Daisy Chained Receptacles in Conduit - 310.15(A) ?

[TwoBlocked]

310.15(B)(3) ... Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230). [310.15(C)(1) in the 2020]

Uh, I don't get it. 300.3 is about different voltage systems. Soooo, if motor power conductors and control conductors for a start stop station are in the same conduit to allow control right at the motor (starter in an MCC), you have to apply the adjustment factor to all the conductors if there is not a control transformer involved. But if there is one, then you do not count the control conductors because the power and control are different systems? That's how I read it, but is that what it says?

 

[kwired]

Uh, I don't get it. 300.3 is about different voltage systems. Soooo, if motor power conductors and control conductors for a start stop station are in the same conduit to allow control right at the motor (starter in an MCC), you have to apply the adjustment factor to all the conductors if there is not a control transformer involved. But if there is one, then you do not count the control conductors because the power and control are different systems? That's how I read it, but is that what it says?

I agree with you, as worded apparently can't use a control circuit tapped directly from the line terminals of the starter but put a transformer there and is fine even if results in same operating voltage, without making ampacity adjustments anyway . Need to look in prior years to see what might have changed, I remember running control wiring with power wiring in the past, and presumably was acceptable to do so. But then not very often was there enough conductors in the raceway that it would impact conductor size after applying ampacity adjustments anyway. I kind of also seem to remember you can only run these control circuits with the power conductors if they are associated with said power conductors, which in many cases would end up limiting your current carrying conductor count as you often would only have one motor and one set of associated control conductors pulled together, but back at the electrical room there may be many coming together in wireways where there is more association and specifically addresses not counting the control conductors for ampacity adjustment purposes.

 

[TwoBlocked]

I agree with you, as worded apparently can't use a control circuit tapped directly from the line terminals of the starter but put a transformer there and is fine even if results in same operating voltage, without making ampacity adjustments anyway . Need to look in prior years to see what might have changed, I remember running control wiring with power wiring in the past, and presumably was acceptable to do so. But then not very often was there enough conductors in the raceway that it would impact conductor size after applying ampacity adjustments anyway. I kind of also seem to remember you can only run these control circuits with the power conductors if they are associated with said power conductors, which in many cases would end up limiting your current carrying conductor count as you often would only have one motor and one set of associated control conductors pulled together, but back at the electrical room there may be many coming together in wireways where there is more association and specifically addresses not counting the control conductors for ampacity adjustment purposes.

Might be best to go by the intent rather than the letter of the law here. Funny thing is, although you are allowed to run 120V control with 480V power (and seems to be allowable without an adjustment) I would be more comfortable running 480V control and 480V power together (which seems to require an adjustment). Then there are the yahoos that provide 24VDC control power completely separate from the 480V power. Open the breaker and the contactor stays pulled in and the system thinks the motor is running...

Maybe someone else has run across this and figured it out.

 

[jap]

Might be best to go by the intent rather than the letter of the law here. Funny thing is, although you are allowed to run 120V control with 480V power (and seems to be allowable without an adjustment) I would be more comfortable running 480V control and 480V power together (which seems to require an adjustment). Then there are the yahoos that provide 24VDC control power completely separate from the 480V power. Open the breaker and the contactor stays pulled in and the system thinks the motor is running...

Maybe someone else has run across this and figured it out.

This is actually refreshing to hear.

Sometimes I think I'm the only one out there battling interlock issues even with all the current sensing relays and motion sensors in place.


JAP>

 

[don_resqcapt19]

Might be best to go by the intent rather than the letter of the law here. Funny thing is, although you are allowed to run 120V control with 480V power (and seems to be allowable without an adjustment) I would be more comfortable running 480V control and 480V power together (which seems to require an adjustment). Then there are the yahoos that provide 24VDC control power completely separate from the 480V power. Open the breaker and the contactor stays pulled in and the system thinks the motor is running...

Maybe someone else has run across this and figured it out.

I never installed an new 480 volt control circuits in my career that started in 1973. Most were 120 volts from a control power transformer in the starter bucket, and now you see a lot of 24 volt controls. However sometimes the distance can cause issues on the low and require a relay to make sure a larger size starter could be pulled in.

As far as the separate control power and the controls system not knowing that the 480 volt power is off, I did one job where the design called for 480 volt relays connected to the load side of the starter, and a relay contact used in the control system to verify that the motor has power.

Have also seen current switches on the T leads used for the same purpose.

On critical loads where there were mechanical things like belts or chains between the motor and the actual equipment, some type of zero speed switch was often used on the actual load, so it is was not spinning for any reason, the control system knew.

