Discuss Replacing VOELCB in the Electrical Forum area at ElectriciansForums.net

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DNS1

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Hi chaps,

Not come across a VOELCB protected system before so apologies if I'm being stupid.

It's a TT system, but the only shock protection is the 30mA RCD on the socket circuits and the (knackered, test button doesn't work) VOELCB on the main isolator.

Just wondering whether to just replace the CU main switch with a 100mA RCD, or to replace the VOELCB unit with a new isolator with RCD protection.

I'm thinking just replacing the CU main switch and leaving the VOELCB to act purely as an isolator. Does this sound ok?
 
D

DurhamSparky

ideally remove the VOELCB from service entirely...!!!! replace the ELCB with 100ma TD rcd
 
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Engineer54

If it's a TT system replace the VOELCB with a 100mA S type RCD either as the main CU switch or in it's own enclosure external to the CU. All circuits on a TT system should be protected by 30mA RCD's or RCBO's. They are the primary means of protection against earth faults on TT systems that have naff Ra values. RCD's are only ''Addition'' protection on DNO TN supplies....
 

Marvo

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There's several ways you could go about it with a 100mA RCD but if the VOELCB isn't functioning correctly I would retire it to the bin, I wouldn't even leave it as an isolator.
 
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D

DNS1

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Cheers for the advice guys.

I'll look at getting rid of the VOELCB and putting an isolator in. Might as well replace the whole board considering how cheap they are and get everything under a 30mA RCD.

Thanks!
 
E

Engineer54

There's several ways you could go about it with a 100mA RCD but if the VOELCB isn't functioning correctly I would retire it to the bin, I wouldn't even leave it as an isolator.
The VOELCB are all 30+ years old now, and most didn't work correctly since the day they were installed, due to parallel earth paths etc, many being by-passed or defeated.... So in all honesty, they should be binned whenever possible...
 
E

Engineer54

Cheers for the advice guys.

I'll look at getting rid of the VOELCB and putting an isolator in. Might as well replace the whole board considering how cheap they are and get everything under a 30mA RCD.

Thanks!
By far a better solution would be to replace the VOELCB with an S type RCD on a TT system, that will then be your ''Additional'' protection for a safer TT system....
 

Marvo

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Yeah, I would agree, they were the best technology available in their day but they were hit and miss at best. Given the low cost of RCD's nowadays replacement on sight would be a good option.
 

sparc

Regular EF Member
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I have a customer with a VOELCB on a TT system. Old fuse boards in use.

He's doing a massive amount of development work to the house, and the electrode is the first thing in the way.

I'd advised him that I should replace the VOELCB and put in a new dual RCD consumer unit before he starts the work, but he was adamant he didn't want to do that until new CU goes in with all new wiring.

So I advised him to check with DNO that PME was available. DNO came out, checked ELCB was working okay - it is (my MFT can't test it, for some reason) - and they confirmed: "PME available if required".

The DNO also said I could do the PME, which I did, installing a MET and connecting the supply head neutral to the MET with 16mm2. Ze now 0.16 and Zs at a selected test socket fell from 22.8 to 0.25

Now, as I understand the way a VOELCB works, it looks at difference in potential between earth spike and internal earth (from the CPC). As the customer was removing the earth spike there was no point in using that earth connection for the VOELCB, so I hooked both earth terminals up to the MET.

Has this turned the VOELCB into just a plain 2 pole isolator, or can it still function? Test button causes it to trip. Ideally, I would install at least a TD 100mA isolator switch in its place, but customer doesn't want to spend anything on electrics at moment.
 
E

Engineer54

The DNO also said I could do the PME, which I did, installing a MET and connecting the supply head neutral to the MET with 16mm2. Ze now 0.16 and Zs at a selected test socket fell from 22.8 to 0.25
Who told you, that you can do the PME conversion on DNO equipment yourself?? The lazy so and so that came to look at your installation?? Be warned, ...Unless you have that permission written on official headed paper, signed by no less than the Area engineer responsible, (which i know you don't have) then you could well find yourself in some serious trouble in the future!!! The DNO's cannot delegate their responsibilities to others outside of their company, or their certified contractors under their employ.




