C1,DII,GD Air Comp

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aanvari3

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Okay, so we're installing an air compressor in a Class 1, Div II, Group D haz location. The air comp comes in an enclosure that includes a soft starter, PLC, motor, and all related switches and transmitters to go to the PLC. We were recommended to do a Z-purge on the enclosure (NEMA 4X), but the Z-purge will be only over the motor starter part of the enclosure, and apparently the vendor is saying th PLC is already rated for Div II, but i think they only meant the outside control panel.

The motor shouldn't be a problem from what I read in the NEC since it is a brushless rotary screw compressor. My main concern is that the PLC uses a temperature switch, pressure switch, and differential pressure switch as well as various pressure transmitters and temp sensors, fuses, relays and contacts that go to the enclosed PLC.

Do all of the switches, transmitters, and PLC parts need to be rated for Div II as well since apparently the Z-purge is only covering the motor starter portion of the enclosure? Or since they are all enclosed in the 4X enclosure is that good enough? Do they need to be NEMA 7 or explosion proof rated?
 
aanvari3 said:
Okay, so we're installing an air compressor in a Class 1, Div II, Group D haz location. The air comp comes in an enclosure that includes a soft starter, PLC, motor, and all related switches and transmitters to go to the PLC. We were recommended to do a Z-purge on the enclosure (NEMA 4X), but the Z-purge will be only over the motor starter part of the enclosure, and apparently the vendor is saying th PLC is already rated for Div II, but i think they only meant the outside control panel.

The motor shouldn't be a problem from what I read in the NEC since it is a brushless rotary screw compressor. My main concern is that the PLC uses a temperature switch, pressure switch, and differential pressure switch as well as various pressure transmitters and temp sensors, fuses, relays and contacts that go to the enclosed PLC.

Do all of the switches, transmitters, and PLC parts need to be rated for Div II as well since apparently the Z-purge is only covering the motor starter portion of the enclosure? Or since they are all enclosed in the 4X enclosure is that good enough? Do they need to be NEMA 7 or explosion proof rated?
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Most PLCs these days all the parts except the relay modules are rated for Div 2.

I am not quite clear just what you have. Is the thing you are purging just a combo motor starter?

You still have to protect the switches and transmitters, which could be XP. If not, you could put barriers in the PLC cabinet and extend the purge to it.
 
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Okay, the compressor comes with an optional Wye-Delta soft starter mounted inside the enclosure. We could probably take the soft starter outside the enclosure and put it in our own XP enclosure or put it in our MCC thats in a nonhaz building, but we kind of want the air comp people to just do the whole thing in one shot. So as far as i'm being told, the Z-purge is for the soft starter, maybe they do plan on having barriers to go to the switches as you suggested. They initially said they coudn't get the electrical to be Nema 7, which i would assume means having XP switches and transmitters, or is that a different term?
 
Not sure if my first reply got through or not.

From what i've been told, it looks like we are purging the wye-delta soft starter that comes with the compressor. We could buy our own soft starter and put it in an XP enclosure or even outside the haz building, but we'd like the air compressor company to do it. They say the air compressor will be rated for Div II now after the purge, so i'm assuming they may use barriers to the switches as simply replacing them with XP rated ones wasn't an option before purging was brought up. The PLC is a CompactLogix and from what i can find online it seems like they are rated for Div II.
 
aanvari3 said:
Okay, the compressor comes with an optional Wye-Delta soft starter mounted inside the enclosure. We could probably take the soft starter outside the enclosure and put it in our own XP enclosure or put it in our MCC thats in a nonhaz building, but we kind of want the air comp people to just do the whole thing in one shot. So as far as i'm being told, the Z-purge is for the soft starter, maybe they do plan on having barriers to go to the switches as you suggested. They initially said they coudn't get the electrical to be Nema 7, which i would assume means having XP switches and transmitters, or is that a different term?
Click to expand...

what the heck is a wye-delta soft starter?
 
aanvari3 said:
Not sure if my first reply got through or not.

From what i've been told, it looks like we are purging the wye-delta soft starter that comes with the compressor. We could buy our own soft starter and put it in an XP enclosure or even outside the haz building, but we'd like the air compressor company to do it. They say the air compressor will be rated for Div II now after the purge, so i'm assuming they may use barriers to the switches as simply replacing them with XP rated ones wasn't an option before purging was brought up. The PLC is a CompactLogix and from what i can find online it seems like they are rated for Div II.
Click to expand...

Unless the CompactLogix is rated as a non-incendive power supply and each connected device to the I/O's can be rated as non-incendive the external components connecting to the PLC, such as solenoids, pushbuttons, temerature and pressure switches still need to be investigated for suitability for Cl. I, Div. 2 locations. Solenoids are probably OK, because they are non-arcing, not-heat producing, all switching devices could employ hermetically sealed switches that makes them suitable for Div. 2 and labeled so. The compressor fabricatior should be able to confirm this in detail, item-by-item.

Star/Delta and soft start are two different animals. Star/Delta not quite being the dinosaurus, but like sabertooth tiger....:D
Star/Delta is a reduced voltage starter, but not bumpless, eg. you will still experience an initial and a transfer inrush. SSRV's are true soft starters, eg. the inrush current is controlled infinitely and does not have the initial magnetizing inrush unless. The startup current is limitied to whatever the application needs and you not stuck with the SQRT3 reduction per the D/Y.
(You really should ask them to use SSRV - Solid State Reduced Voltage - starter.)
 
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Okay I'll request a SSRV. From NEC 501.115 (B) (1) (4), if the starter is solid state does that make it rated for div 2 then? It says if a general purpose enclosure is provided and "The device is a solid state, switching control without contacts, where the surface temperature does not exceed 80 percent of the ignition temperature in degrees Celcius of the gas or vapor involved." I would think it has contacts right?

I know the air comp comes with a high temp shutdown, do SSRV's usually get hot enough to exceed 80% of a group D rating?
 
aanvari3 said:
Okay I'll request a SSRV. From NEC 501.115 (B) (1) (4), if the starter is solid state does that make it rated for div 2 then? It says if a general purpose enclosure is provided and "The device is a solid state, switching control without contacts, where the surface temperature does not exceed 80 percent of the ignition temperature in degrees Celcius of the gas or vapor involved." I would think it has contacts right?

I know the air comp comes with a high temp shutdown, do SSRV's usually get hot enough to exceed 80% of a group D rating?
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Good thoinking, but not so fast Keemosabe:smile:. Many of the SSRV's incorporate a bypass contactor that closes AFTER the start sycle completed and open BEFORE the stop cycle begins. Now the current they switching at that point is very small - only account for the higher internal resistance of the SS element compared to the mechanical contacts, nevertheles it is still to be consdiered an arcing contact. Then you would have the I/O interface of the SSRV - run, fault contacts - to worry about. I doubt that any of those would be sealed contacts, although you can still wire them as non-incedive circuits. Your main problem would remain the bypass contacs.

If you do NOT have an internal bypass contactor have the temperature data confirmed by the SSRV manufacturer, in writing. It should say something to the effect that the maximum surface temperature of any components will not exceed XX Centigrade or Farenheit degrees.
 
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