Motor Disconnects At Sewage Aeration Ponds

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jtester

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Location
Las Cruces N.M.
I am currently in a discussion with an inspector about the need for disconnects immediately adjacent to sewage aeration ponds, to disconnect floating aerators located out in the open ponds. The power for each aerator and blower come from a motor control center located between 100? and 600? away from the blowers depending on which one is being measured. The blowers are all 480 volt 3 phase, and vary from 2 hp to 20 hp.
I based my design on NEC 430.102(B)(2) Exception a and b. The sewer plant is fenced and locked, and you either need a boat to get to these blowers, or you need special training to pull them into shore.
The inspector is insistent that there be a disconnect, in fact he is now asking for cord caps and receptacles at the shore connection.
Does anyone have an opinion about my contention, or the inspectors? Should there be a second disconnect at the pond even though the disconnect at the MCC disconnects the controller and is lockable?
Thanks in advance for any thoughts.

Jim T
 
I would think the only hope would be to get letters from management of the facility that 430.102(B)(2)(b)
is in fact in place and their desire is to omit the switches.
Often an inspector wants some creditable documentation to protect him from liability
 
I won't say what's right and wrong but we've use Mennekes plugs/connectors out on the pond near the aerators. At least this way they can remove individual aerators without much trouble.
 
augie47 said:
I would think the only hope would be to get letters from management of the facility that 430.102(B)(2)(b)
is in fact in place and their desire is to omit the switches.
Often an inspector wants some creditable documentation to protect him from liability
Click to expand...

I am not sure an inspector actually has much in the way of liability for missing a code violation.

I think there are good arguments for either having or not having a local disconnect in such a case, and it seems to me the inspector is not involved in that decision given the clear and unambiguous words as written in the code.

Having said that, these are small motors and disconnect switches for them are probably going to cost less than arguing about it.
 
I am not sure that either part of the exception applies to this installation. You might make a case for (a) but I don't see (b) as applying to a sewage treatment plant.
 
Don

I am interested in your reply, and hope you'll elaborate. Because of the nature of these devices, I couldn't imagine an untrained individual working on them. Each pontoon has 2 motors, an aerator and a mixer, and both should be turned off before any one can be worked on. It seems that this would be best done at the MCC.

Thanks

Jim
 
Here are the exceptions

(a) Where such a location of the disconnecting means
for the motor is impracticable or introduces additional or
increased hazards to persons or property

(b) In industrial installations, with written safety procedures,
where conditions of maintenance and supervision
ensure that only qualified persons service the equipment
Click to expand...


I don't see having any chance at all with (a), in my opinion impracticable basically means imposable, not inconvenient and I don't see increased hazards to persons or property. I asume there are alarms when and if a critical component goes of line, such as someone opening the switch and shutting off the equipment.

http://www.merriam-webster.com/dictionary/impracticable


As far as using plugs, in my opinion that will depend on what reason in 400.7(A) you are using to justify cords. Please see 400.7(B).


400.7 Uses Permitted.
(A) Uses. Flexible cords and cables shall be used only for
the following:

(1) Pendants

(2) Wiring of luminaires

(3) Connection of portable luminaires, portable and mobile
signs, or appliances

(4) Elevator cables

(5) Wiring of cranes and hoists

(6) Connection of utilization equipment to facilitate frequent
interchange

(7) Prevention of the transmission of noise or vibration

(8) Appliances where the fastening means and mechanical
connections are specifically designed to permit ready removal
for maintenance and repair, and the appliance is
intended or identified for flexible cord connection

(9) Connection of moving parts

(10) Where specifically permitted elsewhere in this Code

(B) Attachment Plugs. Where used as permitted in
400.7(A)(3), (A)(6), and (A)(8), each flexible cord shall
be equipped with an attachment plug and shall be energized
from a receptacle outlet or cord connector body.
Click to expand...
 
jtester said:
Don

I am interested in your reply, and hope you'll elaborate. Because of the nature of these devices, I couldn't imagine an untrained individual working on them. Each pontoon has 2 motors, an aerator and a mixer, and both should be turned off before any one can be worked on. It seems that this would be best done at the MCC.

