Surely it's just waiting for that second fault scenario to rear it's ugly head? 
ELI can the meter damage UPS and like?
- Thread starter ericmark
- Start date
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sjwkmje
My background is electronic engineering and as you know an RCD looks at the current waveform and not the voltage waveform as it uses a current transformer. I have worked on inverters in the past actually repairing them.
NOTE: I am not sure what type a DC sensitive MCB / RCD is I think its type A but I might be wrong. I know the units I have used were either MEM or Merlin Gerin as this was all that was used on this particular site.
The best way to find out is to get a differential scope probe and a decent scope (or two x100 probes and an isolation transfer) and go across live and neutral with the ground connected to earth somewhere. Look at the voltage waveform and then for current you need a current transformer and wrap the live around it and look at the voltage waveform again. This gives you some idea of what to look for. When I did this I found that the output had some DC component so our conclusion on the output was to use a DC operated MCB. We did not use RCDs as my conclusion was that the RCD during test would not trip at the voltage and current waveforms that was present and during testing we could not get an RCD to trip in a fault condition. This was an off-line UPS so the inverter was all ways running internally but switched from a PFC SMPS (power factor correction switched mode power supply) fronted to batteries when the mains failed. So for feed the UPS was fed with a type C RCD as this would provide protection 90% of the time until power failed. We tried a type A DC sensitive RCBO and this seemed to work fine on the output for OCD to get rid of the RCD feeding the UPS. Only reasoning I can find is that the current transformer did not like the DC component present and was just saturating the core. The output of this UPS was a chopped sine wave but it did look like a sine wave and not a square wave some of the cheaper units output.
I think that in your case you have an on-line UPS so there should be no issue using an RCD on the output when connected to a shore supply. When in UPS mode you could use a type A RCBO on circuits you wanted to protect to ensure there is protection and on a boat I am guessing this is most circuits.
Its a complex problem. But I have never worked on a boat so not sure what the setup is like.
In the NHS where these units was in use there was no RCDs on the output just on the feed type C RCD they relied on DC sensitive MCBs if required on the output for OCD. I think your going to have more issue providing a decent earth. How do you provide an earth on a boat when its out in water not connected to the shore supply? Sorry for hi jacking just curious.
Adam
NOTE: I am not sure what type a DC sensitive MCB / RCD is I think its type A but I might be wrong. I know the units I have used were either MEM or Merlin Gerin as this was all that was used on this particular site.
The best way to find out is to get a differential scope probe and a decent scope (or two x100 probes and an isolation transfer) and go across live and neutral with the ground connected to earth somewhere. Look at the voltage waveform and then for current you need a current transformer and wrap the live around it and look at the voltage waveform again. This gives you some idea of what to look for. When I did this I found that the output had some DC component so our conclusion on the output was to use a DC operated MCB. We did not use RCDs as my conclusion was that the RCD during test would not trip at the voltage and current waveforms that was present and during testing we could not get an RCD to trip in a fault condition. This was an off-line UPS so the inverter was all ways running internally but switched from a PFC SMPS (power factor correction switched mode power supply) fronted to batteries when the mains failed. So for feed the UPS was fed with a type C RCD as this would provide protection 90% of the time until power failed. We tried a type A DC sensitive RCBO and this seemed to work fine on the output for OCD to get rid of the RCD feeding the UPS. Only reasoning I can find is that the current transformer did not like the DC component present and was just saturating the core. The output of this UPS was a chopped sine wave but it did look like a sine wave and not a square wave some of the cheaper units output.
I think that in your case you have an on-line UPS so there should be no issue using an RCD on the output when connected to a shore supply. When in UPS mode you could use a type A RCBO on circuits you wanted to protect to ensure there is protection and on a boat I am guessing this is most circuits.
Its a complex problem. But I have never worked on a boat so not sure what the setup is like.
In the NHS where these units was in use there was no RCDs on the output just on the feed type C RCD they relied on DC sensitive MCBs if required on the output for OCD. I think your going to have more issue providing a decent earth. How do you provide an earth on a boat when its out in water not connected to the shore supply? Sorry for hi jacking just curious.
Adam
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