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arca 03-27-2011 06:40 AM

Connecting new dishwasher and garbage disposal -- no ground wire in the conduits.
 
Hi folks,

I'm installing new dishwasher and garbage disposal in my apartment-type condo, which was built in the early 1970s and there is no ground wire in any of my (flex metal) conduits. I checked my three-prong outlets -- bubkes, no green wire either, some aren't even self-grounded (all my boxes are metal).

I have two toggle (basic "light-type") switches installed into one two-gang(?) box with one conduit coming in (two hot wires -- red and yellow -- and one neutral) and two going out -- one to the dishwasher, another to the garbage disposal; obviously, the neutral is split into two. I checked the box for ground -- put red probe of my multimeter to the hot wire and the other to the box, it showed 120v. I did the same with the appliance ends of the conduits -- this time testing the hot wire and the conduit itself, 120v again.

Now here is where numerous threads from different forums are confusing: when discussing general safety of flex metal conduit as a ground, most knowledgeable people say it's acceptable -- provided it's done right. However, when it's about major appliances -- particularly dishwashers! -- most folks warn heavily against not running ground wire through the existing conduit. Which I can, just not all the way to my panel. BTW, it does have separate circuit breakers for kitchen appls, including one for dishwasher and one for garbage disposal. Don't ask me how I learned that;).

So, here are my questions:

1. Is it pointless to run ground wire from the appliance to the metal box only? It seams to be grounded well by the conduit that goes to the panel. And while we're at it, can a box itself provide sufficient ground, as one person in a certain home impr. store suggested?

2. If I run a ground wire through the existing conduit, can I use a stranded one? I think it's going to be a lot easier to fish it through the old conduit with two wires already in it. Any preferred method, regardless of the type of wire, will be appreciated!

3. My gas stove is plugged into an outlet that has no ground wire, just two hot wires -- black and blue (yes, blue!) -- and a neutral, white. Again, all this beauty comes from a conduit, attached to the box with a connector. At least this outlet is self-grounded. (The reason for the second hot is another conduit that goes to.. I'm not sure where, possibly the range hood.) Am I safe here? Actually, I don't see any of the feed conduits, but they have to be there, it's the only way to ground the outlets.. I think. Which prompts another question:

4. Is there an easy way to check if the boxes of outlets/switches have ground connection, at least with the panel (I simply don't have a way to go beyond my panel -- it's a multi-unit dwelling). Or, simply, can I check if they are grounded properly?

5. Finally, am I right when I think that connecting either appliance to the wall outlet with a power supply-type cable is stupid, since none of my outlets have a separate ground wire and have to rely on the conduits, too. At least my dishwasher/garbage disposal box will be connected to the appliances by conduits and separate ground wires (if I decide to run them) -- in terms of them being grounded -- not just one prong.

I realize, I might have exposed you to the depth of ignorance you couldn't picture in your worst fears, but let's face it -- if I was capable of making sense in the field of electricity -- I wouldn't be posting questions here to begin with.

Thank you very much in advance!

And yeah, sorry for my English -- it's not my first language.

AllanJ 03-27-2011 08:22 AM

Blue and yellow are standard and acceptable colors for a hot wire in the U.S.

I don't see why a ground wire cannot be run through a conduit but a ground wire may be run outside the conduit when retrofitting an existing system.

Generally a flexible conduit must have a ground wire or metal strip running through it for use as a grounding conductor.

Stranded or solid wires -- does not matter.

A rigid conduit system does not need ground wires running inside. Depending on the flexible conduit type, flexible conduit portions may need to be jumpered around (or have a ground wire run through them and connected to the boxes at both ends). (added later) Specifically the sheath of BX cable is not a good and sufficient grounding conductor.

Do It Right 03-27-2011 09:06 AM

Arca,
From your description it sounds like you have BX cable feeding the dish and disposal.
With metal boxes and the wire properly clamped into them, and properly clamped to your appliances (with a well tightened metal connector), you will have established a good ground.
Problems arise from untrained people not knowing how, or not bothering to install a .50 cent connector with locknut.
It's essential when working with BX cable.

If you have "flex", (which comes without wires in it) you should be able to add a green wire to it (with BX it's not possible). The easiest way would be to replace one of the other wires at the same time as well, tying a green and white wire to the existing white wire, and pulling them through with it. (Of course make sure there is no power to the third wire while you do this).

BigJimmy 03-27-2011 12:53 PM

DOIT has got it.

You probably have a thinwall/EMT raceway system. When installed properly with properly listed connectors, the raceway system is effectively bonded and a separate ground wire is in fact not required. BX/MC cable (that which is sold typically with 2 or 3 wires manufactured as part of the product) has a bare bonding wire installed at the factory. I've seen yo-yo's try to connect this to device grounding studs which is incorrect. It is there to ensure that the cable armor between cut ends maintains a low resistance. Before terminating in the box connector, many installers insert the anti-short bushing in the cable and then bend the bonding wire over it to prevent it from popping out.

