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32 amp circuit breaker for 14 guage wire?


GlennWest
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I have a down converter from Victron that I am yet to install. I have the same concern. Not specifically on the breaker but that the terminals are not really large enough to accept my calculated needed wire gauge. I am going to run larger gauge and then just make adjustment to smaller size right at the terminal. 

 

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Dave, I have a lot of #6 wire. Left over from a 50 amp shore power cord. Think I will use this on 48v and 12v side. It's an over kill but fits better on circuit breakers. They that are suited for 48v have 1/4" studs for wire connection. It also calls for a 2 pole circuit breaker. I don't see benefit in protection on positive and negative side. Either trips all circuit flow stops. 

Edited by GlennWest
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4 hours ago, GlennWest said:

Got my chinese 60 amp stepdown converter. Calls for input wires at 46-60v #14. Also a 32 amp Corcuit breaker. Output wires 12v #6. My question,  isn't 30 amp protection too high for #14 

There are a few exceptions in the NEC to allow smaller wire than expected. Off the top of my head, none of them apply to this situation, but I might be missing something. More info about the converter would help.

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2 hours ago, SCClockDr said:

I'd expect the 32 amp spec applies to the lower voltage output. 32a @ 12v would pull 8a @ 48v.

Calls for circuit breaker on 48v side just in front of the converter. I don't see needing to use a 2 pole breaker. Just positive or negative. Am I wrong? 

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Glenn, glad to see you're thinking about such things, with all you're investing the last thing you need is overloaded wiring and heat or fire !!!

 I will answer your basic overcurrent protection question "in theory" and what the NEC has to say about it, but NOT get into what loads or devices or voltages you're dealing with. I don't know the specs of what you have and that's wasn't your question

 YOU ARE RIGHT the overcurrent protection device current rating must not be greater then the wire its protecting rated ampacity. IE you protect 30 amp rated wire with no larger then a 30 amp overcurrent protection device. The purpose of the overcurrent protection device is to protect the wiring NOT the device/load.

NOTE best I recall one (may be others) exception is for a motor branch circuit in which you can oversize a standard thermal magnetic breaker up to something like 175% in order to allow the motor to start yet  not trip the breaker. They figured the breakers magnetic function would still trip upon a short while thermal concerns would be protected by the motor starter. HOWEVER only if the motor is thermal overload protected !!!! I didn't like to use that exception, instead I preferred Class K5 (think that's right no warranty) Dual Element time delay fuses. They also make HACR circuit breakers to deal with large surge start up requirements.  

Look at the manual and specs and see what they require AND DONT VOID ANY WARRANTY based on my recollections of the NEC or do what I or others here may speculate .

Merry Christmas

John T Live from Avon Park Florida

 

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The maximum current rating of the awg wire size is part of the equation. 14 awg is safe to 30 amps in most locations. There is a different calculation for limiting voltage drop in a circuit.  Larger wire sizes are not usually a problem. With larger wires you can use a larger fuse, again for lower voltage drop. Use the larger 6 awg you have on hand and rest easy.

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What most non electricians don't realize is the ampacity of a certain wire DEPENDS on the Insulation,,,,,,,,,Temperature,,,,,,,,,,,If its a single conductor in free air,,,,,,,,,,,,Or jacketed cable of what type and how many conductors,,,,,,,,,,,Or if in conduit what size conduit and how many conductors,,,,,,,,,,,,, 

When I practiced the NEC wiring ampacity charts could get very detailed and complicated and were NEVER as simple as lay persons thought.

REGARDLESS you cant use an overcurrent protection device with a higher rating then the wires ampacity, its just that ampacity depends on several factors.

Of course bigger conductors means less line voltage drop and its better to be on the safe side....

John T    

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