Surge / Ground / Lightning

In article , bud--
writes

Last I heard UK phone entry protectors did not clamp the voltage to
earth.

You're quite correct. It's a practice that the GPO (forerunner to
British Telecom) abandoned in the 1960s, showing how up to date w_'s
"knowledge" is.

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wrote:

Mike Tomlinson wrote:

... This is an important principle of the UK wiring code. It's
referred to as "equipotential bonding."

I wonder if "ring mains" (an extra wire from the last outlet to make
a loop back to the fusebox) are legal in the US. Seems like a nice way
to improve voltage regulation with a little extra wire, and if the ring
wire only breaks in one place, all the outlets keep working.


No, the are not legal in the US.


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wrote:

W_ denies MOVs are commonly used in typical electonics or modern
appliances too. He had to, because he can't answer the obvious
question of how MOVs can be used effectively in these applications,
yet they can't work in plug-in protectors and the only way to get any
protection is to have a nearby direct earth ground. Faced with the
problem of MOVs providing protection in electronics/appliance without
an earthground, he simply denies MOVs are used in electronics and
appliances. Here's the references that I provvided him on that one:

Here, from Appliance Magazine and Appliance Design websites:

http://www.appliancedesign.com/CDA/A.../BNP_GUID_9-5-...


"New thermally enhanced MOVs help protect a wide variety of low-power
systems against damage caused by over-current, over-temperature and
over-voltage faults, including lightning strikes, electrostatic
discharge (ESD) surges, loss of neutral, incorrect input voltage and
power induction.

I had a microwave oven that had a MOV across the 120V line ahead of the
power switch. The other side of the 120/240 20A circuit supplied a
refrigerator. The loss of the neutral applied a good part of the 240V
across the MOV when the refrigerator attempted to start.

The MOV didn't last long! It would probably have been OK on the load
side of the switch.

I know that refrigerators should be alone on a "home run" circuit, and
neutrals shouldn't be connected with wire nuts, but that wasn't how it was!

My only complaint with some plug-in protectors is that the MOVs are
often much too small. I've also seen some with only a line-line MOV.

--
Virg Wall, P.E.

Mike Tomlinson wrote:

... This is an important principle of the UK wiring code. It's
referred to as "equipotential bonding."

I wonder if "ring mains" (an extra wire from the last outlet to make
a loop back to the fusebox) are legal in the US. Seems like a nice way
to improve voltage regulation with a little extra wire, and if the ring
wire only breaks in one place, all the outlets keep working.

Nick

In alt.engineering.electrical wrote:

| Mike Tomlinson wrote:
|
|... This is an important principle of the UK wiring code. It's
|referred to as "equipotential bonding."
|
| I wonder if "ring mains" (an extra wire from the last outlet to make
| a loop back to the fusebox) are legal in the US. Seems like a nice way
| to improve voltage regulation with a little extra wire, and if the ring
| wire only breaks in one place, all the outlets keep working.

It is not legal in the US. It is also considered technically unsafe.

You could wire a ring circuit with AWG #14 CU rated at 15 amps and protect
it with a 30 amp breaker under the theory that the current would be split
across the 2 paths between the source (breaker) and the load. This is the
most unsafe configuration because if one of the wires breaks, the breaker
will not detect it, and you won't notice until a fire starts.

You could wire the same circuit to two separate 15 amps breakers. In this
case it is somewhat safer because if one wire breaks, you can't get any use
via one of the breakers, effectivly reducing the current that would trip
the circuit via the remaining breaker. This is still unsafe because the
broken wire could merely be loose, and shutting off one breaker would leave
the circuit potentially live via the other breaker as the wire could come
back in contact.

There could also be confusion with separate breakers. The breakers have to
be on the same pole (phase), an issue not present in the single pole single
phase home wiring most homes have in UK. The USA, however, has two pole
single phase wiring. One way around that would be a "tandem" breaker with
the two handles fused together.

The safest case would be wiring both ends of the ring into the same breaker
rated for the current capacity of the wire as if used in a regular branch
circuit. Even this would have a safety issue. If the wire became loose at
one point in the ring, it would still be a potential hot spot that would be
not as easily noticed as a similar loose wire in a branch circuit. That hot
spot could then start a fire.

