Unfused 14 AWG for switches and LEDs?

[tjash]

In planning my eBIAB build I've been checking out all the wiring diagrams I can find. I keep coming across diagrams and photos of 14 AWG directly connected to 10 AWG and run to various switches, LEDs, and alarms.

My understanding is that anytime you drop in conductor size, you need overcurrent protection. Does this not apply to control and indicator wiring?

Thanks for any help or guidance on this!

 

[KBentley57]

It really depends on the circuit. Are the LED's and switchs in parallel with the main lines in the circuit? LED's and lighted switches draw almost zero current, so the wiring to them can be incredibly small without fear of overload.

 

[tjash]

It really depends on the circuit. Are the LED's and switchs in parallel with the main lines in the circuit? LED's and lighted switches draw almost zero current, so the wiring to them can be incredibly small without fear of overload.

Typically, yes. Take a look at Kal's main power switch here: http://theelectricbrewery.com/control-panel-part-2?page=7

The switch is wired with 14 AWG wire connected to the 10 AWG main feed to the contactor from the 30A 240V inlet.

I'm not worried about the typical load these switches and lights draw, but in a fault/short condition are you creating a fire hazard by not having a fuse to protect the smaller gauge wire? Or is that such an uncommon or unusual incident that it doesn't warrant consideration?

 

[SweetSounds]

The short answer is yes - In a fault condition you'd have a hazard if the melting wire doesn't cause an upstream breaker or fuse to trip.

You can get DIN rail mount fuse holders and install 1 amp fuses for the LED's etc, but generally speaking that isn't necessary.

The odds of a wiring fault at a light or switch are slim. Odds are far better that an SSR will melt down or an element will fry. These devices are protected by fuses or breakers.

 

[thargrav]

This is a common practice - the stove & oven in your house have low power 120V accessories split off a 50A circuit without a separate fuse.

But the rules change if you are running power to something on the outside, like a MARCH pump. That circuit should have it's own sub-fuse.

 

[BetterSense]

I'm not worried about the typical load these switches and lights draw, but in a fault/short condition are you creating a fire hazard by not having a fuse to protect the smaller gauge wire?

Yes. You should fuse it.

This is a common practice - the stove & oven in your house have low power 120V accessories split off a 50A circuit without a separate fuse.

If it's a common practice, it's a stupid one. I don't know about stoves and ovens, but most of the industrial equipment I work with has the logic boards and other non-power loads protected by either panel-mount fuses on the back or those pop-out circuit breakers

Fuse holders and fuses are cheap, even at inflated Radioshack prices. The little metal clips for holding glass fuses probably cost 20 cents from the right supplier.
http://www.radioshack.com/family/index.jsp?categoryId=2032302

 

[thargrav]

If you are sitting in front of a desktop computer, it's doing the same thing. The 12 VDC part of the power supply is designed to source over 10 Amps but the 12V case cooling fan draws maybe 0.3 amps? It does not have a separate fuse and the wires running to the fan are not designed to handle 10 amps.

And industrial equipment I work with has all OUTSIDE loads protected with a fuse or circuit breaker. Inside loads like indicator lights, internal fans, etc are not.

 

[tjash]

Any other thoughts on this? Standards or codes that apply to control wiring? So far I've laid out my wiring without internal fuses, other than the PID and pump. Similar to voltin, johnodon, etc, a la PJ's diagrams, but with a main power switch vs. an E-stop.

 

[aquenne]

This can also be seen within your house. A lamp is normally wired using 16, or 18GA wire, yet the 15 amp circuit is hardwired with 14GA. The drop in wire does not warrant a fuse.

 

[tjash]

Makes sense. Didn't we drop the requirement in the US to fuse plugs?

 

[thargrav]

Sure, there are planty of standards driving internal wiring for things like relay coils, indicator lamps, etc. And any good Design Engineer follows them.

The process goes something like this:

A stove, air conditioner, commercial brew controller or whatever has internal circuits that draw a fraction of the external supply. The Engineer determines through researching component specifications what the support parts will draw and sizes the wires accordingly after factoring in a safety margin. For example, indicator lights might need a #28 wire, a cooling fan might need a #24 wire & 2 large relay coils might need #22 wires. Then the overall design is looked at from a cost perspective & they might decide that everything on the control side needs to be done with #22 (the larger size) because it costs less to use just one wire size for the control wiring.

Bottom line is - you will never see these circuits fused internally.

Any other thoughts on this? Standards or codes that apply to control wiring? So far I've laid out my wiring without internal fuses, other than the PID and pump. Similar to voltin, johnodon, etc, a la PJ's diagrams, but with a main power switch vs. an E-stop.

 

[tjash]

Point taken - just wanted to make sure I wasn't missing anything as I'm not that familiar with wiring standards. Thanks for the input and guidance!

Besides... worst case scenario is that I'll never be more than 50' from my rig on brew day. I'm pretty sure I'll smell smoke before the deck burns down!

 

[thargrav]

Point taken - just wanted to make sure I wasn't missing anything as I'm not that familiar with wiring standards. Thanks for the input and guidance!

Besides... worst case scenario is that I'll never be more than 50' from my rig on brew day. I'm pretty sure I'll smell smoke before the deck burns down!

Exactly,

We all go to bed at night with our refrigerators and A/C's or heaters running and they are all designed the same way.