 

[jap]

I never installed an new 480 volt control circuits in my career that started in 1973. Most were 120 volts from a control power transformer in the starter bucket, and now you see a lot of 24 volt controls. However sometimes the distance can cause issues on the low and require a relay to make sure a larger size starter could be pulled in.

As far as the separate control power and the controls system not knowing that the 480 volt power is off, I did one job where the design called for 480 volt relays connected to the load side of the starter, and a relay contact used in the control system to verify that the motor has power.

Have also seen current switches on the T leads used for the same purpose.

On critical loads where there were mechanical things like belts or chains between the motor and the actual equipment, some type of zero speed switch was often used on the actual load, so it is was not spinning for any reason, the control system knew.

This just means you're normal Don.

JAP>

 

[TwoBlocked]

I never installed an new 480 volt control circuits in my career that started in 1973. Most were 120 volts from a control power transformer in the starter bucket, and now you see a lot of 24 volt controls. However sometimes the distance can cause issues on the low and require a relay to make sure a larger size starter could be pulled in.

As far as the separate control power and the controls system not knowing that the 480 volt power is off, I did one job where the design called for 480 volt relays connected to the load side of the starter, and a relay contact used in the control system to verify that the motor has power.

Have also seen current switches on the T leads used for the same purpose.

On critical loads where there were mechanical things like belts or chains between the motor and the actual equipment, some type of zero speed switch was often used on the actual load, so it is was not spinning for any reason, the control system knew.

Yep, seen most of that, too. One place I have installed new starters with 480V coils is for gas drilling auxiliary equipment with combo starters. They get beat up enough and often need repair, so why bother with reducing the voltage on the control circuit? Another place I've seen it is on large across the line well pumps. Takes a BIG control transformer otherwise.

 

[kwired]

I never installed an new 480 volt control circuits in my career that started in 1973. Most were 120 volts from a control power transformer in the starter bucket, and now you see a lot of 24 volt controls. However sometimes the distance can cause issues on the low and require a relay to make sure a larger size starter could be pulled in.

As far as the separate control power and the controls system not knowing that the 480 volt power is off, I did one job where the design called for 480 volt relays connected to the load side of the starter, and a relay contact used in the control system to verify that the motor has power.

Have also seen current switches on the T leads used for the same purpose.

On critical loads where there were mechanical things like belts or chains between the motor and the actual equipment, some type of zero speed switch was often used on the actual load, so it is was not spinning for any reason, the control system knew.

Not even with something that has the control switch(es) on the controller enclosure and your control circuit never leaves said enclosure?

I run into that a lot with 120, 208-240 as well as with 480 volt supplied equipment.

Now with a MCC or other pretty much any other multi motor control setup it will be common to see separately derived/supplied control power of either 120 VAC or 24 AC or DC for all the associated controllers of the setup.

 

[don_resqcapt19]

Not even with something that has the control switch(es) on the controller enclosure and your control circuit never leaves said enclosure?

I run into that a lot with 120, 208-240 as well as with 480 volt supplied equipment.

Now with a MCC or other pretty much any other multi motor control setup it will be common to see separately derived/supplied control power of either 120 VAC or 24 AC or DC for all the associated controllers of the setup.

Worked on some, but never installed any control circuits with a voltage that exceeded 120.

 

[jap]

Controls are controls.

Done one, done em all.

The only difference is how the voltage shows up on your meter when you're troubleshooting them.

JAP>

 

[kwired]

Controls are controls.

Done one, done em all.

The only difference is how the voltage shows up on your meter when you're troubleshooting them.

JAP>

Just don't get in a situation where you have 120 and 240 volt controls that need interlocked somehow and get an unintended back feed from the 240 sending enough voltage to make some the 120 components operate when not intended. Keep the interlocking of the 240 isolated on completely separate aux contacts or by relays if necessary.

If something has all 240 volt controls already and you try to add a 120 volt component, because all you can find that special timer or whatever is in a 120 volt version, you can also have back feed from the other side of the 240 cause unintended operation, so be careful planning how to integrate it into the system.

 

[jap]

Just don't get in a situation where you have 120 and 240 volt controls that need interlocked somehow and get an unintended back feed from the 240 sending enough voltage to make some the 120 components operate when not intended. Keep the interlocking of the 240 isolated on completely separate aux contacts or by relays if necessary.

If something has all 240 volt controls already and you try to add a 120 volt component, because all you can find that special timer or whatever is in a 120 volt version, you can also have back feed from the other side of the 240 cause unintended operation, so be careful planning how to integrate it into the system.

That's just simple common sense.

Jap>