<div dir="ltr"><div>Just a comment: HV differential probes useful for work on mains-powered circuits became cheap enough to have one (or more) in a toolbox "just in case". You can find Micsig probes on ebay for less than $150, and they look like pretty decent product: <a href="http://www.eevblog.com/forum/testgear/new-low-cost-($170)-100mhz-differential-scope-probe-from-micsig/">http://www.eevblog.com/forum/testgear/new-low-cost-($170)-100mhz-differential-scope-probe-from-micsig/</a></div><div><br></div><div>Jacek</div><div>kw4ep</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 23, 2018 at 1:40 PM, Mark Whittington <span dir="ltr"><<a href="mailto:markwhi@gmail.com" target="_blank">markwhi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">I'm really hoping to avoid running a separate circuit for this. It's not something that gets a lot of use, just need a way to isolate a device under test in the rare case where I need to put scope probes on a mains-powered circuit. I definitely would not be comfortable over-sizing the existing breaker and compensating with fuses in this case, because that branch circuit powers something like a third of the outlets on the first floor of my house. This is also a key reason why I suspect that it's just inrush current and not a fault -- it only intermittently trips when I turn the transformer on, and whether it trips or not depends on what else is turned on around the house.<div><br></div><div>As an aside, this house has the most haphazard electrical layout of any modern residence I've ever seen. For example, there's one 15A breaker that services one wall in my office, one wall in the living room, a ceiling fan and one wall of outlets in the master bedroom upstairs on the other side of the house, and the lighting fixtures in two bathrooms. I'm pretty sure the electrician was drunk when he wired this place.</div><div><br></div><div>If I do have to run wiring to fix the problem I'll install a type D breaker and never have to worry about it again, but that is definitely the last resort.</div><div><br></div><div>Also thanks for the article link, very interesting reading.</div><div><br></div><div>Best,</div><div><br></div><div>-Mark</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 23, 2018 at 11:35 AM, Bill Danielson <span dir="ltr"><<a href="mailto:anviljenkins@gmail.com" target="_blank">anviljenkins@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>really we just wire them up and use them, and put in a new one
when they fail :-).I am hoping we all learn something in the
replies :-).</p>
<p><a class="m_-7379952015683989671m_8573248344409565587moz-txt-link-freetext" href="http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/solution-center/technical_library/BUS_Ele_Tech_Lib_Transformer_Protection.pdf" target="_blank">http://www.cooperindustries.co<wbr>m/content/dam/public/bussmann/<wbr>Electrical/Resources/solution-<wbr>center/technical_library/BUS_<wbr>Ele_Tech_Lib_Transformer_<wbr>Protection.pdf</a></p>
<p><br>
</p>
<p>That document there would suggest that what you have going on is
not typical to Industrial stuff. I know our overloads for a lot of
things (not fuses) do have two modes of overload, one is inductive
and one is thermal...this helps cope with the high inductive
current when an AC motor starts ? Industrial fuses also many of
them apparently have a dual mode that allows a higher inrush
current, and then there are "slow blow" versions as well ??<br>
</p>
<p>I am wondering if you would be better to hook your transformer to
a circuit a larger breaker, but use a separate fuse(s) to protect
it ?? Just to fiddle around if you have an electric dryer that
existing circuit and plug would give you safe access to what a 50A
230VAC circuit ?? Then size an industrial fuse like the document
tells us to ??<span class="m_-7379952015683989671HOEnZb"><font color="#888888"><br>
</font></span></p><span class="m_-7379952015683989671HOEnZb"><font color="#888888">
<p><br>
</p>
<p>Bill<br>
</p></font></span><div><div class="m_-7379952015683989671h5">
<p><br>
</p>
<br>
<div class="m_-7379952015683989671m_8573248344409565587moz-cite-prefix">On 05/23/2018 10:55 AM, Mark
Whittington wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hey Bill,
<div><br>
</div>
<div>Thanks for the reply. I suspect if this were isolated on
its own breaker or an industrial breaker there wouldn't be a
problem, but this is on a residential 15A breaker and the
breaker services more than just the transformer. Also my
understanding is that residential breakers tend to have
different (less forgiving) time/current curves than industrial
breakers designed for big inductive loads. This is why I
suspect the problem to be caused by inrush current and not a
fault in the device or in the breaker and why I hope limiting
the inrush will resolve the problem.</div>
<div><br>
</div>
<div>I think I'm going to try the series 75w bulb approach that
Karl suggested and if that mitigates the problem then I'll
probably go the NTC thermistor route for a long-term fix, but
if you or Bill Fenn can suggest some test or another that I
can perform that would identify a problem with the windings in
the transformer or some other problem then I'd love to hear
about it -- don't want to turn an annoyance into a house fire,
right?</div>
<div><br>
</div>
<div>Thanks all for your help thus far.</div>
<div><br>
</div>
<div>-Mark</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, May 23, 2018 at 10:23 AM, Bill
Danielson <span dir="ltr"><<a href="mailto:anviljenkins@gmail.com" target="_blank">anviljenkins@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Back to the OP, I am a Maintenance Technician in a
large mfg plant, we have a LOT of transformers in the
plant and when power is turned off an back on there is
never any issue at all. Sounds kind of strange that this
is going on. I understand some basics of how an inductor
works, that there will be an initial surge until the
magnetic field builds up, but Industrial stuff must be
made to just work on power up and not blow a properly
sized fuse ??<span class="m_-7379952015683989671m_8573248344409565587HOEnZb"><font color="#888888"><br>
</font></span></p>
<span class="m_-7379952015683989671m_8573248344409565587HOEnZb"><font color="#888888">
<p>Bill<br>
</p>
</font></span>
<div>
<div class="m_-7379952015683989671m_8573248344409565587h5"> <br>
<div class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560moz-cite-prefix">On
05/23/2018 10:04 AM, Karl W4KRL wrote:<br>
</div>
<blockquote type="cite">
<div class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560WordSection1">
<p class="MsoNormal">Jerry,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">My speculation is that the
minuscule motion of the laminations against each
other transfer mechanical energy to the coating
on the laminations thereby warming them
slightly. As they become stickier or softer they
do a better job of dampening the emitted sound.
