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Coordination of insulation monitoring devices

Jam
Hi all,


I occaisionally come up againt a requirement to provide an IMD where there already is one elsewhere on the same network (for example, on an IT system where the downstream equipment contains its own IMD out of the box, but has been installed in such a way that it might be disconnected with the distribution circuits still energised, leaving the latter unprotected)


In the past I've been advised by manufacturers that you can't have two separate IMDs monitoring the same network as they'll see each other as faults, so we've ended up with convoluted arrangements to priorise devices such that only one is in use at any time, or simply removed downstream devices.


But this doesn't feel satisfactory to me, and I suspect I'm missing something... Is there a better way to coordinate IMDs?
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    This is really rather a difficult problem, because you are presumably using equipment not designed to work together. Can you give more detail on the application, because the usual way to have multiple circuits with individual devices is multiple isolating transformers or windings. There is also a problem with stray capacitance if the circuits are too long or connected to many items of equipment, although this is not usually met with hospital applications. I don't really see why an appliance should have the IM system, perhaps you can enlighten us?
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    This is really rather a difficult problem, because you are presumably using equipment not designed to work together. Can you give more detail on the application, because the usual way to have multiple circuits with individual devices is multiple isolating transformers or windings. There is also a problem with stray capacitance if the circuits are too long or connected to many items of equipment, although this is not usually met with hospital applications. I don't really see why an appliance should have the IM system, perhaps you can enlighten us?
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