visible disconnect blades

[don_resqcapt19]

I just connected temorary power to a water filter unit that was made in Canada. All of the disconnects have a window so that you can verify the position of the blades. If you lock out a disconnect of this type and look in the window and see that all of the blades are visible and not connected to the power source, can you omit the voltage check that you are normally required to do before you work on the equipment? If not, what is the purpose of the window?
Don

 

[celtic]

In spite of a visual aid, one should always check for potential when working on electrical equipment.

 

[ron]

I would get an extra level of comfort if I could visably see they were open. Voltage check is still required.

NFPA 70E
ARTICLE 120 Establishing an Electrically Safe Work Condition

120.1 Process of Achieving an Electrically Safe Work Condition.

An electrically safe work condition shall be achieved when performed in accordance with the procedures of 120.2 and verified by the following process:

(1) Determine all possible sources of electrical supply to the specific equipment. Check applicable up-to-date drawings, diagrams, and identification tags.

(2) After properly interrupting the load current, open the disconnecting device(s) for each source.

(3) Wherever possible, visually verify that all blades of the disconnecting devices are fully open or that drawout-type circuit breakers are withdrawn to the fully disconnected position.

(4) Apply lockout/tagout devices in accordance with a documented and established policy.

(5) Use an adequately rated voltage detector to test each phase conductor or circuit part to verify they are deenergized. Test each phase conductor or circuit part both phase-to-phase and phase-to-ground. Before and after each test, determine that the voltage detector is operating satisfactorily.

(6) Where the possibility of induced voltages or stored electrical energy exists, ground the phase conductors or circuit parts before touching them. Where it could be reasonably anticipated that the conductors or circuit parts being deenergized could contact other exposed energized conductors or circuit parts, apply ground connecting devices rated for the available fault duty.

 

[don_resqcapt19]

If you can't use this as the required check, then why go to the extra expense to provide the window? How is the window an advantage? If you unplug a cord from the receptacle, do you still have to do a voltage check before working on the equipment?
Don

 

[Pierre C Belarge]

Is the window there as a visual aid? or is it there as "finger" protection as required in certain enclosures.

Eyes are a great source for troubleshooting and other things in our industry, but you may not be able to see some debris behind the blade that could conduct to the contacts, and verification by testing would detect that.

 

[don_resqcapt19]

Pierre,
It is a Sqaure D disconnect with a window to see the blades. You can see the complete blade so there is no way that there could be debris that would complete the circuit. The following is from the Canadian Square D Digest.

Viewing Windows
Cover viewing windows are positioned over the blades to allow visual verification of “ON-OFF’’ status. Viewing windows are not available on
Type 7/9, 4X Fiberglass-reinforced Polyester Enclosures. Consult the table below for availability on standard Heavy Duty Safety Switches.
To order optional viewing windows, factory installed and CSA Certified, add “VW’’ suffix to standard catalogue number.

Don

 

[Pierre C Belarge]

Okay Don I see that now. The only situation left is the OSHA and NFPA 70 requirements that say testing is required. Maybe one day with the advent of these types of disconnects with visual windows that requirement may be modified.

 

[peter]

A knife switch has energized blades. Thinking along this idea, I connected a 100 Anp Square D disconnect backwards. Thus the line feed was always connected to the bottom side fuse holders. We will correct this when we get the parts and if the night crew hasn't walked off with our spare cable.
Note that SquareD does not bother to mark "LINE" and "LOAD" on this device.
In answer to your question, Don, it is good to check both ends of the fuse holders for power before touching any metal therein.
~Peter

 

[don_resqcapt19]

Peter,
I am talking about the use of the "windowed" safety switch at some type of equipment where there is no question of a back feed or other source of power. For example an AC unit with one of these disconnects at it. Even if the safety switch was wired backwards, the visible open blades would insure that there is no power to the equipment. I don't see this any different from not checking for power on cord and plug connected equipment after you remove the plug from the receptacle. Do you check for power before working on unplugged equipment?
Don

 

[ron]

Seems that if the switch is open, you have a good sense that the load is de-energized, but you don't know whether the disconnect load side is de-energized, as it may be wired backward.

 

[iwire]

If you unplug a cord from the receptacle, do you still have to do a voltage check before working on the equipment?
Don

Do we, or are we required to?

Don, given OSHA and 70E IMO we are we required to check for voltage even once we unplug equipment or can see the blades.

 

[petersonra]

If you can't use this as the required check, then why go to the extra expense to provide the window? How is the window an advantage? If you unplug a cord from the receptacle, do you still have to do a voltage check before working on the equipment?
Don

I would say yes. There is always some potential of another power source you are not aware of.

 

[hillbilly]

I guess that it's old habit but...I always check everything before I touch it, plugged in or no.

 

[George Stolz]

Seems that if the switch is open, you have a good sense that the load is de-energized, but you don't know whether the disconnect load side is de-energized, as it may be wired backward.

I agree with Ron, there is always a chance that the switch may be miswired.

 

[don_resqcapt19]

Ron,

Seems t hat if the switch is open, you have a good sense that the load is de-energized, but you don't know whether the disconnect load side is de-energized, as it may be wired backward.

I'm am not talking about working on or in the disconnect, but about working on the equipment served by the disconnect. When safety rules are such that they far exceed common sense, then they are more likely to be ignored.
Don

 

[realolman]

Ron,

When safety rules are such that they far exceed common sense, then they are more likely to be ignored.
Don

A-men to that! ...and rightfully so.

But now because I like arguing so much I'm going to argue with myself.

Maybe it's not always so apparent.

I can't think of any AC equipment to which it would apply, but there were some wicked capacitors in fork trucks that needed to be discharged.

 

[hillbilly]

I don't go overboard about checking for potential, but if there's even a chance that the equipment (even if un-plugged) has a capacitor, I check before I touch. It's all in the learning process. If you live long enough, you'll probably learn what to touch and when not to touch it.
I don't like gettin "bit" by bugs, snakes, dogs, cats, all critters, or most humans. Especially snakes or electricity.
steve

 

[charlie b]

I cannot answer your real question here, which I take to be "why the window." But a visual inspection of the blades cannot prove to you that the load side of this particular disconnect really is connected to the load that is called out on the plans or on the nameplate. Perhaps this disconnect really serves that other pump across the room. This is the kind of "what if" situation that makes it important to always check for voltage before you touch something.

 

[dlhoule]

Don, for what it is worth, I like the windowed disconnects. I still think it is a good idea to check for voltage before proceding to work on anything. It would seem to me you could have a carbon track formed on the back side of the insulators that wouldn't be visible through the window. Better to take a little extra precaution than be knocked on your a** or worse.

 

[don_resqcapt19]

Charlie,
These safety switches were at the equipment and the only electrical connection to the equipment was a length of flex from the safety switch to the equipment. If you look close in the window, you could see the wires landed on the load side of the switch going into the flex that was connected to the equipment.
Yes, the real question is why the window. It doesn't have any purpose if it can't be used to say the equipment is safe to work on.
Don