Ze With TT Installations.

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JimG

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Hi Folks,

It's been a while since I've been working with a TT installation!

Whilst measuring the Ze, the impedence reading came in @ 47ohms - which is most acceptable, but the PFC read @ 5A?

Can someone please advise whether this is ok or not?

The installation we did next door to this location is PME and that read: .25ohms/1KA - which is what I'm used to seeing.

Looking fwd to any advice ......

Cheers,

JimG.

 

Admin 2

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I cant help you sorry JimG, :(

But i can welcome you to the forum. :D

Pull up a chair,

Have a few Guiness DrinkGuiness Drink

And enjoy. :)

 

cheggers

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hi jim

you were reading the ra of the rod and not the ze

the ra reading is ok actually a good reading for a rod

and the prospective fault(pfc) current would be about 5 amps but the prospective short circuit(psc) current would be a lot higher. depending on the test gear you are using you need to put the earth clamp and neutral clamp both on the neutral and the live on the live.you record the highest reading from pfc or psc and record this on your cert.

 
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Hi Folks,It's been a while since I've been working with a TT installation!

Whilst measuring the Ze, the impedance reading came in @ 47ohms - which is most acceptable, but the PFC read @ 5A?

Can someone please advise whether this is ok or not?

The installation we did next door to this location is PME and that read: .25ohms/1KA - which is what I'm used to seeing.

Looking fwd to any advice ......

Cheers,

JimG.
welcome Jim G... :D

sounds like you are forgetting the relationship between Ze & PFC....

Just to remind you (and any other younguns following the thread)

Ze external loop resistance, is the resistance of an earth fault circuit up to the point where it enters your CU main switch.

i.e. up the Live/Phase/Line conductor... then back down the earth conductor.

as you say 47ohm for TT is good. (0.8 ok for TN-S, 0.35 ok for PME/TN-C-S)..

The PFC should be the maximum fault current that can flow in the event of a direct short circuit at the CU..

(obviously the CU switchgear must be able to withstand this fault current).

On a PME because the Earth & Neutral are combined.. there is effectively only one possible short circuit path. L to N(E)

whereas with TN-S & TT there are two possible paths... L to N OR L to E

you should check both of these and note the highest value on the EIC.

your readings are taking the L-E path only.. you need to re-check across L-N!

your PME is approx 230/0.25 = 0.92KA

your TT rod is approx 230/45 = 5.1amps

so your readings are correct values.. just taking the TT PFC across the wrong place! ;)

 
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eh up... :eek:

as per usual ..

while I am chiselling out me letters on the slate..

winding up the clockwork..

and re tensioning the rubber band!

someone has snuk in and writ what I was writin ...

shorter & quicker!! :_| :_|

doh!!! cheggers!Applaud SmileyApplaud SmileyApplaud Smiley;)

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

 

cheggers

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that's what happens when you keep writing these essays

 

Admin1

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IMHO, Your version, so be it longer, is clearer, Specs. ;)

 

The Godfather

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eh up... :eek: as per usual ..

while I am chiselling out me letters on the slate..

winding up the clockwork..

and re tensioning the rubber band!

someone has snuk in and writ what I was writin ...

shorter & quicker!! :_| :_|

doh!!! cheggers!Applaud SmileyApplaud SmileyApplaud Smiley;)

:^O :^O:^O:^O
You do seem to take a considerable time, in posting, your response(s).

Don

 
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You do seem to take a considerable time, in posting, your response(s).Don
Thats why I have trouble keeping up with the number of posts the rest of you do!? :( :|

oops!:OBlushingB-)

Or perhaps... I think it may be because I need....

one of these :z

and two of these between each line!!Guiness DrinkGuiness Drink

Blushing:^O:^O:^O:^O:^O:^O

 

The Godfather

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Thats why I have trouble keeping up with the number of posts the rest of you do!? :( :| oops!:OBlushingB-)
Quantity is not the same as quality.

The Godfather

 

The Godfather

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In any forum, you will have mainstream regulars, who will probably talk till the cows come home.

There are some who try to assert their presence on a forum, by simply being there.

All forums need a balance of members, and believe it or not, all forums need regulars as well as infrequent members (plus the guests and the one off guests).

My point here is simple, the forum is bigger than any member and as much as we might think otherwise, life goes on (regardless).

The Godfather

 
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In any forum, you will have mainstream regulars, who will probably talk till the cows come home.There are some who try to assert their presence on a forum, by simply being there.

All forums need a balance of members, and believe it or not, all forums need regulars as well as infrequent members (plus the guests and the one off guests).

My point here is simple, the forum is bigger than any member and as much as we might think otherwise, life goes on (regardless).

The Godfather
Specs - hide. Think you're on the Godfathers 'list' :eek:

 
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