Class 1, Div 2 inside genset

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mhulbert

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I was thinking about a typical natural gas generator with a weatherproof enclosure , and it seems to me that the inside of this enclosure would be a classified location. I'm thinking Class 1, Div 2, but I am not sure what GROUP natural gas is under. I guess my questions for those that know classified locations are:
1- What group would natural gas be?
2- Is the inside of a generator classified at all?
3- If it was div 2, how owuld you wire it. I am thinking a seal where you have RGC exiting the slab, going to sealtite (501.4 (B)(2)),and if the sealtie is less than 18", into the gensets panel. If more than 18", another seal at the gensets panel, and nipple into the panel.

Does this sound right? If anybody could give me an answer on this, I'd appreciate it

Mike
 
Re: Class 1, Div 2 inside genset

If memory serves me right, it is Group D.

You need the area classified by an engineer but I don't believe it is required to be classified. It will be mounted outside and it has ventilation slots, I don't see a problem.

With all that said, I am not an expert or an engineer. Someone else will have to give you a definitive answer. :D
 
Re: Class 1, Div 2 inside genset

When you have some item of equipment like this where the equipment itself is as or more likely to be the ignition source than standard electrical equipment, I see no reason to classify the area. Do we classify the area around boilers that use natural gas?
Don
 
Re: Class 1, Div 2 inside genset

Charlie's answers are fundamentally correct.
"Natural Gas" is simply methane. I would add that, if the location were classified, you would also need to add a "T-rating" of "T1."

I usually add that proper classification documentation is mandated by 500.4(A).

Having said this, I'd like to caution you that there are many considerations to "proper documentation." Primary are determining the method of delivery of the fuel gas; especially in this case, the pressure and flow rates.

In general, well maintained, closed-piping systems do not require any electrical area classification at all, whether indoor or outdoor, enclosed or open. However, other considerations such as pressure relief systems, methods of valving, flange construction, etc., may affect the determination.

As Don pointed out, alternate "continous ignition sources" may also affect the determination, but with methane's AIT of 680C, electrical ignition sources would be the most likely.

I suspect that a person, experienced in electrical area classification would not find classifying the installation you described necessary.

If, after proper review, electrical area classification was determined to indeed be necessary, only the seal at grade would be required. No additional seal is needed at the generator terminal box. Depending on the control panel construction other seals may be necessary. Finally where "sealtite" is used be careful to observe 501.16(B) whether other seals are used or not.
 
Re: Class 1, Div 2 inside genset

Thank you for the reply. All generator installations I have seen seem to be non-classified, but it seems that if there was a leak in the supply piping or shutoff valve, and the genset started cranking over, there would be problems, especially if it is in an enclosure. However, as Don said, we don't classify the area around a gas furnace or oven, and the genset itself is not listed for a Class I location. I noticed 500.5 (B) (2) FPN No. 2 mentions that "Piping without valves, checks, meters, & similiar would not ordinarily introduce a hazardous condition though used with flammable gasses"

I think a lot of this is left up to the AHJ, probably a fire marshall or similiar person, or a person having experience with this.

Mike
 
Re: Class 1, Div 2 inside genset

Actually, the AHJ would not have the knowledge to classify an area. They should be asking for something from an engineer to show how an area is to be classified. After they know the classification of an area, then they will know the type of wiring methods that should be used. :D
 
Re: Class 1, Div 2 inside genset

In all the gensets I have wired I have never seen one that was classifide. Most have vent grills in each panel covering the genset and with the force air cooled engines I wouldn't think the vapors could build enough to cause combustion. The control panels that are installed by the manufactures in these generators also are not sealed in any way, Thus the problem with field mice getting into them and chewing up the wireing. :eek:
 
Re: Class 1, Div 2 inside genset

As a general statement, most Combustion Turbine Generator (CTG) systems are NOT classified. The primary standard is NFPA 37," Installation and Use of Stationary Combustion Engines." Another generally relevant standard is NFPA 54, the Fuel Gas Code.

On my current project, the CTGs and their immediate auxiliaries are not classified, but the gas metering skid is. The CTGs are fed at 400psi from an onsite compression system that receives it's fuel gas from a line tap off a major natural gas transmission line.

The designer/supplier of the metering/compression system classified parts of the area. The problem is the mechanical seals used for the compressor - not the general piping. The mechanical seals are not necessarily prone to failure, but it is a prudent consideration. I have concurred with the designer.

The problem with 500.5(B)(2) FPN 2 is that some folks think it implies "piping with valves, checks, meters, and similar devices..." IS classified - that is not necessarily the case. It is simply one of the considerations. Just as you "... don't classify the area around a gas furnace or oven," you are not generally required to classify the area around a residential meter either, although some utilities may require specific separations.

As a PE who is an "...individual responsible for approving equipment, materials, an installation, or a procedure," I am also an AHJ - even when it is my design.

[ December 30, 2004, 10:45 AM: Message edited by: rbalex ]
 
Re: Class 1, Div 2 inside genset

Bob,
Given that the vapor density of natural gas is about 0.75, does the classified area extend to the ceiling?
Don
 
Re: Class 1, Div 2 inside genset

Originally posted by don_resqcapt19:
Bob,
Given that the vapor density of natural gas is about 0.75, does the classified area extend to the ceiling?
Don
Click to expand...
Yes, depending on ventilation.

A "lighter-than-air" gas, in a well ventilated area dissipates very quickly, but in a poorly ventilated, enclosed area it will tend to fill the entire volume. The "typical" classified area in a well ventilated area from a 500psi or less point source is Division 2, 15' below or to grade, 15' horizontal and 25' above the source.

At very high pressures (500psi+) methane and hydrogen are often self-igniting from air-friction in minor leaks, but it is still prudent to classify the area as above.

Hydrogen seems to have either nuisance leaks or a major ruptures; there is almost no middle ground. API 500 and NFPA 497 both recognize you can't do much with the electrical installation to deal with a catastrophic failure, so you still wouldn't be required to do much beyond the "typical" classified area.

Methane, having a density close enough to air, has other issues. It will dissipate very quickly at air flows of 3mph or greater, below that it tends to "cloud" around the leak. This is very rare outdoors but in those cases the Division 2 location could extend reasonably beyond the 15' horizontal, but beyond 25' is unlikely.
 
Re: Class 1, Div 2 inside genset

Bob, that was a very interesting dissertation. I wonder about the future where we will be using hydrogen for powering vehicles and even fuel cells for the home. How safe will it be to store hydrogen at home or in a vehicle? :D
 
Re: Class 1, Div 2 inside genset

Other than wanting to know a bit more about the fuel delivery system, I probably wouldn't be any more concerned than I am about my furnace.

For autos I'd like to know a LOT more about the fuel transfer scheme; but once "fueled," I doubt I'd worry too much.
 
Re: Class 1, Div 2 inside genset

Originally posted by rbalex:
I got carried away :D
Click to expand...
They are pretty cool. :D I was involved in the installation of one. My job was the the wiring running to pumps on a skid outdoors that boosted the gas pressure.
 
Re: Class 1, Div 2 inside genset

If UBC applies, look at the table in chapter 3 which lists the exempt amounts. I had to check an indoor diesel this week. 120 gallons was exempt and there was a column for natural gas.
 
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