Conduit feeding gas fired heat panels inside oven

[SamCAT1234]

Recently I discovered that we have standard EMT using set screw couplings feeding 60 gas fired Infrared panels inside a cure oven for large parts. I know this is a mistake from a basic perspective but am trying to determine if this is considered class 1 div 1 or 2 location.

The Oven is fed by a 2 inch gas line branching off to feed the 60 small panels so the gas flow is significantly large. There is an exhaust fan system to evacuate fumes however not so much we cannot maintain temperatures of 330f.

My primary concern is with the conduits. The setscrew couplings come apart exposing the high temp wire to the edges of the conduit and coupling creating a wear hazard on the conductors. We plan to rewire the oven using rigid conduit. My secondary concern is if this does in fact meet Class 1 div1 or even 2 then we need seal offs and other techniques used to quarantine the explosion hazards of un burned gasses.

Please provide me with any feedback you may have regarding determining the classification rating of the ovens interior.

Thank you in advance

Sam

 

[don_resqcapt19]

I don't see any issues with the current installation. Properly installed set screw couplings do not come apart.

I would doubt that the area is classified, but if it is, you are correct that you would need threaded rigid conduit and seal fittings. Any equipment within the classified area would have to be suitable for the classification.

 

[petersonra]

Look at it this way. The reason that you classify an area electrically anyway is so that you know not to put a source of ignition in that area or if you do to find a way to prevent the transmission of flammable gases from the source of ignition out into the general area. An oven has an open flame. It would be pointless to try and make an oven that would be suitable for a classified area if it had an open flame it just couldn't be done because there would be an ignition source

 

[petersonra]

I don't see any issues with the current installation. Properly installed set screw couplings do not come apart.

I would doubt that the area is classified, but if it is, you are correct that you would need threaded rigid conduit and seal fittings. Any equipment within the classified area would have to be suitable for the classification.

I generally agree with most of this however I've seen a lot of EMT that has come apart. I don't know if it's poor technique or something that is just common with EMT. I have often suspected that long runs of EMT are may be susceptible to thermal or other stresses that cause it come apart more readily than with screwed together fittings.

 

[iwire]

I generally agree with most of this however I've seen a lot of EMT that has come apart. I don't know if it's poor technique or something that is just common with EMT. I have often suspected that long runs of EMT are may be susceptible to thermal or other stresses that cause it come apart more readily than with screwed together fittings.

:huh:

I don't believe that is the case at all.

IMO if EMT is coming apart it is because it was not installed with enough supports or it was used where it should be.

 

[ActionDave]

:huh:

I don't believe that is the case at all.

IMO if EMT is coming apart it is because it was not installed with enough supports or it was used where it should be.

I agree. We just did a remodel on a hotel that was wired with EMT in the 60s and it was just fine.

 

[SamCAT1234]

Thank you for the replies. It does appear that there is minimal support for the conduits which may not meet code. Some of them span an air gap of 20 feet unsupported. Also upon closer inspection the structure which supports the gas heater panels has a lot of side to side movement due it being supported only from the base with inadequate upper or side supports.

I see your point regarding classifying the area however there is an argument for the potential for unburned gasses or even a gas buildup which runs a risk of explosion.

We are going to move forward and treat it as a classified environment, replace the EMT, and better secure the new conduits.

 

[don_resqcapt19]

Thank you for the replies. It does appear that there is minimal support for the conduits which may not meet code. Some of them span an air gap of 20 feet unsupported. Also upon closer inspection the structure which supports the gas heater panels has a lot of side to side movement due it being supported only from the base with inadequate upper or side supports.

I see your point regarding classifying the area however there is an argument for the potential for unburned gasses or even a gas buildup which runs a risk of explosion.

We are going to move forward and treat it as a classified environment, replace the EMT, and better secure the new conduits.

So a possible failure of the conduit or other parts of the electrical system is a more likely ignition source than the burner flame?

What equipment does the conduit supply? Is all of this equipment suitable for use in a classified area?

 

[kwired]

Thank you for the replies. It does appear that there is minimal support for the conduits which may not meet code. Some of them span an air gap of 20 feet unsupported. Also upon closer inspection the structure which supports the gas heater panels has a lot of side to side movement due it being supported only from the base with inadequate upper or side supports.

I see your point regarding classifying the area however there is an argument for the potential for unburned gasses or even a gas buildup which runs a risk of explosion.

We are going to move forward and treat it as a classified environment, replace the EMT, and better secure the new conduits.

With any burner from large industrial boilers or process equipment down to your residential gas furnaces, there is risk of explosion fro gas buildup if the ignition controls are not arranged so that there is time for purging air before ignition occurs. There is usually air pressure sensing devices involved to prove that there is airflow for the purge.

 

[SamCAT1234]

So a possible failure of the conduit or other parts of the electrical system is a more likely ignition source than the burner flame?

What equipment does the conduit supply? Is all of this equipment suitable for use in a classified area?

Yes sir. The broken conduits present the possibility of a short circuit at 480VAC which will be quite the spark. They feed the Infrared panels electric pre-heater elements which eventually ignites the gas once applied.

Realizing that this is not your normal situation had the conduits been the proper type and properly installed it may be almost zero risk. We do wish to eliminate any further risk of this kind, and add another layer of security.

There are redundant safety measures in place that are components of the controls systems. Its the wiring installation that is most troubling.

