I have a situation where I'm getting a 0.58-0.6 ohm EFLI and 0.21-0.23 ohm EC for a circuit on a 40A D curve MCB
Cable is X-90 4c+e 10mm/4mm approx 45-50m run via ladder then PVC conduit
Although extremely close I don't believe this meets the requirements and needs to be lowered
I tried to find a trip curve for the MCB but had no luck to see if maybe if get away within the 5s time since it's simply a supply from DB to a pump control panel but didn't think this really applied to MCBs
There is earthed metalwork close by, specifically some cable ladder that someone has opted to earth (let's avoid that discussion this time)
Is 5.7.5 as simple as connecting an equipotential bonding conductor from my panel to the earthed metal work to help lower the EFLI value or is it referencing something else? Any other solutions or input appreciated
5.7.5 Supplementary Equipotential Bonding
Re: 5.7.5 Supplementary Equipotential Bonding
Actually I've just had a proper read and missed the extraneous conductive parts bit, so have realized what I was asking above is not what this clause is talking about
Still welcome any other helpful ideas
Still welcome any other helpful ideas
Re: 5.7.5 Supplementary Equipotential Bonding
You don't need a cure; because there is no problem.
What you've got is a case that the Tables don't cover neatly.
If you did have a problem; then yes adding a bonding conductor that's essentially in parallel with the PEC is an acceptable method of bringing an excessive EFLI value down to an acceptable value.
(It's called a 'bonding" conductor because its primary function is ensuring that touch voltages, caused by passage of high fault current on the PEC, do not exceed safe limits)
But generally better to change the protection, eg to a fuse.
Earth continuity & EFLI are not separate matters, despite the way Section 8 is written
Fact is that earth continuity is part of EFLI,
which in turn is simply a means of complying with a fundamental requirement.
The underlying requirement is in clause 2.4 "fault protection".
There are 3 accepted methods, but mostly we use automatic disconnection of supply.
And whenever we use that method of fault protection; a number of other clauses kick in;
notably 5.7 that sets the max permitted disconnection time.
When we test for EC, or test EFLI, what we're really doing is showing that the protective device will operate within the time ljmit.
There is NO requirement to meet the values in Tables; they are provided as guidance
Note the wording of 8.3.9.2: "... deemed to be satisfied if ..."
similarly 8.3.5.2 Note 3: "these values may be used".
The actual requirement is in 5.7,
Repeated in 8.3.5.2 (a) for EC, and referred to in 8.3.9.3
In 5.7; two times are specified: 0.4 sec for sockets (and some other particular types of equipment), and 5 sec for any other circuit.
We are only required to test EFLI for sockets, and then only if they use automatic disconnection, and even then only of they are not protected by an RCD.
But for every point on every circuit, we must do an EC test - which is really a partial EFLI test.
There are sound reasons for Section 8 not requiring full EFLI test on every point of every circuit;
but I don't want to side-track into theory-of- testing; so for now just stick to 'does it comply?"
Ok, so Point 1 is you've got a submain.
Not a circuit supplying any thing for which 0.4 sec is specified; which has 2 effects.
Most importantly, the permitted operation time is 5 sec; so that's what has to be complied with.
Secondly; far from meeting all 3 trigger conditions of 8.3.9; the circuit meets none of them. So there's no requirement to do an EFLI test, only an EC test.
Point 2 is that the reading you have is 0.2x;
Table 8.2 shows that an EC value of 0.20 is deemed to comply for a 0.4 sec operating time.
So if you had a socket outlet on the end; it would be just slightly on the wrong side - and easily fixable by changing to a C-curve mcb.
But it's a submain; and if you had a fuse (HRC), it would comply with EC as high as 0.7
Similarly your EFLI value of 0.6 is only slightly above the 0.5 accepted as compliant for a D-curve operating within 0.4 sec,
It's below the 0.4 s value for a C-curve, well under the value for a fuse @ 0.4 s, and hugely under the 1.6 ohm acceptable for fuse @5 sec
Why don't the Tables provide values for 5 sec when using mcbs?
Quite simply because they are not needed.
Fuses are thermally operated devices.
Mcbs also use thermal operation for overload function; but for high-current faults they use a magnetic trip.
Both fault protection and short-circuit protection sit on the "instantaneous" part of the mcb's operating curve (see Fig 2.13).
You could carry our a calculation to prove it
But the quick-&-dirty answer is that there's not a chance in hell of your particular circuit not complying with 5.7
For purposes of 8.3.5(a), you can prove that simply by referring to the "deemed-to-comply" value for an HRC fuse.
For 8.3.5 (b), reference to relevant cable data will show that your EC value is not inconsistent with size & length of cable - job done
What you've got is a case that the Tables don't cover neatly.
If you did have a problem; then yes adding a bonding conductor that's essentially in parallel with the PEC is an acceptable method of bringing an excessive EFLI value down to an acceptable value.
(It's called a 'bonding" conductor because its primary function is ensuring that touch voltages, caused by passage of high fault current on the PEC, do not exceed safe limits)
But generally better to change the protection, eg to a fuse.
Earth continuity & EFLI are not separate matters, despite the way Section 8 is written
Fact is that earth continuity is part of EFLI,
which in turn is simply a means of complying with a fundamental requirement.
The underlying requirement is in clause 2.4 "fault protection".
There are 3 accepted methods, but mostly we use automatic disconnection of supply.
And whenever we use that method of fault protection; a number of other clauses kick in;
notably 5.7 that sets the max permitted disconnection time.
When we test for EC, or test EFLI, what we're really doing is showing that the protective device will operate within the time ljmit.
There is NO requirement to meet the values in Tables; they are provided as guidance
Note the wording of 8.3.9.2: "... deemed to be satisfied if ..."
similarly 8.3.5.2 Note 3: "these values may be used".
