(Worn out/Chaffed) Electric plug rewiring for engine block heater - Diesel Forum

Polarbeardiesel · 09-13-2007, 03:25 AM

The end of the plug (for the engine heater) on my 2001 excursion has RUBBED AND CHAFFED though the insulation and has come off. I stripped some wire back and the only one that is colored is the ground in the center which is green. How do I tell which is positive or negative? It appears that there are two black wires and a green ground. I just wanted to get some input on how to test this before I make any major mistakes. Spoke with the Ford dealer and they "offered" to sell me the replacement cord for $70.00. I spoke with the electrical guy at my local hardware and he said worse case it would pop th ebreaker in my house...I just don't want to mess up the truck. I have a Marinco plug end that I was going to put on anyway but didn't know the wiring was not going to be clearly marked.

budman451 · 09-13-2007, 03:45 AM

As long as the green goes to the ground terminal, it will not matter which of the other wires goes to the other terminals in the plug. Just as a side note, AC/household current is not referred to as positive and negative wires like DC in your truck. The terminal is either the "common" terminal/wire or the "hot" terminal.

Buddy

Polarbeardiesel · 09-13-2007, 04:19 AM

Buddy,
Thanks for the help.
--So as long as the ground is correct- then the common and the hot make the circut complete? It should still "pop" the breaker at the house if anything was wrong. I was just wondering about it because any time I'll be using the block heater it will be snowy/wet and I didn't want to get shocked or mess up the truck.
Thanks, Kevin

frobozz · 09-13-2007, 10:05 AM

There is a standard for which wire (hot or neutral) goes to which side of a plug. You'll notice 2-wire plugs are all polarized these days to keep you from flipping them the wrong way. But in this application I can't see how it could possibly matter. The two wires go directly to a resistive heater inside the water jacket and are never even indirectly connected to things on the outside world. (If you had two indoor electrical items next to each other, wired backwards from each other, and grabbed on to both of them, there would be some chance you'd have the full 115V potential leaking to you, which would be bad, which is why there's a standard.)

If you've already got the Marinco plug, I say now is the perfect time to install that! Wire up the green ground to the frame, and the other two wires to the two terminals, and you're good to go!

Duncan

haul_n_horses2 · 09-13-2007, 11:26 AM

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: frobozz</div><div class="ubbcode-body">There is a standard for which wire (hot or neutral) goes to which side of a plug. You'll notice 2-wire plugs are all polarized these days to keep you from flipping them the wrong way. But in this application I can't see how it could possibly matter. The two wires go directly to a resistive heater inside the water jacket and are never even indirectly connected to things on the outside world. (If you had two indoor electrical items next to each other, wired backwards from each other, and grabbed on to both of them, there would be some chance you'd have the full 115V potential leaking to you, which would be bad, which is why there's a standard.)

If you've already got the Marinco plug, I say now is the perfect time to install that! Wire up the green ground to the frame, and the other two wires to the two terminals, and you're good to go!</div></div>Duncan, Why green to the frame and not to the ground pin on the Marinco plug? I may have a bit of a current leak with my existing block heater as their was electrolytic damage to part of the cooling system even with my "waterless" Evans coolant. This was a fairly new part that developed a pinhole leak. Examination of the pipe showed severe electrolytic damage. I am thinking that even a small current leak from the block heater or its circuits could cause this damage. No current detected now without the block heater on. I was planning to replace the electrical cable and put in a Marinco outlet myself.

jimmy · 09-13-2007, 03:40 PM

In effect the white(neutral) is the same as ground, they are sonnected to the same buss strip in breaker box. The reason green goes to ground is to assure that if anything from the household wiring gets in contact with vehicle body it will be connected via the ground wire to actual ground. This makes the truck and the floor you stand on have the same voltage and therefore no voltage difference exists between you and truck and you cannot be electrocuted.
The neutral and ground are isolated from each other except in breaker box. If a fault occurs where the neutral gets shorted to the feed wire (black) and this completes to truck body then you could be shocked. If truck body is grounded it will either blow breaker or flow current through ground wire and not you.
As Frobozz said in an earlier post here, the two poles of that element are isolated from anything so the polarity doesn't matter when connecting them but if the element were to fail and rot and 120V were pased into coolant then it could get to truck body and the neutral would not protect you. The ground wire would protect you in this case. The neutral becomes a path back to breaker box and w/o grounding, you become a path back to the ground you stand on!!

Polarbeardiesel · 09-17-2007, 10:54 PM

Thanks for the help with this guys...I'll let you know how the Marinco mod goes.