I normally use a trailing lead to test EC with the N or MEN disconnected although on long runs this can become difficult due to route or length, this confirms the EC value and also the E is in the correct position
I'm just curious what people believe is the most reliable and safe way for dealing with rather long run while still getting sufficient results?
Do I just need to make up an even longer lead for this purpose? Or are there alternatives that give the same results?
Earth continuity testing on long runs
Re: Earth continuity testing on long runs
I would start with measuring A-E loop (as for EFLI), and then N-E loop as comparison; then back that up with a live EFLI test provided that can be done safely.
"3008" provides ohms/km for most common cables, which is how we can judge " 8.3.5.2 (b).
Remembering that the length is generally double the route length.
For (a), the live EFLI test covers it - noting that the values for mcbs are all for socket circuits (0.4 s max operating time) rather than 5 s we're allowed for non-socket circuits.
"3008" provides ohms/km for most common cables, which is how we can judge " 8.3.5.2 (b).
Remembering that the length is generally double the route length.
For (a), the live EFLI test covers it - noting that the values for mcbs are all for socket circuits (0.4 s max operating time) rather than 5 s we're allowed for non-socket circuits.
Re: Earth continuity testing on long runs
Thank you, I'll have to have a look at doing this when needed, usually my lead is fine but I have run into a few situations where it wasn't really suitable and used a N-E loop and the value was low enough hence E had to be fine but it just got me thinking about what the best way to go about in these situations
Re: Earth continuity testing on long runs
Thinking is good.
Too many people don't.
When doing a loop test, unless the total is below the limit in Table 8.2 it's not technically possible for a single result to "prove" that the PEC is OK.
Can't just assume a proportional split, eg 50/50 for PEC size = N size, or other split where PEC size smaller.
But by doing a set of loops, we can make reasonable deductions.
Main point being we don't need to show PEC resistance doesn't exceed value in Table; just have to show:
a) consistent with size & length of able, and
b) low enough to operate protective device within time limit
The Table gives guidance, but isn't mandated.
Note 2 to 8.3.5.2 just says the values "may be used"
On the other hand, it also doesn't provide "deemed to comply" bum-cover (unfortunately).
So to be absolutely sure of (b); we'd have to do the relevant calculation, using formula @ 5.7.4
Too many people don't.
When doing a loop test, unless the total is below the limit in Table 8.2 it's not technically possible for a single result to "prove" that the PEC is OK.
Can't just assume a proportional split, eg 50/50 for PEC size = N size, or other split where PEC size smaller.
But by doing a set of loops, we can make reasonable deductions.
Main point being we don't need to show PEC resistance doesn't exceed value in Table; just have to show:
a) consistent with size & length of able, and
b) low enough to operate protective device within time limit
The Table gives guidance, but isn't mandated.
Note 2 to 8.3.5.2 just says the values "may be used"
On the other hand, it also doesn't provide "deemed to comply" bum-cover (unfortunately).
So to be absolutely sure of (b); we'd have to do the relevant calculation, using formula @ 5.7.4
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Re: Earth continuity testing on long runs
I remember thinking that if I can a value higher than table 8.2 it was a fail but infact as you say it's just guidance of a value that should mean the device will trip in the required 0.4s trip time but correct me if I'm wrong, due to only socket outlets having to trip in 0.4s then the values could actually be a lot higher due to the 5s limit for most items. Although of course this shouldn't really be the aim, but it's nice to know it's not explicitly a fail if higher than the table 8.2 values.
