Commercial Garage dilemma

[Strathead]

A job I am doing requires proximity sensors to indicate that the garage roll up doors are closed for security purposes. NEC 511 requires the entire floor space below 18" to be class 1 division 2. Oddly enough I am being told that no one makes the drive over switches that are typical for this application classified. You can't use a side mount switch because it would protrude and be above 18", so the door would have to stop before the magnet rolls up in to the door at the top. I can only assume that this is being overlooked across the country, because I don't think we are interpreting the code incorrectly. Has anyone run across this situation, or have a solution?

 

[__dan]

Any type of sensor, magnetic reed switch, PIR, or photocell, is going to be power limited class 2. The question you have to ask is it also intrisically safe. If the manufacturer can list it as intrinsically safe it may be OK to install in hazardous environment, possibly also without explosionproof enclosure, contingent on the manufacturer's listing and regulatory approval.

If the manufacturer wants to pursue that market, they could list an intrinsically safe device for installation in class I, class II class III environments. The manufacturer or their rep would be the first place to inquire.

 

[charlie b]

I may be oversimplifying the situation, but if the bottom of the door is in its proper place, such that security has been achieved, then the top of the door must be in its proper place as well. Can you not put the proximity sensors or roll-over switches or some other devices at the top of the door?

 

[Strathead]

I may be oversimplifying the situation, but if the bottom of the door is in its proper place, such that security has been achieved, then the top of the door must be in its proper place as well. Can you not put the proximity sensors or roll-over switches or some other devices at the top of the door?

What we are exploring is using the limit switch in the door controller, but many of these doors are manual. Regarding your question, Think of a roll up door, it rolls in to a cylinder,anything mounted not on the bottom of the door will roll up in to that cylinder at some point in the process. Since the doors are on rails inside the space, any sensor will also need to stick out past the rail to engage its counter part. This could not roll up in the door.

 

[Strathead]

Any type of sensor, magnetic reed switch, PIR, or photocell, is going to be power limited class 2. The question you have to ask is it also intrisically safe. If the manufacturer can list it as intrinsically safe it may be OK to install in hazardous environment, possibly also without explosionproof enclosure, contingent on the manufacturer's listing and regulatory approval.

If the manufacturer wants to pursue that market, they could list an intrinsically safe device for installation in class I, class II class III environments. The manufacturer or their rep would be the first place to inquire.

Why do you even mention the power limited class 2 parameter? It really has nothing to do with the issue. As you somewhat indicated, it should not be difficult to achieve a class 1 division 2 certification on one of these switches that is already designed tough and generally hermetically sealed. The point is that they are not currently listed, yet this situation has to be common in thousands of buildings across the Country. This leads me to believe that I am probably missing something that makes this not required.

 

[__dan]

I mentioned power limited class 2 because I expected the sensors to already be built that way, and it may be a relatively small step for the manufacturer to also test and list their existing devices as intrinsically safe, with no or minor changes to their existing product line.

I believe they would need the additional testing and listing, have to be listed intrinsically safe and suitable for hazardous environment, but the manufacturer would try to do that with an existing product.

I have seen magnet and reed switch mounted to aluminum brackets higher than 18", if you have part of the door that remains exposed when fully up.

Also don't they make a rubber bladder, tube, that operates a pneumatic plunger switch. The rubber bladder part mounts to the bottom of the door and connects to the switch with an air tube. The door should already have that to stop it, if it comes down on a car or truck in the doorway, door bumper switch?

 

[Strathead]

Also don't they make a rubber bladder, tube, that operates a pneumatic plunger switch. The rubber bladder part mounts to the bottom of the door and connects to the switch with an air tube. The door should already have that to stop it, if it comes down on a car or truck in the doorway, door bumper switch?

An idea that crossed my mind, but it would not actually indicate the the door is closed. I again reiterate with the other that you said. This code has been in place for a long time. Why isn't this a common application?

 

[don_resqcapt19]

There are any number of small prox or magnetic switches suitable for Class I, Division 2 areas. I am sure that you could make one of tehm work. Many are very small.

 

[GoldDigger]

There are any number of small prox or magnetic switches suitable for Class I, Division 2 areas. I am sure that you could make one of tehm work. Many are very small.

With proper design for a magnetic sensor, the magnet will not have to stick out beyond the edge of the door, although some drilling may be required.
And if you use a mechanical linkage the switch contacts of a limit switch can be above 18 inches even though the actuator is at floor level.

 

[rbalex]

If you had posted this in hazardous locations forum, I'd have noticed it earlier.

You will note Section 501.115(B)(1)(1) says nothing about listing. Make sure you also read the primary text [Section 501.115(B)].