Cost effective disconnect/starter for haz. location?

[biofueler]

I am trying to spec a disconnect/motor controller for the following motors, all are in class 1 div 1 group D, all are 480 3ph motors

(6) 1hp motor with start/stop only
(3) 10 hp motor with VSD

Since we are in a hazardous location, I am trying to consolidate equipment to save $$

looking at the small 1hp motors:
According to 430.112C, a single disconnect can service groups of motors 'within sight of the disconnecting means' provided 430.110C is satisfied.

It appears that 430.110C specifies the disconnect must consider both full load current and max locked rotor current. Thus for the 6 1hp motors, we are looking at a combined full-load current of 2.1*6=12.6 A, and a locked-rotor current of 15*6=90A.

According to table 430.251(B), this locked rotor current corresponds to a 15HP switch, which also satisfies the full-load current as per table 430.250.

thus a 60A, 15HP heavy duty safety switch such as square-D H362N is acceptable, correct?

ok, now for the tricky oddball code-interpretation question. The hazardous location room is entered by two double doors. The doors constitute an occupancy separation, and thus should have manual or thermal closures. Ideally I would like to place the VSD's for the large motors outside of the hazardous location room on a facing wall. In other words, if the doors were open, the disconnects and motor controls would be 'in sight' as per code. Is this technically incorrect, to assume the doors would be open under normal operation? Otherwise, to gett out of the classified area, I end up having a lot of dead space in the room to get the 8' separation from hazardous area.

I have contemplated providing a large purged and pressurized enclosure to contain the vsds and disconnects as per 500.7D, but fear this may get prohibitively expensive as well.

One final question, would a local start/stop switch or panic button that could break current to the coil on a remote magnetic motor starter be considered acceptable as a local disconnect? Not sure if this would fall under 430.109(A)(1) as a 'HP rated motor circuit switch'. I think thatey mean the larger safety switches as I stated above, but the haz. loc pushbutton control boxes are quite common and affordable.

Thanks in advance, as always!

 

[dpc]

You've raised a lot of issues that create other questions. It's difficult to design this via a message board, so some general comments:

Per 430.102 of NEC, a local disconnect within sight of the MOTOR is NOT required if you meet certain conditions - most importantly that you have a disconnecting means before (and within sight of) the motor controller that can be locked in the OPEN position. Your company/facility may have more strigent safety rules that trump the NEC, but if possible, I would locate the starters and the VFD in a non-hazardous location if at all possible, and eliminate the local disconnects at the motors.

The only way to "share" a disconnect switch would be to use a common disconnect on the supply side of the motor starter. You can't share individual local motor disconnects.

A pilot device such as an emergency stop button or lockout stop button might be a good idea but it does NOT meet the requirement for a motor disconnecting means per the NEC.

Also, any room adjacent to a Class 1, Div 1 room will be Class 1, Div 2 by definition, unless requirements to de-classify the area are met.

Oh, and I doubt that an inspector would buy your idea that looking through an open door would constitute "within sight". But maybe that's just me.

Hope that helps - good luck.

 

[biofueler]

further reading of 430.102(B) this would seem to fit well - "where such a location is impractical or introduces additional or increased hazards to persons or property".

Now I suppose it could be argued that the elimination of local disconnects is primarily for cost reasons, and that an explosion-proof switch would not introduce addl hazards. But by going with the premise of 'keep it simple', I think a remote magnetic starter and lockable disconnect would work. It would still be located within sight technically, but not claimed so by the design. It appears I will lose the ability to service multiple starters with a single disconnect this way however.

 

[dpc]

There are thousands of motors in the US that do not have local disconnects at the motor, relying on the disconnect at the motor starter. NFPA has been slowing tightening this loophole in the past two NEC revision cycles, but I doubt they will be getting rid of it entirely for quite a while.

You'll be thankful you have individual disconnects for each starter.

 

[biofueler]

well, assuming the starter and safety switch are located remotely, what would be an acceptable local disconnect then? It appears that a listed lockout station ("system isolation equipment") is required.

 

[dpc]

Any NEMA/UL listed disconnect switch, aka "safety switch" is acceptable as long as it has locking provisions and a horsepower rating.

Normally, the motor short circuit protection, either a molded case circuit breaker or a fused disconnect can do double duty as the disconnecting means and no other additional switch is required at the starter.

 

[jraef]

I deal with a lot of very large motors which makes local disconnect switches impractical. I always interpreted this issue as being that you need to have a local disconnect within sight of the motor, OR the disconnect that is in another room must be capable of being locked open / off. I have never been challengend on that by an inspector.

Lately however I have been seeing a trend in every project of having Lock-Out-Stop push buttons hard-wired back to the controller control circuit mounted close to the motors, where in the past it was a local plant safety protocol only. I asked an electrician about that last week on a jobsite and he told me it was new in the code. This is going to make me read these sections again for changes.

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[dpc]

jraef,

I don't see anything like that in my 2005 NEC. It would not be considered a "disconnecting means". Local lockout stop might be required for other safety reasons, such as for conveyor or other driven equipment that someone could get caught in. But I don't think a pilot device of any kind can be considered a disconnecting means to satisfy the requirements of Article 430.

 

[biofueler]

right, that was my initial question, I would prefer to have simple push-button start stops at the motor location for safety and practicality, but this is not a disconnect as per code.

So I am looking at remote mounted lockable safety switch and remote starter, with a local pushbutton as a design feature. the pushbutton station would be the only xp equipment then.