Fuses Needed to Comply with ABYC Rules

[CharlieJ]

waterdancer's tale is a classic case of a locked rotor, in this case with almost disastrous results.

During seminars, I will deliberately overfuse a small Rule centrifugal pump, jam the impeller with a screwdriver and then apply power and continue the lecture. Within about 10 to 15 minutes the pump starts to smoke. NOTE: THE FUSE NEVER OPENS DURING THIS DEMO! And this is why marine equipment manufactures are required to provide the fuse rating for their rotating equipment.

Here is the applicable section from the ABYC E-11 Standard:

11.10.1.2.1 Motors and motor operated equipment, except for engine cranking motors, shall be protected internally at the equipment, or by branch circuit overcurrent protection devices suitable for motor current. The protection provided shall preclude a fire hazard if the circuit, as installed, is energized for seven hours under any conditions of overload, including locked rotor.
NOTES:
1. It may be necessary to use thermally responsive protection devices on the equipment or system if the motor is not capable of operating continuously at maximum possible loading.
2. It may be necessary to test as installed in order to assure compliance with the locked rotor requirement. Voltage drop, due to wire size, and delay characteristics of the overcurrent protection device may have to be adjusted to protect the motor.

In the case of the Rule 500, if it was a 12VDC model, the technical specification is to protect it with a 2.5A fuse or circuit breaker. Rule 500 > ITT Flow Control - Engineered for life.

There is generally a lot more to this stuff then meets the eye.

Charlie will now relinquish his soapbox.

Hope this helps.
Charlie

[smurphny]

Originally Posted by CharlieJ

waterdancer's tale is a classic case of a locked rotor, in this case with almost disastrous results.

During seminars, I will deliberately overfuse a small Rule centrifugal pump, jam the impeller with a screwdriver and then apply power and continue the lecture. Within about 10 to 15 minutes the pump starts to smoke. NOTE: THE FUSE NEVER OPENS DURING THIS DEMO! And this is why marine equipment manufactures are required to provide the fuse rating for their rotating equipment.

Here is the applicable section from the ABYC E-11 Standard:

11.10.1.2.1 Motors and motor operated equipment, except for engine cranking motors, shall be protected internally at the equipment, or by branch circuit overcurrent protection devices suitable for motor current. The protection provided shall preclude a fire hazard if the circuit, as installed, is energized for seven hours under any conditions of overload, including locked rotor.
NOTES:
1. It may be necessary to use thermally responsive protection devices on the equipment or system if the motor is not capable of operating continuously at maximum possible loading.
2. It may be necessary to test as installed in order to assure compliance with the locked rotor requirement. Voltage drop, due to wire size, and delay characteristics of the overcurrent protection device may have to be adjusted to protect the motor.

In the case of the Rule 500, if it was a 12VDC model, the technical specification is to protect it with a 2.5A fuse or circuit breaker. Rule 500 > ITT Flow Control - Engineered for life.

There is generally a lot more to this stuff then meets the eye.

Charlie will now relinquish his soapbox.

Hope this helps.
Charlie

That's great info. I'm going to have to double check the ratings on my two electric pumps to make sure the fuses are not too large. Have never even thought about a bilge pump lighting up!

[Lars_L]

That part of the paragraphs in post #16 sounds quit logical and reasonable. But earlier in post #9 in this thread they say that you don’t need any fuse for the start motor. Are those texts from the same paragraphs?

[cburger]

Originally Posted by Lars_L

That part of the paragraphs in post #16 sounds quit logical and reasonable. But earlier in post #9 in this thread they say that you don’t need any fuse for the start motor. Are those texts from the same paragraphs?

I am under the impression that ABYC has upgraded the regulation to include properly rated fusing at the battery terminal. I installed the Blue Sea terminal fuse holder and fuses for a customer who's surveyor had speced theese citing ABYC standard. They are very inexpensive and should take care of any issues with the starter motor, no?

Terminal Fuse Block (MRBF - Marine Rated Battery Fuse) - Blue Sea Systems

[GordMay]

Originally Posted by Lars_L

That part of the paragraphs in post #16 sounds quit logical and reasonable. But earlier in post #9 in this thread they say that you don’t need any fuse for the start motor. Are those texts from the same paragraphs?

They're separate paragraphs, of the same section.

Starter motors are not REQUIRED to be fused. However, nothing precludes the fusing of starter circuits.

ABYC E-11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent protection within a distance of seven inches (175mm) of the point at which the conductor is connected to the source of power measured along the conductor. (See FIGURE 15.)

EXCEPTIONS:
1. Cranking motor conductors.

11.10.1.2.1 Motors and motor operated equipment, except for engine cranking motors, shall be protected internally at the equipment, or by branch circuit overcurrent protection devices suitable for motor current.

[sdowney717]

what happens when it is real cold, the motors are real stiff and the starter motor will be drawing more current than normal. 300 amps is not enough. I also wonder if the fuse would have an effect on the current-voltage drop when electricity flow is close to fuse amperage.

http://dolphinmarineservice.homestead.com/Ele3.html
When a starter is first engaged, the current required can be as high as 300 to 400 amps for a V8 engine

how about when the starter lugs like in a gas motor when the timing is too advanced, preignition from too hot. starter is rotor locking then letting go over and over. so starter current draw will shoot skyhigh. then the fuse blows and you cant start at all. I would view this as a nuisance fuse.

[smurphny]

I would think that once the starter's maximum amperage rating has been reached (when it stops turning because of some excessive load), that's exactly when you want the fuse to blow. Does not make much sense to keep pressing the starter button if the starter is not turning. Any further load may well cause some internal part to melt down/start burning. It does not take that much heat to start burning off wire insulation and once the bare wire hits a grounded part, it's major meltdown time. If the amp rating on the particular starter exceeds the maximum fuse size, then you're stuck with no good fusing solution.

[sdowney717]

likely we have all tried to crank over engines in our life sometimes that are not cranking like they should be cranking. you can always hear the motor crank or not crank properly, how many people just keep the crank switch on start carelessly? The starter wires on my boat wont melt, the starter will burn up and then go dead.

one thing i could do is sleeve the wire in a rubber hose for a little extra protection. that might encourage heat retention. I never noticed the wires get warm after cranking.
starter wires should be attached along their length so they cant get caught on the motor parts.

[foggysail]

Just a comment on the Rule and other pumps. If the manufacturers know and understand the problems outline in this thread, they are open to expensive liability suits that could put them out of business.

The extra cost to make them magnetically coupled could be less than a law suit.

Foggy

[sdowney717]

some already have electronics that can detect a load of water vs spinning in air. rotor locking means high amps likely also detectable. Why arent poeple using this right sized breakers?
if it breakered properly it cant burn up the motor.

I will deliberately overfuse a small Rule centrifugal pump

sounds like burned up pumps are mostly an installation issue.

[smurphny]

Originally Posted by sdowney717

some already have electronics that can detect a load of water vs spinning in air. rotor locking means high amps likely also detectable. Why arent poeple using this right sized breakers?
if it breakered properly it cant burn up the motor.


sounds like burned up pumps are mostly an installation issue.

The surprising information above, in CharlieJ's post is the low amp rating on the Rule 500 he mentions. Most folks wire their bilge pumps with #12/14 wire. The usual way to fuse at a main panel is by wire size, not device ampacity. If these Rule 500s burn up above 2.5a, a #14 wire, with a 15amp fuse/breaker would NOT blow.