Peter Chadwick wrote:
>
>Mauri says:
>
> >The differential switch is actually placed between a local ground point
>
> >and the neutral wire,
>
>Interesting. We use to have that system in the UK, but it is no longer allowed.
>These were called ELCB - Earth Leakage Circuit Breaker - popularly called
>'voltage trips'. These days, we have 'current trips', which work on the basis
>of
>live and neutral currents differing by more than 30mA.
Rich mentioned a few days ago that these circuit breakers can be subject
to RFI. Presumably that would be the voltage-operated type.
The 'current trip' (Residual Current Circuit Breaker) has both L and N
wires passing straight through a toroidal transformer. When the L and N
currents are equal and opposite, there is no net flux in the toroid. A
third winding detects any out-of-balance current and operates the trip
solenoid. Common-mode rejection is amazingly good - a 60A surge through
L and N will not trip a 30mA breaker.
It's hard to see how such a passive, low-impedance, low-frequency device
could be subject to RFI from HF or above. Anybody ever heard of RFI
problems with *current* operated breakers?
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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