Can I use VOELCB as Main isolation switch

[Stuart981]

A rough sketch where a single bonded water pipe creates a short across the coil. As Flameport has said there are other items whose bonding will create a short

Many thanks for your informative reply Bernard.

 

[EFLImpudence]

The VO stands for Voltage Operated.

 

[flameport]

s would that small amount flowing through the earth electrode build to a level that would eventually trigger the device?

Current doesn't 'build' - it flows depending on the voltage applied and the impedance of what is connected to that voltage source.
What voltage appears across he VOELCB coil depends on the current there, and therefore what percentage of fault current flows via that path compared to others.

Whether the VOELCB would work or not depends on the exact circumstances, including where the N-E connection is relative to the other fault, what the impedance of the N-E connection / circuit wiring / electrode is, and various other factors. For theoretical models, such things can be calculated. For a real installation, it's entirely unknown and unpredictable.

 

[JohnW2]

Thank you for that detailed reply. You say most of the fault current will flow through the N-E connection and very little via the earth electrode. My question is would that small amount flowing through the earth electrode build to a level that would eventually trigger the device?

i would say that what flamepotrt didn't fully explain is that it 'depends' - on the nature of the 'E' of the N-E fault, and the presence or otherwise of #'parallel paths' to earth from that 'E'.

If the fault is from Neutral to the 'earth' of the installation (i.e. a CPC) then if there are no other paths to (true) earth from the installation's earth, the all of the fault current would go through the VOELCB to the earth electrode - and hence cause that device to trip i the current were high enough.

However, as has been said, 'parallel paths' to true earth from an installation's 'earthing system' (CPCs) are common (e.g. because of bonded metal water/gas supply pipes), and that has the potential to largely undermine the operation of a VOELCB.
'
Kind Regards, John

 

[JohnW2]

The VO stands for Voltage Operated.

It does, but it is potentially confusing terminology, given that what causes the device to operate is current flowing through its coil. It operates when the voltage across the coil is equal to the resistance/impedance of its coil multiplied by the current required cause cause a 'trip'.

I suppose one could, equivalently claim that an MCB was 'voltage operated', since it operates when the voltage across it is equal to it's internal resistance/impedance multiplied by the current at which it is designed to 'trip' - but I've never heard anyone trying that one

Kind Regards, John

 

[bernardgreen]

They were referred to as "Voltage Operated" because they were designed to operate ( trip ) before the voltage difference between CPC and Ground reached 50 Volts which was considered to be a safe voltage.

The current that was necessary to cause the electro -magnet to trip the mechanism varied depending on the make and model of the VOELCB as they did not all have the same resistance. The only fixed parameter was the 50 Volt hence they were voltage operated when in reality they, like all electro-magnetic devices, were current operated

 

[JohnW2]

They were referred to as "Voltage Operated" because they were designed to operate ( trip ) before the voltage difference between CPC and Ground reached 50 Volts which was considered to be a safe voltage. .... The current that was necessary to cause the electro -magnet to trip the mechanism varied depending on the make and model of the VOELCB as they did not all have the same resistance. The only fixed parameter was the 50 Volt hence they were voltage operated when in reality they, like all electro-magnetic devices, were current operated

Indeed so - essentially as I said.

As you say, I presume the only reason why these (electrically, 'current-operated') devices were described as 'voltage operated' was because the current at which they operated was designed to be that which would result if there were a pd or 50 V between the installation's CPCs and the earth electrode.

Kind Regards, John

 

[Stuart981]

Thanks for all your replies chaps. If non conductive inserts on incoming pipes, water and oil in my case and easily installed, were fitted then would leaving a working VOELCB in place provide a similar level of safety to an RCD inside the home.
Thanks Stuart

 

[flameport]

would leaving a working VOELCB in place provide a similar level of safety to an RCD

No, that will never happen.

A VOELCB is not an RCD, and cannot ever provide the same protection that an RCD does.

