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I have received a private message in response to this locked post in which the writer Googleberry raises concerns about my post.
My comment
Googleberry states use transformers and I questioned use of a transformer. Note singular and plural. To use an isolating transformer on every computer may be OK. However to use a single isolation transformer, for all computers, would not. The point being multi-faults could result in having 230vac between computer cases.
Using a single transformer to feed each power supply would mean like the shaver socket any single fault to earth would not allow current to flow either in the person or any other conducting medium so one could not get a shock. However computers are rather larger than the shaver and consideration would have to be given as to if you could ever get multi-faults to earth.
Since computers often use UPS systems and the individual units basically do same as an isolation transformer, once main power is removed. I would therefore consider it to be an acceptable risk. However it would require a full risk assessment by whoever installed the system.
At £40 for 200va isolation transformers RS price plus enclosures it seems a very expensive option £800 for 20 transformers would I think raise some eye brows in most organisations and I am sure you could split the supply into two, with 10 PC’s on each for far less money.
Having tried to get an isolation transformer for my son for his boat I found they are not cheap. In fact to transform down to 110vac then back up to 230vac was cheaper than single 230vac to 230vac I suspect because of quantity made.
So I would consider the whole idea of isolation transformers to prevent erroneous tripping of RCD’s as a non starter.
However from Googleberry comment I think he assumed I was advocating removal of an earth wire which I was not. What I was trying to point out was anything after the transformer would not be able to use the earth unless one leg of the output was earthed. and if that is done plus fitting a 30ma RCD then there would be no advantage over the original system.
I am Dyslexic and I realise I can easy write in a way others can misinterpret and sorry if that was the case. He had pointed out the misspelling of “amateur” which was because an update in Firefox had disabled my spell check unknown to me at the time and over the years I have come to rely on it.
So to re-cap I did not advocate in any way removing of earth wires. What I was trying to say is that an isolation transformer (singular) would not help assuming it was correctly fitted including linking one output to earth.
I would have answered as a comment back but Googleberry has not enabled that on his account so this is only way to reply.
Out of interest I note the same problem was posted on IET web site and it was felt labelling the sockets "Computer Only" removed the need for RCD protection! "(b) a specific labelled or otherwise suitably identified socket-outlet provided for connection of a particular item of equipment." I had considered it would need to be computer XYZ and just computer would not do however reading the 17th they do have a point.
My comment
seems to have raised the concern and from the post it seems either I have not made my self plain or it has been miss understood either way I feel this needs clarifying.
Googleberry states use transformers and I questioned use of a transformer. Note singular and plural. To use an isolating transformer on every computer may be OK. However to use a single isolation transformer, for all computers, would not. The point being multi-faults could result in having 230vac between computer cases.
Using a single transformer to feed each power supply would mean like the shaver socket any single fault to earth would not allow current to flow either in the person or any other conducting medium so one could not get a shock. However computers are rather larger than the shaver and consideration would have to be given as to if you could ever get multi-faults to earth.
Since computers often use UPS systems and the individual units basically do same as an isolation transformer, once main power is removed. I would therefore consider it to be an acceptable risk. However it would require a full risk assessment by whoever installed the system.
At £40 for 200va isolation transformers RS price plus enclosures it seems a very expensive option £800 for 20 transformers would I think raise some eye brows in most organisations and I am sure you could split the supply into two, with 10 PC’s on each for far less money.
Having tried to get an isolation transformer for my son for his boat I found they are not cheap. In fact to transform down to 110vac then back up to 230vac was cheaper than single 230vac to 230vac I suspect because of quantity made.
So I would consider the whole idea of isolation transformers to prevent erroneous tripping of RCD’s as a non starter.
However from Googleberry comment I think he assumed I was advocating removal of an earth wire which I was not. What I was trying to point out was anything after the transformer would not be able to use the earth unless one leg of the output was earthed. and if that is done plus fitting a 30ma RCD then there would be no advantage over the original system.
I am Dyslexic and I realise I can easy write in a way others can misinterpret and sorry if that was the case. He had pointed out the misspelling of “amateur” which was because an update in Firefox had disabled my spell check unknown to me at the time and over the years I have come to rely on it.
So to re-cap I did not advocate in any way removing of earth wires. What I was trying to say is that an isolation transformer (singular) would not help assuming it was correctly fitted including linking one output to earth.
I would have answered as a comment back but Googleberry has not enabled that on his account so this is only way to reply.
Out of interest I note the same problem was posted on IET web site and it was felt labelling the sockets "Computer Only" removed the need for RCD protection! "(b) a specific labelled or otherwise suitably identified socket-outlet provided for connection of a particular item of equipment." I had considered it would need to be computer XYZ and just computer would not do however reading the 17th they do have a point.
