How would you explain how PME works?

[ColJack]

the guy is only counting at the front gate, not the back one.. so he only sees the cars comming out the front gate..


there IS no difference between N and E on a PME system.. and things will work if you put them across live and earth..

it's only that the RCD is watching one wire, but not the other..

the earth just bypasses the rcd on it's way back out..

 

[securespark]

and things will work if you put them across live and earth....

As indeed they do on TN-S.

 

[JohnD]

avoid the N/E PD. RCDs don't have to do it. Current balancing covers their function adequately.

 

[ColJack]

or any TN system for that matter..

the neutral is earthed at some point..

the neutral is broken by the rcd, that's why you have a seperate rcd neutral rail, and why you get trips if you put an RCD protected circuits neutral on the non-rcd neutral bar.. it's another bypass..

 

[securespark]

I'm sorry. I'm a bit lost now!

Let me try to rephrase what I said earlier...

An RCD counts electricity out & counts it back again. So, if some does not return via the neutral, but diverts down the earth, how is this detected when they are one & the same supply conductor?

It is late...

 

[ricicle]

Because they are only one before the cutout.The RCD is looking at the installation where they are seperate.If a phase fault to earth exists it will take a parallel path outside the RCD ie the CPC, not through the neutral.
The earth fault will rejoin the neutral at the cut-out

 

[ColJack]

i refer you back to my car park analogy..

there is a main road to the car park.. cars come in on the left, and leave on the right..

right by the entrance to the car park there is a service road down the side of it for emptying the bins..

all the cars that go down that main road have to come back up it..

so the guys who sneak out the back and down the service road still end up on the main road back out...

but the guy on the gate still think's the car park is full... he's only watching what goes in and out of his gate..

 

[davy_owen_88]

See below ...

 

[JohnD]

(edited) your first pic doen't seem right tome

 

[davy_owen_88]

Yes they are, but there are a few errors in the diagrams which I missed first time round, I'll sort them in a sec...

 

[ColJack]

looks right to me.. where's the bad?

 

[davy_owen_88]

Here you go, I sorted a few errors...

Balanced RCD (Doesn't trip):

Unbalanced RCD (Does trip):

 

[JohnD]

Here you go, I sorted a few errors...

Balanced RCD (Doesn't trip):

yes it does. In that pic,the current going through L is equal to the combined current going through N and E. But L current is not equal to N ,so it trips.

Oops,my mistake.in that first pic, there is no fault,right?

 

[davy_owen_88]

Here you go, I sorted a few errors...

Balanced RCD (Doesn't trip):

yes it does. In that pic,the current going through L is equal to the combined current going through N and E. But L current is not equal to N ,so it trips.

Oops,my mistake.in that first pic, there is no fault,right?

Indeed, no fault in the first pic.

 

[JohnD]

I can't keep up. Time I was