Article 430.75 questions

[KJLanger]

I have some questions regarding the interpretation of Article 430.75 as it applies to the attached control circuit. Our motor control circuit is a motor starter with a 24VDC coil, controlled by a PLC output. We monitor the states of the DIS, the MCP, and the motor starter. If the DIS, or MCP is turned off (open), our program will not allow the motor starter output to turn on. Would this be considered as "disconnected from all sources of supply"? If I used safety I/O instead, would it then be considered disconnected?

I have seen where an auxiliary contact from the DIS is run in series between the PLC output and the motor starter coil, to supposedly comply with this article, but I don't understand how that addresses the article any better than the method I use above. Couldn't the motor starter still be mechanically activated allowing the presence of high voltage at the line side of the disconnect?
Is the intent of the article to ensure no voltage is present at the line side of the DIS? If so, shouldn't logout/tagout be employed at the MCP to prevent this? It seems like the disconnecting means to the motor control circuit in my example would be the MCP, not necessarily the DIS, in which case the 24VDC motor starter coil power should be disconnected when the MCP is open, but not necessarily the DIS. Can you comment on that?

If the intent of the article is to ensure no voltage whatsoever is present at the line side of the DIS, then power to the DIS aux contacts should also be removed, correct?

Thank you,

 

[petersonra]

If this is a type F combination starter (and it appears to be), the MCP can be considered to be the disconnecting means for both the motor and the motor controller. The DIS is a motor disconnect.

If the DIS or MCP is open, the motor can't run anyway, so the aux contacts are superfluous to being a disconnecting means.

The control interlocks do not matter any as far as being legal disconnecting means.

there is no requirement to remove power from the auxiliary circuits. only from the motor and/or the motor controller.

 

[augie47]

there is no requirement to remove power from the auxiliary circuits. only from the motor and/or the motor controller.

Dang! Old dog, new trick AGAIN
I had always read that to mean there was a requirement to disconnect all power sources to the starter including power to auxiliary contacts. (Whats worse is that I have enforced that).

 

[petersonra]

Dang! Old dog, new trick AGAIN
I had always read that to mean there was a requirement to disconnect all power sources to the starter including power to auxiliary contacts. (Whats worse is that I have enforced that).

There has to be some means of disconnecting the power to the aux contacts so you can work on them and it is generally convenient to do it with the controller disconnect. But I do not believe that it is a requirement that it be done that way.

Because it is so common to do it this way I used to believe it was a requirement as well, but I was never able to find such a requirement in the code to support that idea.

i could be wrong about this. It would not be the first time I have been wrong.

however this is what the code actually says:

430.103 Operation. The disconnecting means shall open
all ungrounded supply conductors and shall be designed
so that no pole can be operated independently. The disconnecting
means shall be permitted in the same enclosure
with the controller. The disconnecting means shall
be designed so that it cannot be closed automatically.

i don't see how a control circuit powering an aux contact can be considered a "supply".

 

[petersonra]

I am surprised there is not more comment on this one.

 

[david luchini]

There has to be some means of disconnecting the power to the aux contacts so you can work on them and it is generally convenient to do it with the controller disconnect. But I do not believe that it is a requirement that it be done that way.

Because it is so common to do it this way I used to believe it was a requirement as well, but I was never able to find such a requirement in the code to support that idea.

i could be wrong about this. It would not be the first time I have been wrong.

i don't see how a control circuit powering an aux contact can be considered a "supply".

I agree with Bob. 430.75 seems clear that the disconnecting means for the power supply for the motor, and the disconnecting means for the power supply to the motor control circuits can be separate devices. However, it also requires that the disconnecting means be located adjacent to each other (unless you can meet the exceptions) which is probably why it is common to use the one disconnect to do both.

 

[petersonra]

I agree with Bob. 430.75 seems clear that the disconnecting means for the power supply for the motor, and the disconnecting means for the power supply to the motor control circuits can be separate devices. However, it also requires that the disconnecting means be located adjacent to each other (unless you can meet the exceptions) which is probably why it is common to use the one disconnect to do both.

I am not sure there is a requirement to disconnect the control circuits from the motor controller. In fact, I think there is not.

the disconnects required are for the motor and for the motor controller. not the control or monitoring circuits for either.

 

[david luchini]

I am not sure there is a requirement to disconnect the control circuits from the motor controller. In fact, I think there is not.

the disconnects required are for the motor and for the motor controller. not the control or monitoring circuits for either.

Bob, there is a requirement to disconnect the motor control circuits from their source of power in 430.75. This can be either by the same disconnect as the motor/control power supply, or be a separate disconnecting means. However, the disconnecting means must be located adjacent to each other.

