Will probably be replacing a standard house circuit breaker with a surge
protector circuit breaker to provide protection for a furnace board that
seems to be pretty succeptible to lightning strikes (please see my previous
The furnace runs off a dedicated 15 amp line, protected by its own breaker
in the main house panel.
Apparently they come in two flavors.
One being the standard "surge protector," and the other type a "transient
voltage surge protector".
They both seem to be available incorporated into 15 amp circuit breakers
that fit in the main house panel box.
Which do I probably want ?
Why ? What are the differences re protection, etc. ?
If you've got a link or anything to show those items,
it might be possible to make some judgements. Any
surge protector is a "transient voltage" surge
suppressor, so why they'd have two different names
within one product line is interesting.
The two most important specs you want are the number of
joules of energy it can withstand, and the length of
time it can withstand that much power. There are other
relevant specs of course, but to get too far into them
here isn't relevant, IMO, without knowing more about
I'm offering to check them out because I've been
considering the same sort of thing too, but haven't
gotten too serious about it yet.
I'm sorry, much as I'd like to help, I don't open
attachments. Perhaps someone else will take a look for
you, but I cannot make exceptions.
Perhaps someone could put them on a web site for you
and then just post the URL here?
Surges are long duration events, with not that high of a voltage.
Transients are very fast very high voltage events. While some
protectors will do both, it's not necessarily so.
Lightning generates transients. Usually not surges.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
Errr, that's sort of a generalization and not really
very descriptive? A transient voltage is a passing,
not permanent, voltage. In general, a surge is an
increase in the supplied voltage, yes, and may last for
several cycles or more. A transient voltage is really
one which appears and then is gone, its duration
generally being "short", but that's not very
descriptive either. It's "short" when compared to a
sixteenth of a second though, and then it becomes more
LIghtning originates transients, which may actually be
in the initial order of seconds of current flow. A
lightning strike is not a mS or a uS event; it's
actually many hundreds of transients all at once, which
can in turn have the effect of causing a "surge" after
it's gone against all the capacitive power factor
equipment on the lines and the inductive properties of
many transformers. Add to that the many expanding and
collapsing electrical fields along miles of wire and
you have a surge.
I used to use mains recorders and got to examine a lot
of lighting strikes in South Dakota where the power
lines aren't all that good and none of them were
underground. I recall one strike which created a 168
cycle long surge at the outlets; of over 400 volts peak
on a 330V reference, in one direction, and another set
of 4 second ringing that peaked at 3xx volts for about
three more seconds. THAT was a surge! <g>
You'll find, actually, that most "transient"
voltages, spikes or whatever you'd like to call them,
are generated from within the premises of a building
where they are a problem. It's interesting stuff.
Dunno why we're discussing this; memories, I guess.
I think they are the same thing but if there is a difference, I would expect
the transient one to react faster but not significantly different. To
compare, you want to look at the amount of energy they will absorb in the
event of a surge. This is usually in units of Joules if it is even listed.
It will protect you from a modist surge from a distant strike but probably
will fry if you get a direct strike. It's sacrifice may save something else
down the line though.
I got one that is the size of a double breaker and the model number was
listed on the inside sticker of the panel's door. I got it just for CYA
purposes cause we don't get much lightning here in SF bay area but surges
can happen when equipment fails during wind storms or car accidents with
utility poles. Hard to say if it ever did anything.
From an engineering POV, Transients are short duration events while surges
can last quite a bit longer but as long as they are temporary, can be called
transient as well.
First, it does now matter whether that circuit breaker
protector is on a furnace circuit or installed as a 20 amp
breaker for another circuit (on the same phase). Either
provides the same transient protection to that furnace. Or as
that Siemens app note says, "An electrical surge, whether it
is caused by electrical equipment or lightning, always seeks
ground. Any component between the source of the surge and
ground can be damaged."
IOW the protector inside that Siemens circuit breaker
connects as if just another light bulb - connects in parallel
- is not electrically located between a lightning cloud and
the furnace. The protector does not stop or block surges. It
Second, protector is not the open contacts of a circuit
breaker. That would be (futilely) stopping or blocking
transients. A 'whole house' protector inside that breaker
protects by 'shunting' a surge to earth ground. IOW the
internal protector operates independently of the circuit
They are called shunt mode protectors. This Siemens breaker
installed on any circuit (of same phase) protects the
furnace. Protector inside that circuit breaker shunts the
transient to earth ground - whether it is a 15 amp furnace
circuit breaker or any other (same phase) 20 amp breaker.
