Control panels

Have a question.
On a production type piece of equipment is there some type of rule or electrical code that requires that the door to the main control panel has to somthing that can only be opened with the use of tool. This tool can be screw driver, etc.., just not able to be opened by a operator or non technical person by hand.
Thanks

A lot depends on the voltages inside (though "Main Control Panel" suggests 480VAC), but what you're talking about is a general requirement of NFPA 79 and UL508.

I use a lot of rotary disconnect handles, and there's a nice white paper from ABB that discusses both rotary and lever type disconnects and how those meet the locking and opening requirements of NFPA 79 and UL508.

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/14cf7fa9c1afbeb0852577730076f16d/$File/1SXU301080G0203.pdf

NFPA 79 6.2.3 Disconnect shall be interlocked with control enclosure door where voltages higher that 50VAC or 60VDC are present.

6.2.3.2. The door interlock can be defeated using a device or tool to allow access by qualified persons.

6.2.4 Enclosure access were there is no disconnect requires the use of a tool or key.

I have summarized those sections and not included the full text as its longer than I can take time to type out. You should invest in a copy of NFPA 79 Electrical Standard for Industrial Machinery. Its not expensive.

...electrical code that requires that the door to the main control panel has to somthing that can only be opened with the use of tool.

Click to expand...

Wrong focus! The goal is to prevent opening of an electrical device enclosure IF POWER IS NOT DISCONNECTED. There are disconnect and circuit breaker operator handles that have built-in bypass devices that allow opening the door with the power on (not recommended generally).

I once worked as a contractor in an electrical box during a plant modification. The main 480 volt disconnect switch was OFF and locked out, the plant foremen assured me that all power in this panel was OFF. So I check a few of the hundreds of terminals with my meter and read 0 volts. Here I go pulling wires and relabeleing and rerouting wires. I happen to touch the tip of my left hand across two screw terminals, then feel a tingle and smell burning flesh. Jerking my hand away, I then had two small brown scorched and burned places on the tip of my left index finger - the exact distance apart as those two screws.

That was over 40 years ago. Since then, those two white dead spots have moved from the tip of my finger up to about halfway between the tip and the first joint. About once a month, they grow out of the skin like a wart and I have to trim off the tops with nail clippers. Sitting here looking at them, I wonder how far they will move before I kick the bucket. I also wonder how many electrical panels are still out there without the required warning label: "THIS PANEL IS FED FROM MORE THAN ONE SOURCE".

Lancie1 said:

"THIS PANEL IS FED FROM MORE THAN ONE SOURCE".

Click to expand...

I work as an electrician most of the time when not doing small automation jobs. I often encounter cabinets without this labelling, and have been shocked literally many a time. I hate all the POS sparkies that do this! It takes no time at the very minimum to grab a marker and write "LIVE WHEN MAIN SWITCH OFF" on the duct work above the terminals or relays.
That said, isolator to door interlocks that cannot be bypassed are the biggest pain I ever come across. It causes all sorts of grief for some of my customers when trying to fix their limping process as it requires the isolation of the machine to open the door, then the subsequent restart, which if its a corrugator can take 15 minutes. Fix the problem, then another shutdown to close the panel. Then the restart. Then I have to shut them down again because I left my meter in the cabinet. I usually modify the isolator extension handle to remove the interlock so long as the cabinet still requires a tool to open, e.g the rittal panel key.
I notice Schneiders new range of NSX breakers have an interlock system that is hopeless at the best of times. It requires a very small alle key or similar diameter tool, and the plastic striking part doesn't last. I like the USA style AB steel panel handles the best. The ones with the big slotted screw driver interlock bypass.

HJTRBO said:

I like the USA style AB steel panel handles the best. The ones with the big slotted screw driver interlock bypass.

Click to expand...

What I like most about the flange mounted lever disconnects is that if you lock the disconnect out then it remains locked out even after you open the door. Most through the door disconnects are no longer locked out once the door is opened - once the rotary handle disengages from the shaft to let the door open the disconnect can be turned back on.

I'm not a fan of 'through-the-door' disconnects, but I do use them on smaller panels. I have yet to find one where the shaft and handle stay lined up after repeated use. The disconnect gets worn, and the shaft droops. I've seen a LOT of panels over the years with the shaft laying in the bottom of the panel...

Flange mounted disconnects are just so much better! I use the Square-D 9422 series.

Many places also destroy the keyed door latches because they lost the proper key. The triangle shaped locks are the hardest to get open without the proper key. I carry one of these in my pocket.



(Click picture for link)



-Eric

I still favor the disconnect switch mounted on the outside of the panel. If I need the power off then it is off and unless dual fed (or interlocks) I can do what I want in there. I also do not need to worry about hot line terminals on the disconnect if mounted in the panel.

Thru the door handles are a joke and waste of money. As already mentioned a royal pain to get lined up when worn.

Dan Bentler

I still favor the disconnect switch mounted on the outside of the panel

Click to expand...

I agree except for the aesthetics

the best is the new cable fed disconnects. no worries about a shaft lining up

I have been using disconnects that mount on the side of the panel. The reason is once the disconnect is off everything in the panel is off and you don't need flash protection. We normally put master locks on the doors to keep out anyone else. As far as non electrical personal opening the door. That will get them wrote up or fired and that no longer is a problem. Areas around the panel are also taped off when working on a panel and lock outs are used on the disconnects.

The reason is once the disconnect is off everything in the panel is off and you don't need flash protection.

Click to expand...

Everything is off - unless someone at some time runs in a couple of hot wires from another panel for a relay or something.

Lancie1 said:

Everything is off - unless someone at some time runs in a couple of hot wires from another panel for a relay or something.

Click to expand...

It would be nice if someone made a main disconnect that had a few aux poles for this. That way when you break the disconnect the cabinet is deasd even if it's being fed from another cabinet.

This is another reason I try to tie disimilar systems together with comms where possible and avoid hardwiring.

Going back to the original question, it very much depends what voltages are inside and are you able to touch any live parts?
ie are the terminals to IP2X (Cannot touch with your finger, in the UK).

I like door interlocked isolators!The trick is not to have a long shaft. Oooh err Missus!

It would be nice if someone made a main disconnect that had a few aux poles for this.

Click to expand...

I have seen disconnect switches with extra or auxiliary contact add-ons, but I don't remember the brand or model.