Voltage Trips

[huntos33]

Just wondering how sensitive the old crabtree voltage trips are compaired to a RCD ?

 

[richy3333]

yep...been out filey today....BS3036-6 way...TT=87.6 ohms.... crabtree VO ELCB....were gonna do away with the voelcb on second fix=test and put a stand alone RCD for the 3036 as its good for continued service .....

What, you're gonna keep a 3036 board in use, no forced RCD board change, you'll have the Electrical Trainee's foaming at the mouths

 

[GLENNSPARK]

What, you're gonna keep a 3036 board in use, no forced RCD board change, you'll have the Electrical Trainee's foaming at the mouths

yes...but you do what needs to be done to ensure compliancy...nowt less.....and nowt more unless the person ordering the work asks for it....i have IR`d all final circuits being fed from that C/U...so i know when we introduce an earth leakage device into the mix there should be no nasty surprises.....:38:

 

[Guest123]

If you come across one of these VO ELCB units to BS 842 1965, when conducting an EICR, industry guidance suggests a minimum of a code 3 be attributed even if the device is found to be operating correctly.

If the install is old enough to still have one of these present, chances are the earth path may be still be via a metallic service pipe which would warrant a minimum of a code 2.


IMHO, even functioning units of this type are unfit for contiuned service and should be removed & replaced as a matter of course.


Early versions of the newer grey Chilton units were also VO ELCB's but soon changed to become ELCB's BS 4293 1968, these were early versions of the humble RCD. Care should betaken when identifying these, the simplest indicator is the rating of the unit, VO ELCB's will have 50V written on them ELCB's will have a mA rating.

 

[hermetic]

As I said, If you test with the units test button, AND by simulating a fault at the remote end of the installation ( which rules out parralell earth paths), they provide protection which is better than fuses alone. there are 1001 things a DIYer can do to render an installation dangerous. Someone mentioned touch voltage, they are irellevant in this case as as soon as the earthed metal starts to conduct a fault current, it trips the ELCB. Actually it is the same with an RCD as long as the metalwork is earthed, it will also trip.As I also said, the earth spike/connection needs to be maintained (as does all parts of any electrical system, remember "This installation should be periodically checked and tested" etc etc) You can mark anything down as "potentially dangerous" just as any human being is a potential murderer! I have seen many modern installations that I consider to be "potentially dangerous" not becuase they are badly installed or incorrectly specified, but because some of the modern equipment is so poorly made with exposed live parts, poorly fttting clamping screws,and dubious looking cable clamps that hardly look able to carry their rated current etc etc. Only time will tell if the RCD will be as reliable, and safe (and "fail safe") as everyone seems to believe it will be. whilst typing this, a thought occurs to me, it seems ok to subject a householder to a "touch voltage" to operate an RCD under certain circumstances, and yet there now seems to be an embargo on neon screwdrivers on HSE grounds...............just a thought. I have used a neon all my working life, and still do, the only time I ever got a belt of it was when one of my "mates" fitted a slightly smaller resistor............but I got my revenge on the B*****D
Phil

 

[GLENNSPARK]

As I said, If you test with the units test button, AND by simulating a fault at the remote end of the installation ( which rules out parralell earth paths), they provide protection which is better than fuses alone. there are 1001 things a DIYer can do to render an installation dangerous. Someone mentioned touch voltage, they are irellevant in this case as as soon as the earthed metal starts to conduct a fault current, it trips the ELCB. Actually it is the same with an RCD as long as the metalwork is earthed, it will also trip.As I also said, the earth spike/connection needs to be maintained (as does all parts of any electrical system, remember "This installation should be periodically checked and tested" etc etc) You can mark anything down as "potentially dangerous" just as any human being is a potential murderer! I have seen many modern installations that I consider to be "potentially dangerous" not becuase they are badly installed or incorrectly specified, but because some of the modern equipment is so poorly made with exposed live parts, poorly fttting clamping screws,and dubious looking cable clamps that hardly look able to carry their rated current etc etc. Only time will tell if the RCD will be as reliable, and safe (and "fail safe") as everyone seems to believe it will be. whilst typing this, a thought occurs to me, it seems ok to subject a householder to a "touch voltage" to operate an RCD under certain circumstances, and yet there now seems to be an embargo on neon screwdrivers on HSE grounds...............just a thought. I have used a neon all my working life, and still do, the only time I ever got a belt of it was when one of my "mates" fitted a slightly smaller resistor............but I got my revenge on the B*****D
Phil

and this is why i aint a believer in the `magic` 1667 ohms rule as a way of getting round high Zs....

