Fuses for 12V LED Lights

[jbox84126]

Hey folks,

I'm still fairly new to the world of 12v circuits and trying to be overly cautious about my wiring setup. I recently replaced all the bulbs in my cabin from incandescent to LED. As far as I'm aware, there are no fuses in this circuit, which is on a 15A breaker.

Did the filaments themselves function as a fuse and do I need to put a smaller fuse ahead of each LED bulb with the switch?

Thanks! Jon

[Stu Jackson]

There are two reasons for fuses, Jon. One is to protect the equipment. Second is to protect the wire.


In case One, the LEDs "load" is minuscule, compared to the lights they replaced. So changing a fuse any fuse, for LEDs makes no sense.


In the second case, if you haven't changed the wiring, then leave the fusing as it is, nothing to change.


The REASON on "fuses to protect the wire" is this: think of your batteries as a big BOMB. If the wires FROM the battery get shorted out for whatever reason, you want the fuse to protect the wires downstream from the power in the batteries.



Blueseas has great wring and fuse sizing tables.


Here's the link to the page, scroll down for the PDF download of the Protect Your Boat With The Correct Size Wire And Fuse - Wire Size Chart: https://www.bluesea.com/support/reference which links to this table:
https://d2pyqm2yd3fw2i.cloudfront.ne...ence/20010.pdf

[jbox84126]

Thanks...all makes sense...
Follow-up Q: I'm installing a cockpit light that came with very small gauge wire (20-22 AWG) connected. When i connect these into the main lighting circuit (14 awg with a 15A breaker) do i need a separate fuse to protect these smaller wires from burning out in the case of a short?

[Jammer]

Typically an additional fuse isn't used in that case.

[krid2000]

Originally Posted by jbox84126

I'm installing a cockpit light that came with very small gauge wire (20-22 AWG) connected. When i connect these into the main lighting circuit (14 awg with a 15A breaker) do i need a separate fuse to protect these smaller wires from burning out in the case of a short?

Look up the amperage limits for AWG 22 wiring.
I would put a fuse on it.

HTH
Dirk

[jbox84126]

Originally Posted by krid2000

Look up the amperage limits for AWG 22 wiring.
I would put a fuse on it.

HTH
Dirk

Thanks Dirk!

[jbox84126]

Oooook more fuse / gauge questions if folks are up for it. I'm working on installing some 12v sockets / usb ports in my berths.

I bought this outlet from Amazon and there's some things about it that mystify me.
It claims it can provide up to 150W (or 12.5A) but comes with 18 gauge wire and a small fuse that would quickly burn out if I were to hit that max.

I'm planning to ignore the provided wires and run 14 awg to the outlets directly without a fuse because its on a 15A breaker.

Anything I'm missing?

[Spot]

Some random thoughts:
-12V is really 12.7 or more if system is being charged by alternator or solar or a power converter
-they make a step-down crimp connector for hooking those smaller wires to bigger wires like the LED light pigtails to 14 ga.
- If you routinely need higher amps at 12V you may want to consider something more robust than the old 'cigarette lighter' format
-check that the socket has correct polarity. I installed one reversed and then tested with an incandescent probe, which shows power but not polarity...and then 'let the smoke out' of the cheap USB adapter I plugged into it.

[GordMay]

Pigtails*, less than 7 inches (175mm) in length, are exempt from overcurrent protection, and minimum wire size, requirements.

* “Pigtails” are conductors, integral to an electrical component or appliance [ie: LED lighting], for the purpose of connection to external circuits.

Hence: A 15 Amp Circuit breaker [or fuse], protecting a #14 AWG branch circuit, to which a LED lamp[s], with an unfused #22 AWG pigtail, is connected, is considered normal good practice, and acceptable.

[CaptTom]

Originally Posted by jbox84126

I bought this outlet from Amazon and there's some things about it that mystify me.
It claims it can provide up to 150W (or 12.5A) but comes with 18 gauge wire and a small fuse that would quickly burn out if I were to hit that max.

I do what you're planning to do. Use the same gauge wire as the rest of the fused circuit.

Reading between the lines, I think that's the expectation for the cigarette lighter side of the set you bought. "up to" 150W, but only if you have something like an actual cigarette lighter which needs that much, and only if you connect it to wiring and in a circuit which can handle that much.

Originally Posted by Spot

Some random thoughts:
-12V is really 12.7 or more if system is being charged by alternator or solar or a power converter...

My battery chargers and alternators put out a lot more than that. An internally regulated "dumb" alternator may remain at almost 14V. I've never found this to be a problem for devices like the one linked, which are designed to live in a boat, car or RV. I've got them all over the boat.

[Jammer]

Originally Posted by jbox84126

Oooook more fuse / gauge questions if folks are up for it. I'm working on installing some 12v sockets / usb ports in my berths.

I bought this outlet from Amazon and there's some things about it that mystify me.
It claims it can provide up to 150W (or 12.5A) but comes with 18 gauge wire and a small fuse that would quickly burn out if I were to hit that max.

I'm planning to ignore the provided wires and run 14 awg to the outlets directly without a fuse because its on a 15A breaker.

Anything I'm missing?

You're buying an iffy electrical product from a no-name vendor that: hasn't been designed or tested to any sort of industry standards (UL, CE, etc), is unlikely to perform reliably at its stated capacity, and handles enough power to pose a fire risk.

Switching out the lead wires won't change any of that.

Adding a 15 amp breaker ahead of an unsafe component doesn't make it into a safe component.

[Spot]

The device is stamped and the packaging marked for CE...does the price point or retailer make these markings suspect?

[Jammer]

CE is a self-certification program so it comes down to whether you trust the supplier. Who knows, perhaps they made more of an effort than I gave them credit for.

[Spot]

No worries Jammer. I did not know that CE is self-certified.

[jbox84126]

Originally Posted by Stu Jackson

There are two reasons for fuses, Jon. One is to protect the equipment. Second is to protect the wire.

Stu, to your point should I have smaller fuses by the usb port to protect the devices we'll be charging?

Jon