Exported earth

[a2]

KME!!!!!!

Scooby Snack time M8 me thinks???

You deserve one just for that post alone

 

[SPECIAL LOCATION]

Have we tipped 100 yet Dave??

We have now!

:^O :^O:^O:^O

 

[welshwizard]

Afternoon Spec.

 

[SPECIAL LOCATION]

Afternoon Spec.

R - tis - that!

Keeps raining up here...

but I got jobs in the garden that I need to get done!! :_| :_|

dohX( X(

 

[welshwizard]

R - tis - that!Keeps raining up here...

but got I jobs in the garden that I need to get done!! :_| :_|

dohX( X(

Dry and Humid, down here Mate.

 

[Nicky Tesla]

Dave in a tn-s system if the Zs at the garage is too large but volt drop is okay, then simply put in an RCD at say 100mA then a Zs of 500ohms is ok.

Right everybody listen, and that includes the supreme being commonly known as steptoe.

The confusion in all this, stems from the assumption that the fault has a zero ohm contact, this may be true some micro seconds down the line, but initially not.

Picture this: a live conductor coming into contact with an earthed piece of steel. The live conductor being at 230v and the steel being at zero volt. When the conductor gets very close, a spark may be seen to go through mid air between the gap of them both. This spark at the very first instant has 230V across with all the energy being dispersed as heat, light and even noise. This means the steel is still at zero volts. Then, current starts to flow in the earthed steel to gnd and a voltage begins to build up. The closer the live conductor gets to the steel the smaller will be the spark but the higher will be the current, so if at one point 10v has appeared across the steel to earth then 220v will be dissapated across the live conductor and the spark, and the spark at this point may have say for example 210v across it. This is why the current builds up from zero to its limit, and the limit being found out by assuming the fault contact has zero ohms. The zero ohms will come into play when the two come into full contact with each other and the voltage has stabilized, therefore the zero contact assumption is only there to make calculations easier. This is why 230v can never appear on the cpcs .

ohms law strikes again.

 

[Nicky Tesla]

Perhaps to help a bit..

are you aware that to identify quoted text you can..

a) use to button on the edit window.

B) quote the whole text when reply

c) put the word

 

[Nicky Tesla]

so it is only possibly where the earth path is left open circuit?

Lets consider an illustration..

3a] R1+R2 (5m 2.5mm) = 0.09755 ohms (from table 9A pg158 O-S-G.)

Zs = 0.72 + 0.09755 = 0.81755 ohms

PFC at light = 249/0.81755 = 304.6amps (0.3kA)

3b] Potential @ MET with ref to mass of earth;

(PFC x Ze), 304.6 x 0.72 = 219.3v

3a 2.This time at 20metres away, in a garage for example cos a mere 5m is a bit close.

r1 + r2 x 20 = 0.3902

Zs = 0.3902+0.72=1.1102ohms

pfc=249/1.1102= 224.28 amps

voltage at met=224.28 x 0.72 = 161.48volts maximum

Nowhere near 230volts

The 161.48volts is the figure the fault current will be TRYING to achieve, but the mcb will try to prevent by limiting this to 5 times its rating for type b.

 

[SPECIAL LOCATION]

so it is only possibly where the earth path is left open circuit?3a 2.This time at 20metres away, in a garage for example cos a mere 5m is a bit close.

r1 + r2 x 20 = 0.3902

Zs = 0.3902+0.72=1.1102ohms

pfc=249/1.1102= 224.28 amps

voltage at met=224.28 x 0.72 = 161.48volts maximum

Nowhere near 230volts

The 161.48volts is the figure the fault current will be TRYING to achieve, but the mcb will try to prevent by limiting this to 5 times its rating for type b.

Well yes..

thats bloomin obvious if its a longer run..

I agree with that one

And whats more...

the post was far easier to follow

non of them nasty capitals...

should make debating far more fun all round;\

and whether we...

agree to agree...

agree to disagree...

disagree to disagree...

disagree to agree...

or any other combination (series or parallel? )

I'm sure neither of us want to go givin ZeeSpark another headache!!! :^O

Shall I turn the light out and close the door?

or does anyone else want to use the room?? ]

 

[kme]

evenin` all.

