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Date:      Thu, 17 Oct 2013 14:44:23 +0100
From:      Frank Leonhardt <frank2@fjl.co.uk>
To:        freebsd-questions@freebsd.org
Subject:   Re: OT: UPS buying suggestion
Message-ID:  <525FE9B7.6080307@fjl.co.uk>
In-Reply-To: <1382015420.5852.97.camel@archlinux>
References:  <CACo--msUpY-6r7MkuEvrPDpSVdFZyBotSA-eS7aLGMFDeq_vDQ@mail.gmail.com> <alpine.BSF.2.00.1310150911510.97788@wonkity.com> <CACo--mvUfcAy=0hyun21DZwSmdd=SmP7EeU-FVxJyiT_h4Rxkg@mail.gmail.com> <525F0138.1020304@fjl.co.uk> <20131017093820.6a8428de@X220.ovitrap.com> <alpine.BSF.2.00.1310162309200.14022@wonkity.com> <1381988697.5852.16.camel@archlinux> <20131017142910.61325830@X220.ovitrap.com> <1381992680.5852.45.camel@archlinux> <525FD4C8.1090600@fjl.co.uk> <1382015420.5852.97.camel@archlinux>

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On 17/10/2013 14:10, Ralf Mardorf wrote:
> On Thu, 2013-10-17 at 13:15 +0100, Frank Leonhardt wrote:
>> On 17/10/2013 07:51, Ralf Mardorf wrote:
>>> On Thu, 2013-10-17 at 14:29 +0800, Erich Dollansky wrote:
>>>> Industry is much worse. Their machines made early computers fail when
>>>> the bigger machines started work.
>>> I worked for an audio company. The audio workshops were rented rooms on
>>> a farm, and the boss missed to check the values of the RCCB, which
>>> nearly killed a friend. Bigger machines are a PITA ;). The RCCB had a
>>> value that high, that it was dangerous to life for an audio workshop. A
>>> big machine not only pollutes the mains, if you turn it on, it also will
>>> "eat" the complete power and lots of it going in, doesn't come out. A
>>> "normal" RCCB would turn off immediately.
>>>
>>>
>> Most RCCB (aka ELCB, RCD) work (hereabouts anyway) work with
>> counter-wound coils on the input and output of the supply such that he
>> magnetic field is neutral if the current is the same. If it goes out of
>> balance, it trips the switch. Normally 30mA difference is the rule. They
>> don't have a value, as such. I heard that only 10mA is needed to
>> interrupt your heart, but I've also heard 100mA. They're all potentially
>> dangerous. It depends on the route taken by the current passes through
>> your body - you'd have to try quite hard to get even 10mA in the wrong
>> place, but I guess you could do it with rubber shoes and grasping the
>> mains one your one hand and an earth spike with the other. I was taught
>> to keep my left hand in my pocket when poking around stuff that might be
>> live, and do it quite subconsciously.
> The one at home, in Germany called FI, has got a value of 0.03A for my
> flat, the one at the farm had a value of 1A.
>
> "Handelsüblich sind Fehlerstromschutz-Schutzschalter in der Bauart A für
> Bemessungsdifferenzströme von IΔN=10 mA, 30 mA, 100 mA, 300 mA, 500 mA
> und 1 A." -
> https://de.wikipedia.org/wiki/Fehlerstromschutzschalter#Kennwerte
>
> The keyword is "Bemessungsdifferenzströme", sorry I can't translate it.
> 30mA is save, 1A will kill you, since it won't turn off the power if
> your body should become the resistor.
>
> As mentioned before, a workshop in addition must use an isolating
> transformer, by this galvanic isolation you can't get an electric shock
> if you only have contact to the phase and ground. You need to have
> contact to phase and neutral conductor to get a shock.
>
>

Bemessungsdifferenzströme = residual current rating (i.e. trip current). 1A! No good to stop a human being zapped, but might prevent a fire in the circuit. It'd be completely illegal in England, including in the workplace (I THINK). Certainly no more than 30mA for shock protection (or 10mA for low-voltage application like 110V. I know it's possible to fit 300mA where only fire prevention is needed; I've never seen anything higher than that, but I'm not an electrician.

As you say, your friend was lucky!





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