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Old 09-04-2017, 11:36 AM   #1
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Is this AC distribution hooked up correctly?

Trying to sort out some electrical issues. With my multitester I don't get 12v coming across the fuses but I get 12v from the red to the white posts. These feed directly from the 12v batteries. Seems like there should be 12v across the fuse terminalsClick image for larger version

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Old 09-04-2017, 11:54 AM   #2
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You will not see 12 volts across the fuses. You may read 12 volts across a fuse if it is blown depending on the load.
To check fuses the black lead of your VOM should be connected to the common/ground side of the circuit. Then the red lead is used to check the fuses. 12 volts means they are probably good.
Depending on the input impedance of your meter you could read across the carbon path of a blown fuse. While somewhat unlikely it does happen.
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Old 09-04-2017, 11:58 AM   #3
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In looking at the pic you posted. It appears the common/ground buss is the one on the bottom with the white wires connected.
The top buss is the +12 volt buss which provides power to one side of all the fuses.
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Old 09-04-2017, 12:11 PM   #4
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Hi

One minor point, that's a DC (as in 12 VDC) distribution setup. An AC setup would likely be feeding 120 VAC around. Having exposed terminals like that at 120 V would be quite dangerous ....

Sometimes a light bulb tester is a quick way to sort out blown fuses. You don't have to glance over at the meter and wait for it to settle. On your meter, "12V" can be anything from 10.5V up to about 14.5V depending on the state of your batteries and charger. If something is really wrong, it (obviously) could be quite a bit less than 10V.

A trick you see on factory fuse panels is to put an LED and resistor across the fuse. When the fuse blows, the LED lights up. The gotcha is that it only lights up as long as the load is still on the line. If the fuse was blown by a brief short, you can have a blown fuse and the LED is still out ..... No system is perfect.

Sorting out blown fuses should be a rare occurrence. Unless you are working on something and have an accident, they should not blow. If you find yourself digging into this on a regular basis, that's not a good sign. Time to step back and evaluate how things are set up ....

Lots of fun !!!!

Bob
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Old 09-04-2017, 01:11 PM   #5
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You are correct Uncle Bob that's my D.C. Is the white side traditionally the ground side?
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Old 09-04-2017, 06:34 PM   #6
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I guess you did not read my post #3. White is common/ground.
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Old 09-05-2017, 10:39 AM   #7
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You are correct Uncle Bob that's my D.C. Is the white side traditionally the ground side?
Hi

To the extent anything is "standard" in an AS, white in a DC circuit is the negative return / common / ground. It's sort of a "trust but verify" kind of thing whenever you are working with DC wiring. Different outfits / different fields had very divergent ideas about color codes. Even today, the US and Europe have different ideas about AC wires and color codes.

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Old 09-05-2017, 11:01 AM   #8
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Hi

To the extent anything is "standard" in an AS, white in a DC circuit is the negative return / common / ground. It's sort of a "trust but verify" kind of thing whenever you are working with DC wiring. Different outfits / different fields had very divergent ideas about color codes. Even today, the US and Europe have different ideas about AC wires and color codes.

Bob
So, Uncle Bob, which way do you think the electrons flow? Not that I "know", learning, not gottcha.
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Old 09-05-2017, 11:08 AM   #9
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In your case it does not matter which way they flow. Only that they do flow.
Connect your meter to the top and bottom buss in the pic you posted. You should get a reading of at least 12 volts.
If the converter is on and you have AC 120 volt power you should see something north of 13 volts.
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Old 09-05-2017, 11:17 AM   #10
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In your case it does not matter which way they flow. Only that they do flow.
Connect your meter to the top and bottom buss in the pic you posted. You should get a reading of at least 12 volts.
If the converter is on and you have AC 120 volt power you should see something north of 13 volts.
So, I guess it's not a gift when asking a specific bit of knowledge?
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Old 09-05-2017, 01:24 PM   #11
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It flows from negative to positive.
Does that give you a better perspective?
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Old 09-05-2017, 06:13 PM   #12
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It flows from negative to positive.
Does that give you a better perspective?
THAT'S a better answer
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Old 09-05-2017, 09:47 PM   #13
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The direction of the flow of electrons answers reminds me of an incident during my Air Force days. While briefing our Wing Commander on a combat mission plan the CO asked my tail gunner how he kept his left and right directions straight for telling the crew where the threat was coming from while he was flying backwards. To the CO's utter amazement, my gunner very calmly told him, "While I am flying backwards, I superimposes my right on my left and my left on my right, Sir." You never saw a SAC Wing Commander remain so quiet. It seemed like hours before he said, "I See."
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Old 09-06-2017, 09:20 AM   #14
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So, Uncle Bob, which way do you think the electrons flow? Not that I "know", learning, not gottcha.
Hi

The correct answer is "whichever direction the Poynting vector makes them go". The cute part about that is that it works for electromagnet fields in free space. We talk about current flow being electrons, but that's a simplification. In reality the electrons move a bit slower than the current in a conductor.

Yes, this gets really weird in a big hurry ....

Bob
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Old 09-06-2017, 09:23 AM   #15
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Did you jump back to AC?

That vector thing is the only reason my couple of brief brushes with 120v & 440v were not more conclusive.
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Old 09-06-2017, 09:28 AM   #16
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Oops, my bad, that's what you get for talking electrons with a knuckle dragging mechanic. I thought you mis spelt pointing, and then thought phase change vectors.

I'll stick to moon phases and plumbing.
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Old 09-06-2017, 11:08 AM   #17
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Oops, my bad, that's what you get for talking electrons with a knuckle dragging mechanic. I thought you mis spelt pointing, and then thought phase change vectors.

I'll stick to moon phases and plumbing.
Hi

Actually it's a pretty cute way to win a nerd beer bet. The vector thing is obscure enough that there are a lot of people with EE degrees that don't catch on to it. The spelling is part of that. Having EMAG classes early in the morning (they *always* are early) is the other part of it.....

Bob
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