NEMA 4X Box Upgrade to Meet Hazardous Area Qualification

Sure, put the 4X enclosure inside a type 7 enclosure.

Sounds like a "change of scope".

This should have been caught at a preliminary review.

Make it safe!

That's a good idea, but wouldn't it void the NEMA rating since we will be tempering with the boxes. They are installed on a wall.

Installation has been accepted, but it hasn't been commissioned yet.

Can't do what you said, NRC is watching us.

Can't do what you said, NRC is watching us.

What's NRC stand for?

Nuclear Regulatory Commission - Wikipedia, the free encyclopedia

bestofalis, please tell me you are NOT in Arizona.

Good luck.

Please confirm the installation is no closer than 1500 miles from Dodman's Lane Level Crossing....

They are your next door neighbors, better pack up.

Then don't ever do it. Do exactly what is required by code. Do not short circuit the code.

If you fear the NRC now wait until one of their inspectors spot the non-compliant installation. BOHICA MAXIMUS

Seriously, if you do not correct the installation; you and everyone associated with it will be in extreme danger as well as serious personal jeopardy of heavy fines and/or incarceration if anything should ever happen now or at any time in the future. (No expiration date or time limit for negligence.)

There is also severe personal risk of litigation and monetary loss associated with this error in judgement that also has no time limit.

Shut it down and replace it.

A US installation, NEC500 Class I Division I? Not what I am certified for but I will take a crack at it.

What is the existing VFD panel certified to, because if it is NOT certified and only has a NEMA (weather) rating then it is not suitable for installation in a Division 1 application as you mention above and must be mounted in the safe area outside the zone.

Putting an industrial (non-Ex certified) piece of equipment in to a box with a higher NEMA rating won't work (although it may if you stick it into a flameproof box and get the whole thing certified, just don't expect to be able to buy a box and do it yourself as the certification does not allow this).

What does your inspector say?

There is nothing you can "cover" a NEMA 4 enclosure with to make it NEMA 7, it's like asking if there is some special paint I can put on my Chevy to make it a Cadilac.

The only possible way to ressurect the enclosed system as it is now might be to use a "purged air" system, but it requires that you have instrument grade clean compressed air at the box location. Here's an example:

http://www.isa.org/InTechTemplate.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=83590

What's wrong with re-routing the hydrogen dryer discharge somewhere else? After all, it would be easier.

I thought about this too but came to the conclusion that it would likely only drop the zone classification down to Class I division 2 (gas not likely to occur and for short periods only) rather than down to a safe area, which still wouldn't fix the problem given the industrial (uncertified) nature of the equipment.

In principle, how would one attend to the settings on the front panel of a VFD mounted inside inside a flameproof/NEMA7 enclosure without obtaining a Hot Work Permit and opening the enclosure <rhetorical question - NNTR>?

The mechanical guys will have a cow to move the H2 Dryer.

Oh well, too bad. Electrical wins this time.

Win/lose? How abstruse.

Ya sure can. Use a Bebco Class 1 Div 2 purge system. Sold many of these over the years and no one ever had any issues with them.

Yep, we are actually the contractor for utility company, and it is at a nuclear plant.

Purging system sounds like an idea.

Thanks for all your detailed responses and suggestion. I am going to present these ideas to the client and see which one is more feasible for them. Money is no issue in nuclear plants, although schedule is. So, they got their options, it will be the matter of what idea they like the most and go forward with.

Bestofalis,

Are you familiar with vortex cooling systems. They use plant air through a cleverly-designed device that splits the air into two streams as it is released through a nozzle. One is hot (exhausted) and the other cold (into the enclosure). You must have a suitably clean air supply at an SCFM capacity to run the cooler. They can be thermostatically controlled, however. I don't know how they would work in an enclosure that must be otherwise sealed and pressurized (to about 0.8 inches of water). The original patent holder was Vortec (if I recall correctly), but I recently saw them (probably by license) in a Hoffman catalog.

--JMM

Being long enough in oil & gas and technical HSE & risk, please do not mess with anything that may lead to dire consequences...

If the client messed up, inform him objectively that it is "not good / safe enough" and he needs to change. Note that the design ownership is on you. They would have set aside a budget for variation orders before the project started and changing the panel will not kill their careers or company.

If the client refused, issue a technical query with all the technical facts and implications, get his answer in black and white, to cover yourself (just in case)....

Question - using hydrogen to cool a generator? This is new to me...the hindenburg disaster would have put a restain to this design...

And if hydrogen is involved, please also get a panel that is suitable for use in the hydrogen environment...i.e. Gas Group B panels...

Good luck...

Thong,

Actually, Hydrogen is very commonly the cooling gas of choice for the generators and the power bus duct from them to the switchyard. Hydrogen molecules are the fastest and have the smallest size so they can penetrate into the windings better than anything else. A lot of care is taken to ensure that the gas remains pure, but there have been a couple times when sufficient contaminating air entered that there was an explosion. In big power plants, the problems to be overcome because of the use of hydrogen are fairly small compared with the overall complexity of the entire plant.

--JMM

Hello JMM, thanks for the education. I did not know about this. However, in offshore oil and gas facilities, (at least during my years) I have never come across this method for cooling the generators. I guess this would apply to only onshore power plants then?...

Sir: Yes, and very large ones typical of the central utility generating plants. When I worked shutdowns at the Arkansas Nuclear One, they were there (two 1500mW generators, if I recall correctly). --JMM

You can purge the enclosure. You can buy either an X-purge for Division 1 spaces, or Z-purge for Division 2 spaces. Although 5ft from a hydrogen source is most likely Division 1, so you're looking at an X-purge.
These are air purge kits that attach to the outside of the enclosure. You supply them with compressed air (hopefully available) and they purge the inside of the enclosure so that a NEMA 4X enclosure can be installed inside an electrically rated area. The incoming power to the enclosure gets routed through this purge system such that loss of purge pressure will automatically disconnect power to the enclosure. Bebco makes them as well as Pepperl+Fuchs. Or, you have to buy another enclosure, properly rated NEMA 7 as you said.