How essential is an isolation transformer?

[Mark Hennessy]

Mm, this was a good question to pose. I may reassess my first instinct to employ one. What the replies on this thread demonstrate, plus those on the link David (Yorkie) gave, is that I should reconsider and properly plan my workbench arrangement. This I shall now do

Any additional information and advice will be very welcome.

Thank you

Nick

Nick, to get this slightly back on topic (not that being off-topic is a problem, of course), please do ask away. Perhaps start by describing what you currently have in mind?

For what it's worth, here's what I have always done in a workshop (as you might have already seen in that other thread):

• Sockets that are powered 24/7, for computers, clocks and similar items. These have a double-pole isolator switch, but this is left on.
  
• Sockets that are powered when the workshop is in use. Also switched by a double-pole isolator, and fed via an RCD.
  
• Sockets that are isolated. If you only have one isolation transformer, you'll only have one of these. I have a pair of transformers that I built into a case. I only switch these on when needed (not very often) as they run warm and are a little bit noisy.
  

All sockets are clearly differentiated - coloured sockets are useful here.

Where is your workshop? Is it in the house, or is it in an outbuilding? Do you have an RCD in the consumer unit?

In my case, the workshop is in the cellar, and the sockets in the cellar are on the main house ringmain, so already have RCD protection. If a fault was to occur on the bench, there's no way of telling whether the bench RCD would trip before the house one, but the odds of the former are higher than if there was no bench RCD. If the bench RCD trips first, that saves the minor hassle of resetting clocks and computers around the house. I've yet to cause the RCD to trip, so can't being to guess...

Having double-pole isolators is a good plan because you can quickly hit them if your DUT starts emitting its magic smoke. Or, someone else can knock the power off should you be receiving an electric shock that the RCD doesn't know about (Live to Neutral). Put them as near to the door and the bench as you sensibly can.

Good lighting is essential, of course. Depending on how your house is wired, it will hopefully stay on should the RCD supplying sockets trip in the consumer unit. If there is a chance of being plunged into complete darkness in that event, consider emergency lighting (I really must get around to installing mine). I recently picked up an LED fitting from CPC for £12 - bargain!

Perhaps the best advice is this: always *think* - never fall into auto-pilot. Never assume the safety you think you have provided will work - it is only there for when all else fails, and it won't always help.