24-11-2015, 05:28 PM
As has been said earlier in this thread, the use of isolation transformers is frequently misunderstood.
At one time I worked on special cable TV receivers based on the ITT VC100 chassis but the tuner unit, which had an external wired 22 button channel selector was earthed, as was the distribution system (isolation was in the IF connection rather than the aerial isolators used on domestic receivers).
Initially we used RS isolating transformers which were free standing on the benches and could be moved around as required but we were required to move out of that building into a permanent workshop in the main building. As our network was expanding, we needed more engineers and more bench space, so this came at an appropriate time!
The Chief Engineer was told that we required isolation transformer fitted to every bench position. This point was duly noted and carpenters and electricians moved in to fit the place out.
I and a colleague paid a visit to see how work was progressing. By the door was a consumer unit with mains switch and metal trunking running down to the floor except that part way down was a large square louvred box ...
'What is that?', I asked. 'Oh that's your isolation transformer!' came the reply.
They had summed up the total demand, based on the transformer rating they been given but couldn't find a suitable transformer anywhere so they'd had one wound specially - which would have fed all the benches in parallel!
After we'd pointed out the error of their ways, all the bench positions bar one had individual isolation transformers fitted beneath them.
The remaining bench had a very hefty isolated supply!
At one time I worked on special cable TV receivers based on the ITT VC100 chassis but the tuner unit, which had an external wired 22 button channel selector was earthed, as was the distribution system (isolation was in the IF connection rather than the aerial isolators used on domestic receivers).
Initially we used RS isolating transformers which were free standing on the benches and could be moved around as required but we were required to move out of that building into a permanent workshop in the main building. As our network was expanding, we needed more engineers and more bench space, so this came at an appropriate time!
The Chief Engineer was told that we required isolation transformer fitted to every bench position. This point was duly noted and carpenters and electricians moved in to fit the place out.
I and a colleague paid a visit to see how work was progressing. By the door was a consumer unit with mains switch and metal trunking running down to the floor except that part way down was a large square louvred box ...
'What is that?', I asked. 'Oh that's your isolation transformer!' came the reply.
They had summed up the total demand, based on the transformer rating they been given but couldn't find a suitable transformer anywhere so they'd had one wound specially - which would have fed all the benches in parallel!
After we'd pointed out the error of their ways, all the bench positions bar one had individual isolation transformers fitted beneath them.
The remaining bench had a very hefty isolated supply!
