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Discussion Starter · #1 ·
So I'm not an electrician. But I have a rough idea of the things that can go wrong and what will happen when they do. In the case of the QO, it's got 2 nasty faults :

1. There is no secondary cover over the main terminal lugs and the main breaker panel. This means that even if you turn off the main breaker, the box is not completely safe to work on - you have to always be watching where your tools go, where any wires you pull go, etc, because you might touch a bare ground wire you just trimmed to the main terminal lug while you are trying to adjust things, etc.

Even worse, there's an immense danger if my hunch is correct. Every time you unscrew the 3 screws keeping the cover on, if you aren't careful as the cover comes off, you'll jab a corner of the cover into the main terminal lugs and make a connection between the terminal lugs, the cover, and the ground of the box. As I understand it, this kind of intermittent connection has enough resistance that there will be a huge electrical arc flash and an explosion - oh and it may also electrocute the person doing this if they don't have protective gloves on.

2. Even though it's now mandatory for new breakers to cost about $50 more each, a single 200 amp disconnect switch is not part of the breaker box. If I were designing one, I'd require a disconnect switch, and make it mechanically impossible to even take a breaker cover off without putting the disconnect into the "off" position. (you could turn it back on after you remove the cover if you need to test circuits with a multimeter)
 

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Except for Canadian panels, I have not seen a residential panel with any protection over the main lugs. As far as the cover, it seems you were not careful. It would take a lot to tip the cover into the panel by accident.

Many consider Square D to be the Cadillac of panels.
 

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So I'm not an electrician. But I have a rough idea of the things that can go wrong and what will happen when they do. In the case of the QO, it's got 2 nasty faults :

1. There is no secondary cover over the main terminal lugs and the main breaker panel. This means that even if you turn off the main breaker, the box is not completely safe to work on - you have to always be watching where your tools go, where any wires you pull go, etc, because you might touch a bare ground wire you just trimmed to the main terminal lug while you are trying to adjust things, etc.

Even worse, there's an immense danger if my hunch is correct. Every time you unscrew the 3 screws keeping the cover on, if you aren't careful as the cover comes off, you'll jab a corner of the cover into the main terminal lugs and make a connection between the terminal lugs, the cover, and the ground of the box. As I understand it, this kind of intermittent connection has enough resistance that there will be a huge electrical arc flash and an explosion - oh and it may also electrocute the person doing this if they don't have protective gloves on.

2. Even though it's now mandatory for new breakers to cost about $50 more each, a single 200 amp disconnect switch is not part of the breaker box. If I were designing one, I'd require a disconnect switch, and make it mechanically impossible to even take a breaker cover off without putting the disconnect into the "off" position. (you could turn it back on after you remove the cover if you need to test circuits with a multimeter)
Are you in Canada or the US? I can't recall ever seeing a US panel with a cover over the main lugs.
 

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You are right, you are not an electrician.....

I have the same panel.....I'm not an electrician...but I am an engineer...and I've done a panel swap on my house...twice...1st time with a Murray and the second time with the SD panel.

1. If you look closely, you will see the Allen screws for main lugs....and those Allen screws are in a TB that has raised sides. There is NO way the cover is going to touch those main lugs while you are taking it on or off. If so, there is no way the panel would have gotten the UL stamp.

2.
Even though it's now mandatory for new breakers to cost about $50 more each, a single 200 amp disconnect switch is not part of the breaker box. If I were designing one, I'd require a disconnect switch, and make it mechanically impossible to even take a breaker cover off without putting the disconnect into the "off" position. (you could turn it back on after you remove the cover if you need to test circuits with a multimeter)
Not sure where you are getting the 'mandatory' part from. And I'm not sure where you think the panel needs a 'disconnect'. Much less why power needs to be turned off when you remove the cover. (see #1 above)

I personally think it would be a real PIA to have to remove power to remove the cover and then turn power back on. Pretty much the same way I hate control panels that have that safety interlock that kills all power when you open the door. The same interlock that usually gets bypassed from the start of a project. If the person opening the door does not understand there are dangerous voltages behind the door, they should not open the door.
 

