fault loop impedance query

grousedogtom

Hi , while testing fault loop impedance on socket circuits between live an earth my fluke 1653 is much slower to test than between live and neutral , just wondering whats the reason behind this?

M cebee

dunno



L-N loop impedance isn't a fault loop or standard test that i know of

-nothing to stop you checking it if you're looking for supply problems


you'd be using both loops when checking prospective fault current on single phase to see which is higher

Randyleprechaun

It's perfectly normal. I have the same model tester and it takes a bit longer to give a reading when testing loop impedance, live to earth.

I'm not sure what the reason is.

Bruthal

grousedogtom wrote: »

Hi , while testing fault loop impedance on socket circuits between live an earth my fluke 1653 is much slower to test than between live and neutral , just wondering whats the reason behind this?

It might be possibly using a lower test current to calculate the L to E loop impedence to prevent tripping RCD`s, where as when testing L to N it can use a higher one and get a quicker result. Just a guess anyway.

The actual loop being measured is the same realy and only differs from where the neutral and earth split at the neutralising point to the tester on neutralised installations.

M cebee

Zl is prob higher than l-n loop with domestic t+e

commercial work -the fault loop is prob lower because of steel

i usually keep in mind -with fault loop impedance and prospective fault current you're looking for the highest possible readings

in other words 'discounting' parallel paths such as main bonding for fault loop

and worst case scenario for fault current

Bruthal

Would not think the L - E impedence would be so much higher in a domestic installation to make the test longer with regard to the smaller earth conductor compared to neutral, its only the difference from the DB to the socket of 1.5 compared to 2.5

Its an interesting one though. The user selects L-E on the tester and maybe it just uses different test current with L-E with a view to avoid tripping RCD`s. Or maybe not.

Its domestic i was referring to in the previous post alright. Bit different for an industrial one with steel conduit/trunking etc in parallel, but the tester would still trip RCD`s if the test current was higher that the 30ma L-E on socket circuits.

M cebee

ya-i dunno anything about the tester or problem


might be what you're saying

Bruthal

I dont think there is an actual problem in the OP`s testing, sounds like they are more curious about the reason its slower L-E. Because L-N or L-E is selected on the tester itself, to be tested by the user with 3 probes connected, maybe the tester uses different test currents in each mode which would be shown if a multimeter set in AC amps was connected between the Live terminal and the tester Live probe. If someone had nothing else to do anyway.

M cebee

ya problem question:pac:same thing

Bruthal

What was the question again:D

grousedogtom

Was just curious why L to PE is slower, the smaller current makes sense to avoid rcd tripping.

Bruthal

Whatever current is used, an instant calculation could be made for any given current even if its a very small one.

But it could just be doing several lower current pulses to get an average or something like that when doing it through the earth. The higher the test current the more accurate a quicker result most likely, maybe because if this it does a longer test in the L-E setting at a lower test current. Or it could even be doing very short current pulses over a time period, pulses too quick to trip an RCD and giving an average.