Wednesday, Jan 06, 2010 at 23:19
Hi Allan
Yes it going to get ugly.
#1::Firstly I gather that you have some involvement in the electrical industry, possibly an electrician? I too have been involved in the electrical industry as an electrical engineer, for a lifetime, multi qualified and widely experienced. So I claim that
mine is bigger than yours!
#2:Your suggestion that I do a "little research on RCD's and ELCB's" is amusing to say the least. I was working with ELCB's long before RCD's were developed.
They are NOT the same thing although the electrical industry initially erroneously referred to the new RCD's as ELCB's and many such as you still do so.
#3"The term "Safety Switch" is a popular term for an RCD but it is not a engineering or definitive term.
#4:An ELCB (Earth Leakage Circuit Breaker) was exactly that.... Earth leakage. Prior to 1980 and the introduction of the MEN (Multiple Earthed Neutral) system, protection from electric shock from appliances was managed by the Direct Earthing System whereby the installation earth wire was connected to the town reticulated water pipe. In locations where there was no reticulated water mains Voltage operated Earth Leakage Circuit Breakers were employed.
#5:The installation used an insulated earth wire which connected to the coil of the ELCB with the other side of the coil connected to an earth stake. The neutral conductor of the supply mains was connected to an earth
grid at the point of supply, typically the supply transformer.
#6In the event of insulation failure and leakage from the active conductor to the earth wire, a current would pass through the ELCB coil and cause it to trip thus isolating the supply from the installation. The ELCB then needed to be manually reset. The system suffered from a number of problems but was the best that could be provided at the time.
#7:The introduction of the MEN system rendered the ELCB redundant and provided electrical installations with a means of directing earth fault currents back to the supply source via the neutral line and not through the water pipes, a definite improvement especially where no water pipes were available. The subsequent development of the RCD added a great improvement to electrical safety but unfortunately their introduction was somewhat piecemeal and they were called by several different names including ELCB's as they performed a similar task. Eventually the "official" name was assigned as Residual Current Devices (RCD's) and that is all they should now be called. The bad habits of the industry however are not dying easily and many including even suppliers still refer to them as ELCB's but incorrectly.
AS/NZS 3000 Wiring Rules uses ONLY the term RCD. The only single reference in that standard to ELCB is in clause 5.1.4(c) where reference is made to "former direct earthing or voltage operated ELCB systems".
#8Earth leakage relays continue to be used in certain industrial installations and in particular electricity distribution equipment such as large transformers to provide alarms and trips in the event of earth leakage currents.
#9:So Oldtrack, do you still think I need to "do a little research" on this subject?:
I damn near wrote the book on it! Don't try to teach your grandmother to suck eggs!
#10And I repeat, an RCD will work satisfactorily and properly on an isolated power source. It does not need a direct earth or MEN system. If you understood the device and how it operates you would realise that. If the current being delivered by the "active" conductor does not fully return by the "neutral" conductor it must be getting back by another path possibly your body and the RCD will detect this and interrupt the supply possibly saving your life. Just because you have not experienced such installations does not mean that they do not exist. They are an excellent life-saving safety device and I would not operate an electrical installation, either fixed mains fed, or portable inverter or generator fed, without a RCD with the exception maybe of inverter and double insulated appliance within the vehicle. "
You sure have problems with your teminology.
From reading your post YOU are obviously referring to RVDs ,"RESIDUAL VOLTAGE DEVICES" that Do NOT & CANNOT work with an EN /MEN system
Thet are only now coming onto the market for general use WITH FULLY ISOLATED POWER SUPPLIESsuch as gennys &
inverters
So here goes
#1
well i will leave others to judge by the end of this post
#2 Perhaps power suppliers teminology is differrant but I believe you were working with RVDs ,which detect a leakage between either line to earth & trip & as you say had to be manually reset
Throught the trade in AUS they have been referred to as ELCBS then &now RCDs
But when 1st on market, in late 50s ,early 60s from memory, they were called "core balance cb" The name says it all "Core balance" equal currents in active & neutral .
They had no direct connection to earth .They did not carry earth current.
#3
I agree the term "safety switch" which is creeping in & is what lay people know them as, is not a good or acceptable term my reason for saying this is it may lead to a false belief that one isc completly protected from elecric shock
#4
I think I've explained that in#3 But I'll just add a bit.
Brisbane had 2 suppliers, in thelate40s /early 50s, one used direct earthing ,the other used MEN
You had be sure whose area you were in as they tended to intertwine.
ELCBS were not in use .
The 1st ELCBS/CORE balance cbs as stated above did not come on to the market till about the late 50s early 60s.
#5
I think I have explained that too but again end users did not have an elcb monitoring earth currents
#6
At the suppliers lines ,yes but not in the customers premises & i believe the correct term was RVD
#7
to save repetition read the above
#8
RVDs Are now coming onto the market for use with FULLY isolated power sources such as gennys & inveters
#9
Better get to grandma & see if she can teach you how to suck eggs
#10
What can I say except you have no idea of how a RCD works.
Please, if you cannot understand what i have posted sit down & draw it out & see if you can find away for the curent to get back to the power source without an EN link
I repeat THEY monitor current flowing in active & neutral THEY have no direct connection with earth
THEY detect the out of balance currents which can only return to the source via an EN bond.
THEY simply cannot work on a fully isolated system.
Your last statement is a real frightener, RCDs offer no protection for direct contact between Active & neutral
But just to make you feel better you are not the only one who has made similar wrong statements. & believe RCDs can operate without the bond /link
I strongly you do do a bit of research ON RCDs, RVDs
I hope any one reading this now understands it is something that only a licenced & QUALIFIED[ conversant with ALL the rquirement of the regs] electrician should carry out see my earlier post.
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