Even in an installation with a perfectly working VOELCB, if a person touches a live wire, they get a severe electric shock and will be injured or killed.

 

[JohnW2]

Thanks for all your replies chaps. If non conductive inserts on incoming pipes, water and oil in my case and easily installed, were fitted then would leaving a working VOELCB in place provide a similar level of safety to an RCD inside the home.

It would certainly be more likely to work than without such non-conductive inserts, but you still could not rely upon it to offer any 'levelof ssafety' - as flameport has said, since it is inevitably decades old, and relies on moving parts for its proper operation, there's no guarantee that it would work at all when it should, even if the 'electrics' were optimal.

Furthermore, even if did work 'as intended', whilst it would then hopefully clear faults (e.g. an L-E) one before they had a chance to result in electric shocks they would not, in the way that an RCD does, offer any useful degree of 'protection' to someone who was receiving a shock.

An RCD will trip very rapidly if more than about 30mA flows through a person to earth, thereby considerably limiting the potential duration of the shock. On the other hand, if I recall correctly, VOELCBs had coils with resistances/impedances in the range of 150 - 500 Ω. Given that they were designed to operate when there was ~50V across the coil, the current through a person would have to be in the range 100 - 333 mA (plenty high enough to kill) before the device operated.

Kind Regards, John

 

[Stuart981]

Thanks for all that chaps. One further question if I may:

If the VOELCB test button trips the power can I take that as proof that the device is serviceable.

Regards Stuart

 

[JohnW2]

Thanks for all that chaps. One further question if I may: If the VOELCB test button trips the power can I take that as proof that the device is serviceable.

I nearly mentioned that. If pushing the test button causes it to trip, that obviously means that it was capable of 'working', but it would be wrong to derive too much reassurance from that, not the least because it would tell you nothing about 'reliability' (e.g. whether it would trip every time if you pressed the button several times).

In any event, as I said, even if it were working perfectly and reliably (like 'the day it was born') it could still not give you (some) 'protection' in the event of to an electric shock in the way that an RCD could - and, even when someone isn't getting a shock (and for the same reason) a fault has to be quite a lot 'worse' (higher fault current) to trip a VOELCB than would be required to trip an RCD.

At the very best, a perfectly functioning VOELCB is only 'better than nothing' - but it really is not a satisfactory form of protection in the 21st century (and wasn't for the latter part of the 20th century, either).

Kind Regards, John

 

[Stuart981]

Hello chaps. Me again with a further question if I may

To recap I have a TT system with an earth leakage that I haven’t had a chance to track down. The TT system is connected to an old Wylex fused board with a Crabtree VOELCB connected to an earth spike.

I briefly borrowed an earth leakage meter and because of the standing fault I was able gauge the relationship between 3 earths that I managed to identify.

• Bonding lead from CU to rising main – 70mA
• Bonding lead from CU to incoming heating oil pipe – 30mA
• Bonding lead from CU to earth spike via VOELCB – 1mA

What I am proposing is to disconnect the earth cable at the earth spike and re-connect it to the rising main. Would that provide any additional safety.

Regards Stuart

 

[EFLImpudence]

I haven't read the whole thread, but -

to find earth leakage, the Line and Neutral of various circuits are clamped; not the CPCs(earth wires) or bonding conductors.

You need to find out where the earth leakage is originating, not where it is going.

 

[conny]

I haven't read the whole thread either but he started this in late January. He has emphatically been told that he cannot use the VOELCB in his installation, yet he continues to ask more and more questions pertaining to trying to use it at this current time.

To the OP, @Stuart981, are you going to accept that this device is functionally useless and your playing around with it actually constitutes a danger to yourself and your family?
Your wiring needs to be updated as a matter of concern and you will have to accept the fact that you need to have it done professionally as soon as possible. This is not like playing about with a board & switches etc in a college lesson using extra low voltage equipment. This is playing about with a 'real world' situation where you, or others, could be seriously hurt or killed.