</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Karl W4KRL</p>
<p class="MsoNormal"> </p>
<div>
<div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> jerome
whelan <a class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560moz-txt-link-rfc2396E" href="mailto:whelanjh@gmail.com" target="_blank"><whelanjh@gmail.com></a>
<b>On Behalf Of </b>Jerome Whelan<br>
<b>Sent:</b> Tuesday, May 22, 2018 10:17 PM<br>
<b>To:</b> <a class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560moz-txt-link-abbreviated" href="mailto:W4KRL@arrl.net" target="_blank">W4KRL@arrl.net</a><br>
<b>Cc:</b> Mark Whittington <a class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560moz-txt-link-rfc2396E" href="mailto:markwhi@gmail.com" target="_blank"><markwhi@gmail.com></a>;
Tacos <a class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560moz-txt-link-rfc2396E" href="mailto:tacos@amrad.org" target="_blank"><tacos@amrad.org></a><br>
<b>Subject:</b> Re: Advice sought -
isolation transformer inrush current
limiting</p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Please pardon my jumping in
on this issue, but I think this might be an
opportunity to increase my knowledge on
magnetostrsiction… I have observed that a large
transformer, when initially energized at
no-load, generates a loud power-frequency sound
which fades out over ten to fifteen seconds… </p>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">What causes the
time-decaying character of the hum sound ?</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">Jerry AB3SX</p>
</div>
<div>
<p class="MsoNormal"> </p>
<div>
<div>
<p class="MsoNormal"><br>
<br>
</p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal">On May 22, 2018, at
14:29 PM, Karl W4KRL <<a href="mailto:W4KRL@arrl.net" target="_blank">W4KRL@arrl.net</a>>
wrote:</p>
</div>
<p class="MsoNormal"> </p>
<div>
<div>
<p class="MsoNormal">Mark,</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">This is due to
remanent flux in the transformer
core. If the first half cycle of the
line tries to magnetize the core in
the same polarity, it will saturate
the core and draw high current. One
possible approach is to put a
resistor in series with the line and
cut out the resistor after the
transformer core resets. An
incandescent bulb, say 75W if you
can find one, would be a good
resistor.</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">That said, try an
SL22 10008 NTC.</p>
</div>
<div>
<p class="MsoNormal"><a href="https://www.ametherm.com/inrush-current/transformer-inrush-current.html?gclid=CjwKCAjw_47YBRBxEiwAYuKdw6_IzT-R5wYlOv0eMMWHP5owpuxpxYzNUo4YC3SoXzx-6Xj7CdVNiBoCnDsQAvD_BwE" target="_blank"><span style="color:#954f72">https://www.ametherm.com/inrus<wbr>h-current/transformer-inrush-c<wbr>urrent.html?gclid=CjwKCAjw_47Y<wbr>BRBxEiwAYuKdw6_IzT-R5wYlOv0eMM<wbr>WHP5owpuxpxYzNUo4YC3SoXzx-6Xj7<wbr>CdVNiBoCnDsQAvD_BwE</span></a></p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">Karl W4KRL</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal"><b>From:</b><span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span>Tacos <<a href="mailto:tacos-bounces+karl.w4krl=gmail.com@amrad.org" target="_blank">tacos-bounces+karl.w4krl=gmai<wbr>l.com@amrad.org</a>><span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span><b>On Behalf
Of<span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span></b>Mark
Whittington<br>
<b>Sent:</b><span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span>Tuesday,
May 22, 2018 6:57 AM<br>
<b>To:</b><span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span>Tacos
<<a href="mailto:tacos@amrad.org" target="_blank">tacos@amrad.org</a>><br>
<b>Subject:</b><span class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560apple-converted-space"> </span>Advice
sought - isolation transformer
inrush current limiting</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<div>
<p class="MsoNormal">I've got a 1KW
isolation transformer that usually
trips the 15A breaker at the
breaker box when I turn it on,
load or no. I'm considering
installing a pair of NTC
thermistors on the input side of
the transformer, but I've no idea
how to size them or if there might
be a better option.</p>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Any advice
would be appreciated.</p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Cheers.</p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">-Mark</p>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"LucidaGrande",serif">______________________________<wbr>_________________<br>
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</div>
</blockquote>
</div>
<p class="MsoNormal"> </p>
</div>
</div>
</div>
<br>
<fieldset class="m_-7379952015683989671m_8573248344409565587m_1653725220471390560mimeAttachmentHeader"></fieldset>
<br>
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</pre>
</blockquote>
<br>
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</div>
</div>
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</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</div></div></div>
</blockquote></div><br></div>
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<br></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature" data-smartmail="gmail_signature">Given a choice between two theories, take the one which is funnier </div>
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