 
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nick611

why dont you just replace the voelcb with a 30ma rcd untill the work is finished put in another electrode temp for now and see if you can have pme at the finish. this will give you correct protection on all circuits + keep the builders safe
 

Des 56

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Leaving aside for the moment the self connected 16mm
Was the bonding also brought up to standard in order to avail yourself of the Pme facility
 
D

Deleted member 26818

By far a better solution would be to replace the VOELCB with an S type RCD on a TT system, that will then be your ''Additional'' protection for a safer TT system....
I'm not aware that a 100mA RCD can be used as additional protection.
To my mind it would primary fault protection, and a 30mA device would be additional.
 
E

Engineer54

I'm not aware that a 100mA RCD can be used as additional protection.
To my mind it would primary fault protection, and a 30mA device would be additional.
Really, how do you work that out then, there is little chance of ADS working as primary protection on a UK TT system?? The 100mA S type isn't going to trip before a 30mA, even if both 30's (dual RCD CU) are up to the limit in natural leakage... Unless this is just a play on words!!
 
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Engineer54

Only RCDs rated upto 30mA are recognised as providing "additional protection" so surely Spin is correct?
And when that 30mA RCD device fails for one reason or another on a TT system?? The ADS isn't going to be doing anything for you is it!!!

Look, ...it doesn't matter what you call the S type upstream RCD, primary or additional protection it's better to have than not to have on a TT system, especially a UK TT system as it stands now!!
 
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sparc

Regular EF Member
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257
Location
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Who told you, that you can do the PME conversion on DNO equipment yourself?? The lazy so and so that came to look at your installation?? Be warned, ...Unless you have that permission written on official headed paper, signed by no less than the Area engineer responsible, (which i know you don't have) then you could well find yourself in some serious trouble in the future!!! The DNO's cannot delegate their responsibilities to others outside of their company, or their certified contractors under their employ.
I'm playing piggy-in-the-middle here. The customer wants to get the earthing arrangement sorted so he can get rid of the spike, but isn't getting any help from the DNO - they don't seem to regard converter the TT system as their responsibility. I've also sat down with DNO engineers - in the DNO's operations offices - and been told I CAN put the PME link in place, provided I re-seal the main fuse after, adding one of their stickers - which they have given me.

That may be burning bacon you can smell but, frankly, I'm up for that argument after getting the run around on this issue so many times in the past.
 
E

Engineer54

That's totally up to you Sparc, but nothing in writing, and a few years down the line when something goes wrong, be it of what you have done or not, the fingers going to be pointing at you. Do you honestly think a so-called responsible DNO Engineer is going to own up to giving you permission to alter DNO equipment?? Not on your Nelly will he!!!
 

sparc

Regular EF Member
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257
Location
Berkshire
This is second situation in as many weeks in which the supply is being moved around the building site and the DNO(s) are messing the customer around. This is another configuration that's going to get demolished in next few weeks, and a new supply head, meter and earth are going to get installed in what will be a newly built part of the house. So I see my responsibility here as being making the customer as safe as possible in this transition period. He's getting no help from the DNO on that. When I got there today to look at this PME the customer admitted the electrode had been dug up by the builders, and was sitting on the ground - my 22.8 Ohms reading probably reflected the fact that it's been p******g down for over 24 hours here, and site is a marsh.

All that aside... it's this VOELCB that's got me thinking. If the trip function doesn't work without separate external earth reference (my understanding of a VO-ELCB). So was the configuration safer as a TT system with a working VOELCB, or now as a TN-C-S without one - but with a nice low Zs value? I've still got the option of putting in a 100mA type S RCD, got a standalone here on my desk.
 
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Engineer54

Your far better off with a PME supply than a low value unstable TT system. Nothing to stop you driving in a rod and connecting that to MET, in fact it's good practice to do so!! But not much point if it's just going to be a 200 ohm short twig like spike!!!

Very few of those old VOELCB ever worked correctly from the day they were installed... lol!!!
 

sparc

Regular EF Member
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Berkshire
I think I'll put the 100mA S RCD in place of that VOELCB - even at my own expense. Better than sleepless nights! :-0
 

sparc

Regular EF Member
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Location
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Just to close the loop on this, I did email the DNO noting down everything from the various phone calls on this subject. Got a receipt response back, showing it had been received, but no answer back ....
 
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