RCD socket outlets are garenteed to disconnect in the 0.4 second time so is the EC value actually important here? Would a high value above the 0.4s table 8.2 values be a fail? Or would a high value still be compliant because the protective device will still trip in the 0.4s time limit regardless
Non-RCD socket outlets, although we have to confirm EC regardless, we also have to do a EFLI test as you know but would a high EC value mean a fail if the overall EFLI passed? My thinking was that although we test EC the value isn't really important if the EFLI passes later on because that there is confirming the E has a low enough value to trip the device in the required time
RCD socket outlets are garenteed to disconnect in the 0.4 second time so is the EC value actually important here? Would a high value above the 0.4s table 8.2 values be a fail? Or would a high value still be compliant because the protective device will still trip in the 0.4s time limit regardless
Non-RCD socket outlets, although we have to confirm EC regardless, we also have to do a EFLI test as you know but would a high EC value mean a fail if the overall EFLI passed? My thinking was that although we test EC the value isn't really important if the EFLI passes later on because that there is confirming the E has a low enough value to trip the device in the required time
Re: Earth continuity testing on long runs
A value of PEC resistance higher than indicated in the Table is not a fail provided the value meets mandatory results (a) & (b).
And if it's a circuit not supplying sockets, the the EFLI value can also be higher than indicated by that table.
Now much higher depends on doing the calc, but the values given for 9HRC) fuses give some indication
And if it's a circuit not supplying sockets, the the EFLI value can also be higher than indicated by that table.
Now much higher depends on doing the calc, but the values given for 9HRC) fuses give some indication
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Re: Earth continuity testing on long runs
If testing for "verification of impedance" 8.3.9 though, dont we have to follow 8.3.9.2 for socket outlets not protected by RCD's?
8.3.9.2 says "deemed to be safe if" (a) Rphe doesn't exceed the value in Table 8.2 when no power available.
8.3.9.3 (a) says we may use an ohm meter to do the tests, then 8.3.9.3(ii) second paragraph "the measured value of resistance Rphe shall not exceed the value in Table 8.2 for the appropriate conductor size and protective device"
I assume this is correct?
8.3.9.2 says "deemed to be safe if" (a) Rphe doesn't exceed the value in Table 8.2 when no power available.
8.3.9.3 (a) says we may use an ohm meter to do the tests, then 8.3.9.3(ii) second paragraph "the measured value of resistance Rphe shall not exceed the value in Table 8.2 for the appropriate conductor size and protective device"
I assume this is correct?
Re: Earth continuity testing on long runs
For sockets not protected by RCD, where an EFI test is require;
and if there's no supply available - so allowing use of method (a) - then we're tied to the values for Rphe in Table 8.2.
But that doesn't require the PEC resistance to be under the Re value.
We will have already ensured, under 8.3.5, that the PEC resistance is
(a); low enough to operate the protective device within time limit (in this case - because sockets - 0.4 sec); and
(b); consistent with length & CSA.
The EFLI test then adds a third requirement; either the full earth fault loop (preferred),
or - if no supply available - the A+E part-loop,
complies with relevant Table - but this test is only required IF it's non-RCD sockets.
If it's RCD-protected sockets; then the RCD time of 0.3 sec will comply almost regardless of how high the Re reading is - basically anything less than an open circuit PEC; because an RCD doesn't require a high fault current to operate.
And if it's not sockets; then the time is 5 sec,
so both the loop reading and the Re reading can be much higher than what Tables indicate for mcbs, while still being compliant.
To work out just how far you can push this, you have to do the calc.
But for most situations we shouldn't be pushing it at all.
and if there's no supply available - so allowing use of method (a) - then we're tied to the values for Rphe in Table 8.2.
But that doesn't require the PEC resistance to be under the Re value.
We will have already ensured, under 8.3.5, that the PEC resistance is
(a); low enough to operate the protective device within time limit (in this case - because sockets - 0.4 sec); and
(b); consistent with length & CSA.
The EFLI test then adds a third requirement; either the full earth fault loop (preferred),
or - if no supply available - the A+E part-loop,
complies with relevant Table - but this test is only required IF it's non-RCD sockets.
If it's RCD-protected sockets; then the RCD time of 0.3 sec will comply almost regardless of how high the Re reading is - basically anything less than an open circuit PEC; because an RCD doesn't require a high fault current to operate.
And if it's not sockets; then the time is 5 sec,
so both the loop reading and the Re reading can be much higher than what Tables indicate for mcbs, while still being compliant.
To work out just how far you can push this, you have to do the calc.
But for most situations we shouldn't be pushing it at all.