How does grounding work with 2 wire cable?

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Old 02-15-20, 08:39 AM
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How does grounding work with 2 wire cable?

Recently had to pull the old dishwasher out and noticed the cable to dishwasher has only hot and neutral, no ground:



All the other cable I've seen in the house has a ground, so this is the first time I'm seeing this. The dishwasher has a little electrical box with a ground screw to a metal plate, so I connected the bare copper wire there.

But how does this actually work? If the dishwasher's frame gets energized, what happens? The copper wire and the cable clamp it's attached to will also become energized, but doesn't seem like there's anywhere for that current to flow since this isn't armored cable.
 
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Old 02-15-20, 08:52 AM
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That's braided jacket but thermoplastic covered wiring. (newer style)
That should have a smaller gauge ground wire in it. Have you checked for a cut off ground wire ?
 
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Old 02-15-20, 09:20 AM
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I've seen miles of NM cable just like that with no grounding conductor, usually from houses built in the 1950s or very early '60s. Later in the 1960s there was much plastic jacketed 2-wire NM cable used.with no grounding conductor. Back in the 1060s when NM cables became available with the grounding conductor, it wasn't yet a requirement to use the grounded cable and both types were available. Many just continued using the ungrounded cable as it was cheaper. It's also good to remember that back then there were still a lot of areas around the country that had no inspections.

But how does this actually work? If the dishwasher's frame gets energized, what happens? The copper wire and the cable clamp it's attached to will also become energized, but doesn't seem like there's anywhere for that current to flow since this isn't armored cable.
What happens? You had a hot dishwasher, that's what happens. Someone obviously thought they were grounding the dishwasher with that small copper wire, but they weren't.
 
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Old 02-15-20, 09:42 AM
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@PJmax, no cut offs available. The other wires in the house I've looked at had the same housing (at least to my eyes), but those did have a ground wire. So it does seem strange that this doesn't appear to; I may just have to cut open a bit of the housing to check.

But it could be as
@CasualJoe suggests. This house was built in the early 60s, so maybe the earliest wiring doesn't have ground, and wire added shortly afterward (since it uses the same outer housing) does have ground wire, and it just so happens that the latter is what I've seen up until now.

@CasualJoe yeah I guess whoever installed it thought they were accomplishing something by connecting the dishwasher's ground screw to the cable clamp with a bit of bare wire.
 
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Old 02-15-20, 10:00 AM
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What's that bare ground wire in the picture? Are you sure it is not from the cable. They used to take the ground and back wrap them on the cable and put the clamp over them.
 
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Old 02-15-20, 10:24 AM
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This is likely also why the code has been changed to require GFCI protection for dishwashers in 2017.
 
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Old 02-15-20, 10:47 AM
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@joed - possibly! I assumed it was just a separate piece of wire. I'll have to get under there and take a look. What would be the purpose of wrapping the ground wire that way, as opposed to how we do it today - attach ground wire to grounding screw?
 
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Old 02-15-20, 10:51 AM
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@Tolyn Ironhand - are modern dishwashers hard-wired like the older models? If so, I guess people are putting them on circuits with a GFCI breaker.
 
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Old 02-15-20, 11:07 AM
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(quote) What would be the purpose of wrapping ...

Long long time ago, folding back the ground wire in the feeding Romex cable and squashing it in the box clamp (metal boxes) with the cable end was considered sufficient to ground the box and anything else (such as a similarly squashed ground wire in a downstream cable so) bonded to the box. Twisting together all of the Romex cable ground wires entering a box without using a wire nut lasted a little longer, at least until 1985.

Also, long ago, a ground wire a size smaller, such as 16 gauge in a 14- gauge Romex cable, was considered sufficient.

Ground fault circuit interrupters work on ungrounded circuits and still provide near perfect protection from accidental electrocution.

(copied from another forum) An otherwise ungrounded outlet may be grounded by running a separate grouind wire to the panel with the breaker for that branch circuit, exactly, approximately, or vaguely following the route of the circuit conductors. Should this new wire first reach a fat ground wire (grounding electrode conductor) from a panel to a ground rod or to an appropriate water pipe connection or (new) first reach an outlet with a correct grounding it may end and be connected there.
 
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Last edited by AllanJ; 02-15-20 at 11:25 AM.
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Old 02-15-20, 11:18 AM
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From the picture I was thinking the ground in the cable had been back looped from the inside of the jacket back through the clamp making it look like a short piece had been added.?
 
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Old 02-15-20, 06:02 PM
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The method is often called a Boston back wrap. I have no idea why.
 
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Old 02-16-20, 06:08 AM
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are modern dishwashers hard-wired like the older models?
Sometimes. However, it is more common nowadays for a receptacle to be installed under the sink for the dishwasher.
 
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Old 02-16-20, 09:26 AM
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What used to be a pretty simple task of hard wiring a dishwasher back 30 or 40 years ago is today a terribly difficult thing to do. There just isn't enough room down there although it isn't impossible. Back in the day there was plenty of room to work at the dishwasher connection box. Today it's much easier to lay the dishwasher on it's back and connect a dishwasher cord and then plug it in under the sink base cabinet.
 
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