Panel Laws

[MikeW]

Mark,

Refer to James' post #10, what's going to contain the plasma when there is a arc flash event? Do you play Russian Roulette? If you are allowed to blow unfiltered air into an open cabinet at your plant, I never want to go inside that plant, life's too precious to take unnecessary risks. Whomever makes that decision to do this needs to be the one standing about two feet away from the open door and warn others to stand back at least eight feet.

 

[FLAengineer]

My thoughts (late Friday so very brief):
1. unfiltered air as previously stated.
2. summer/winter variations in cooling from the office HVAC (as stated)
3. NEMA rating of cabinet voided (if not already by the exisiting A/Cs)
4. Possibility of smoke/ozone migration back up the duct if something in the panel gets hot/burns.
5. I would think a better temporary solution would be some type of rental A/C unit, like trailer mounted if need be. Many sizes available in my location, we kept our VFD room cool with a trailer mounted unit for over a month while the A/C units were being replaced. This was for 1760hp VFD, 2-4 running at all times...
Good luck!

 

[The Plc Kid]

3. NEMA rating of cabinet voided (if not already by the exisiting A/Cs)

For that matter it would be voided when you install an HMI, Pushbutton, Vent, Alarm buzzer or anything else.

 

[iant]

Has this panels A/C ever worked?
Is it possible that the panel internal air flow is fighting itself
I would suggest that the two unit mounting positions might be the cause of this problem.

I do need to ask about this ARC flash

We have entered the age of electronics haven't we?
The old panels of 30 plus years ago when it was getting hot the idea of putting an external fan to cool the thermal overloads was common place.
I might be wrong . But this is the second post I have seen where arc flash is a concern
I understand this is related to a full three phase short fault. As much as it might be a problem. How big is the risk?
Maybe I am being complacent. I have seen a 2000 amp aluminium bus melt and blow a 100 amp 22KV fuse
But this is one fault in 37 years

 

[geniusintraining]

I do need to ask about this ARC flash

Its an fear that if you open a panel door and not wearing a full hood, gloves and boots the electricity will jump out and kill you.... oh wait I am wrong, its just another way for someone to make tons of money for no reason and sell your company a bunch of **** that no one will even wear.

95% of the arc flash happens because some one has no business being in the panel in the first place and they are doing something that I have no idea of the out come. When you buck phases or make your own shunt there is only one out come and its not good

When we talk about un-filtered air I have been doing industrial maintenance troubleshooting for almost 30 years, I have seen a ton of cabinets and built a couple hundred... the only clean panel I have seen was the one being installed, the lack of maintenance is out of this world, I have been in a few class 10,000 clean rooms and if you open the electrical door you will see a mess, so I have no doubt that arc flash happens but its NOT magic...

 

[iant]

thanks for that - just what I thought
I have a High Voltage ticket - now days it is limited to site and site apporval. Initially I was taught to 220,000 V
the latest renewal of the ticket showed the mat and gloves for LV.

Now talking LV Only
Personally I teach apprentices and electricians, that if they open a panel door, to treat the area inside as live.
I even explain that to point in the area use the handle end of a screwdriver or something non conducting.

Arc flashes have been documented where tools have come in contact with live terminals, As you stated, WTF. it is an accident that normally comes with complacency. not all these end up with good results.

but LV can jump 100 feet cant it

 

[Mark Buskell]

While it might not be the best ideal to blow unfiltered air in a cabinet, one does what needs to be done to keep production going especially when this happens in the middle of the night on a weekend. The entire area was roped off and only qualified personal where allowed near the cabinet. The door was also only partially opened. The enclosure also sits behind the machine so its not even a high traffic area. A new upgraded unit was ordered and installed as fast as possible.
While arc flash is always a possibility, all rules where followed and I agree with the viewpoint of geniusintraining.

 

[mmnoelte]

Do they now about AC units designed for control cabinets . I just installed one on the CNC for my company's plasma cutter.

 

[iant]

Do they now about AC units designed for control cabinets . I just installed one on the CNC for my company's plasma cutter.

what is the problem?

 

[icky812]

My question in all of this is; "How will the office air circulate through that cabinet?"

You can't just push air in with no where for it to go. Cooling doesn't work that way.

If you just push the office air out into the plant, where is the make up air coming from for the office?

Now add in if you have any open ignition sources into the office such as a water heater or gas heat. Where is the firing air for these devices coming from? I certainly hope that none of the gas fired devices have holes in the exhaust piping what with the vacuum that will be pulled by the external venting to the enclosure.

 

[iant]

i think that they would know that an AC needs a return air duct.
not really my concern

 

[geniusintraining]

You can't just push air in with no where for it to go. Cooling doesn't work that way.

Sure it does, most units that we are talking about will have a fresh air make up, they normally run 10-20% if the trunk line is about 48" and you take 6" off then you are never going to see it gone, so as far as the AC being affected for the office they will never know, also these industrial units do not cycle on and off, the evaporator fan runs 24-7

The cabinet I did it on had a vent on the other end, so blowing air out was normal, these also had a chiller and a coil heat ex-changer so by running the 60ish deg air into that and not just the ambient air of 100deg+ it was enough to help

 

[allscott]

Sure it does, most units that we are talking about will have a fresh air make up, they normally run 10-20% if the trunk line is about 48" and you take 6" off then you are never going to see it gone, so as far as the AC being affected for the office they will never know, also these industrial units do not cycle on and off, the evaporator fan runs 24-7

The cabinet I did it on had a vent on the other end, so blowing air out was normal, these also had a chiller and a coil heat ex-changer so by running the 60ish deg air into that and not just the ambient air of 100deg+ it was enough to help

I think what he was trying to say is that if you just push air into the panel with no way for it to escape all you will do is pressure up the panel and no cooling will actually occur.

 

[iant]

he was also talking about 'Office Air'
you could simlpy exhaust direct from cabinet but - if the air goes to heating there could b a problem.
For that reason you would require to have a return air duct to keep the system closed