seperate buckets in MCC using one control transformer for both starter coils

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JAMESMARSALIS

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Carthage, TX, USA
This is ultimately a code question for which I need the correct section and subsection with which to make my case for ordering the parts I need to make this issue correct. Here goes:
I have 2 motors that both do the same job but are designed to operate independently of each other. They each have their own start/stop and power circuit, their own start/stop station (although the 2nd one is not being used because it has the wrong type of contacts for the start/stop station...it's a normally closed contact on a temporary pushbutton to break(stop) the power to the holding contacts in the circuit). I know this already sounds confusing but the "powers that be" think since it's working as is, why mess with it and my telling them it's not to code is being met with resistance and stopping me from purchasing the correct mushroom and contacts. To continue- the 1st motor circuit is using a mushroom style allen-bradley 800T FXNP16XA7 push/pull start/stop. The 2nd motor is started using a jumper from the auxiliary contact on the coil from the first starter to pull in the coil on the second starter and hold it until the 1st motor is turned off which also disconnects the control power to the second coil. Why is this setup like this? I ultimately have to guess a little but the original setup had 4 buttons to control 2 circuits (a N/O pushbutton for the start and a N/C pushbutton for the stop) but was changed to 3 mushroom style push/pull start/stops to handle 4 circuits while the 4th pushbutton was never changed. I don't know why...there's no notes in the prints and I suspect the prior electrician was under pressure from the drilling guys to just "get them both working" and did so with the intention of it being a temporary fix that would later be corrected and ultimately never was. Thus, the one mushroom push/pull start/stop is starting both motors and stopping both motors. Yes, it's working and yes it's worked for a long time this way, years I'm sure but now I know about it and I can't allow it to remain in this setup. Please direct me to the correct section and letter in the codebook to cite when I tell them why it's wrong.
Thank you and I apologize if any of this is confusing. Please ask any questions you feel need to to clear up any confusion I've possibly communicated.
 
Follow up

Follow up

It doesn't matter that there is no way to turn only one motor on and off? It's "designed" to operate only one motor at a time which is why each bucket has it's own 480/120v control power transformer and start/stop circuit. In it's current setup, if one motor goes down then they both go down. I'm not trying to be difficult, I just want to be sure I'm not being my own worst enemy by miscommunicating the setup and concerns.
 
JAMESMARSALIS said:
It doesn't matter that there is no way to turn only one motor on and off? It's "designed" to operate only one motor at a time which is why each bucket has it's own 480/120v control power transformer and start/stop circuit. In it's current setup, if one motor goes down then they both go down. I'm not trying to be difficult, I just want to be sure I'm not being my own worst enemy by miscommunicating the setup and concerns.
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I've seen many such situations where control circuits are customized to suit (or make do). Many MCC buckets have a terminal strip just for that purpose (custom control). The NEC doesn't cover control design elements.
 
JAMESMARSALIS said:
It doesn't matter that there is no way to turn only one motor on and off? It's "designed" to operate only one motor at a time which is why each bucket has it's own 480/120v control power transformer and start/stop circuit. In it's current setup, if one motor goes down then they both go down. I'm not trying to be difficult, I just want to be sure I'm not being my own worst enemy by miscommunicating the setup and concerns.
Click to expand...
The code doesn't care if the equipment works...it only cares about having a safe electrical system.
 
It's a little hard to follow, but I agree, on the surface it appears to not be a code issue. The only possible issue is that in the MCC bucket for the unit that is powered via the CPT in the other unit, you must have an aux contact of the disconnect device which will kill the "foreign source" of control power before you can open the door. Other than that, how you control the starters is not the concern of the code.

That said, it's not a good idea from the sounds of it, because if the breaker trips /fuses blow in the starter with the CPT, you will lose them both. I would approach it from the standpoint of down time risks.
 
In the bucket without the CPT, you have two sources of power. This is allowed, but there are specific requirements for labeling and disconnecting of the control circuit, otherwise its a violation.
See 430.75
Its very simple to add a CPT to the other bucket.
I like to have each motor controller independent of others. Sometimes if I can't get around this, I will install an aux contact on the disconnect, there are kits for this purpose.
 
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