PME or TT ?

[sprigsteen]

Hi Everyone, New to the site, newly qualified Part P installer. I have encountered two properties which appear to be TT systems with ZE readings of 65 and 100 ohms, on live testing ring main ZS results 0.5ohms and 0.56 ohms. There is no PME earthing connections at DNO cutout fuse. Does this mean the DNO have connected neutral and earth at the pole? How do I know if it is PME? Cheers guys.

 

[soulman]

Hi Sprigsteen, your question has been answered in post 18. I sometimes think the guys on the forum are a bit harsh when people ask questions, but after reading your OP i see why they are. I retrained when I was 37, i done 3 years at college, 1 year nvq with another electrician. Then went on to do 2391, AM2, regs, etc; I did all of this while working full time. I now have 2 years experience working as an electrician. I am continually reading books & learning all the time.
I find it hard to believe that people would have the confidence to work in properties with such a lack of basic knowledge. This could be dangerous not only to yourself but to the owners of the property. I mean no disrespect what-so-ever, but working in domestic premises you should understand the earthing systems. The OSG & GN3 would be a good start.

 

[GLENNSPARK]

well....
i suppose i could have given him a....talking to....

but to be honest i`m getting really fed up by it all....

 

[Knobhead]

I agree with you Glenn but for what a main switch and enclosure costs , is it worth the saving ?

Yes they are worth keeping. An isolator is off load ONLY. VOELCB's are fault make and break.

 

[Rockingit]

Yes they are worth keeping. An isolator is off load ONLY. VOELCB's are fault make and break.

I thought the issue here was that they are unreliable to operate under fault, full stop. I know there's an amount of logic in simply keeping them without the earthing as a DP isolator, but surely that's all? It does actually state in the official Building Regs guide to Part P that they should be removed out of service, btw.

 

[GLENNSPARK]

I thought the issue here was that they are unreliable to operate under fault, full stop. I know there's an amount of logic in simply keeping them without the earthing as a DP isolator, but surely that's all? It does actually state in the official Building Regs guide to Part P that they should be removed out of service, btw.

so whats this got to do with being used as a manual DP iso?

 

[Rockingit]

so whats this got to do with being used as a manual DP iso?

I was wondering where Tony was going with his comment about fault make or break, that's all.

 

[GLENNSPARK]

I was wondering where Tony was going with his comment about fault make or break, that's all.

the point he was making is that theres much more meat in em....and that you`d happily break a substantial load with them....

 

[Jay Sparks]

I thought the issue here was that they are unreliable to operate under fault, full stop. I know there's an amount of logic in simply keeping them without the earthing as a DP isolator, but surely that's all? It does actually state in the official Building Regs guide to Part P that they should be removed out of service, btw.

Here Glenn


I need to post quicker..lol

 

[Knobhead]

I thought the issue here was that they are unreliable to operate under fault, full stop. I know there's an amount of logic in simply keeping them without the earthing as a DP isolator, but surely that's all? It does actually state in the official Building Regs guide to Part P that they should be removed out of service, btw.

Yes they should be disabled as E/L protection. Relabelled they make an excellent ON LOAD main switch.
Take one to pieces and see what the contacts are like. Fast make and break plus arc chutes.

Regarding condemning breakers with a “yellow” test button. 40 years ago RCCD test buttons were yellow.

 

[Marvo]

I'd prefer to see any device removed if it can no longer reliably perform the function for which it was designed, manufactured and installed. Under my local regs this would be a requirement.

 

[Knobhead]

I'd prefer to see any device removed if it can no longer reliably perform the function for which it was designed, manufactured and installed. Under my local regs this would be a requirement.

Marvo, this argument has been rumbling on for years.

If you’ve never taken a voltage operated VOCB apart you won’t know what they are like.
Many of the old school have and trust them as an On Load switch. Unlike a RCD there is nothing in the current path other than the contacts, with the trip disabled it is a high quality switch. Even E54 has said this in the past when it’s cropped up.

 

[GLENNSPARK]

I'd prefer to see any device removed if it can no longer reliably perform the function for which it was designed, manufactured and installed. Under my local regs this would be a requirement.

yeah...well we work to BS 7671 around here..

and i still fail to see what the hell would be wrong with using it as a DP isolator.
As Tony (quite rightly) points out....this one has been doin the rounds for years....

nowt wrong with its new found use as a (very reliable) DP iso....

crack on i`d say...

 

[davesparks]

The only potential issue I can see is that most of the ones I have come across have been rated at 60Amps whereas our standard single phase supply is 100Amps these days.
Obviously there won't be much of a problem as the average house rarely goes over 20/30 amps consumption most of the time, but in theory something doesn't quite add up there

 

[Engineer54]

Marvo, this argument has been rumbling on for years.

If you’ve never taken a voltage operated VOCB apart you won’t know what they are like.
Many of the old school have and trust them as an On Load switch. Unlike a RCD there is nothing in the current path other than the contacts, with the trip disabled it is a high quality switch. Even E54 has said this in the past when it’s cropped up.

I have indeed, ...as a double pole on load switch, there is probably nothing to touch them. Why throw away a free perfectly good DP switch??

Have a good look at those moving and fixed contacts on these VOELB switches, then look at a modern 100A isolating switch and tell me what one you would trust handling 80A/100A?? Not that you'll ever see anywhere near 80A/100A on 99.99% of domestic installations.

Think how many old Wylex 3036 CU's (that were only ever made with 60A main switches) have been and still are working perfectly fine for literary donkey's years with 80A DNO service fuses, and probably in more than a few cases 100A services fuses.

 

[GMES]

Yes they should be disabled as E/L protection. Relabelled they make an excellent ON LOAD main switch.
Take one to pieces and see what the contacts are like. Fast make and break plus arc chutes.

Regarding condemning breakers with a “yellow” test button. 40 years ago RCCD test buttons were yellow.

Tony are they anything like Parachutes