IT earthing system cable calculation

[Lc1]

Hello,
Does anyone know if Trimble can be used for cable calculations for equipment with an IT earthing system? If not could you please point me in the direction of an example calculation if possible.

Thank you

 

[timbobelfast]

Lc1, not sure about Trimble. But ElectricalOM has IT earthing system selection. What are you designing?

 

[Lc1]

Thanks for this. Rough project at the moment. Is electrical OM a software package?

Thank you

 

[Lister1987]

Yes, Electrical Design, Cable Sizing and Certification Software - http://www.electricalom.com - believe it offers a trial too

 

[Lc1]

Great. Thank you for this

 

[timbobelfast]

Thanks for this. Rough project at the moment. Is electrical OM a software package?

Thank you

Yes, electrical design software.

 

[pc1966]

IT systems are usually very specific cases like ships or medical facilities. The normal CCC & VD aspects are the same but they obviously don't have the same conditions for earth-fault ADS as often that is the whole point - not to disconnect on a single fault!

 

[Lc1]

Thanks for this. Could you point me in the direction of an example calc as I do not believe this can be done on Trimble and I have just asked for a trail of electrical OM.

Thanks again.

 

[pc1966]

What are you trying to calculate, and for what sort of system?

IT systems are either small for single loads like shavers, etc, or if larger and multiple loads they normally have to be under skilled supervision and to have earth fault monitoring in place.

 

[Lc1]

What are you trying to calculate, and for what sort of system?

IT systems are either small for single loads like shavers, etc, or if larger and multiple loads they normally have to be under skilled supervision and to have earth fault monitoring in place.

Still early on project but would be multiple loads “ large” loads and have earth fault monitoring.
Thanks again.

 

[Lister1987]

IT systems are usually very specific cases like ships or medical facilities. The normal CCC & VD aspects are the same but they obviously don't have the same conditions for earth-fault ADS as often that is the whole point - not to disconnect on a single fault!

I wouldn't mind seeing one in tht flesh as I find it hard to visualise it

 

[timbobelfast]

I wouldn't mind seeing one in tht flesh as I find it hard to visualise it

Lister1987, IT Earthing Systems are common practice for offshore installations. See attached overview of one in the flesh

 

[pc1966]

Lister1987, IT Earthing Systems are common practice for offshore installations. See attached overview of one in the flesh

Interesting to see that, clearly most systems able to be isolated / alternate feed to keep going even if something has failed.

Also it looks like the "VFD" board (centre bottom) is really DC but 6-phase rectification (from the delta to delta+star transformers)?

 

[pc1966]

I wouldn't mind seeing one in tht flesh as I find it hard to visualise it

Essentially there is no "hard" linking of a live conductor to earth to define neutral, so if any fault to earth then only a small current flows and you don't lose power at sea or during an operation, etc.

Simplest monitor in older / smaller systems was a pair of lamps (single phase) or 3 lamps (3-phase) from the live conductors to earth. If all was normal they would glow the same dim level, if one phase was faulted to earth it's indicator would go off and the other light glow at full brightness.

In that sort of a system it is not safe for shock as easily 30mA is available due to the lamps (and potentially just through capacitance in large system), but for the likes of medical use, etc, electronic monitors would be much higher impedance.

 

[timbobelfast]

Interesting to see that, clearly most systems able to be isolated / alternate feed to keep going even if something has failed.

Also it looks like the "VFD" board (centre bottom) is really DC but 6-phase rectification (from the delta to delta+star transformers)?

Yes , redundancy through out. And yes the VFD board is all DC drilling equipment.

You can almost predict when the galley starts preparing meals, as the earth fault alarms ping through when they turn on the grills and hot plates lol!