Re: GFIs and TCs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Matthew Smith <matt-at-kbc-dot-net.au> 

Tesla list wrote:
>Original poster: "Randy & Lori" <rburney6-at-comcast-dot-net>
>Does a GFI act as a circuit breaker in addition to just comparing currents 
>on both lines? (Will it trip for excessive currents even if both lines 
>have matched currents?)
>Also, do GFIs work well in TC applications? (would a rail strike trip the 
>thing every time?)

Just to clarify, I believe that there may be two types of devices in 
discussion here.

A GFI (ground fault interruptor?) sounds like what I'd call an ELCB (earth 
leakage circuit breaker).  As far as I am aware, this operates on current 
flowing through the earth conductor as opposed to an RCD (residual current 
device) or RCCB (residual current circuit breaker) which trips when there 
is a difference in current flowing through the phase/live/active/hot and 
neutral conductors.  I seem to recall something from college about RCCBs 
taking over from ELCBs.  Someone please correct me if I'm wrong.

An RCD will trip if you sneeze in the wrong direction or don't speak to it 
nicely - I have no personal experience of them supplying power to a TC 
service but think that they would be Bad News(tm) as some of the "noise" 
thrown back into the supply could cause them to trip.  Good filtering and, 
if available, a nice big isolation transformer could help here.

To answer the original question, our new consumer unit has a pair of 40A 
RCDs, each protecting a number of circuits.  That's a 40A over-current trip 
plus a 30mA differential (RCD) trip in one switch.  Devices such as an 
immersion heater and oven/hob do not pass through RCDs.  My thought would 
be to a) have a separate supply for your TC, not passing through an RCD, 
provided that local wiring regulations permit it or b) if forbidden, ask 
them to wire a point for your new electric oven in your shed/cellar/etc ;-)

Cheers

M

-- 
Matthew Smith
Kadina Business Consultancy
South Australia
http://www.kbc-dot-net.au