EFL Protective Device Exceeds 200AMPS

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TPower
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EFL Protective Device Exceeds 200AMPS

Post by TPower »

If I’m livening mains exceeding 200amps. Where should I obtain EFL values that are acceptable? Table 8.1 in 3000 only goes up to 200amps. I’m thinking I would need to get this information from the manufacturer of the protective device?

Secondly, if I’m connecting the fuses at a transformer, is it acceptable to calculate EFL based off the transformer name plate details? I guess this method just wouldn’t take into account the impedance of the mains. I just find some testers can give quite different results, when testing larger capacity supplies. Perhaps it’s just cheaper, less quality testers.

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AlecK
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Re: EFL Protective Device Exceeds 200AMPS

Post by AlecK »

If you're livening mains, then you're dealing with a PEN supply.
On a PEN supply, there's no PEC, so EFLI is A+N rather than A+E as for final subcircuits & submains.

When livening, all this stuff should already have been certified, as all certification, inspection must be done BEFORE connection, and connection must be done before livening is possible.

Yes, there's still a requirement for the fault protection of mains to operate within time limit; but ESR 32 makes this the responsibility of the network company.
And yes, they would need to know the prospective fault current at the point of connection of the mains, based on the details of the transformer and the impedance of the distribution lines up to that point; as well as the operating characteristics of the protective device they install to provide the necessary fault & short-circuit protection for the mains.
(Overload protection is not their problem; that's down to the installation designer / installer.)

because the mains are part of the installation; "3000" requirements apply to the SC & fault protection; requirements being in clause 5.7.
The calculation in 5.7.4 is specified as meeting the requirement; and there is further guidance in App B.

Table 8.1 is valid only for mcbs and HRCs on final subcircuits; as the values are calculated using estimates for several of the factors.
TPower
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Re: EFL Protective Device Exceeds 200AMPS

Post by TPower »

Thanks. I appreciate the very informative response.

Yes, I understand what you’re saying regarding a site having to be tested, certified and inspected prior to livening. I find with the larger capacity sites, it’s usually connected at the NCP by a line mechanic and the other end at the MSB is also connected by the electrician. My job is the inspector, I come along (afterwards) inspect, test and liven. But I’m doing this after it’s actually connected (just the fuse links aren’t in), so I believe the order of events is wrong? I am however just an employee in my company, so it’s difficult for me to change work practices that seem to be ingrained. It’s different if the site is WC metering that I’m fitting, that way I’m doing the last piece of PEW/final connection. But this doesn’t really work with CT metering.

That’s interesting what you say about table 8.1 being only for final sub circuits. I’ve always thought we should refer to this table when testing fault impedance on mains, when testing at the MSB/main switch.

For example. With a 63 amp fuse at the NCP, to ensure a fusing time of no longer than 5 seconds (under short circuit) I’ve always taken the max impedance value as being 0.94 ohms. I thought mains and submains were required to disconnect within 5 seconds, under short circuit?

Seems I may have been referring to the wrong part of 3000. I’ll need to have a good read through the parts you’ve referenced. Thanks again.
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Re: EFL Protective Device Exceeds 200AMPS

Post by AlecK »

Inspection is required to happen before connection to supply.
for mains; that's connection at the network end.
A line mechanic (or anyone else) who connects prior to sighting both CoC(s) & RoI is breaking the law.
And yes, it doesn't often happen the way it should; while Energy Safety's attitude has been "stop complaining, find a way to make it work".
which is fine until something goes wrong; at which time we'll be found not to have followed the letter of the law.

As an inspector; our job is to inspect high risk PEW that has been certified on the C.oC.
Provision of fault & short circuit for mains isn't work on an installation, so there are NO certification requirements - and no risk classification either.
So inspection of it isn't required; which makes it simply not our business.

you're correct that the required operating time for mains fault protection is 5 s; but it's not something we are required to check.
The s-c time will be different (set by a different clause and using a totally different calculation; but again s-c protection of mains is not part of inspecting HRPEW.
Noting that short circuit is A-A or A-N, so higher voltage than for EFLI, resulting in PSSC being higher than PFC.

And yes the Table may be valid enough; impedance is impedance.
But as i said it's based on a number of assumptions - and you need to read / study Appendix B to even begin to understand them. (I don't claim to be an expert on EFLI at that level).
The real point of Tables 8.1 is for use when EFLI is required to be tested.
The ONLY time such testing is required is for socket outlets that don't have RCD protection.
In 2018 edition; it's clearly stated that the mcbs / fuses are on final subcircuits.

So we're probably safe to use the Table if we happen to want to check mains fault protection, but since we don't have to why put yourself at risk?
It's a live test, and ESR 100 (via "4836" says we don't do anything live unless we have to.
Note also that 5s times are only given for (HRC) fuses. That's not because mcbs are never used on circuits with 5 s max time, but because for an mcb it's in the 'instant" part of the trip curve

The livening aspect is not part of inspection; it's not even PEW.
That's a main point of the system; to ensure that tings CAN'T be livened until they've been tested, certified, and (if required) inspected.
The crunch is connection to a supply, because after that it could be livened by anyone (or even a trained monkey).

for WC metering (as an example), we have to deal with mains in 2 parts.
The part upstream; and the part downstream.
The upstream part has to be certified & inspected before being connected to supply.
It can't be certified as safe to connect if the conductors are floating about unterminated in the meter enclosure.
Whoever connects that part must issue an ESC;. The ESC must detail exactly what was livened (eg part mains, all mains, all installation, etc.
while this connection may be work on "works" and not work on an installation, an ESC is still required (ESR 74A 1AAA)(c) was specifically introduced to make this clear).
Again this mostly just doesn't happen.

if it's just that upstream part of mains; then whoever connects the next bit(s) must issue another ESC. And so on.
Noting that installing meters isn't part of 'inspecting" either;even if it happens to be done by someone who holds an 'Inspector" PL; they are not acting as an inspector. When we undertake more than one role in this process; we need to be constantly aware of which hat we are wearing at any particular time.

It doesn't help that there are almost as many interpretations of what "should" be done when inspecting as there are Inspectors.
There are "inspector" courses offered; but the course content is all about ESRs / wiring Rules (ie the content of the exam),
often taught by people who may have only a poor understanding of what they are teaching, and who are (often hugely) removed form actually working as Inspectors - some of them may have never inspected anything
There's SFA in offer about the practical process of inspecting; what we should expect, what to look for, etc
(Rant over)
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Re: EFL Protective Device Exceeds 200AMPS

Post by TPower »

Thanks for the feedback on this Alec, it’s been very helpful
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