Nema 4 prox switches in class 2 div 2 environment

[james_mcquade]

Hi everyone,

i am at odds with one of my customers over the use of prox switches in the following situation.


from the plc inputs, we have standard 24 volt prox switches ( rated ip67 / Nema 4) detecting metal cans filled with areosol paint/other chemicals.
last week, one of these cans tipped over and destroyed (1) of these prox
switches resulting in the electronics being exposed.
i argued with the customer that the prox switches were not safe and could have ruptured the can that turned over due to the confined area and thus cause a fire / explosion.

he didn't seem to care because the switches are rated Nema 4.

i explained to him that the Nema / IP rating of a switch is to let the user
know what the sensors outer case will protect the electronics against: dust, oil,water, ice.

i went on to explain that the electronics of the 24 volt prox was not intrensically safe because you had 24 volts and how ever many milliamps/
amps of power the circuit was fused at powering the device. i also stated that intrensically safe sensors were designed in such a way that if the sensor was destroyed, the electrical potential of the device would not have enough energy to ignite the paint.

he stated that he would get his safety department to address my concern.

did i miss something or am i making a mountain out of a mole hill?
there are 10 people that will be in the line of fire if one of these cans are
ignited due to these prox switches.

thanks in advance,
james

 

[don_resqcapt19]

I see no code issue with the use of electronic devices that do not have any arc producing contacts and have a normal operating temperature of 80% or less than the ignition temperature of the products involved being used in a Class I, Division 2 location in a NEMA 4 enclosure or even in a NEMA 1 enclosure. See the exception to 501.105(B)(2) in the 2008 code.

 

[james_mcquade]

Don,

thanks for the reply.

my concern is that there is a 24 volt, 3 wire proximity switch, fused at 2 amps
being hit by a can of highly flamable paint. this time the prox switch did not spark or puncture the can, but next time?

i have seen sparks from a 24 volt prox switch only one time before and i an wondering what others are thinking.

regards,
james

 

[petersonra]

Don,

thanks for the reply.

my concern is that there is a 24 volt, 3 wire proximity switch, fused at 2 amps
being hit by a can of highly flamable paint. this time the prox switch did not spark or puncture the can, but next time?

i have seen sparks from a 24 volt prox switch only one time before and i an wondering what others are thinking.

regards,
james

You may have a legitimate safety issue, but the NEC is pretty clear that electrically it is allowed.

 

[weressl]

Hi everyone,

i am at odds with one of my customers over the use of prox switches in the following situation.


from the plc inputs, we have standard 24 volt prox switches ( rated ip67 / Nema 4) detecting metal cans filled with areosol paint/other chemicals.
last week, one of these cans tipped over and destroyed (1) of these prox
switches resulting in the electronics being exposed.
i argued with the customer that the prox switches were not safe and could have ruptured the can that turned over due to the confined area and thus cause a fire / explosion.

he didn't seem to care because the switches are rated Nema 4.

i explained to him that the Nema / IP rating of a switch is to let the user
know what the sensors outer case will protect the electronics against: dust, oil,water, ice.

i went on to explain that the electronics of the 24 volt prox was not intrensically safe because you had 24 volts and how ever many milliamps/
amps of power the circuit was fused at powering the device. i also stated that intrensically safe sensors were designed in such a way that if the sensor was destroyed, the electrical potential of the device would not have enough energy to ignite the paint.

he stated that he would get his safety department to address my concern.

did i miss something or am i making a mountain out of a mole hill?
there are 10 people that will be in the line of fire if one of these cans are
ignited due to these prox switches.

thanks in advance,
james

Based on your argument, there would be no Division 2 areas only Division 1.

 

[james_mcquade]

thanks again for your responces,

james