Voltage drop to small, 120 VAC control panel

[ramsy]

Just do a standard voltage drop calculation.

Roughly 1A of load, 1500 feet of wire, 2.5 ohms per 1000 feet. A bit less than 4V of drop.

The AC formula from Tbl.9 Note #2 gets ~7 volts dropped with Tbl.9 default pf=0.85

If excess capacitance from 1500ft of cable results in negative pf=(-0.01), voltage drop is near Zero, before it hits Ctrl-Panel power supply.

If UL listed control panel uses a class-2 power supply for control voltage, or external wall wort, this inductive reactor may remove branch-circuit capacitance, before feeding control circuits.

 

[Isaiah]

The AC formula from Tbl.9 Note #2 gets ~7 volts dropped with Tbl.9 default pf=0.85

If excess capacitance from 1500ft of cable results in negative pf=(-0.01), voltage drop is near Zero, before it hits Ctrl-Panel power supply.

If UL listed control panel uses a class-2 power supply for control voltage, or external wall wort, this inductive reactor may remove branch-circuit capacitance, before feeding control circuits.

The control panel does not use a class 2 power supply for control voltage. It comes from the control power transformer in the MCC bucket.


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[ramsy]

The control panel does not use a class 2 power supply for control voltage. It comes from the control power transformer in the MCC bucket.

Perhaps a separate reactor product or UPS powering the control panel would resolve branch-capacitance issues, if class-2 control panel is not more practical.

 

[Isaiah]

Perhaps a separate reactor product or UPS powering the control panel would resolve branch-capacitance issues, if class-2 control panel is not more practical.

I can’t change or modify the panel - it has already been purchased by the client. UPS sounds like good idea for a 120V power source.


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[ramsy]

You might want to avoid UPS products that just monitor the circuit with a trickle charger to battery, or use inverters that cause more line noise than your relays can handle.

One of my clients got a UPS from Amazon that trips everything in the house. A simple line reactor may be more practical.

 

[DrSparks]

Wouldn't a choke in the control circuit mitigate the capacitance?

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[Arester]

Engineering wants to install a new local control panel approximately 700 feet from the MCC. The schematic shows 120VAC power to the panel from a 130VA CPT within the associated ‘combo-starter’ MCC bucket. The panel contains 3 ‘ice cube’ control relays, 2 limit switches and 2 LEDs.
My question is, will there be enough voltage to energize these small devices at 700’ from its 130VA source using #14 AWG wire, XHHW-2, 600V insulated CU?


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The voltage drop with #14 would be just below 4 V (Download a VD calculator based on NEC ( https://www.mc-group.ca/voltage_drop_calculator.htm - works for free up to #6 AWG) But is sounds to me (and I maybe wrong) like you should just move the control transformer (and associated fuse) from the MCC bucket to the local disconnect serving the controlled load. That way the load and associated control will be fully isolated for maintenance and there will not be a VD issue to tackle.

 

[Isaiah]

The voltage drop with #14 would be just below 4 V (Download a VD calculator based on NEC ( https://www.mc-group.ca/voltage_drop_calculator.htm - works for free up to #6 AWG) But is sounds to me (and I maybe wrong) like you should just move the control transformer (and associated fuse) from the MCC bucket to the local disconnect serving the controlled load. That way the load and associated control will be fully isolated for maintenance and there will not be a VD issue to tackle.

Yes, I’ve already proposed that option. Client will make a decision tomorrow.
Thanks for your input.


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