Earth Loop Question

[Hundleton1]

Hi guys, i after some help with an Earth Loop question, first thing first this is not coming from a sparks prospective so the regulations are not relevant here to a point.


I work in the domestic appliance industry, i contract to one of the big manufactures, as part of our initial tests on the equipment such as earth continuity and Insulation resistance we perform a no trip earth loop test, out testes first confirm the socket wis correctly wired and that an earth is present, then we perform the test, we are to regardless of the system e.g. TT,TNCS, TNS a reading of 200ohm or below is acceptable for out point of view, over 200 and we issue an notification of a possible issue with the system.


because we have no legal requirement of the installation is self we are testing to ensure the socket we are connecting the appliance to is safe for the engineer to work on and should there be an issue protection devises (RCD/MCB) will trip.

Now here is where the issue is, in discussions with other engineers of various skills some understand more than others some are concerned that 200ohm is wholly inadequate and down rite dangerous, its been pointed out that at 200ohm you would only get fault current of 1A, not enough to trip a 32a mcb, if the is an RCD then its fine BUT its no non RCD we are concerned about.


now i have been doing electrical maintance for over 10 years, i did my 2330 years ago but not been deeply involved with installation for years.

the Manufactures have set a blanket reading to make it easier on the engineers and they must have come up with this for a reason

am i missing something here?

 

[kingeri]

These days a TT system would always be fitted with an RCD....simply because the disconnection times cannot be met. Older installs should be brought up to date, simply for safety's sake!

 

[Plonker 3]

Sorry but where has the 200 ohm figure come from?

Every MCB, fuse, RCBO has a different tripping charcteristic so your figure should be underneath the relevant one on the circuit being used not just a random figure.

 

[Richard Burns]

If you have guidance that states in writing that if the EFLI is <200 ohms then it is safe for your engineers to test the appliances then you can work to that value.

However you would need to be aware that this is not a safe value for EFLI if there are no RCDs present or if the RCDs do not work. If you were to use an RCD adapter whilst testing your equipment then it would be (somewhat) safe.

If you wish to advise customers of problems with their fixed wiring then 200 ohms is not a suitable figure, admittedly if it is over 200 ohms then there is a problem, but there is also a problem for the next 199.2 ohms down!
The only source from which I could assume the 200 ohms was derived is from a recommendation in the wiring regulations stating that for a TT system a value of >200 ohms may not be stable, however this is pretty much irrelevant to the safety of an installation and totally irrelevant unless the installation has TT earthing.