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Discussion Starter · #10 · (Edited)
Well, to be fair, I didn't short to the main lugs and I didn't find out if it's actually possible to stab them with the cover. I know they are recessed. I am an engineer as well, and I say it's a bad design * - there is an inherent danger here that no amount of skill and experience can make zero. Canada has it right. (I'm referring to the possibility of someone having a muscle spasm while working and stabbing or touching the exposed lug, or accidentally touching a piece of bare ground wire to them while trying to pull the ground to the terminal block a few inches below, etc)

Sure, an experience electrician is unlikely to make a mistake. Even an amateur who knows the danger is unlikely to make a mistake. But the possibility is still there. It's the same reason OSHA requires climbing harnesses even for experienced antenna tower climbers who are unlikely to screw up and fall.

* The part I'm deferring to the electricians on is that I don't actually know what usually happens if you short to a lug. I know it's dangerous, and I know it's poor design - in other industries this would not be permitted, no matter the fact that experienced and trained personnel "should" never make this mistake - but I've never seen it happen. Maybe it's not really that bad. After all, even though the main lugs can provide hundreds of amps of current (basically the limit is the resistance on the mains wires themselves if it's a perfect short), most momentary contacts probably have a high resistance in the circuit. Maybe most of the time there's just a brief flash and nothing else. One electrician I talked to said that getting mildly shocked happened frequently and was no big deal...
 

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Well, to be fair, I didn't short to the main lugs and I didn't find out if it's actually possible to stab them with the cover. I know they are recessed. I am an engineer as well, and I say it's a bad design * - there is an inherent danger here that no amount of skill and experience can make zero. Canada has it right. (I'm referring to the possibility of someone having a muscle spasm while working and stabbing or touching the exposed lug, or accidentally touching a piece of bare ground wire to them while trying to pull the ground to the terminal block a few inches below, etc)

Sure, an experience electrician is unlikely to make a mistake. Even an amateur who knows the danger is unlikely to make a mistake. But the possibility is still there. It's the same reason OSHA requires climbing harnesses even for experienced antenna tower climbers who are unlikely to screw up and fall.

* The part I'm deferring to the electricians on is that I don't actually know what usually happens if you short to a lug. I know it's dangerous, and I know it's poor design - in other industries this would not be permitted, no matter the fact that experienced and trained personnel "should" never make this mistake - but I've never seen it happen. Maybe it's not really that bad. After all, even though the main lugs can provide hundreds of amps of current (basically the limit is the resistance on the mains wires themselves if it's a perfect short), most momentary contacts probably have a high resistance in the circuit. Maybe most of the time there's just a brief flash and nothing else. One electrician I talked to said that getting mildly shocked happened frequently and was no big deal...


Well Mr Engineer, I hope you have never gotten into a pool or hot tub, because the inherit risk of either of those no matter how well designed and installed is not 0.

Oh, and the available amperage at the main lugs during a fault is typically thousands or tens of thousands of amps, it's called available fault current.

One downside to putting terminal covers on is you cannot get a reading with a thermal imager if you do so. Just a thought.


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It's the same reason OSHA requires climbing harnesses even for experienced antenna tower climbers who are unlikely to screw up and fall.
If you are going to quote OSHA at us, why didn't you chose something more applicable to the subject at hand ? Like the PPE, clothing, tool restrictions you should have been using when you entered a panel with live parts.

I disagree that the "Canadian style" covers make things safer. If you have to open/remove a cover to access a live part it often brings you into closer proximity of the hazard, than if you can directly access that part (e.g. to take a voltage reading).

Maintaining a safe working distances from exposed energized parts, is part of the training of electrical workers. Accessing where the contact hazards are, and the quantifying the risk of the individual hazards is something you do for each panel that you open.

Perhaps removing the dead front on the panel is another task best left to people with training or experience at it.
 

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The Canadian approach is probably safer because of the propensity of untrained homeowners to open the panel cover. Oso's concern is important and should be reflected in the panel design, but ultimately the Canadian approach is going to result in many fewer unskilled people working in a box that has live power in it.

Of course we can say you shouldn't work in the box if you don't understand the issue, lack an awareness of safety, etc..., and that's all true; but ultimately people are going to do it anyway. And we can either protect them or not.
 
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