Electrically safe working condition

Aleman

Senior Member
Location
Southern Ca, USA
Finally got to go to a 70E class but it was mostly a quick overview. One question I should have asked and didn't I'll ask here.
My question is if I turn off the disconnect to a control panel is it considered electrically safe? Because line voltage will be present
at the top of the disconnect so there would still be a flash potential. Or would I have to kill all power to the panel to achieve a
safe working condition with PPE?
 
Finally got to go to a 70E class but it was mostly a quick overview. One question I should have asked and didn't I'll ask here.
My question is if I turn off the disconnect to a control panel is it considered electrically safe? Because line voltage will be present
at the top of the disconnect so there would still be a flash potential. Or would I have to kill all power to the panel to achieve a
safe working condition with PPE?
In the case where the top of the disconnecting means is touch-safe, like a circuit breaker with terminal barriers in place, some safety experts consider those to be safe and not to present an arc-flash hazard. The usual procedure goes like this:

  1. Review the single diagram of the subject equipment to assure that all power sources are identified.
  2. Donning appropriate arc-flash PPE: open the disconnect.
  3. Lock the disconnect in the open position.
  4. Open the enclosure door.
  5. Test that all three phases of the disconnect are open.
  6. Observe the incoming lines to assure that there are no exposed live parts present.
  7. At this point you may doff(remove) the PPE associated with arc-flash and electrocution protection.
 

Aleman

Senior Member
Location
Southern Ca, USA
In the case where the top of the disconnecting means is touch-safe, like a circuit breaker with terminal barriers in place, some safety experts consider those to be safe and not to present an arc-flash hazard. The usual procedure goes like this:

  1. Review the single diagram of the subject equipment to assure that all power sources are identified.
  2. Donning appropriate arc-flash PPE: open the disconnect.
  3. Lock the disconnect in the open position.
  4. Open the enclosure door.
  5. Test that all three phases of the disconnect are open.
  6. Observe the incoming lines to assure that there are no exposed live parts present.
  7. At this point you may doff(remove) the PPE associated with arc-flash and electrocution protection.
This panel has a lexan shield mounted over the entire disconnect and distribution block. The top lugs are tapped and 3 wires run to a touch safe circuit breaker for control voltage 24VDC. I would call
it touch safe. We did this so we could keep on control power while working on VFD's, contactors etc. I'm not sure I like the taps, I want to run them through another small disconnect but the eng says
it's ok as is. The circuit breaker functions as a disconnect for the taps, which are clearly marked and colored yellow.
 
This panel has a lexan shield mounted over the entire disconnect and distribution block. The top lugs are tapped and 3 wires run to a touch safe circuit breaker for control voltage 24VDC. I would call
it touch safe. We did this so we could keep on control power while working on VFD's, contactors etc. I'm not sure I like the taps, I want to run them through another small disconnect but the eng says
it's ok as is. The circuit breaker functions as a disconnect for the taps, which are clearly marked and colored yellow.
I refuse to play cat-and-mouse game, where an original scheme is presented, then in subsequent posts that OP is changed, altered and modified. Present the whole picture AT the beginning!
 

Aleman

Senior Member
Location
Southern Ca, USA
Wasn't trying to offend. My question was general, is a panel in a safe work condition with disconnect off. You gave me a set of conditions that might make it so.
Some of our panels have shields over the disconnect terminals. We have the one with the taps. So I mentioned that. There are probably over 20 panels where I work.
You guys are a little touchy. But you know your stuff very well and I appreciate the insight and help.
 

petersonra

Senior Member
Wasn't trying to offend. My question was general, is a panel in a safe work condition with disconnect off. You gave me a set of conditions that might make it so.
Some of our panels have shields over the disconnect terminals. We have the one with the taps. So I mentioned that. There are probably over 20 panels where I work.
You guys are a little touchy. But you know your stuff very well and I appreciate the insight and help.
We can get a little touchy because we have long experience with people who phrase questions in ways that make it hard to give a good answer and then after an answer is given the circumstances of the question change.

To be candid about the shields over live parts issue, most of the home made ones I have seen I would say are not safe enough to warrant claiming they do any good.