 

[petersonra]

Bob, there is a requirement to disconnect the motor control circuits from their source of power in 430.75. This can be either by the same disconnect as the motor/control power supply, or be a separate disconnecting means. However, the disconnecting means must be located adjacent to each other.

I have come to read 430.75 as a disconnecting means is required for the motor control circuits, but that it does not have to be either the motor controller disconnect or the motor disconnect, but it can be.

it specifically says that the motor control circuit disconnect can be a separate device. I do not see how this can be read as requiring the motor control circuit disconnect to be the motor disconnect or the motor controller disconnect.

430.75 Disconnection.
(A) General. Motor control circuits shall be arranged so
that they will be disconnected from all sources of supply
when the disconnecting means is in the open position. The
disconnecting means shall be permitted to consist of two or
more separate devices, one of which disconnects the motor
and the controller from the source(s) of power supply for
the motor, and the other(s), the motor control circuit(s)
from its power supply. Where separate devices are used,
they shall be located immediately adjacent to each other.

 

[augie47]

What I missed in the past, an a bit of an oddity to me, is there does not seem to be a related requirement to disconnect circuits other than the motor power and control circuit nor to caution of it's presence.
If I have an external power source feeding thru a set of auxilairy contacts to a device that sourse would still be energized when the starter and control circuits was disconnected. TH

 

[petersonra]

What I missed in the past, an a bit of an oddity to me, is there does not seem to be a related requirement to disconnect circuits other than the motor power and control circuit nor to caution of it's presence.
If I have an external power source feeding thru a set of auxilairy contacts to a device that sourse would still be energized when the starter and control circuits was disconnected. TH

I find it odd that three separate disconnecting means are associated with a motor, and can be three separate devices, but can be just 1 or 2.

 

[david luchini]

I have come to read 430.75 as a disconnecting means is required for the motor control circuits, but that it does not have to be either the motor controller disconnect or the motor disconnect, but it can be.

Isn't that what I said? Together with the fact that the separate control circuit disconnect is required to be mounted immediately adjacent to the controller disconnect.

 

[Smart $]

I find it odd that three separate disconnecting means are associated with a motor, and can be three separate devices, but can be just 1 or 2.

Actually, it can be more. I'm certain 430.75 Exception No. 1 exists for a reason, and it is regarding more than 12 motor control circuit conductors.

I believe your initial response to be in error. The diagram supplied in the OP indicates the motor control circuit is supplied by the 24V DC supply for the I/O module. In the more traditional set ups, the control circuit power is derived from the load side of the controller disconnect, and the automated control uses that power source for I/O. That does not appear to be the case here.

 

[Smart $]

Isn't that what I said? Together with the fact that the separate control circuit disconnect is required to be mounted immediately adjacent to the controller disconnect.

Depends on what you mean by separate. It can be a common or combined disconnect, e.g. one that disconnects both the motor supply through the controller and the motor control circuits. Just the actual contacts may have to be separate.

 

[david luchini]

It can be a common or combined disconnect, e.g. one that disconnects both the motor supply through the controller and the motor control circuits.

Isn't that what I said?

 

[Smart $]

Isn't that what I said?

I don't know, I can't hear you from here.

 

[KJLanger]

Actually, it can be more. I'm certain 430.75 Exception No. 1 exists for a reason, and it is regarding more than 12 motor control circuit conductors.

I believe your initial response to be in error. The diagram supplied in the OP indicates the motor control circuit is supplied by the 24V DC supply for the I/O module. In the more traditional set ups, the control circuit power is derived from the load side of the controller disconnect, and the automated control uses that power source for I/O. That does not appear to be the case here.

Yes, the motor control circuit is supplied by the 24V DC supply for the I/O module. If one agrees that this source of power supply must be disconnected when the disconnecting means is open, would turning off the PLC output for the motor starter be considered as disconnected, or am I required to have a hard-wired circuit to disconnect the circuit? Does it make any difference that my control circuit is < 50V? It seems that this article may have been written to address more traditional set-ups where the control circuit power may have been derived and was likely to be a higher voltage. Or might have been written to address situations where a control circuit wired out to the motor might still have power applied (to pick up a motor thermal switch for instance).

Do you think the intent of this article was to ensure that someone who opened the disconnecting means to work on the motor was not surprised that voltage was still present at the motor? Or do you think the intent is to prevent voltage presence at the line side of the disconnect, because I don't think the article's provisions completely safeguard against that? Thanks.

 

[Smart $]

....

Do you think the intent of this article...

Discussing intent is substantiated by seemingly ambiguous requirements. This one seems specific enough, IMO, that discussing (or rather speculating on) intent would not change its implementation.