Motor Controllers and Remote Control: LVP, LVR and the Control Circuit

What the rule requires

Which controller the service demands

Four services are named in the regulation: fire pump, elevator, steering gear, and any auxiliary vital to the vessel's propulsion system. A controller on one of those must have low-voltage release, provided automatic restart after a voltage failure is not hazardous. Where automatic restart is hazardous, that same controller must have low-voltage protection instead. One service is carved out of the LVR requirement by name: a vital propulsion auxiliary that can be restarted from a central control station. 46 CFR §111.70-3

The trigger has two parts, and both must be read before answering. First, what service does this motor perform. Second, is an unattended restart hazardous. A question that gives you a fire pump and stops there is testing the first part. A question that gives you a machine that could injure someone on restart is testing the second.

Motors outside that vital group are handled from the other direction. They must not have low-voltage release unless the starting current and short-time sustained current of the additional LVR load falls within the capacity of one ship's service generator. That is a prohibition with a capacity test attached rather than a design option. Automatic sequential starting of LVR controllers is accepted as a way of satisfying the limit, which is how a plant with several LVR loads keeps the aggregate restart demand inside one generator.

Everything else gets low-voltage protection. Two controllers are excepted: one that has low-voltage release under the vital-service paragraph, and one serving a motor of less than 2 horsepower (1.5 kW).

A 1.5 hp fresh water pressure pump. Is a controller with neither LVP nor LVR acceptable?

Yes. The blanket low-voltage protection requirement excepts a motor controller for a motor of less than 2 horsepower (1.5 kW). Watch the wording on the exam. Two horsepower exactly is not "less than 2 hp," so a 2 hp motor is inside the requirement, and 1.5 kW is the metric equivalent of the same threshold, not a second, separate one.

Remote control, interlock and indicator circuits

The controller must be designed so that an accidental ground in a remote control circuit cannot cause the stop switches to fail to operate, and cannot start the motor. 46 CFR §111.70-7 A candidate who understands that one requirement will still get most control-circuit questions right, because the remaining paragraphs are built around the same problem: energy left inside an enclosure after the operator believes it is dead.

Control, interlock and indicator potential must be derived from the load side of the motor and controller disconnect device. Opening the disconnect then removes the control circuit along with the power circuit. The exception is a control function that requires circuits common to two or more controllers, which cannot be fed from one controller's load side; that case falls to the alternative switching arrangements.

Where those arrangements apply, the design must first take all practicable steps to eliminate all but one source of power in the enclosure. If that is impracticable and the control, interlock or indicator circuit voltage is more than 24 volts, one of two arrangements is required:

Each control conductor is disconnected from all sources of potential by a disconnect device independent of the motor and controller disconnect device. The two devices must be adjacent, and a fixed sign on the exterior of the main disconnect device door must warn the operator to open both.
Each control conductor is disconnected by a device actuated by opening the controller door, or the power must be disconnected before the door can be opened, with no uninsulated or unshielded surface on the device, its connections, or the terminal blocks for the vessel's wiring. Used on a vital auxiliary circuit, this arrangement requires a nameplate on the door warning that opening it will trip a vital auxiliary off-line.

Overcurrent protection of the control conductors themselves is required unless one of four conditions is met: the conductor is wholly within the controller enclosure; the branch circuit overcurrent device is rated or set at not more than 300 percent of the control conductor's current-carrying capacity; there is an overcurrent device in each side of the line at not more than 300 percent of that capacity, relaxed to the supply side of one line only where there is no appreciable difference in potential between the external conductors under operating conditions; or opening the circuit creates a hazard. Steering gear control and indicator circuit overcurrent protection is directed to Subpart 111.93.

Marking and enclosure

Seven items must appear externally on each motor controller and motor control center: manufacturer's name or identification, voltage, number of phases, current, kW (horsepower), identification of the motor being controlled, and current rating of the trip setting. Inside, on the door interior, each controller carries heat durable and permanent elementary wiring and schematic diagrams. Since this is an open-book module, work the marking question by opening the list and counting off the options rather than trusting memory. The distractors are built from plausible items that are not on it.