So far I have only described issues with the hot wiring. There are issues
with the neutral wiring as well. In all the above configurations, a neutral
would have to be wired in from both ends of the ring, and each be wired in
a separate hole (not doubled up) in the neutral bus bar. A loose neutral in
all these cases would go unnoticed just like a hot wire. But in cases where
the total current available (either the 30 amp single breaker, or tandem 15
amp breakers, described above) exceeds the wiring (when neutral is AWG #14 CU)
a wiring overheating problem exists.

The grounding wire would also have to be wired correctly from both ends.

An even greater double hazard potential exists when the neutral on one end is
broken while the hot on the other end is broken (or shut off at the breaker).
This creates a large inductive loop which can energize other wiring and cause
various problems with many metallic constructions.

Very little is gained by doing this over direct branch circuits. The issue
of voltage stability is addressed by keeping branch circuits short. It is
my understanding that UK ring circuits tend to be longer and run all around
the portion of a house (often an entire floor). Branch circuits in the USA
tend to be shorter.

Very long circuits can have voltage issues. An example is a home with a 1000
foot long driveway into the property, and a string of many lights along the
way. The more distant lights would be dimmer. This can be addressed to at
least balance out the dimming by using a loop-back circuit, which is still a
branch circuit. This is a more expensive circuit that is done by having an
extra hot wire run with the circuit in the same cable or conduit. Each lamp
is connected between the extra wire and the neutral. The extra wire is then
connected to the fed hot wire at the last lamp in the string. There is no
other connected to the fed hot wire other than the last lamp and the source
controlling switch. With this loop-back circuit, each lamp has the same
circuit length, and thus will have the same voltage drop.

The above technique was discussed on electrical-contrator.net a while back,
but they have since changed web site software, and my old links do not work.

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|WARNING: Due to extreme spam, I no longer see any articles originating from |
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In alt.engineering.electrical VWWall wrote:

| I had a microwave oven that had a MOV across the 120V line ahead of the
| power switch. The other side of the 120/240 20A circuit supplied a
| refrigerator. The loss of the neutral applied a good part of the 240V
| across the MOV when the refrigerator attempted to start.
|
| The MOV didn't last long! It would probably have been OK on the load
| side of the switch.
|
| I know that refrigerators should be alone on a "home run" circuit, and
| neutrals shouldn't be connected with wire nuts, but that wasn't how it was!

How would you connect a neutral? Doubled up on a receptacle device screw?
The usual practice is to wire the neutral in a wire nut so it can feed the
device in that box, as well as connect up and down stream, even if the
device is removed.

OTOH, I don't like wire nuts. I've seen them come loose even when wired
together well. Maybe it was a defective nut. I definitely will try to
avoid them when my new house gets built (a lot of bad electrical things
will be avoided in it).


| My only complaint with some plug-in protectors is that the MOVs are
| often much too small. I've also seen some with only a line-line MOV.

You had a plug-in protector for a double line (240V) circuit? Or are you just
referring to the neutral as one of the lines?

I'm still on the hunt for a plug-in surge suppressor power strip for 240V
with NEMA 6-15P plug and NEMA 6-15R outlets. The MOVs between each line
and ground need to be the ones appropriate for 120V (330V clamp rated) and
the ones between the two lines appropriate for 240V (660V clamp rated).

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In alt.engineering.electrical Eric wrote:
| wrote:
| In alt.engineering.electrical Eric wrote:
|
| | I can attest to vhf/uhf content in lightning strikes. I worked for a
| | communications outfit. We owned and maintained a number of comm sites
| | with towers and antennas. One strike on an antenna destroyed the LDF rf
| | cable all the way to the polyphaser at the bottom of the tower. It had
| | blowouts at about 1 foot intervals all down it's length suggesting a
| | 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of
| | energy at that frequency..
|
| Apparently you had some kind of resonance involved. Maybe the antenna itself
| can cause that. Or the output tank circuit in the transmitter. Once you have
| the resonance to narrowband the energy, it would only take a reflection back
| up the line and you turn a propogating surge into standing waves.
|
| Pretty much what we determined. Also in another thread I stressed that
| the rise time by itself does not determine frequency content. One needs
| to know the rate of change, or slew rate, to determine that. A
| lightning pulse may have a rise time of 1.2 microseconds but in that
| short time the current can rise to thousands of amps, generating a large
| amount of vhf,uhf energy.

