winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Rather than hijacking the splicing thread, I'll continue this here:
http://forums.mikeholt.com/showpost.php?p=698051&postcount=17
http://forums.mikeholt.com/showpost.php?p=698051&postcount=20
I think that I made the mistake of being intentionally obscure thinking that I was being clever.
I made the claim that 'It is _always_ possible to work hot safely, given sufficient _money_ for PPE and equipment. '
What I really should have said was:
It is _always_ possible to safely work on a piece of equipment while maintaining the _function_ provided by that piece of equipment, given sufficient resources for PPE and other equipment.
1) This _may_ be via actual 'hot work', using suitable PPE, where there is a real risk of a person touching conductors or conductors touching each other. The suitable PPE and work procedure reduces this risk to a reasonable and acceptable level. An example would be the sort of stuff that outside linemen do every day.
2) This _may_ be via providing the service in an alternate fashion. John mentioned industrial lighting as an example of a situation where power could not be removed: http://forums.mikeholt.com/showpost.php?p=697959&postcount=15 and this is a perfect example. While it may be the case that a particular room must remain well lit, this does not mean that power could not be removed from the lighting circuit in question. With sufficient funding, alternate lights could be set up, the normal lighting circuit shut down, and then the circuit itself worked cold. Computer services can be provided by backup machines, and if a company computer is so important that it cannot tolerate being shut off for safety, then that company is _foolish_ to not have a backup method in place.
3) This _may_ be via spending more money at the initial design and installation stage, providing the necessary tools to maintain service when components need repair work. If a process is so gosh darn valuable that it 'cannot be shut down', then redundancy needs to be designed in from the start. If a computer _must_ remain up, then IMHO the answer is not to risk a life by having an electrician work on a live circuit; instead that computer needs to have been designed with a redundant power supply, so that the computer can remain up even as the circuit is taken down.
I can't say that this means that one will never work 'hot' nor that it is possible in the real world to _always_ eliminate risk. Sometimes the cost of the necessary equipment to eliminate a risk is simply far too high. But it is important to remember that when someone says that it is _impossible_ to shut a circuit down, what they really mean is that it is _expensive_ to shut that circuit down. Sometimes the cost actually does justify a certain amount of risk to life (there is _never_ zero risk, or perhaps it is better said that zero risk means infinite cost), but most of the time the situation is someone willing to risk _your_ life for _their_ pocketbook.
-Jon
http://forums.mikeholt.com/showpost.php?p=698051&postcount=17
http://forums.mikeholt.com/showpost.php?p=698051&postcount=20
I think that I made the mistake of being intentionally obscure thinking that I was being clever.
I made the claim that 'It is _always_ possible to work hot safely, given sufficient _money_ for PPE and equipment. '
What I really should have said was:
It is _always_ possible to safely work on a piece of equipment while maintaining the _function_ provided by that piece of equipment, given sufficient resources for PPE and other equipment.
1) This _may_ be via actual 'hot work', using suitable PPE, where there is a real risk of a person touching conductors or conductors touching each other. The suitable PPE and work procedure reduces this risk to a reasonable and acceptable level. An example would be the sort of stuff that outside linemen do every day.
2) This _may_ be via providing the service in an alternate fashion. John mentioned industrial lighting as an example of a situation where power could not be removed: http://forums.mikeholt.com/showpost.php?p=697959&postcount=15 and this is a perfect example. While it may be the case that a particular room must remain well lit, this does not mean that power could not be removed from the lighting circuit in question. With sufficient funding, alternate lights could be set up, the normal lighting circuit shut down, and then the circuit itself worked cold. Computer services can be provided by backup machines, and if a company computer is so important that it cannot tolerate being shut off for safety, then that company is _foolish_ to not have a backup method in place.
3) This _may_ be via spending more money at the initial design and installation stage, providing the necessary tools to maintain service when components need repair work. If a process is so gosh darn valuable that it 'cannot be shut down', then redundancy needs to be designed in from the start. If a computer _must_ remain up, then IMHO the answer is not to risk a life by having an electrician work on a live circuit; instead that computer needs to have been designed with a redundant power supply, so that the computer can remain up even as the circuit is taken down.
I can't say that this means that one will never work 'hot' nor that it is possible in the real world to _always_ eliminate risk. Sometimes the cost of the necessary equipment to eliminate a risk is simply far too high. But it is important to remember that when someone says that it is _impossible_ to shut a circuit down, what they really mean is that it is _expensive_ to shut that circuit down. Sometimes the cost actually does justify a certain amount of risk to life (there is _never_ zero risk, or perhaps it is better said that zero risk means infinite cost), but most of the time the situation is someone willing to risk _your_ life for _their_ pocketbook.
-Jon