Enclosures must meet either NEMA ICS 2 and NEMA ICS 2.3, or Table 1 of IEC 60092-201:2019, as appropriate for the location of installation, and an enclosure in a hazardous location must additionally meet subpart 111.105. NEMA ICS 2.4 is the reference for the differences between NEMA and IEC devices in motor service.

Telling it apart: LVP against LVR

Both types drop the motor off the line when the voltage falls. What separates them is the behaviour when normal voltage returns. NAVEDTRA 14104 Ch. 12 — Controllers

Low-voltage protection (LVP) — cuts out automatically when electric power fails and must be restarted manually. Most shipboard controllers are this type. Misfiled case: candidates assign it to the fire pump because "protection" sounds like the safer choice, when the regulation requires release for that service.
Low-voltage release (LVR) — disconnects the motor when supply voltage drops below a predetermined level and automatically restarts it when supply voltage returns to normal. Used primarily with vital loads. Misfiled case: candidates treat it as a general upgrade and put it on a cargo winch or a machine shop lathe, where it is prohibited unless the generator capacity test is satisfied.

The names run against intuition, and that is why the pair produces so many wrong answers. Instructors commonly teach reading the words from the motor's point of view rather than the ship's: release releases the motor to restart on its own, while protection protects against an unexpected restart. The hook settles the behaviour but not the assignment. Do not let it carry you into thinking LVP is always the more conservative answer. On a fire pump, steering gear, elevator or propulsion-vital auxiliary, LVR is what the regulation requires, because a pump that needs a man in the space to restart it is no use during a blackout.

There is also a circuit-level tell, useful when a question shows you a schematic instead of naming the type. A three-wire start/stop scheme with a holding, or seal-in, contact keeps the motor running after the start button is released but drops out on loss of voltage, and the motor will not restart by itself when power returns until the start button is pressed again. NEETS Mod. 3 §3-2 A momentary start pushbutton sealed in by a contact is low-voltage protection.

A steering gear pump controller is arranged so that the motor comes back on the line by itself after a blackout. Is that a deficiency?

No, that is the required arrangement. Steering gear is one of the four services named for low-voltage release, and automatic restart of a steering gear pump is not hazardous. A steering gear controller that stayed dropped out until an engineer went below and pressed start would be the deficiency.

Working a question

Take an engine room with three motor-driven auxiliaries: a 40 hp electric fire pump, a 30 hp cargo winch, and a 1 hp lube oil priming pump. A question asks which controllers must have low-voltage release.

Identify the service first, not the horsepower. The fire pump is named in the vital-service list. The winch is not, and it is not an auxiliary vital to the vessel's propulsion system. The priming pump is not on the list either. 46 CFR §111.70-3
For the named service, test whether automatic restart is hazardous. A fire pump restarting on restoration of the bus is the intended outcome. So the fire pump controller must have low-voltage release. Had the machine been one whose unattended restart endangers personnel, the same paragraph would have required low-voltage protection.
Check the central-control-station carve-out. It applies only to a vital propulsion auxiliary. A fire pump is not one, so the carve-out does not reach it, and the LVR requirement stands.
Dispose of the non-vital motors under the prohibition. The winch must not have low-voltage release unless its starting current and short-time sustained current, as an added LVR load, are within the capacity of one ship's service generator. Absent that showing, its controller has low-voltage protection.
Apply the horsepower exception last. The 1 hp priming pump is under 2 horsepower (1.5 kW), so it is excepted from the low-voltage protection requirement altogether. The exception addresses whether LVP is required; it does not put the motor into the LVR group.

Answer: the fire pump controller only.

Work the steps in that order. A candidate who starts with horsepower will read "40 hp fire pump" and go looking for a size threshold that governs nothing here.

