I am having a problem with some display units for computers fed via RCCBO's. Each display unit has a single supply running to it fed via a 20A 30mA RCCBO. The display units have anywhere between 12-20 computers/laptops on them and are switched on via a single switch. The problem is when the units are switched on the RCCBO's trip. I have measured the start up currents on the circuits using my clamp meter and no circuit is overloading. I know that upon start up computers can generate a high leakage current so I suspect this is why the RCCBO's are tripping upon switch on. How do I get round this problem?
RCCBO's and computers
- Thread starter tangerinepiemuncher
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I would say you need less computers on each circuit.
Try posting in "electrics uk" there are plenty of guys there who know more about circuits with high leakage currents.
Try posting in "electrics uk" there are plenty of guys there who know more about circuits with high leakage currents.
Leakage current will likely be constant. There are three ways around this problem:
1. Use a 100mA or 200mA RCCBO if you can get them.
2. Use isolating transformers
3. Connect fewer computers
Now here's a thought...
If these circuits are radials, then things could get nasty in event of a single fault condition: if the earth were to fail at the supply end, then all the computer cases, assuming they were metal, would come up to mains potential, with the sum of their leakage currents available to anyone who touched them. If you had installed a 200mA RCCBO, and the leakage current was say 195mA, the unfortunate victim would get the lot and the RCCBO would not trip!
Best use isolation transformers and keep the 30mA RCCBO!
If these circuits are radials, then things could get nasty in event of a single fault condition: if the earth were to fail at the supply end, then all the computer cases, assuming they were metal, would come up to mains potential, with the sum of their leakage currents available to anyone who touched them. If you had installed a 200mA RCCBO, and the leakage current was say 195mA, the unfortunate victim would get the lot and the RCCBO would not trip!
Best use isolation transformers and keep the 30mA RCCBO!
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How does an isolating transformer help. Yes it will stop it tripping but you have removed completely the safety earth.
Only by using an isolating transformer per computer with Class II power supplies on computers could that be safe. i.e. Same as shaver socket.
Only option is to split the supply and feed less computers from each RCD.
This does make one think about the UPS often used as never seen independent earth connections to UPS and since with power failure you could also lose the earth I would have thought as with stand-by generators you would need an independent earth i.e. not relying on that provided with a TN supply.
Maximum leakage permitted without special earthing is 3.5ma see 543.7.1.1 so 5 computers just under max leakage with a trip that trips just over min could trip it out. Realistic 10 items with filters is about the max to comply with 314.1 (iv) so the installation would not comply.
This I see as a problem with domestic as if it trips due to leakage of less than 3.5ma per item the installation fails yet having only 10 sockets per ring main would be seen as going OTT. I have 10 sockets in my living room alone. Maybe this is the argument for radials? But how a house with two RCD's can ever comply with 314.1 (iv) I don't know. I have two RCD's and has been that way for last 18 years and it does trip every so often without fault. OK may be 4 months between each trip but nothing in 314.1 (iv) gives a time so it fails?
Some day I will fit new consumer unit. It has been planned for last 10 years just never got around to it.
Only by using an isolating transformer per computer with Class II power supplies on computers could that be safe. i.e. Same as shaver socket.
Only option is to split the supply and feed less computers from each RCD.
This does make one think about the UPS often used as never seen independent earth connections to UPS and since with power failure you could also lose the earth I would have thought as with stand-by generators you would need an independent earth i.e. not relying on that provided with a TN supply.
Maximum leakage permitted without special earthing is 3.5ma see 543.7.1.1 so 5 computers just under max leakage with a trip that trips just over min could trip it out. Realistic 10 items with filters is about the max to comply with 314.1 (iv) so the installation would not comply.
This I see as a problem with domestic as if it trips due to leakage of less than 3.5ma per item the installation fails yet having only 10 sockets per ring main would be seen as going OTT. I have 10 sockets in my living room alone. Maybe this is the argument for radials? But how a house with two RCD's can ever comply with 314.1 (iv) I don't know. I have two RCD's and has been that way for last 18 years and it does trip every so often without fault. OK may be 4 months between each trip but nothing in 314.1 (iv) gives a time so it fails?
Some day I will fit new consumer unit. It has been planned for last 10 years just never got around to it.
This is a repeat post, the topic already exists further down the page.
I should have told the OP to have the thread moved instead of reposting in Electrics Uk.
I should have told the OP to have the thread moved instead of reposting in Electrics Uk.
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