Terry Woods
Member
Table 430.22(E) indicates that accomodations have to be made for motors that operate under particular conditions. Fine. The idea makes sense. However, the terms used to describe the various conditions, as defined in Article 100, do not quite make sense... exactly.
Duty, Continuous
Operation at a substantially constant load for an indefinitely long time.
This one is pretty sensible.
Duty, Intermittent
Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.
Here it starts to get a bit foggy...
I can only assume that...
"load" = running with a load
"no load" = running without a load
"rest" = not running
If so, then...
(1) "load and no load" = constantly running, but the load is intermittent.
In this case, except for the initial start-up, there is no repeated starting-current issue.
(2) "load and rest" = running with a load, stopping under load, then restarting under load.
In this case, along with the initial start-up, there is repeated starting-current, and since it is restarting under load that current might be extreme.
(3) "load, no load, and rest" = running under load, then running under no load, then stopping.
In this case, along with the initial start-up, there is repeated starting-current. However, since it is restarting without a load the starting current won't be too extreme... maybe.
All of that makes sense... sorta, except there is no time-frame associated with the events.
Duty, Periodic
Intermittent operation in which the load conditions are regularly recurrent.
OK, so now this is the Intermittent Duty with a periodic time-frame... however, what is the time-frame? Every 30-seconds? Every 5-minutes? Every hour?
Duty, Short-Time
Operation at a substantially constant load for a short and definite, specified time.
This also makes sense... sorta, except what the heck would that specified time be? Every 10-seconds? Every 30-seconds? Every 5-minutes?
Duty, Varying
Operation at loads, and for intervals of time, both of which may be subject to wide variation.
It doesn't say anything about "rest" so the motor must always be on.
"...both of which are subject to wide variation." must be referring to the size of the "load" and the duration of the "load".
It appears that this is referring to the situation where the motor is subjected to any kind of loading, from light to extreme, and for any length of time, from short periods to long periods.
So... here is the question...
How is the motor of a rock-crusher classified?
Sure, I can't go wrong by saying that it is classified as "Varying Duty"... but is that the appropriate (right) classification?
It seems that, by definition, the rock crusher could also be classified under case (1) of Intermittent Duty...
"...alternate intervals of (1) load and no load"
It probably couldn't be classified as "Periodic" because there is no way to "know" that the load is "periodic".
And since there is no way to assure that all of the rock is consistent in density, there is no way to assume that loading will be consistent even if the rock is fed at a constant rate.
So... how would a rock crusher be classified?
Duty, Continuous
Operation at a substantially constant load for an indefinitely long time.
This one is pretty sensible.
Duty, Intermittent
Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.
Here it starts to get a bit foggy...
I can only assume that...
"load" = running with a load
"no load" = running without a load
"rest" = not running
If so, then...
(1) "load and no load" = constantly running, but the load is intermittent.
In this case, except for the initial start-up, there is no repeated starting-current issue.
(2) "load and rest" = running with a load, stopping under load, then restarting under load.
In this case, along with the initial start-up, there is repeated starting-current, and since it is restarting under load that current might be extreme.
(3) "load, no load, and rest" = running under load, then running under no load, then stopping.
In this case, along with the initial start-up, there is repeated starting-current. However, since it is restarting without a load the starting current won't be too extreme... maybe.
All of that makes sense... sorta, except there is no time-frame associated with the events.
Duty, Periodic
Intermittent operation in which the load conditions are regularly recurrent.
OK, so now this is the Intermittent Duty with a periodic time-frame... however, what is the time-frame? Every 30-seconds? Every 5-minutes? Every hour?
Duty, Short-Time
Operation at a substantially constant load for a short and definite, specified time.
This also makes sense... sorta, except what the heck would that specified time be? Every 10-seconds? Every 30-seconds? Every 5-minutes?
Duty, Varying
Operation at loads, and for intervals of time, both of which may be subject to wide variation.
It doesn't say anything about "rest" so the motor must always be on.
"...both of which are subject to wide variation." must be referring to the size of the "load" and the duration of the "load".
It appears that this is referring to the situation where the motor is subjected to any kind of loading, from light to extreme, and for any length of time, from short periods to long periods.
So... here is the question...
How is the motor of a rock-crusher classified?
Sure, I can't go wrong by saying that it is classified as "Varying Duty"... but is that the appropriate (right) classification?
It seems that, by definition, the rock crusher could also be classified under case (1) of Intermittent Duty...
"...alternate intervals of (1) load and no load"
It probably couldn't be classified as "Periodic" because there is no way to "know" that the load is "periodic".
And since there is no way to assure that all of the rock is consistent in density, there is no way to assume that loading will be consistent even if the rock is fed at a constant rate.
So... how would a rock crusher be classified?