Where candidates lose the point

Reversing the two names. "Protection" is read as the type that keeps the motor available, so a fire pump question is answered LVP. One sentence of the regulation fixes it: the vital-service controllers must have low-voltage release where automatic restart is not hazardous.
Stopping at the service and skipping the hazard clause. A question that names a vital service and then describes a machine whose restart endangers a person is testing the second half of the trigger, where the answer flips to low-voltage protection.
Answering that every controller must have LVP. The blanket requirement is stated in those words, which is what attracts candidates, but two exceptions follow it: a controller with LVR under the vital-service paragraph, and a motor of less than 2 horsepower (1.5 kW).
Attaching the 300 percent figure to the motor. The figure is a ceiling on the branch circuit overcurrent device relative to the current-carrying capacity of the control, interlock or indicator conductor, and it is one of four alternatives to protecting that conductor directly. 46 CFR §111.70-7
Treating LVR as permitted anywhere it might be convenient. For motors outside the vital group it is prohibited unless the starting and short-time sustained current of the added LVR load is within the capacity of one ship's service generator. Automatic sequential starting is the accepted means of keeping that aggregate demand inside one generator, and a question describing several LVR loads brought up in sequence is describing a compliant plant.
Applying the alternative switching arrangements to any control circuit. They bite only where feeding from the load side of the motor and controller disconnect is impracticable and the control circuit voltage is more than 24 volts.
Losing the warning-sign detail. Where two independent adjacent disconnect devices are used, the fixed sign goes on the exterior of the door of the main disconnect device and tells the operator to open both. Confuse it with the vital-auxiliary nameplate, which goes on the controller door under the second arrangement, and you have answered the wrong half of the paragraph.

Check yourself

You are inspecting a controller for a ventilation fan motor rated 5 hp, non-vital. It is arranged to restart automatically when the bus is restored, and no generator capacity calculation is on file. Acceptable?

No. A motor outside the vital group must not have low-voltage release unless the starting current and short-time sustained current of the additional LVR load is within the capacity of one ship's service generator. Without that showing, the arrangement is not permitted, and the controller should have low-voltage protection.

An elevator motor controller: which type, and what would change your answer?

An elevator is one of the four named services, so low-voltage release, unless automatic restart after a voltage failure would be hazardous. In that case the same paragraph requires low-voltage protection. The service puts you in the paragraph; the hazard assessment picks the type.

A 60 hp lube oil service pump vital to propulsion can be restarted from the central control station. Must its controller have LVR?

No. A motor controller for a vital propulsion auxiliary which can be restarted from a central control station is excepted by name from the low-voltage release requirement.

A remote control circuit for a 120-volt controller is fed from the line side of the motor and controller disconnect because the circuit is common to two controllers. What does the installation now require?

One of the two alternative switching arrangements, since the control voltage exceeds 24 volts: either an independent disconnect device adjacent to the main one with a fixed warning sign on the exterior of the main disconnect door, or a disconnect actuated by opening the controller door (or power removed before the door will open), with no uninsulated or unshielded surfaces on the device, its connections or the terminal blocks. Before either, the design must take all practicable steps to eliminate all but one source of power in the enclosure.

A controller door is opened and you find the elementary wiring diagram missing. Where should it be, and what condition must it meet?

On the door interior, and it must be heat durable and permanent. The seven data items — manufacturer, voltage, phases, current, kW (horsepower), identification of the motor being controlled, and current rating of the trip setting — are marked externally.

A schematic shows a momentary start pushbutton with a seal-in contact across it and a stop button in series. The vessel's chief calls it an LVR starter. Is he right?

No. That is the three-wire start/stop arrangement with a holding contact: loss of voltage drops out the contactor, and the motor will not restart when power returns until the start button is pressed. That is low-voltage protection.

A motor controller is installed in a hazardous location. Meeting NEMA ICS 2 and NEMA ICS 2.3 for that location — is the enclosure compliant?

Not on its own. An enclosure in a hazardous location must also meet the requirements of subpart 111.105, on top of the NEMA or IEC 60092-201:2019 Table 1 requirement appropriate to the location.