 

[hermetic]

Hi Lenny,
Most of the ones I have seen recently use seperate earth spikes. We always used to fit a polythene insert in the incoming water supply, and never used a water pipe earth for an ELCB, although if the pipe earth is good enough I can't see a problem with it. They were actually very sensitive, they would trip with a boiled over pan on an electric cooker, or a steam iron (constantly) in fact nuisance tripping could be a major problem. I do take on board what you say though.

 

[Guest123]

Testing of a VO ELCB, taken from the 14th Ed.......


"For the purpose of this test a voltage not exceeding 45 volts, obtained from a double-wound transformer connected to the mains supply, shall be applied across the neutral and earth terminals (or neutral and frame terminals of a voltage-operated earth-leakage circuit-breaker) and the circuit-breaker shall trip instantaneously. The transformer shall preferably have a short-time rating of not less than 750VA (see Figures 2 and 3).

When, in accordance with the requirements of Regulations D.10-13, cross-bonding to other services is carried out in an installation where a voltage-operated earth-leakage circuit-breaker is provided, this may result in a direct earth connection of low impedance being introduced in parallel with the path through the earth-leakage circuit-breaker. Thus an increased value of earth-leakage current would need to flow before the circuit-breaker came into operation, and in some instances the cross-bonding may well remedy the deficiency which originally gave rise to the need for the earth-leakage circuit-breaker. These effects are not harmful; it is common practice to use the best solid earth available (e.g. suitably spaced earth electrodes) in parallel with an earth-leakage circuit-breaker. The circuit-breaker would still be effective in preventing the exposed metalwork of the installation from rising to a dangerous voltage".

 

[hermetic]

Spot on Lenny! I have just dug mine out and was reading section D (14th Ed metric reprint 1970, my college copy)

 

[GLENNSPARK]

i dont know if theres a `niche` market now for these older editions.....wouldn`t mind getting my paws on a 1st edition though....

 

[Guest123]

wouldn`t mind getting my paws on a 1st edition though....

It was only 4 A5 sized pages.

I've got it on PDF somewhere.

 

[GLENNSPARK]

It was only 4 A5 sized pages.

I've got it on PDF somewhere.

but its the actual book Lenny....i wonder if theres many around.....

 

[GLENNSPARK]

i have seen it....they seem to have understood about insulation etc....

 

[Knobhead]

Where the a parallel path exists the VO ELCB will still trip if the voltage rises to the trip value.
It begs the question that given a parallel path exists, what current must flow in the fault to achieve the trip voltage?

 

[Engineer54]

but its the actual book Lenny....i wonder if theres many around.....

No, as Lenny said it's just a few pages worth!! I think they published that first edition in one of the editions of the Reg's, but can't remember which edition it was, ...One of the 15th or 16th editions anyway...lol!!!

 

[spark 68]

Where the a parallel path exists the VO ELCB will still trip if the voltage rises to the trip value.
It begs the question that given a parallel path exists, what current must flow in the fault to achieve the trip voltage?

That's what I thought Tony,
by installing main bonding and/or parallel paths, you are effectively trying to reduce the touch voltage (as it is supposed to do), unless you have a large current flow to earth, so effectively negating the purpose of the VO ELBC, as the voltage needs to rise to a suitable level to trip the device, and you are trying to keep it as low as possible! (if that makes sense ?), sort of conflicting purposes so to speak.

Have I got this correct ?,