If a 5 amp circuit breaker really trips at 6.5 amps, why don't they call it a 6.5 amp circuit breaker instead of a 5 amp circuit breaker? One of life's mysteries? Gary Wyngarden S/V Shibumi H335
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Derek Rowell
I think you'll find...
... a 5 amp fuse doesn't blow at 5.00 amps either. The current ratings are the maximum working currents. So a 5 amp breaker is designed to operate at 5 amps, not break at 5 amps.
... a 5 amp fuse doesn't blow at 5.00 amps either. The current ratings are the maximum working currents. So a 5 amp breaker is designed to operate at 5 amps, not break at 5 amps.
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Don Alexander
Because -
It will conduct 5 amps reliably. Like a 5 amp fuse or 5 amp fusewire, both are okay at 5 amps (for 1000 hours) but will go open circuit at higher currents. Often it needs double to cause them to blow. The rating is intended to match the needs of the appliance which it feeds. However breakers and fuses are NOT intended to protect appliances they are to protect the BOAT. i.e from fire or melt down. Regards, Don A.
It will conduct 5 amps reliably. Like a 5 amp fuse or 5 amp fusewire, both are okay at 5 amps (for 1000 hours) but will go open circuit at higher currents. Often it needs double to cause them to blow. The rating is intended to match the needs of the appliance which it feeds. However breakers and fuses are NOT intended to protect appliances they are to protect the BOAT. i.e from fire or melt down. Regards, Don A.
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eugene
working current and breaking current
The circuit breaker has two characteristics working current and breaking current. The working current it what we see in the specs. When you design you electrical systems you have to figure out the MAX current what your equipment required and choose the circuit breaker with the same working current. If the manufacture put the breaking current in spec it can be a lot of confusion - you install the pump with max load 10 A, connect it to the circuit breaker 10A. What will happen when you turn it on? The circuit breaker will shoot it off. It is just easy the way it is. Eugene.
The circuit breaker has two characteristics working current and breaking current. The working current it what we see in the specs. When you design you electrical systems you have to figure out the MAX current what your equipment required and choose the circuit breaker with the same working current. If the manufacture put the breaking current in spec it can be a lot of confusion - you install the pump with max load 10 A, connect it to the circuit breaker 10A. What will happen when you turn it on? The circuit breaker will shoot it off. It is just easy the way it is. Eugene.
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Peggie Hall/Head Mistress
Rated load vs. maximum load
Current from shore power and generators isn't absolutely level...various things can cause it to dip and spike. Every fuse and breaker has a little extra "running room" above its rated load to keep it from blowing every time there's even the slightest power surge. If it didn't, fuses and breakers would be blowing every time anyone turned something on, 'cuz electrical devices pull more current when they start than they use while running.
Current from shore power and generators isn't absolutely level...various things can cause it to dip and spike. Every fuse and breaker has a little extra "running room" above its rated load to keep it from blowing every time there's even the slightest power surge. If it didn't, fuses and breakers would be blowing every time anyone turned something on, 'cuz electrical devices pull more current when they start than they use while running.
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Vince
slow blow or instantaneous
Usually when you switch on any electrical device, i.e. a lightbulb, there is an instantaneous surge in current. This current is usually more than the continuous rating of the device. For example, a light bulb that normally draws 1 amp may draw as much as 5 amps when you first flip the switch on. Fuses come in different types. One type that is often chosen in this situation is one known as a "slow blow" fuse. These fuses take a little longer to open than a standard fuse (typically a few milliseconds), but are your closest guarantee to a fuse that won't trip pre-maturely. However, be careful, there are places a slow blow should not be used. For example, the high-current that they allow to pass for fractions of a second may damage solid-state electronics (Radios, TV's, etc.).
Usually when you switch on any electrical device, i.e. a lightbulb, there is an instantaneous surge in current. This current is usually more than the continuous rating of the device. For example, a light bulb that normally draws 1 amp may draw as much as 5 amps when you first flip the switch on. Fuses come in different types. One type that is often chosen in this situation is one known as a "slow blow" fuse. These fuses take a little longer to open than a standard fuse (typically a few milliseconds), but are your closest guarantee to a fuse that won't trip pre-maturely. However, be careful, there are places a slow blow should not be used. For example, the high-current that they allow to pass for fractions of a second may damage solid-state electronics (Radios, TV's, etc.).
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Stan
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Jim Sullivan
And this too
In addition to all of the above consider>>> Most circuit protective devices use heat which is produced by overcurrent to function. Either melting an element (fuse) or heating a bimetal (circuit breaker)which will cause circuit interruption. These devices are designed to operate at ambient temperatures of around 80º F, but if it is much cooler or warmer the reliability will vary. Also 5 amp is a nominal value. What does that mean? What does a 2x4 board or a 3/4" pipe actually measure? Ans: some variable which may be close to the above. <big grin> Any way: Good luck and good sailing Jim Why Knot!
In addition to all of the above consider>>> Most circuit protective devices use heat which is produced by overcurrent to function. Either melting an element (fuse) or heating a bimetal (circuit breaker)which will cause circuit interruption. These devices are designed to operate at ambient temperatures of around 80º F, but if it is much cooler or warmer the reliability will vary. Also 5 amp is a nominal value. What does that mean? What does a 2x4 board or a 3/4" pipe actually measure? Ans: some variable which may be close to the above. <big grin> Any way: Good luck and good sailing Jim Why Knot!
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Doug T.
Protecting what...
As someone else pointed out, the circuit breakers in a distribution panel are intended to protect the boat, not the equipment. The breaker should be sized to protect the wire and all connectors from overheating and/or melting. Remember, you might have more than one piece of equipment (or light or whatever) attached to any particular circuit. If you need to protect a piece of equipment from too much current, it needs it's very own fuse (or breaker). For example, you might have all of your basic nav equipment (depth sounder, knotmeter, GPS) wired to one breaker labeled "nav equipment". The breaker and the associated wires should be rated for the total current on the circuit. The individual components need their own individual fuses to protect them from surges that would damage them. Some devices are a lot more sensitive than others, so they need different kinds of fuses. Generally, they should be rated at the drawing capacity of the component. That way the component won't get more current than it ever really needs. Components like light bulbs don't need a fuse -- if there's a surge, it's far cheaper to simply replace the bulb than it is to wire in fuses to all the lights and then change the fuse!!
As someone else pointed out, the circuit breakers in a distribution panel are intended to protect the boat, not the equipment. The breaker should be sized to protect the wire and all connectors from overheating and/or melting. Remember, you might have more than one piece of equipment (or light or whatever) attached to any particular circuit. If you need to protect a piece of equipment from too much current, it needs it's very own fuse (or breaker). For example, you might have all of your basic nav equipment (depth sounder, knotmeter, GPS) wired to one breaker labeled "nav equipment". The breaker and the associated wires should be rated for the total current on the circuit. The individual components need their own individual fuses to protect them from surges that would damage them. Some devices are a lot more sensitive than others, so they need different kinds of fuses. Generally, they should be rated at the drawing capacity of the component. That way the component won't get more current than it ever really needs. Components like light bulbs don't need a fuse -- if there's a surge, it's far cheaper to simply replace the bulb than it is to wire in fuses to all the lights and then change the fuse!!
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