier - the 'IEEE surge guide'.

 

[Mark R]

MOVs are voltage limiters, and their current smoothly (but rapidly) rises when the voltage increases (they don't "fire"). They can conduct thousands of amps for a very short time. The voltage will then be significantly over the nominal clamp voltage.

If the MOVs are connected in parallel one is likely to conduct at a lower voltage. High current drives the voltage higher, which causes MOVs with close clamp voltage characteristics to conduct. If using MOVs from the same manufacturing lot the characteristics are pretty similar and I would expect the surge to be largely shared. If not from the same lot not likely. (Paralleling is a side issue.)

Technically, you are correct. However, the voltage/current curve for a MOV is so steep in the clamping region, that it is practically vertical (even on a log scale), hence I used the word "fire" inaccurately, but to emphasise this fact.

It is so steep that even a 1% difference in threshold can result in current being shared 10:1 in favor of the more sensitive move. With typical MOV "bins" being 10-15V wide, a 100:1 split is optimistic.

Most MOV manufacturers specifically warn against paralleling MOVs (even from the same bin and lot) precisely because even minute differences in sensitivity result in completely disproportionate current sharing.

 

[westom]

bud's job is to promote grossly undersized protectors that have no earthing. The OP has two wire receptacles. Using bud's products would be a human safety violation. Why is he recommending something that the OP cannot use? bud's following me everywhere to post nasty and disparaging comments. Where does all that energy - hundreds of thousands of joules - dissipate? Certainly not in bud's MOVs rated at hundreds of joules.

bud says his protector will clamp a surge. Clamp to what? Nothing. OP has two wire circuits. Effective protector located in the breaker box connects low impedance to earth. Effective 'whole house' protectors have an always required and dedicated wire to clamp hundreds of thousands of joules to earth. That solution works even in the OP's two wire house.

Every responsible source including the NIST and IEEE say earthing is critical. The NIST on page 19 of 24 describes as "useless" products he is paid to promote:

A very important point to keep in mind is that your surge protector will work by diverting the surges to ground. The best surge protection in the world can be useless if grounding is not done properly.

The OP has no safety ground on receptacles. Products promoted by bud would even be a human safety violation. The NIST also calls bud's products "useless". So why is he posting? Everything he promotes is useless for the OP, is called useless by the NIST, and is irrelevant to this thread.

 

[JSt0rm]

not to hijack but while all you brains are here fighting...

why is dimming unsafe? My gf house lights dim but not with the appliances they just do it from time to time.

 

[westom]

why is dimming unsafe? My gf house lights dim but not with the appliances they just do it from time to time.

Wires are so oversized that no dimming should happen. Dimming implies a defective connection. Usually solved by simple inspection. In rare cases, can cause a fire. Especially dangerous if your wires are aluminum.

Dimming is almost never dangerous. But may also indicate a serious human safety problem. Easy to eliminate. Should not be ignored.

 

[bud--]

bud's job is to promote grossly undersized protectors that have no earthing.

1. Westom repeats the lie for the 17th time that I have something to do with the surge industry. That is what happens when you don't have valid technical arguments.

2. To pass UL tests a plug-in protector has to survive intact a set of test surges. The UL test provides a floor for the protection you get. (Any surge protector in the US, including UPSs with surge protection, should be listed under UL1449.) Protectors with high ratings are readily and cheaply available, including one of mine that has ratings of 590J/11,000 surge amps for each of 3 MOVs. But since westom can't figure out how plug-in protectors work he stupidly thinks they must absorb all of the surge that hits the house.

3. Westom's religious belief (immune from challenge) is that surge protection MUST directly use earthing. Since plug-in protectors don't westom believes they can't possibly work. The IEEE surge guide explains how plug-in protectors actually work if westom could only read and think.

Where does all that energy - hundreds of thousands of joules - dissipate? Certainly not in bud's MOVs rated at hundreds of joules.

Of course not.

Mark R wrote "The surge energy isn't actually dissipated by the protector - it is diverted away from the protected device." Neither plug-in or service panel protectors work by absorbing a surge. (But both of them absorb some energy in the process of protecting.)

With minimal ability to think poor westom could figure out where surge energy dissipates. I explained it in a response to LiuKang. But westom can not read anything that conflicts with his religious belief that surge protection must use earthing.

Effective 'whole house' protectors ....

Repeating from the NIST surge guide:
"Q - Will a surge protector installed at the service entrance be sufficient for the whole house?
A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless."

A service panel protector will very likely protect equipment connected only to power wiring. By itself it will not necessarily protect equipment connected to power and phone/cable/dish/....

The NIST also calls bud's products "useless".

They aren't my products.

Westom actually believes his delusions.

Repeating what the NIST surge guide really says about plug-in protectors: They are "the easiest solution".
And "one effective solution is to have the consumer install" a multiport plug-in protector.

Westom is an internet nut.