NFPA70 409.30, NFPA79 5.3 & UL 508a

[brinkmann27]

For a few customers we build control panels which are for groundwater remediation systems. They usually have an UL489 breaker or a disconnect, breakers for other equipment and control logic. We use a thru door disconnect for the main breaker.

Seeing this was too easy, a customer wanted a cable type disconnect with the handle on the enclosure not the door. This started me on the "door interlock" search on the forums. Of which I found many opinions as to whether they were need or not. If you look at NFPA 70, it bascially says go see UL508A. NFPA79 says you do with a few exeptions. From what I understand NFPA 70 and UL508A are rules, NFPA 79 is a suggestion.

UL508A says if it is a "General Use Industrial Control Panel" The is UL paragraph 30 (Disconnect Switches) doesn't require the interlock. But the handle must be able to be locked in the off position.

UL508A also has what it calls Part 2 - Specific Use Industrial Control Panels Types, starts at paragraph 62. This includes, Industrial Machinery, Crane Control, Service Equipment Use, etc.

Inside of Industrial Machinery, it lists Metalworking Machine Tools, Plastics Machinery, Wood Machinery, Assembly Machimes, etc. Equipment you would see at Coca Cola bottling plant or where plastic milk jugs are made.

UL at this point says the door interlock is required along with other panel changes. (internal wire size).

So, I try to determine what my panel is. I don't see it fitting into Industrial Machinery as we are not building or making anything. This, in my little mind, would put us into the "General Use" catagory. This logic would say the interlock is not required, the lock on the handle is.

Sorry for the long post......Any comments as to my logic?

Thanks

 

[dbaird]

Many of OSHA's safety standards are based on national consensus standards. A list of voluntary consensus standards developed by the American National Standard Institute and incorporated by reference in OSHA standards can be found in 29 CFR 1910.6.

NFPA 79 appears in several places including:

http://www.osha.gov/SLTC/etools/machineguarding/additional_references.html

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[JHanson717]

Although you may be able to find a way to justify exclusion, the incremental cost of keeping someone from opening the door with it energized would seem insignificant.
Also if there ever was an incident, OSHA inspectors often site the General Duty clause, basically covering anything they want.

Typically, in a foundry environ, I use flange mounted disconnects with door interlocks. The Hubbell enclosures I buy have the flange pre-punched, so the in-house fabrication time is reduced, offsetting the additional cost.

 

[jraef]

Going by memory of NFPA here, so forgive me my trespasses...

All main power disconnects need to be EITHER interlocked with the main enclosure door to prevent opening when energized, OR there needs to be some other established and monitored safety method employed that prevents unauthorized access altogether. That "other" method can be anything from a padlock hasp with restricted access to the key, or even just a sign making it essentially an offense warranting termination to open it etc. etc. The caveat on the "other" method is that it must be a facility with an engineering / safety staff that controls these sorts of things. So to that end, a "ground water mediation" control panel is not likely to fall into that category even with the loosest of interpretations. You need a door interlock.

What has changed in NFPA79 recently is that the handle operating mechanism must remain in control of the disconnect device at all times, even when the door is open. Older through-the-door rotary operators did NOT do that; when you opened the door, the handle stayed on the door and you had to have a tool to operate the disconnect. What happened was a series of electrocutions where someone re-energized the disconnect for testing and when they got shocked, nobody could kill power fast enough. So the new rule addresses that by at least making sure there is always a way to operate it without a tool. Flange mount disconnect switches inherently provide this feature. Newer rotary operating mechanisms for circuit breakers and disconnects are now being offered with this feature as well. It is essentially a 2nd handle, usually red, attached to the shaft that remains attached to the disconnect switch.

NFPA 70 has to do with Arc Flash, and how that relates is that some mfrs are now addressing the issue of isolating the line disconnect mechanism so that when the door is opened, the line terminations (which remain live even when the disconnect is open) are enclosed in a separate space, not shared with the remainder of the control panel. That way, it is felt that the Arc Flash calculations become relevant only for that enclosed space, freeing the user to applying a lower PPE label to the overall enclosure door.


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[brinkmann27]

The comments as to our logic is not an intent "get around anything."

We were trying to see how others in the control panel industry defined their control panels. Until you do this it's hard to know which standards must be met.

As per UL NITW guide info there is a "General Use Industrial Control Panel" and an "Industrial Control Panel for Industrial Machinery". They are totally different. The same as for a hazardous location panel would be.

Not mentioned but they also have one for marine, crane control, flame control, etc. They all invoke additional requirements. Machinery control does invoke NFPA 79. Base line for all pnaels would be the NEC Article 409

And yes the local authority has the most control over the rules. We were just trying to find a starting point.

Thanks again.