Thanks

Jim
Click to expand...
Jim,
I was not commenting on the training part of the exception. I just don't think a sewage treatment plant is an industrial occupancy. I don't see an issue with qualified people and a remote lockout, just with what is an industrial occupancy.
 
I wouldn't think it'd be too much of a stretch to call a sewage treatment plant an industrial facility? They get wired similarly from what I've seen, it's definitely a lot more industrial than commercial in my opinion.

But, the bottom line seems to be, it's a judgement call.
 
Cow said:
I wouldn't think it'd be too much of a stretch to call a sewage treatment plant an industrial facility? They get wired similarly from what I've seen, it's definitely a lot more industrial than commercial in my opinion.
Click to expand...


Any definition of industrial or industry I find refers to producing a product.

But, the bottom line seems to be, it's a judgement call.
Click to expand...


I agree, the AHJ is the one that can make that call.
 
For reference only.

In 240.90, the NEC talks about 'supervised industrial facilities', and then it goes on to clarify with "exclusively for manufacturing or process control activities".

There is also 240.2 which lists 3 qualifications to be considered a 'supervised industrial facilitiy' and uses the word 'process'.
 
jtester said:
I am currently in a discussion with an inspector about the need for disconnects immediately adjacent to sewage aeration ponds, to disconnect floating aerators located out in the open ponds. The power for each aerator and blower come from a motor control center located between 100? and 600? away from the blowers depending on which one is being measured. The blowers are all 480 volt 3 phase, and vary from 2 hp to 20 hp.
I based my design on NEC 430.102(B)(2) Exception a and b. The sewer plant is fenced and locked, and you either need a boat to get to these blowers, or you need special training to pull them into shore.
The inspector is insistent that there be a disconnect, in fact he is now asking for cord caps and receptacles at the shore connection.
Does anyone have an opinion about my contention, or the inspectors? Should there be a second disconnect at the pond even though the disconnect at the MCC disconnects the controller and is lockable?
Thanks in advance for any thoughts.

Jim T
Click to expand...

The exception should stand.

The installation of disconnects around an areator pond is disasterous. They would be disintegrating, faulting in relatively short order.
 
I don't see the exceptions applying to a WWTP, I have worked on and around sewer/water facilities for 30 years. Not having a disconnect may force workers to take shortcuts. Install a SS non fused disconnect.
 
tom baker said:
I don't see the exceptions applying to a WWTP, I have worked on and around sewer/water facilities for 30 years. Not having a disconnect may force workers to take shortcuts. Install a SS non fused disconnect.
Click to expand...

See other post why the industrial exception arguably applicable.

What will happen on the inside of a SS enclosed disconnect? Would you rather be working with a potentially unsafe disconnect or be able to lock out in a safe location? Would you rather be wearing your Mars-suit in the outdoor, or in a controlled indoor environment?
 
jtester said:
The inspector is insistent that there be a disconnect, in fact he is now asking for cord caps and receptacles at the shore connection.
Click to expand...

If on the shore they still do not meet definition of "in sight from" if it is more than 50 feet to the equipment.

AHJ here would not even question using the MCC as the disconnect in this case.

What does your AHJ say about disconnect location for a submersible well pump? Should you put submersible disconnect within 50 feet of the pump within the well casing?
 
kwired said:
What does your AHJ say about disconnect location for a submersible well pump? Should you put submersible disconnect within 50 feet of the pump within the well casing?
Click to expand...

As far as the 50' from the pump that falls under the impracticable exception, as in 'it can't be done so you don't have to do it'.

But IMO the AHJ would be within the NEC to require a disconnecting means at the top of the well casing.
 
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