[sdiy] OT: Mains Safety PSA

S Ridley spridley1 at gmail.com
Sat Jan 15 12:12:22 CET 2022


 12A breaker is not designed to trip at 12A.   It's trip is designed to
protect a 12A circuit.

It should allow 12A to flow indefinitely, and probably allow higher
currents briefly (e.g. inrush current when you switch things on) but should
trip before other elements in the circuit (wire, connectors) fail.  Here is
a graph of MCB trip characteristics, and you'll see that at 36A it might
still take 5 seconds to trip - maybe longer on a cold day.

https://www.ti-soft.com/img/panelcad/mcb_tripping_iec60898.png

Up to a certain point it's a thermal mechanism, and increasing the current
decreases the trip time.  At high currents, a magnetic mechanism comes in,
and trips PDQ.
The trick is to have a low earth loop impedance so that if you have a
short, sh1tloads of current flows and the trip trips in a very short time.

Steve






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On Fri, 14 Jan 2022 at 22:13, cheater cheater via Synth-diy <
synth-diy at synth-diy.org> wrote:

> The breaker is rated 12A. I can get it to trip at 34A. I think that's
> all that needs to be said.
>
> On Fri, Jan 14, 2022 at 5:22 PM Chromatest J. Pantsmaker
> <chromatest at azburners.org> wrote:
> >
> > I'm in the US, and I've done extensive house wiring here, but I know
> nothing about what is acceptable or even legal in other countries.
> >
> > In the US, we run 120V for regular wall outlets.  The regular
> receptacles are rated at 15A.  The wiring needs to be rated for at least
> 15A, and the fuse/breaker can be rated no higher than the rating of the
> smallest wiring conductor between the breaker and outlets.  This is
> typically 14 gauge (with a 15A breaker) or 12 Gauge (with a 20A) breaker.
> That breaker typically supplies *multiple* 15A receptacles, with the idea
> that they aren't going to all draw their rated maximum at the same time (if
> ever).  And if they do, the breaker trips or the fuse blows to protect the
> wiring.
> >
> > So my question is, do other countries allow wiring with oversized
> breakers?  Why didn't Cheater's fuse/breaker save the day?  I would expect
> breakers in 240V countries to be even smaller thanks to Mr. Ohm.
> >
> > On Fri, Jan 14, 2022 at 8:13 AM Mike Bryant <mbryant at futurehorizons.com>
> wrote:
> >>
> >> 26 Amps is also marginal for the house wiring in many European
> countries.    Europeans never did understand the advantages of UK ring
> mains which are of course compulsory here in most situations :-)
> >>
> >> -----Original Message-----
> >> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> Gordonjcp
> >> Sent: 14 January 2022 13:55
> >> To: synth-diy at synth-diy.org
> >> Subject: Re: [sdiy] OT: Mains Safety PSA
> >>
> >> On Fri, Jan 14, 2022 at 12:33:06PM +0100, cheater cheater via Synth-diy
> wrote:
> >> > So as recent experience shows, 18 - 26 amps max continuous load for
> >> > months was a tad optimistic for this unknown brand Schuko wall socket,
> >>
> >> 18A is somewhat and 26A is grossly out of spec for Schuko.
> >>
> >> If you're going to pull that kind of power you need to look into
> getting a dedicated circuit and IEC60309 sockets fitted.  We use the 16A
> version for our "small" cabinets (where they mostly just power a single 24V
> rackmount PSU, with extra "UK plug" BS1363 sockets for plugging in test
> equipment.  For our server cabs we use the 32A version.
> >>
> >> You might want to use the 32A version, too.
> >>
> >> --
> >> Gordonjcp
> >>
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