Voltage on earth ar cu when earth disconnected from earth bar and mcb on

[Jimbo8]

How exactly is disconnecting them from the Earth bar a good test for anything? And voltage is a potential difference so can only ever be between more than 

It's not a test I'm asking you a question never mind why not move onto someone else if you cant answer the question all the best thanks 

 

[Sharpend]

Let’s stop right there shall we? jimbo you have asked a question that has been answered, it has also been suggested that you’re actions are dangerous, you for some unknown reason now want to turn the good advice into something bad as if you’ve been insulted or attacked? 

We all have to learn and if it’s something you don’t understand that’s fine but to insult those that are trying to educate you then that’s not right. 

If there is something else about this that you don’t understand then please ask, otherwise try to understand the advice you’ve been given. 

Getting defensive serves no purpose other than to prevent people gaining assistance when needed. 

 

[kerching]

I would have thought an Electrician would know what an Earth Clamp meter is...maybe it's just me

 

[Doc Hudson]

Hi everyone I'm after some advice I've just noticed that my earth had voltage on when I disconnected from earth bar in cu when mcb was on could any one shed a bit of light on this thanks it is on ring mains and light ccts 

Some appliances can have natural earth leakage, on occasions relatively high protective conductor currents, (hence section 7.5 of On-Site-Guide). Some appliances can produce earth currents due to faults or deterioration over time. Or an accessory wired incorrectly between live and earth can all produce earth currents / voltages that would not trip and RCD under normal conditions. Unless a full evaluation of exactly what is still connected to a circuit has been made, it is risky attempting to disconnect any conductors of a live circuit. Hence the Legislation against live working. Don't forget 30ma @ 230 is just under 7watts. so a 5watt LED lamp wired between Live & Earth may not trip an RCD, but would put a significant voltage onto the CPC!

on a very simplistic level consider one of these DIY type socket testers https://www.toolstation.com/socket-tester/p82826?searchstr=socket tester  If you disconnect the CPC on a live circuit with one of these still plugged in, depending upon the make of tester it is not uncommon to measure 100+ Volts ac between a disconnected earth and real earth.  

Doc H.

 

[Jimbo8]

Some appliances can have natural earth leakage, on occasions relatively high protective conductor currents, (hence section 7.5 of On-Site-Guide). Some appliances can produce earth currents due to faults or deterioration over time. Or an accessory wired incorrectly between live and earth can all produce earth currents / voltages that would not trip and RCD under normal conditions. Unless a full evaluation of exactly what is still connected to a circuit has been made, it is risky attempting to disconnect any conductors of a live circuit. Hence the Legislation against live working. Don't forget 30ma @ 230 is just under 7watts. so a 5watt LED lamp wired between Live & Earth may not trip an RCD, but would put a significant voltage onto the CPC!

on a very simplistic level consider one of these DIY type socket testers https://www.toolstation.com/socket-tester/p82826?searchstr=socket tester  If you disconnect the CPC on a live circuit with one of these still plugged in, depending upon the make of tester it is not uncommon to measure 100+ Volts ac between a disconnected earth and real earth.  

Doc H.

Thankyou doc really appreciate  advise pal 

 

[Jimbo8]

Let’s stop right there shall we? jimbo you have asked a question that has been answered, it has also been suggested that you’re actions are dangerous, you for some unknown reason now want to turn the good advice into something bad as if you’ve been insulted or attacked? 

We all have to learn and if it’s something you don’t understand that’s fine but to insult those that are trying to educate you then that’s not right. 

If there is something else about this that you don’t understand then please ask, otherwise try to understand the advice you’ve been given. 

Getting defensive serves no purpose other than to prevent people gaining assistance when needed. 

I wasnt being rude to him I was just asking for advise if anyone had seen this before all the best 

 

[Murdoch]

Hi Murdoch just in twenty plus years of doing this and have never seen it before I wonder how many sparks have never noticed this with the earths I understand what ur both saying and not to disconnect earths while mcb is on but how would we ever know this is happening  if I never did do it 

Hum .........

My MFT, if I try and do a Zs and get odd looking voltages displayed on the screen either L-N or L-E , and it refuses to do the test - is usually symptomatic of a floating N or E. 

Odd you've not seen this in 20 years on the tools. Floating neutrals are often why lights don't work!

 

[Rob.]

Hum .........

My MFT, if I try and do a Zs and get odd looking voltages displayed on the screen either L-N or L-E , and it refuses to do the test - is usually symptomatic of a floating N or E. 

Odd you've not seen this in 20 years on the tools. Floating neutrals are often why lights don't work!

Thing is, this isn't likely now that we have had further information a floating neutral. (Although was my first thought with the limited original information provided).

It's likely earth leakage from a device being powered by the circuit. 

Most electricians wouldn't notice this, as they would switch the circuit off to move the CPC in the consumer unit. 

 

[Jimbo8]

Hum .........

My MFT, if I try and do a Zs and get odd looking voltages displayed on the screen either L-N or L-E , and it refuses to do the test - is usually symptomatic of a floating N or E. 

Odd you've not seen this in 20 years on the tools. Floating neutrals are often why lights don't work!

My tester wont ket me do test if voltage not correct I meant not seen voltage on earths before but like I say never disconnected earth before either was just a off chance that i did and noticed it 

Thing is, this isn't likely now that we have had further information a floating neutral. (Although was my first thought with the limited original information provided).

It's likely earth leakage from a device being powered by the circuit. 

Most electricians wouldn't notice this, as they would switch the circuit off to move the CPC in the consumer unit. 

That's very true rob pal all I'm asking is anyone else seen this and if so what was there  findings thanks 

 

[Sidney]

Any loads on the circuit?

 

[Jimbo8]

Any loads on the circuit?

No pal nothing 

 

[Jimbo8]

If you got an actual spark, this is suggesting a more sinister fault. 

A floating capacitive voltage, shouldn't have enough energy to produce a visible spark. 

All other circuit testing ok? 

TNCS earthing by any chance?

Yes rob pal it is a tncs I believe the reason behind this is because neutral  earth combined and disconnecting earth would become live because off connection to neutral 

 

[Sidney]

Could be a high resistance joint on the neutral between the head and DB.

 

[Jimbo8]

Could be a high resistance joint on the neutral between the head and DB.

It's because it's a tncs earth system if you disconnect the earth while cct on the voltage will be there because its connected to neutral at the head 

 

[binky]

if cct is energised it induces votage in the CPC as mentioned above. I've had small sparks on CPCs before, turning cct off normally stops this! I have spent many hours puzzling non-issues because I've done things out of normal sequence. 

 

[Jimbo8]

if cct is energised it induces votage in the CPC as mentioned above. I've had small sparks on CPCs before, turning cct off normally stops this! I have spent many hours puzzling non-issues because I've done things out of normal sequence. 

Yes binky  it was a head scratch pal never seen it before has I always turn cct off just forgot on this occasion  thankfully it was in my house with no one here but just shows we are all still learning no many sparks seen this by the comments