In some plots of voltage rises I've seen in the past, the rise was not at all
a smooth one. It went up in steps. Of course if one _thinks_ there will be
no VHF or UHF energy and does measurement with a ssytem only capable of lower
frequencies, that would smooth out how the rise appears.

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|WARNING: Due to extreme spam, I no longer see any articles originating from |
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On May 6, 2:45 pm, Sjouke Burry
wrote:
Can you trim W_tom with that?? Or is he incurable?

He is incurable as long as others post outright lies and myths while
denying what really provides surge protection. Now to discuss what is
relevant.

If in sand, a single ground rod is probably insufficient earthing.
For example, a FL couple suffered repeated direct lightning strikes to
their bathroom wall. They have lightning rods installed. Lightning
again struck that exterior wall. Lightning rods were earthed by 8'
ground rods only in sand. Plumbing inside that wall connected to
deeper (more conductive) limstone. Lightning found a better
connection to deeper limestone via the bathroom wall.

What will provide sufficient earthing? Without knowledge of the
underlying geology, some will expand that earthing with a buried wire
around the entire building (halo or ring ground). Others will may
install a large and interconnected network of ground rods. Do you
need that much? Expanding the earthing may be easier than learned
later it was not sufficient. Also useful is to canvas the
neighborhood to learn what others have experienced for ten or more
years.

Reducing earth resistance is not as important as creating single
point ground with a shorter connection, more conductive (impedance)
than any other path, AND creating equipotential beneath the building.
Too many assume a water pipe is better because it is longer. But a
better earth ground meets two slightly different criteria -
conductivity and equipotential. IOW some ground rods located short to
all 'whole house' protectors may be superior earthing than the water
pipe. Appreciate that wire length may be more critical than the size
of an earthing electrode.

On May 6, 5:01 pm, Mike Tomlinson wrote:
Indeed. This is an important principle of the UK wiring code. It's
referred to as "equipotential bonding." Such a concept, of course,
would be far beyond the understanding of w_'s lone brain cell.

UK wiring code alone does not provide sufficient earthing for
something not intended to address. Code addresses earthing for human
safety. Proper earthing for surge protection must both meet and
exceed code requirements. Essential for surge protection is that all
utilities be earthed very short to the same earthing electrode. UK
code does not require that. In fact, many UK master sockets have no
earthing connection meaning no phone line protection.

Mike Tomlinson posts insults when he does not have facts. Those who
would promote magic box plug-in protectors are same who also post
these insults. Same technique used by Rush Limbaugh to prove Saddam
had WMDs.

Single point earth ground remains essential to surge protection -
which only makes people like Mike Tomlinson post more insults. A
protector is only as effective as its earth ground. An effective
protector makes a 'less than 10 foot' connection to that earth ground
rod.

On May 6, 1:00 pm, bud-- wrote:
w_ can't understand his own hanford link. It is about "some older
model" power strips and says overheating was fixed with a revision to
UL1449 that required thermal disconnects. That was 1998.

Bud will only challenge the hanford link because he cannot challenge
those 'scary pictures'. One is a Boston building fire last year
created by a plug-in protector. Another is a fire marshal describing
why plug-in protectors can create house fires. And pictures from fire
departments showing a problem seen too often.

And then Bud posts a half fact. UL1449 was created on 28 Aug 1985 -
not in 1998 as Bud claims. Why would Bud do this? Profits are at
risk - another fact that Bud must avoid admitting.

So where is this plug-in protector spec that claims to provide
protection? Oh. It does not exist because plug-in protectors do not
even claim to provide this protection. Bud refuses to post a
specification for one simple reason. There is no plug-in spec that
claims what Bud is posting. So Bud posts insults. In reply, this is
what Bud is really promoting - these 'scary pictures':
http://www.hanford.gov/rl/?page=556&parent=554
http://www.westwhitelandfire.com/Art...Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html
http://tinyurl.com/3x73ol or
http://www3.cw56.com/news/articles/local/BO63312/

Pictures of protectors typically located on a pile of desktop papers
or buried in dust balls on a rug.