Back to Brian's mail about the basis for the 1500A interrupt rating, my
assumption has been that it stems from some other common requirement or
application that made this the next step up. Presumably it isn't economical to
have a bunch of different common interrupt ratings.
Cheers,
Gary
My assumption as well
Perhaps, but keep in mind that the impedance specified by 60725 is a maximum
value that 90% of household service would not exceed. It might be 1/2 that
value on average.
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
In UK, because of the ring-main wiring, the effective conductors to a
wall-socket are 5 mm^2.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-20 20:21, Richard Nute wrote:
In the USA, at the load end of a 2-meter #18 power cord,
I suspect the IEC 60725 impedance is at the service entrance, not through the
breaker box, building wiring, connectors, and power cord. By the time all
these resistances are taken into account, I suspect that the total resistance
is at least twice that specified in IEC 60725.
Rich
In the USA, at the load end of a 2-meter #18 power cord, you can expect 100-200
amps short-circuit current, but not more, due to the resistance of the power
cord, the connectors, and the wiring to the breaker box.
If you assume that the source resistance is almost 1 ohm, the short-circuit
Ralph, et al,
My long term understanding is that the fault current is a curve. High
values initially draining to lower values as the stored charge in the adjacent
wiring is pulled thru the short circuit and maintained by the supply impedance
at the longer term value.
'Reference value' 0.4 + j0.25 ohms in IEC TR 60725 for household-type
single phase connections, leading to a fault current of 488 A at 230 V.
But impedances lower than the reference value occur quite widely in some
countries. I measure about 80% of the reference value at a wall socket,
not
According to IEC/TR 60725, 90% of customers in the UK and in Australia, will
have electricity supply impedance less than or equal to 0.25 + j0.23 ohms.
That according to a survey or residential service for 230V/50Hz
That tells me that short circuit current would be at least 680A, but could be
Mr. Woodgate,
Is there a recently published spec for a 'typical' 230V mains impedance for the
EU? Have also noted that the source Zs in 61000-4-5 for the instrument seem
rather high. So what is the basis for 1500A interrupt rating?
For U.S., even for an artificially low-Z electronic AC source,
I'm afraid that's not so. The short-circuit current of a 20 A circuit is
normally at least 500 A, maybe 1500 A.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-18 03:49, Joe Randolph wrote:
Yes, that is a very good point. I may
Yes, that is a very good point. I may have misinterpreted what the term
“adequate breaking capacity” means. If all it means is that the fuse must be
able to safely break the short-circuit current, then a 20 Amp, 250 VRMS fuse
would be fine for use on a 20 Amp, 240 VRMS circuit.
Of course,
I agree with this step-wise route to failure. But I wonder about the
intended meaning of 'adequate breaking capacity'. In the context of the
fuse standard IEC 60027 (multi-part), this means that the fuse must not
shatter or arc-over with the largest fault current that can be applied
to it.
I have not performed any actual testing, but I believe that the basic problem
is that MOV leakage current increases slightly each time the MOV experiences a
big surge. So, in the early stages of this mechanism, the leakage current will
increase step-wise each time the MOV experiences a big
In my experience (and opinion), only slightly more than 15 watts is necessary
to raise plastic material to ignition temperature.
If a MOV is used as a SPD, then it should only operate (be conductive) in the
event of a transient over-voltage. If the transient event is the 1.2x50
waveform,
I wonder if a 1A fuse would protect against MOV flameout just as well as a
100mA, if these MOV fail as an avalanche. (get hotter = more leakage)
I've seen some standards use 240VA (assume 240W) as a power limit for
protection against fire. However, I wonder if a MOV could burn nicely at say
I've see MOVS flame after being hit repeatedly with 6kV combination wave surges
too quickly (30s apart), during type testing to ANSI C62.45
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
-Original Message-
From: Joe Randolph
Hi Joe:
You said:
" Unfortunately, Annex Q does not help to define the term "adequate breaking
capacity" as called for in clause 1.5.9.2 for fuses required in series with the
MOV."