The actual requirement is in 5.7,
Repeated in 8.3.5.2 (a) for EC, and referred to in 8.3.9.3
In 5.7; two times are specified: 0.4 sec for sockets (and some other particular types of equipment), and 5 sec for any other circuit.
We are only required to test EFLI for sockets, and then only if they use automatic disconnection, and even then only of they are not protected by an RCD.
But for every point on every circuit, we must do an EC test - which is really a partial EFLI test.
There are sound reasons for Section 8 not requiring full EFLI test on every point of every circuit;
but I don't want to side-track into theory-of- testing; so for now just stick to 'does it comply?"
Ok, so Point 1 is you've got a submain.
Not a circuit supplying any thing for which 0.4 sec is specified; which has 2 effects.
Most importantly, the permitted operation time is 5 sec; so that's what has to be complied with.
Secondly; far from meeting all 3 trigger conditions of 8.3.9; the circuit meets none of them. So there's no requirement to do an EFLI test, only an EC test.
Point 2 is that the reading you have is 0.2x;
Table 8.2 shows that an EC value of 0.20 is deemed to comply for a 0.4 sec operating time.
So if you had a socket outlet on the end; it would be just slightly on the wrong side - and easily fixable by changing to a C-curve mcb.
But it's a submain; and if you had a fuse (HRC), it would comply with EC as high as 0.7
Similarly your EFLI value of 0.6 is only slightly above the 0.5 accepted as compliant for a D-curve operating within 0.4 sec,
It's below the 0.4 s value for a C-curve, well under the value for a fuse @ 0.4 s, and hugely under the 1.6 ohm acceptable for fuse @5 sec
Why don't the Tables provide values for 5 sec when using mcbs?
Quite simply because they are not needed.
Fuses are thermally operated devices.
Mcbs also use thermal operation for overload function; but for high-current faults they use a magnetic trip.
Both fault protection and short-circuit protection sit on the "instantaneous" part of the mcb's operating curve (see Fig 2.13).
You could carry our a calculation to prove it
But the quick-&-dirty answer is that there's not a chance in hell of your particular circuit not complying with 5.7
For purposes of 8.3.5(a), you can prove that simply by referring to the "deemed-to-comply" value for an HRC fuse.
For 8.3.5 (b), reference to relevant cable data will show that your EC value is not inconsistent with size & length of cable - job done
- Rating: 16.67%
Re: 5.7.5 Supplementary Equipotential Bonding
Just had another look at the wording after being prompted by AlecK’s comment “In 5.7; two times are specified: 0.4 sec for sockets (and some other particular types of equipment), and 5 sec for any other circuit”, and was surprised that the wording may not be as clear cut as I initially suspected.
I note in Clause 5.7.2 (b) that 5s is applicable to “other circuits where it can be shown that people are not exposed to touch voltages that exceed safe values”. Doesn’t those words imply that the 5s seconds cannot arbitrarily be relied on? These words appear to suggest that only after the circuit has been individually considered and “shown” (could this mean in writing as a result of measurement or calculation?) to be safe that the 5s seconds then applies. How should these words be understood?
I note in Clause 5.7.2 (b) that 5s is applicable to “other circuits where it can be shown that people are not exposed to touch voltages that exceed safe values”. Doesn’t those words imply that the 5s seconds cannot arbitrarily be relied on? These words appear to suggest that only after the circuit has been individually considered and “shown” (could this mean in writing as a result of measurement or calculation?) to be safe that the 5s seconds then applies. How should these words be understood?
Re: 5.7.5 Supplementary Equipotential Bonding
Fair point.
Even with those words, they don't say "where it has been shown" or "where it is shown", or "if it is shown".
It just says "where it can be shown".
And since there's no suggestion that any other time applies instead; the correct interpretation of these words is as an explanation of why these other circuits don't have to meet 0.4 s.
And if you look at 1.5.5.3, there's no doubt that 5 s applies for any other circuit .
Nobody ever "shows" this (except maybe when explaining electrical theory to students). It's assumed, based on well-established principles.
See App B, particularly B4, for more detail - including equation B2 for calculating touch voltage.
And if you follow those principles, you "can" show it .
You don't have to, but it can be done.
And because it can be done, is why the longer time limit applies
A person can only get a shock from touch voltage if they happen to be touching an item that is at elevated potential - compared with local ground or other earthed equipment that they can simultaneously touch - during the few moments that the potential is actually elevated.
Note we're not trying to completely eliminate all differences in potential; just to keep any touch voltage within permitted limits.
Bottom line; there's not a chance in hell of your circuit not meeting the fault protection requirement.
Even with those words, they don't say "where it has been shown" or "where it is shown", or "if it is shown".
It just says "where it can be shown".
And since there's no suggestion that any other time applies instead; the correct interpretation of these words is as an explanation of why these other circuits don't have to meet 0.4 s.
And if you look at 1.5.5.3, there's no doubt that 5 s applies for any other circuit .
Nobody ever "shows" this (except maybe when explaining electrical theory to students). It's assumed, based on well-established principles.
See App B, particularly B4, for more detail - including equation B2 for calculating touch voltage.
And if you follow those principles, you "can" show it .
You don't have to, but it can be done.
And because it can be done, is why the longer time limit applies
A person can only get a shock from touch voltage if they happen to be touching an item that is at elevated potential - compared with local ground or other earthed equipment that they can simultaneously touch - during the few moments that the potential is actually elevated.
Note we're not trying to completely eliminate all differences in potential; just to keep any touch voltage within permitted limits.
Bottom line; there's not a chance in hell of your circuit not meeting the fault protection requirement.