Wire gauge vs volt/amp question

I have relay sockets wired with 16 gauge and relays rated for 40 amps. Socket leads are 6 inches so that's 1ft of 16 gauge at the start of my circuit causing a 1% voltage drop.

If the rest of the circuit is 14 gauge will it be 14awg drop + the 1% from the 16awg, or will it act as a choke point for the circuit causing additional drop?


I thought about replacing the 87/30 leads but that's half the socket and kinda eliminates the point of having a socket.

Which is why you should get unwired relay sockets, and put them together yourself.

Any time you've got a smaller wire in a circuit, you've got a choke point - and plan on using the ratings of the smaller (16AWG) wire.

Voltage is a function of insulation ("breakdown voltage," "dielectric voltage,") which is why you can have the same size (AWG) wire rated for different voltage levels. Current generates heat, and that's why conductor size becomes an issue for ampacity - because you need enough surface area to dissipate the heat safely (without, say, melting the insulation.)

I'm sure that's a simplistic approach, but I'm not an EE/EET. Hopefully, Tom Houston will chime in (he's our resident electrical/electronic expert.)

5-90 said:

Any time you've got a smaller wire in a circuit, you've got a choke point - and plan on using the ratings of the smaller (16AWG) wire.

Voltage is a function of insulation ("breakdown voltage," "dielectric voltage,") which is why you can have the same size (AWG) wire rated for different voltage levels. Current generates heat, and that's why conductor size becomes an issue for ampacity - because you need enough surface area to dissipate the heat safely (without, say, melting the insulation.)

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I get that but 16 awg is ok for 4 ft at 40 amps 13.8v. If I only have a foot of it it I should only be losing that 1%. obviously later 14 awg isn't going to get that 1% back but it will reduce overall resistance of the circuit.
That's how it's working in my head anyway Lol.

I would look at it as a series resistance problem and add the resistance values for your run of 14 ga + your run of 16 ga. I'd expect that you'll come up with a total of "not much" voltage drop.
I'm with 5-90, in that i've almost never been happy with a pre-wired socket. I do them myself now.
That said...If you're doing headlights, you'll be better off than factory even keeping your 16 ga leads. I wired it all with 12 just for overkill. Overkill means you only do it once.

yossarian19 said:

I would look at it as a series resistance problem and add the resistance values for your run of 14 ga + your run of 16 ga. I'd expect that you'll come up with a total of "not much" voltage drop.
I'm with 5-90, in that i've almost never been happy with a pre-wired socket. I do them myself now.
That said...If you're doing headlights, you'll be better off than factory even keeping your 16 ga leads. I wired it all with 12 just for overkill. Overkill means you only do it once.

Click to expand...

Thanks That's what I was thinking.
I haven't gotten to the headlights yet, on the list though, this is for a relay box.

Do you know where to find connectors that work with the socket? mine has a tab down the middle that bends out.

Your local carquest/napa should have a variety of different pins/connectors, etc. Just go in and ask.

AIbandit said:

Do you know where to find connectors that work with the socket? mine has a tab down the middle that bends out.

Click to expand...

I've had a hard time finding these specific terminals in brick and mortar stores, but I'd love to find a place that has them.

I get them from this place because they have a selection for different gauges of wire: http://www.cycleterminal.com/spade-terminals.html

Susqehanna Motorsports also sells them along with the sockets but their shipping prices suck. I've also had good luck with ebay vendors, especially this guy for the nice waterproof relays and fuses. He does custom work too if you send him a message: http://stores.ebay.com/northlandindustrialsurplus/

I guess "locking tab" is the secret word
Got me on the right track thanks.
suppose I could of got them there but I like Ebay in case there's issues.
http://www.ebay.com/itm/250-6-3mm-F...Parts_Accessories&hash=item3a8718e1a0&vxp=mtr

I get using the relay rating as the "Worse case scenario", but that's some 552watts. Are you sure you'll be drawing that per light?

Anywho...

Per Uglies P.72
16awg copper wire has a resistance of 5 ohms/thouand ft (.005ohms/ft).
14awg copper has a resistance of 3 ohms/thousand (.003ohms/ft).

To calculate voltage drop:
E=I*R where E=Voltage, I=Current, and R=Resistance

The voltage drop across the wire will be the current flowing though it (assuming 40A) times the wire resistance.
The voltage drop across the harness is: 1*.004*40
or about .2V loss

But I suspect if you're running 100W lamps, that's (rounded up) 10A per lamp.
So across that 12" of 16awg, you will drop .04V across each socket harness.

So what you use as a wire run from that harness to the master Switch/Relay will be the real determining factor of how much voltage you loose across the entire circuit, and whether you run to one light, then carry on, or T-Tap somewhere in the middle will also have an affect on the voltage drop seen at each lamp.

-Ron

After a quick review of the thread, it seems I may have read the scenerio just a bit backwards. However the resistance and equations are the same and I hope you find them useful.

Kelly, at DC wire gauge has nothing at all to do with heat dissipation, and everything to do with conductivity.

Del city usually has a nice selection if you haven't got stuff ordered yet. Although I don't care for their online catalog, if you order they will send you a hard copy which is much easier to find things in.

www.delcity.net

It's not really related to lights just wiring in general.
Having smaller gauge before larger gauge and it looks like as long as that smaller gauge doesn't drop too much it helps to switch to larger to keep the over all resistance down.
I'm using this calculator
http://www.gtsparkplugs.com/WireSizeCalc.html

AIbandit said:

It's not really related to lights just wiring in general.
Having smaller gauge before larger gauge and it looks like as long as that smaller gauge doesn't drop too much it helps to switch to larger to keep the over all resistance down.
I'm using this calculator
http://www.gtsparkplugs.com/WireSizeCalc.html

Click to expand...

Pretty much that.
For high amprage runs, keep the wire diameter on the large side to handle the overall current over a distance. Short pigtails likely won't be a big issue if they don't drop much voltage.