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#139984 - 01/09/04 06:10 AM Voltage-Operated Earth-Leakage Circuit-Breaker
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I've answered a query about the old British voltage-operated ELCB recently, and thought it a good opportunity to dig one out of my junk box and post some pictures.

This is the Crabtree E60 type, which was quite common in rural residential use in the 1960s and early 1970s. These old units were quite substantially built compared to their modern RCD counterparts, and this one is about 7 x 2 inches overall:





The supply enters via the top terminals, while the lower section contains the load terminals and the connections for the operating solenoid:



The lower cover displays a test instruction for the customer:


Along with some specifications inside:


On the rear is a small removable paxolin panel which gives access to the test button contacts and associated wiring:





{Continued next message...}

[This message has been edited by pauluk (edited 01-09-2004).]

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#139985 - 01/09/04 06:11 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
And finally, the main mechanism and switch contacts. The solenoid coil is just above and to the left of the yellow test button:



Another view, clearly showing that the main contacts are open:


Note that the operating toggle is the "free trip" type, so the breaker cannot be held closed against a fault.



[This message has been edited by pauluk (edited 01-09-2004).]

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#139986 - 01/09/04 11:09 PM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Hey great pictures Paul!,
As I am sure, we are all aware that these are not old RCD's, these are Voltage-operated, not Current operated devices, that we are all used to.
Actually Honeywell used to make all of the gear we used here, them and GeneralElectric.
This sort of gear is pretty rare here now, it was really only installed where the basics of the MEN Earthing system, couldn't be provided.(0.2 ohms between the earth stake at the transformer pole and the Installation earth)
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#139987 - 01/10/04 08:39 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Over here, PME (MEN or TN-C-S) in the past was confined to those rural areas where it was difficult to obtain a satisfactorily low reistance value with a ground rod. Each PME distribution system required consent from the Secretary of State for Energy. Thus the majority of rural areas with overhead distribution had homes where the ground rod was the sole method of earthing (TT system), and the ELCB was therefore very common.

PME has only really come into much more widespread use over the last 20 years or so.

Urban areas always had TN-S systems with the cable armor acting as a separate fault path right back to the transformer, so the ELCB was pretty much a rural device.

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#139988 - 01/12/04 01:12 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
Dapo Offline
Member

Registered: 03/04/03
Posts: 52
Loc: Australia
Paul,
We use the TN-C-S if my interpretation of the term is right.
TN-C-S systems where the neutral and protective functions are combined in a single conductor but only in a part of a system.
Is this the correct interpretation of TN-C-S?

If so thats the system we use in Australia.
We use a MEN system where the neutral is bonded to earth at Transformers, every few poles and at the earth stake at the consumers residence.

Am I right to understand if that system is used in the UK, you must have a voltage operated ELCB protection on the Main switch in case you get an open circuit main neutral?

If so we are not that fortunate here as a broken service neutral can result in a raised potential of any earthed metal part and there is no protection to stop this happening.

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#139989 - 01/12/04 01:52 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Gidday there Dapo!.
Just a small question,
With respect to Neutral and Earth Busbars in switch-boards, when our Regs changed here in 1992, we were told that you were no longer allowed to connect the Main Earthing Lead to the Neutral B/bar, which was where it had been connected to in all the houses wired previous to this change.
The Main Earth lug, was usually placed on the same stud as the Main Neutral and the Neutrals of the Range and the Hot-Water Cylinder, was this ever the case in Australia at any time?.
Nowadays, the Main Earth is required to be connected to the Earth B/bar and it is actually illegal to fit it to the Neutral bar, there must be a link that can be readily removed for testing purposes.
Just wondering.
Oh, sorry Graham, what I forgot to mention was the fact a lot of houses here, never even had an Earth Busbar, but just had a Line Tap in the back of the switch-board that was joint to a thick wire, (normally 7/.036") and that connected to the Neutral bar.
And to a certain extent, quite a few houses here didn't even have 3 core wire or a suitable Earth Electrode!.

[This message has been edited by Trumpy (edited 01-12-2004).]
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#139990 - 01/12/04 01:54 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Dapo,

yes, that's the system and no, the voltage operated ELCB was for use on TT systems where the neutral was not bonded to the earth. An earth fault caused a raised voltage on the earth rod which then tripped the ELCB. Today an RCD would serve the same purpose. But your idea is interesting! It would provide a means of eliminating the dangers associated with loss of neutral.

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#139991 - 01/12/04 03:26 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
djk Offline
Member

Registered: 12/26/02
Posts: 1269
Loc: Ireland
Paul,

They were used in exactly the same way on TT supplies in Ireland although the ESB would have determined when they were necessary and installed them after the meter as part of the service. The contractor just installed the fuse board and internal cabling.

TT supplies here are, however relatively rare. The ESB has full authority to choose the most appropriate earthing system for a particular supply / group of supplies. They never needed to consult any political / state athority to do their job and seem to have always favoured avoiding TT where at all possible.

ELCBs were also regularly installed on normal supplies too though as an optional extra safety device before mandatory RCDs arrived in 1980. Plenty of urban houses would have had them along side a big panel of diazed fuses.

Most rural supplies here are hooked up as individual taps into the 10/20kV 3-phase distribution system using pole mounted can-type transformers feeding a 220V supply into the house via a short cable drop (usually a twisted pair) / underground cable. I am not 100% sure what the general earthing / neutralising arrangements are with those supplies.

Any ideas?

I know very little about rural supplies in general other than what I've read / observed.

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#139992 - 01/12/04 04:25 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
excellent pix Paul


i can't help but wonder when CMP-2 here will smarten up and realize the 02' nec states 'international' on the cover

btw~ nec digest held a neat little article on CMP-2 dealings, quite a lengthly backpedalling for that rag

for those of you whom this is unclear to, imagine installing 40 of these little jems in a panel instead of one...

~S~

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#139993 - 01/12/04 04:39 AM Re: Voltage-Operated Earth-Leakage Circuit-Breaker
David UK Offline
Member

Registered: 10/03/02
Posts: 134
Loc: Inverness, Scotland
The voltage-operated elcb system is now obsolete, their use has been prohibited under IEE regs since the mid-1980s.
They were never that popular in this part of the UK, probably due to local soil conditions. I've seen very few of these devices in service, by far the most common method of earthing I find in older rural installations is PME (TNC-S) where the main earth is terminated in the supply company's neutral block.
A large proportion of older installations are only earthed via the water pipe, which can provide surprisingly good (low) earth loop impedance values, providing all the supply pipes are still metallic. This method of earthing is also now (since 1966) prohibited, although equpotential bonding of metallic service pipes is mandatory.
Where I find old installations without suitable TN-S or TNC-S earthing facilities, the local PoCo will provide an earth terminal, usually free of charge.

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