The term "adequate breaking capacity" means the authors (committee) did not
know how to determine the
Hi Mick:
Annex Q in 60950-1 shows that the authors were concerned about increased
leakage current in MOVs that are subjected to multiple surges. Perhaps the
authors assumed that if the equipment passed the earth leakage test with new
MOVs, allowing the MOVs to deteriorate by up to 10% after
Hi John:
I’m not an expert on MOVs, but I am generally familiar with their construction,
behavior, and failure modes.
Based on my reading of G.8, it would be difficult for an MOV, by itself, to
pass the electric shock tests in G.8.2, unless the Joule rating and/or working
voltage of
I think IEC TC108 needs to review this urgently. If no MOV can meet
G.8, then the standard should not ask for the unattainable.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-13 16:40, Joe Randolph wrote:
Hi John:
I understand
Hi John:
I understand that it might seem preferable to just use 62368-1 instead of
60950-1. In this case, though, there are two reasons why 60950-1 appears
preferable:
1) In a few weeks, the product will be entering the testing process for
compliance in Australia. As far as I can
For my sins I am currently editing a 40 page MOV application guide. As
the guide was written by a Chinese expert I have the additional task of
translating the Chinlish to English. However this forces understanding
and I found the document contains many gems I did not appreciate. On
degradation
You are quite right, but I wonder how many products actually use High
Breaking Capacity (HBC) fuses, rated at 1500 A or so.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-12 03:37, Ted Eckert wrote:
I would like to attempt a
It would be better to concentrate on 62368-1, because 60950-1 is on the
way out.
Regarding 'adequate breaking capacity', this is in the relevant Part of
IEC 60127, probably Part 3.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On
Hi Rich:
Thanks for your feedback on this topic.
My impression is that the intent of the requirement for a fuse in series with
an MOV is not related to concerns about protecting users from surge transients.
I believe the intent of the requirement is to protect users from the effects
of an
IEC 63386-1 seems to introduce a lot of new terms I have not seen used in other
IEC standards. ( but I haven't read everything out there)
I would add that a "skilled person" perhaps is a "qualified person" , but
qualification is often associated with formal training by an accredited
institute,
The definition of "reliable earthing" appears in clause 5.6.7 of 62368-1, and
it seems reasonable. Equipment that has a permanent earth connection, or
equipment with an industrial "Type B" plug, is considered to have a reliable
earth connection. However, for the ordinary "Type A" plugs used
'Reliable' earthing would be per construction and test requirements of the
scoped standard. Note the term "Reliable Earthing" is not defined in the IEV,
but the various earthing and bonding terms are covered. As we all know, the
earthing bond itself is supposed to be the current path for a
Thanks everyone for the helpful input. If I am understanding the situation
correctly, it can be loosely summarized as follows:
IEC 60950-1
Clause 1.5.9.2
MOVs connected mains-to-earth or across the mains must have a fuse in series.
The fuse must have “adequate breaking
Having had a look at 62368-1 Ed 2, I think the relevant clause in that is
5.5.7. “SPDs” (“Surge Protective Devices”),
5.5.7.1 “Use of an SPD between the mains and earth”
“Where a varistor is used between the mains and earth:
– the earth connection shall comply with 5.6.7; and
– the
Hi Joe,
IEC60950, clause 1.5.9.2 requires - for the protection of the VDR - "an
interrupting means having an adequate breaking capacity shall be connected in
series with
the VDR"
Best regards
Kris Carpentier,
From: Joe Randolph [mailto:j...@randolph-telecom.com]
Sent: dinsdag 31 oktober 2017
Joe,
I'm away from my data at present. I think IEC 62368-1 in clause 1
states that where a consistent connection to PE/ground cannot be
guaranteed, such as with pluggable equipment, protection from mains to
the PE requires to be a GDT and varistor to be connected in series.
Regards,
32 matches
Mail list logo