The Siemens breaker (like all shunt mode protectors) does
not stop, block, or absorb surges. It shunts. It must have a
single point earth ground to shunt to. That means earthing
may need be upgraded to meet or exceed post 1990 NEC
Third, the effectiveness of a protector during one transient
is determined by quality of that earth ground.
Effectiveness of a protector over many transients is
determined by its joules rating. A protector shunts - just
like a wire. More joules means 'the wire' is thicker. Any
protector that fails during a first transient was woefully
undersized - totally ineffective - too few joules - just like
so many plug-in protectors. An effective protector shunts
direct lightning strikes to earth and remains functional.
Joules and amps numbers determine protector's life
expectancy. Install two such Siemens breakers in the circuit
box (to double the number of joules); life expectancy of both
breakers increases exponentially.
For residential 'whole house' protectors, minimally
sufficient is 1000 joules and 50,000 amps. Does not matter
whether it is a "surge protector" or a "transient voltage
surge protector". Joules determine protector's life
expectancy. Earth ground determines its single transient
Fourth, the Siemens solution has one difference over other
'whole house' protectors. Once a protector has failed, then
that circuit cannot be reset; circuit breaker must be
replaced. The circuit breaker trips long after a transient
has come and gone. For example, 300 consecutive transients
could come and go before the circuit breaker trips. The
circuit breaker is not protection. But once the internal
protector has failed, then a Siemens breaker will no long
provide power to the furnace.
Fifth, there is no 'functional' difference between TVSS and
surge protectors. Both are only as effective as their earth
ground, as the Siemens app note even suggests. Most critical
is the quality of that single point ground AND how wire to
that earth ground is routed. For example, sharp wire bends
mean a compromised protector. Ground wire bundled with other
wires may induce transients on those other wires. And so to
summarize it: a protector is only as effective as its earth
Earth ground determines a protector's effectiveness during
one transient. Joules determines the protector's life
expectancy. The difference between TVSS and surge protector
is irrelevant. Your concern is two important parameters -
joules and how the protector is earthed.
I generally agree with the post, it gives a good description.. The TVSS
is warranted only for the circuits connected downstream from it
(connected to the 2 circuit breakers). The TVSS; (and SURGE protector)
are connected to both phases. They would protect L1-L2, L1-GND, L2-GND.
The TVSS is connected on the load side of its breaker. The current it
causes may cause the breaker to trip.
The protector will shunt to ground. This could cause the ground voltage
to rise over the 'real' ground potential. The furnace would see the
hot-neutral-ground voltage and would not know that the potentials
suddenly rose over the 'real' ground potential. Unless there is another
ground reference, like a telephone line, I don't think a ground is as
important as indicated, though one certainly wants a good ground.
A strike on a lightning rod (now called air terminals?) will raise the
potential of the local ground above 'real' ground. The lightning rod
ground must be bonded to power and other building grounds. The potential
of the whole house will temporarily float up.
The joule rating is the energy the device can pass in one event. If I
remember right, MOVs are progressively damaged when they shunt high
energy/high amps. The joule rating is generally related to the life.
Actually the surge current rating probably indicates a 'thicker wire'
and the joule rating would be the heat dissipation rating of the wire -
so the wire doesn't melt.
As I read the note, the TVSS/breaker may trip when a surge hits and have
to be reset. If the device fails, the pilot lights go out but the
circuit breaker probably will still set.
The SURGE supressor, according to the note, meets the same standard as
the TVSS plus an additional one. It can be connected ahead of the
service disconnect (but I don't know how this connection is made). If
connected downstream from a 20A breaker, the alternate method shown, it
is similar to the TVSS.
I presume both could cause the breaker to trip on a long event - in the
1 cycle range (if the SURGE protector is connected downstream from a
breaker). The TVSS would still protect the 2 circuits it is connected
to, the Surge protector wouldn't protect anything after the trip.
The TVSS has a $20K warranty for the 2 circuits downstream. The SURGE
protector has a $10K warranty but limited to 3 years, and the device
must be installed by a "qualified" electrician. The SURGE protector has
a significantly higher Joule and surge current rating.
When installing these devices it is important the keep wires short. For
best system protection install the device breaker in the nearest
position to the service breaker.
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