If you can post a picture of a specific example you want an opinion on, that would probably work better than asking a very general question.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I refuse to play cat-and-mouse game, where an original scheme is presented, then in subsequent posts that OP is changed, altered and modified. Present the whole picture AT the beginning!
Great idea. Put down the keyboard. Step back from the computer.

....and asking and expecting help?!
We can get a little touchy because we have long experience
Note to all of us that participate not just LZ and bob. This is just an example of one of many lately:
Give this some thought. If they knew eough to give all the pertinent information upfront, probably they would already know the answer. And would not bother coming here since we are likely becomming known as a bunch of arrogant gits.

And then there are the questioners that phrase such as to get the answer they want to hear. So tell them that, or in LZ's case don't play.

The forum invites all levels of knowledge - so take a chill pill

Just some random personal thoughts from one with zero authority.

So sayeth the worm
 
Great idea. Put down the keyboard. Step back from the computer.





Note to all of us that participate not just LZ and bob. This is just an example of one of many lately:
Give this some thought. If they knew eough to give all the pertinent information upfront, probably they would already know the answer. And would not bother coming here since we are likely becomming known as a bunch of arrogant gits.

And then there are the questioners that phrase such as to get the answer they want to hear. So tell them that, or in LZ's case don't play.

The forum invites all levels of knowledge - so take a chill pill

Just some random personal thoughts from one with zero authority.

So sayeth the worm
When I ask for help, I am trying to be informative and describe the problem as throughly as I understand it. This OP didn't all of a sudden get a revelation about the other aspects of the issue, by his own admission, he knew it well all along.

After I received the help, I am trying to express some sort of gratitude, since the person offering the help had given it purely from goodwill, expecting or receiving nothing in return. Just basic human decency.

Sorry for all of you if you who don't think that it should be the minimum standard.
 

Aleman

Senior Member
Location
Southern Ca, USA
It was an honest general question. The class I went to was pretty fast and light on substance. I work in panels a lot, and I don't want to wear gear when
I have killed the disconnect. I know there is power at the disconnect so I assume it presents a flash hazard. If I can make these touch safe and if that will
make these safe to work on without gear then that's great. Lazlo mentioned touch safe which is why I brought up the specific panel which he took offense
to. I have been working on making the rest of our panels touch safe cause some of our stuff is pretty scary.

I will post a pic of the shields I use.

And no I don't know this stuff as well as you guys which is why I asked.

Thanks for the help.
 
Lazlo mentioned touch safe which is why I brought up the specific panel which he took offense
to.
No, the irritation came about when you provided additional parameters to the original question. One tries to honestly answer the OP(Original Post) and when you change and add to that setup, the answer changes. Sometimes, when either the question is vague, or a salient point can be made to the general issue I often elaborate on the subject, just for general sharing.


I have been working on making the rest of our panels touch safe cause some of our stuff is pretty scary.
I strongly recommend against doing that. Either it is a manufacturer or UL listed panel fabricators provision, or it isn't safe, because it is not a tested assembly by a third party. If there is an incident involved in a 'home' installed feature, whoever provided that modification is personally liable for the modification and the Company will not - legally - protect you.
 

petersonra

Senior Member
I think there are ways you can make things less unsafe, maybe even safe. I am not convinced that the typical home made plastic shield I see is the proper way to do it though.

Forgetting the potential liability issues for the moment, they just do not provide an adequate degree of protection.

We install them in panels we build sometimes because some of our customers want them. I cringe when they are referred to as "fingersafe".

There are some exposed terminals on some devices that can be completely insulated with heat shrink tubing. I think that is a reasonable way to remove them from the category of exposed and energized parts, and it is a product made for the purpose of being an electrical insulator.

Other products have insulating boots or shrouds that can be added, sometimes they are even sold by the manufacturer of the device.

Some situations do not lend themselves to an easy answer. The least expensive and always a safe solution may be to just add an external disconnect switch. You can spend a lot of money screwing around and end up with something that really is not a lot safer than what you started with.
 
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Aleman

Senior Member
Location
Southern Ca, USA
Here's a pic of the disconnect shield that I have been using. It is only meant as a accidental bump shield. Not for flash etc. You can get
your fingers behind it. The standoffs are 1" min away from lugs. They were closer but at the class they told me 480 approach is 1".
So I moved them. The OEM shrouds are about $75. Nuts. But I might buy them.
 

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