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- 25 Mar 2007
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Hello,
Quick Question, wel quite long actually
I have 2 quite large UPS's at my office, each connected to one 240v 13A double socket on a ring main protected by a 32A MCB. These are the only two devices on the ring main.
There is then an RCD that protectes all of the MCB's in the consumer unit (80A RCD 30mA Trip) apart from the two lighting circuits and the alarm which are on the other side of the split load. The whole lot is isolated by a 100A 2pole Isolator.
When I test the UPS's by switching them off at the wall, they kick in and run properly and the whole building is fine. When I switch then back on, the RCD in the consumer unit trips cutting power to everything but the lights. I then have to run as fast as I can down 4 flights of stairs into the celler to reset the RCD before the UPS's run out of battery power. When I reset it everything is fine and the UPS's start charging again. However the 32A MCB protecting the ring main does NOT trip atall. Hmmmmm....
So I am guessing that when the UPS's come back online, they take a surge of power which trips the RCD?
But why doesnt the 32A MCB inbetween trip first?
Why does the 80A RCD trip?
I was thinking of getting the site electrician to move the 32A MCB over to the non RCD protected side of the consumer unit? Is this wise? or should we use a RCBO?
It would be excellent if anyone could help
Thankyou Very Much
Matthew
Quick Question, wel quite long actually
I have 2 quite large UPS's at my office, each connected to one 240v 13A double socket on a ring main protected by a 32A MCB. These are the only two devices on the ring main.
There is then an RCD that protectes all of the MCB's in the consumer unit (80A RCD 30mA Trip) apart from the two lighting circuits and the alarm which are on the other side of the split load. The whole lot is isolated by a 100A 2pole Isolator.
When I test the UPS's by switching them off at the wall, they kick in and run properly and the whole building is fine. When I switch then back on, the RCD in the consumer unit trips cutting power to everything but the lights. I then have to run as fast as I can down 4 flights of stairs into the celler to reset the RCD before the UPS's run out of battery power. When I reset it everything is fine and the UPS's start charging again. However the 32A MCB protecting the ring main does NOT trip atall. Hmmmmm....
So I am guessing that when the UPS's come back online, they take a surge of power which trips the RCD?
But why doesnt the 32A MCB inbetween trip first?
Why does the 80A RCD trip?
I was thinking of getting the site electrician to move the 32A MCB over to the non RCD protected side of the consumer unit? Is this wise? or should we use a RCBO?
It would be excellent if anyone could help
Thankyou Very Much
Matthew