 

[SamCAT1234]

With any burner from large industrial boilers or process equipment down to your residential gas furnaces, there is risk of explosion fro gas buildup if the ignition controls are not arranged so that there is time for purging air before ignition occurs. There is usually air pressure sensing devices involved to prove that there is airflow for the purge.

The part of the system that meets this criteria is the exhaust fan. It does have a differential pressure sensor to prove it is creating a draw from the oven.

 

[don_resqcapt19]

Yes sir. The broken conduits present the possibility of a short circuit at 480VAC which will be quite the spark. They feed the Infrared panels electric pre-heater elements which eventually ignites the gas once applied.

Realizing that this is not your normal situation had the conduits been the proper type and properly installed it may be almost zero risk. We do wish to eliminate any further risk of this kind, and add another layer of security.

There are redundant safety measures in place that are components of the controls systems. Its the wiring installation that is most troubling.

If the conduits are not properly installed, then you could have a problem, but where properly installed and in areas not subject to physical damage, I don't really see that much difference between EMT and rigid.

I still don't really understand your point about an increased risk....the flame is there all the time to provide an ignition source...the electrical system is only an ignition source if there is an electrical failure

You can't say it is a classified area just for the conduits. It is is a classified area it is a classified area for everything. If you make the area Class I, Division 2, you will have make all of the electrical equipment in the classified area suitable for the classification.

It appears that your real concern is the improperly installed conduits. If that is the case, why not just repair or replace the conduit without changing the area classification.

 

[SamCAT1234]

If the conduits are not properly installed, then you could have a problem, but where properly installed and in areas not subject to physical damage, I don't really see that much difference between EMT and rigid.

I still don't really understand your point about an increased risk....the flame is there all the time to provide an ignition source...the electrical system is only an ignition source if there is an electrical failure

You can't say it is a classified area just for the conduits. It is is a classified area it is a classified area for everything. If you make the area Class I, Division 2, you will have make all of the electrical equipment in the classified area suitable for the classification.

It appears that your real concern is the improperly installed conduits. If that is the case, why not just repair or replace the conduit without changing the area classification.

I am doing a conduit layout and plan to replace that as I type. I need to correct myself, there is no open flame, these are infrared heaters where the combustion is contained somewhat within the elements. You are probably right that it may not meet the definition of C1 Div 2. Yes my primary concern is with the installation, and the less likely event of a gas leak, rather than the existence of gas under normal operating conditions. My confusion is with how class definition is set up. Is it determined by risk levels based on normal operation, or risk levels based on the possibility of a failure which can leak gas.

 

[rbalex]

I am doing a conduit layout and plan to replace that as I type. I need to correct myself, there is no open flame, these are infrared heaters where the combustion is contained somewhat within the elements. You are probably right that it may not meet the definition of C1 Div 2. Yes my primary concern is with the installation, and the less likely event of a gas leak, rather than the existence of gas under normal operating conditions. My confusion is with how class definition is set up. Is it determined by risk levels based on normal operation, or risk levels based on the possibility of a failure which can leak gas.

I agree with Don. As long as you are simply upgrading the conduit installation, there is no real problem other than expense. However, actually classifying the location can open up several issues. Once you do, everything electrical must comply, not just the raceways,

You should familiarize yourself with NFPA 497. It isn't that long and is available on NFPA's online website. It deals with several issues you should consider such as an open flame may not be necessary, only a source of ignition under normal operations. Under US domestic considerations, classification is determined by "possibilities" rather than "probabilities". BTW if flammable consentrations could occur under normal (not necessarily common) conditions, you have a Division 1 location.

 

[kwired]

I am doing a conduit layout and plan to replace that as I type. I need to correct myself, there is no open flame, these are infrared heaters where the combustion is contained somewhat within the elements. You are probably right that it may not meet the definition of C1 Div 2. Yes my primary concern is with the installation, and the less likely event of a gas leak, rather than the existence of gas under normal operating conditions. My confusion is with how class definition is set up. Is it determined by risk levels based on normal operation, or risk levels based on the possibility of a failure which can leak gas.

The "flame" is behind the infrared panel but is sort of still within the same space. Should the burner fail to ignite and gas continues to flow it will still fill the oven with gas and any spark or heat source would ignite it. Pretty good chance there is some sort of flame or heat detection that cuts off the gas if flame isn't proven. Failure of that can be a hazardous condition, but doesn't make it a classified area for wiring, should the regular ignition source suddenly start to function when the oven is gas filled you still have a potentially dangerous situation, that is why depending on the burner specs, certain ratings of the controls are necessary - usually FM standards more so then UL standards.

 

[SamCAT1234]

The "flame" is behind the infrared panel but is sort of still within the same space. Should the burner fail to ignite and gas continues to flow it will still fill the oven with gas and any spark or heat source would ignite it. Pretty good chance there is some sort of flame or heat detection that cuts off the gas if flame isn't proven. Failure of that can be a hazardous condition, but doesn't make it a classified area for wiring, should the regular ignition source suddenly start to function when the oven is gas filled you still have a potentially dangerous situation, that is why depending on the burner specs, certain ratings of the controls are necessary - usually FM standards more so then UL standards.

Thanks to everyone for the good feedback and response. I hope to be able to help others on this forum out in the future albeit my focus is on automation, robotics, and process controls.