SL: finish the box off m8.B) Don`t worry about the wasted energy; I`ll turn the light off for ya! :^O

 

[Zeespark]

Headache? well past that stage now gents. popping valium and drinking copius amounts of black coffee trying to take this in (and try and calm down a kid that I consider close enough to be my lad as his parents are shouting at eachother and beating eachother up).

Andy:x

 

[Nicky Tesla]

so it is only possibly where the earth path is left open circuit?3a 2.This time at 20metres away, in a garage for example cos a mere 5m is a bit close.

r1 + r2 x 20 = 0.3902

Zs = 0.3902+0.72=1.1102ohms

pfc=249/1.1102= 224.28 amps

voltage at met=224.28 x 0.72 = 161.48volts maximum

Nowhere near 230volts

The 161.48volts is the figure the fault current will be TRYING to achieve, but the mcb will try to prevent by limiting this to 5 times its rating for type b.

One more thing before i put me calculator away and try another topic, the 161.48 volts is not the touch voltage. The touch voltage is the voltage from the fault to the met. When the met is at 161volts this means that all other bonded metalwork is also at 161volts to make the faraday cage. The touch voltage in this case will be just the voltage created along the ccts cpc wire, so we must calculate 1.5(from the table) x 20m x 224amps = .o1210x20x224=54volts.

So the touch voltage in this case is 54volts

Good night mind the bugs dont bite.

 

[welshwizard]

Thanks for that Nicky.

KME - You left the light on.

 

[welshwizard]

Actually, Nicky did - he was the last to leave this room.

 

[steptoe]

Dave in a tn-s system if the Zs at the garage is too large but volt drop is okay, then simply put in an RCD at say 100mA then a Zs of 500ohms is ok.Right everybody listen, and that includes the supreme being commonly known as steptoe.

.

first time to be called everything I suppose.

and its like Ive said many times before.

Im not always that interested in the beginners guide that is called BS7671.

but if anyone is stoopid enough NOT to make it a TT system when it obviously should be,

then you better have a very good solicitor when the occupier gets a shock and cleans your ass up in court.

this is the sort of scenario that separates the COMPETENT people from those that just have a pile of certs and think they know everything.

Ive learnt some stuff from this topic, only an idiot couldnt, but some people are obviously beyond teaching!

 

[kme]

On form Mr. Toe. I have to agree with the majority of your post.

I admit to refering to "the bible" occasionally; purely to confirm my thoughts, however I tend recently to float the thoughts on here, especially if they`re a bit unusual.

 

[steptoe]

so it is only possibly where the earth path is left open circuit?3a 2.This time at 20metres away, in a garage for example cos a mere 5m is a bit close.

r1 + r2 x 20 = 0.3902

Zs = 0.3902+0.72=1.1102ohms

pfc=249/1.1102= 224.28 amps

voltage at met=224.28 x 0.72 = 161.48volts maximum

Nowhere near 230volts

The 161.48volts is the figure the fault current will be TRYING to achieve, but the mcb will try to prevent by limiting this to 5 times its rating for type b.

can someone clarify this for me please.....

since when did an MCB limit the voltage to 5 times its rating,

that would make it over 1Kv for a standard MCB so that is both nonsense and rubbish,

an MCB is a current limiting device, nothing to do with voltage....

 

[kme]

can someone clarify this for me please.....

since when did an MCB limit the voltage to 5 times its rating,

that would make it over 1Kv for a standard MCB so that is both nonsense and rubbish,

an MCB is a current limiting device, nothing to do with voltage....

I was HOPING someone else would say that.

Thought I was going n*****g futs!

I can clarify that AFAIK, that ranks along with:

COS A HIGH CURRENT FLOWING THROUGH A HIGH RESISTANCE WILL CREATE A HIGH VOLTAGE..SIMPLE ELEMENTARY STUFF

erm........Anyone for a stiff whisky?

 

[steptoe]

I was HOPING someone else would say that.

Thought I was going n*****g futs!

I can clarify that AFAIK, that ranks along with:

erm........Anyone for a stiff whisky?

just give me the bottle...

WTF...

your sig makes more sense.....

I think that speaks for itself,,,

talk about big holes and jumping in them,,,,

deffo makes a very good case for enforced euthanasia... ]

 

[kme]

:^O :^O:^O:^O