Putting a new three-prong plug on my car's heater - which is neutral prong?

Factual Questions
1

I need to put a new three-prong plug on my car’s block heater. The cord coming out of the car clearly indicates which one is neutral, and which is the ground (green). But, the replacement plug doesn’t indicate which prong is the neutral and which is the live one.

Both are the same width, so which one should get the neutral wire? The left or the right, (when I hold the plug with the third prong on the bottom, with the prongs facing away from me and towards the outlet)?

Thanks!

2

are you talking about the plug that goes into the outlet on the wall? On the outlet, neutral will be the wide blade on the left, the narrower one on the right is hot.

3

It shouldn’t really matter right? I believe the only time you need to worry about which is which is with lamp sockets, because you want to be sure the metal thread part that people might touch isn’t hot. For something like a block heater it shouldn’t matter at all. But I could be wrong.

4

thanks for the replies. Yes, I’m talking about the plug that goes into the wall - the replacement that I’ve got doesn’t have a difference between the two prongs.

So, the prong that goes into the broader slot is the neutral one?

And, you’re right, GreasyJack - it’s not like a lamp. but, never hurts to follow the normal practice.

5

Since you’re using AC power, it doesn’t normally matter much because the electricity doesn’t have a directional flow in the same way that a DC current does. However, I applaud your decision to wire it correctly anyway; it’s good form and good practice to do so. In many wiring situations, the two screws that attach the wire to the plug are silver and gold. The gold is intended to be the hot, while the silver is intended to be the neutral. If your plug has color-coded screws, this is the best way to tell.

6

Do you still have what’s left of the old plug? I kept it and used a multimeter on it when I had to replace the one on my parent’s van. (Don’t recall which was which anymore)

7

correct, for a typical 5-15 receptacle:

http://www.leadsdirect.co.uk/technical/americanplugwiring.html

three-prong plugs are not required to have different size prongs for hot and neutral because the third (safety ground) prong enforces polarity; you can’t plug it in the wrong way.

8

Generally, the hot side of the plug will have a brass colored screw and the neutral will be silver colored.

ETA: Sorry I missed appleciders post.

9

This is correct. If there is any exposed metal (similar to what you have in a lamp base) then you want that to be the neutral. If the heating element does not have anything like this though (which it probably doesn’t) then it doesn’t matter.

However, if there is a switch in the block heater, that switch should turn off the hot leg and not the neutral leg. Most of the ones I am familiar with don’t have a switch.

10

Gold = Hot

Silver = Cold

Thanks! now I get the code.

I’ve never heard of a block heater with an on-off switch? You just plug it in when the temperature dips, and away you go in the morning.

The background to all this is that at some point during the winter, either Mrs Piper or I forgot to unplug and drove away, so I wanted to replace the plug on the chance it had been damaged. When I did it the other day, I discovered that the force unplug had actually stripped the neutral and hot wires out of the screws inside the plug, thus explaining why I was worried that my block heater wasn’t working anymore.

11

I’ve heard of people putting switches on them. They leave the block heater plugged in with a cord long enough that the switch is inside. When they want to use the vehicle, they turn on the switch (making sure to give themselves enough time for the block to actually warm up before use). Then they don’t have to go out into the cold to turn on the block heater, and they don’t have to let the block heater run all of the time which wastes electricity.

All of the ones I have ever seen in a store haven’t had a switch on them though. Most folks do exactly like you say, just plug it in when it gets cold.

12

I use a wireless switched outlet combined with an extension cord with an orange bulb moulded into the end to show when it’s powered. I can see the light from a window so I can confirm what state the outlet is in. Roll out of bed, push the remote and by the time the rest of my morning routine has finished the block has been warmed for at least an hour, which has so far been good enough.

Here’s an example

I got mine from Wal-Mart and I can’t remember what brand it is. I have seen them at Home Depot and Rona, also.

13

You’ve spoiled my fun - I was going to ask you how many times you drove away without unplugging to make this fix necessary. :smiley:

We use a timer on our block heater cords - works just fine.

14

if you use an extension cord or timed or remote switch make sure they are rated to handle more than the heater needs. ones made for lamps or decorative lightning may not be of the rating to handle your heater.