Bees2699 said:

Although i know that for at least some of these circuits there is likely to never be an issue i cant prove it,

Is it within the scope of the EICR to prove someone else's design? Not usually.

If the Client has the information, and it makes sense to you to include for it, then excellent. However, at this point all you can report to the Client is that, according to the general data (not "as designed") you can't say it complies?

This is, after all, Construction Work as defined. If the Client had information that was relevant, it was their obligation to provide it before the EICR work started.

I wouldn’t trust standard test instruments at these values of In. Likely large cables, X being increasingly important and not affected by temp. Can the length and cable make-up be determined? If Ze is below 0.1 you might be shooting in the dark with that also. Tx characteristics and interconnected cable data could be used if available. Or, fit ground fault to MCCB or supplementary bonding. What is the extended disconnection time, does it matter shock and thermal wise?

I have now done what I should have done first and looked up the TM100D datasheet As far as I can tell the instant setting is 800A and fixed, as is 15 secs at 600A .  Only the slow trip current is adjustable from 70A to 100A. Of coures than may not actually be your model, but I think it is.

So I assume your answers meet 800A if the supply is 240V  (so less than 0.30 ohms ), but not with enough slack to trip at a supply reduced to 80% of nominal and to allow for the resistance of the live cores pre-heated by full load. (so more like 0.22 ohms)

Would it make the 600A 15 second trip ( everything is now 4/3 easier) - not ideal but gets you from 'risk of building fire' to 'risk of cable damage' and maybe from a C2 to a sternly worded C3. If it misses that boat  it is wrong as designed, if designed by experts with a computer or not.
So was your test with the cable cold or hot? Are you looking for wiggle room that is more than  0.1 of an ohm - probably no chance of that without some new cable or extra earth bonding or is it off by a few tens of milliohms (might be a pass on a mates 'identical' meter.)

I too caution that most hand held  meters with normal single contact probes are not that great at the 10s of milliohm level, and give you a misleadingly precise but untrustworthy answer - more of a fruit machine than a meter in the last digit.
Mike

Thank you for all the replies, I have revisited the test forms and allowed some minor adjustments to take into consideration the test equipment used, using the accuracy percentages from the manufacturers data and the calibration test sheets. Although this small amount hasn't made a massive decrease it does allow on the larger MCCB's that have adjustable magnetic settings for these to be reduced allowing the circuit to comply. I have done the calculations for the client to what they would need to be set at and the client can now check whether these settings will be suitable in regards to the downstream loading and potential start up currents etc.

They are the units I was referring to Mapj1, there is only 2 circuits which fail currently on these type of units and both are out by a reasonable amount, the first one can be changed to the 80A MCCB with 640A fixed magnetic which then squeezes a pass, this would mean that the current unit at 15secs would be achievable but given the downstream load would be sufficient on an 80A MCCB then this feels the better option, even if they may not agree. 

The last one is to far out and in my opinion likely designed wrong, i have suggested that a switch fuse be connected somewhere along the circuit run where the Zs would be achievable to the switch fuse and then installing fuses to BS88 to allow for a higher Zs to be achieved at the DB.

Currently on a 100A MCCB with a max Zs at 100% of 0.228 allowed 0.18 at 0.8. The measured Zs is 0.33 so way off the mark even with tester in accuracy, this one was also tested by myself with my tester that was calibrated only a couple days before the job so I am confident in this result (it is also around the result gained 3 years ago but the failure was not picked up). A switch fuse with 80A fuses at 5s disconnection time would allow 0.55 at 100% and 0.44 at 0.8. 100A fuses would squeeze a pass but the downstream load does not require a large supply and the wiggle room would be nice.

It will now be down to the client to decide what they wish to do. 

Most of the testing would of been cold, thermal imaging at the time of testing does not suggest that the circuits were running much above ambient, between 20 & 30 degrees for the submains. 

Hmm 0.33 ohms is not good, fault of ~ 650A on a good day. The others are probably just a squeeze with bit of an eye-roll and some clucking.  No RCD /earth fault relay I suppose ?

Does this stack with the cable type and length? - for copper use the rough and ready rule of 16 to check (a single copper core 1mm2 is 16 millioms, so take 16 milliohms, multiply by the length as you have XX metres, and then divide by the no of mm2, as you have lots of square mm in parallel - well on a 100A line I expect 25 or more of them !!.)
This becomes a rule of  18/19 ish with hot cables, but allows the sort of walk around inspection where you  can look up and say  'clear pass/ clear fail/ well that needs more accurate verification' while less experienced types are still either running back to the van for the book of tables or re-booting the fondle-slab. (also allows a sanity check of figures.)

Mike.

There is something a little curious here. You say the 0.4 or 5 second disconnection times are the same in the data. This says that all trips are "instant" and not thermal. I have looked online for the tripping data and it does not appear in the data sheets offered, which is curious. Where is the data coming from? The data sheet simply says the instant trip time is achieved at 600 A (100A unit).

You say the 0.4 or 5 second disconnection times are the same in the data. This says that all trips are "instant" and not thermal.

There could still be a thermal element there - just that it's slower than 5s where it takes over from the magnetic - that's the case with B & C type MCBs, but not D types. The thermal element is still useful for overload protection.

    - Andy

This depends on the trip characteristic and for an MCCB this might not be so simple. However it will do here but the actual data for the exact device into AMTEC may not give the same result. I am concerned that this inspection is finding fault here, and this is basically a design point, the data from which is not available. The conductor heating is also of no concern, provided the circuit conductor is correctly sized the adiabatic will always give a "safe" value, the correct size suiting the protective device rating. Reverse engineering is very difficult to make work!