Electric Panel Problem: Conductive Dust Deionization?

Two things come to mind

1) Buy dust proof or NEMA 4 panels. These are usually a completely welded consrtuction with Gasketed doors and covers.

2) the refineries some time have panels that have a positive pressure inside. This prevents any dust or explosive gases from getting inside the panels

2) the refineries some time have panels that have a positive pressure inside. This prevents any dust or explosive gases from getting inside the panels

Good point. This method is recognised as an acceptable form of explosion prevention provided the power to the panel is isolated from elsewhere while a purging and pressurising operation takes place using air obtained from outside the hazardous area. BS5345 recognises the method of protection as 'Ex p' and the European community has standardised it as 'EEx p' (Google for more). Lose the internal overpressure and the panel should de-energise until after the purge-pressurise sequence takes place, which makes working on the contents of the panel while live rather awkward.

The original post doesn't specify that the panels are in a hazardous area, though by the problems that are being experienced, the hazards would appear to be caused by something other than a potentially explosive atmosphere!

dda gave two good solutions.

Get a good panel that is sealed so that the atmosphere outside will not get inside. The problem with some panel installers is that they defeat the NEMA 4 rating by punching holes for the cable entries and not sealing the holes properly.

Injecting air (compressed air) into the panel will also work since the positive pressure will prevent outside air from getting in.

There are a number of issues to be delt with in this question.

#1. ALWAYS wear properly rated Arc Flash PPE when working on LIVE equipment!!!

NFPA 70e will help you choose the right equipment.

#2. Are the breakers all properly sized to the load? Sometimes with old breakers, the thermal unit in the breaker will no longer TRIP the breaker effectively turning the breaker into nothing but a switch and giving plant personnel a false sense of security.

#3. Has a study been done in the plant to classify your particular environment? The National Electric Code (NEC) section 500 discusses Hazardous Areas and requires equipment to be rated for the environment.

As you work through this problem, the short term solution would be as suggested earlier, to provide a positive air pressure with filtered air on the panel.

BE SAFE and WELL

In North America, we call that a Hazardous Location, probably Class 2, Division 1 in your case. As others have said, you need to make sure the dust does not settle on the circuit breakers. There are many ways to accomplish this.

Agreed on the necessity to put positive pressure into the breaker box or have a completely sealed unit at the least. That means special strain reliefs on the box perimeter as well.

The othe issue might be that the breakers have fatigued with age and use / abuse. You need to do a load analysis of each circuit (the motors will draw more as they age as well) and decide if the conduit can handle the extra load. If it can a bigger breaker might be one solution. If it can't new breakers might minimize the problem.

But the first thing is to get the dust out of the breaker box.

You might want to consider what the dust is doing to your lungs too.

My $0.02...

MOVE THE PANEL!

If the dust is conductive why would you expose a worker to it to repair the panel. MOVE IT!

On top of the dusty condition, you may have the problem with the available magnitude of short current in the plant and the rating of your panel and breakers.

1. Get the study the available short current value

eg. If this transformer taped from MCC which is supplied from 1MVA transformer typical transformer impedance is 5.5% and Z of cable is negligible then

ISC=(1,000,000/(1.73x600)) x 100/5.5 = 17,500Amp

if your equipment is rated for 14kA then it does not properly isolate the fault, it ignites.

2. If the equipment rating is okay get assessement on your hazardous area classification properly done, and specify your requirement based on this classification.

3. If your company ignoring this problem you can talk to your local safety authority to contact your employer.

Can someone point him in the right direction how to properly classify the environment. In North America, possible your insurance company ( Factory Mutual, Hartford Boiler Etc) can help.

Until you understand the risk in this conductive dusty environment these panels are in, you should stay out. Could this dust possibly ignite the entire building?

I sounds like this forum went in a direction away from your original inquiry. To the best of my knowledge this industry does not address this situation by treating the air chemically.

There may be a recognized standard for a number of air exchanges per minute to get the conductive dust out of the room. If you know what this dust is, there may be a acceptable Parts per million level that you can address.

Get the panel out of this environment, and think twice about entering it yourself.

Thats my two cents worth. Hopefully someone else in this forum is an expert in this area and can help you out

If the dust is metallic, it means that somewhere the processes in the rest of the area have a problem, either with generating the dust or in containing it. Somewhere, there is value leaking out of the plant! If the dust is conductive, then there is likely to be a metallic nature to it, and there will be a maximum occupational exposure limit for it, and which side of the limit the area is on is the principal concern. So, the first step is to get the dust under control, so that personnel can enter the area safely.

"C.A.T.N.I.P." - cheapest available technology not involving prosecution.

Rather than de-ionising the air, even if it were possible, find a way to contain the dust and thereby eliminate it from the switchroom.