FMC (flexible metallic conduit), commonly known as Greenfield, is sold empty and is intended to have conductors pulled through it following its installation. Code requires installation of an EGC for lengths over some minimal length. I cannot remember the specification as I always install one regardless.

If you take a piece of FMC and twist it against the direction in which the coil was made, you'll notice that it will begin to expand and the individual, adjacent ribs will start to loosen and "cage." If you keep going, you'll eventually wind up with something that looks like a cork screw. At this point, the conduit can start to electrically look like a coil of wire, i.e. an inductor or choke. In electronics, the choke is used to resist changes in current. Acting as an EGC, this is bad since under a fault/short condition, it will present resistance to current. To prevent this, an explicit EGC is pulled through to ensure a low-resistance ground path through the conduit.

Jimmy

Jim Port 03-27-2011 01:06 PM

The use of non-typical conductor colors from a cable assembly makes me think that the OP is dealing with a conduit type setup.

arca 03-27-2011 06:04 PM

Thanks guys, I really appreciate your advices. That "pull-new-wires-with-the-existing-one" technique is clever, but I'm afraid to do it -- what if the whole thing gets stuck half-way through? With my luck, it will probably happen.

I do have an FMC and Home Depot website says their aluminum FMC can be used "As a grounding conductor for lengths up to 6 feet". I don't know if mine is aluminum, it's certainly metal, so I don't think it matters much. But it's definitely less than 6 feet.

I think I'm gonna try to fish a ground wire anyway. And can I please ask you again: Can I pull that wire only from the dishwasher to the box that houses switches for it and garbage disposal (it's above the counter)? Will it make sense? Because I don't think I can run ground wire from that box to the panel -- it's too complex for me.

Again, thank you very much, your help means a lot to me!

BigJimmy 03-27-2011 08:36 PM

ARCA-

So, is the piece of FMC greater than 6ft? If not, why bother? If it is required, you only have to run the ground conductor (EGC) through the length of FMC and bond it in the box and at the appliance. Here's a tip for pulling (pushing really) the wire: Take a pair of duckbill or needlenose pliers and bend the end of the wire back on itself. This will help it pass through the FMC connector especially if it is one of the screw-in kind with a throat. You can also straighten the flex with your free hand as you push the extra wire to help your effort. I wouldn't worry about it getting stuck. If it jams, it should pull back.

arca 03-27-2011 08:47 PM

Thanks, Jimmy.

I just bought some 16 gage stranded wire (green, of course!) and will try to pull it through the conduit. If I wont succeed -- I'll have to get by conduits as ground. Is it better to connect the ground wire to the box itself (will have to drill a hole) or to the ground screws on the sides of switches?

Thanks.

BigJimmy 03-27-2011 09:12 PM

Quote:

Originally Posted by arca (Post 618251)
Thanks, Jimmy.

I just bought some 16 gage stranded wire (green, of course!)

Um, you need 14 or 12 gauge wire to match the gauge of the circuit conductors!

Most metal boxes have holes in which a grounding screw can be installed. There are also clips that can be used to connect the EGC to the sides of metal box.

arca 03-27-2011 09:26 PM

Quote:

Originally Posted by BigJimmy (Post 618268)
Um, you need 14 or 12 gauge wire to match the gauge of the circuit conductors!

Most metal boxes have holes in which a grounding screw can be installed. There are also clips that can be used to connect the EGC to the sides of metal box.

My bad, it's 14 gage and I was able to pull it through!!! Longer than I thought it was -- at least 8'.

My box is ancient, it's actually a box and some kinda front frame attached to it. There are holes on the back wall of the box, but I don't want to drill a hole to my neighbor! So I found a good spot on the side of it, I'll drill a little hole and use self-tapping screw for both ground wires -- dishwasher and disposal. Can I use one grounding hole/screw to attach two ground wires from different appliances?

Thanks.

BigJimmy 03-27-2011 09:44 PM

Quote:

Originally Posted by arca (Post 618274)
Can I use one grounding hole/screw to attach two ground wires from different appliances?

Thanks.

Use a piece of left over green wire and attach one piece of your green wire to the box as a pigtail and then wire nut it to the other EGC's. Use green screws or clips (for instance T&B GS 1-SC or GEE, respectively).

arca 03-27-2011 09:52 PM

Quote:

Originally Posted by BigJimmy (Post 618290)
Use a piece of left over green wire and attach one piece of your green wire to the box as a pigtail and then wire nut it to the other EGC's. Use green screws or clips (for instance T&B GS 1-SC or GEE, respectively).

Thanks man!

BigJimmy 03-27-2011 10:26 PM

Quote:

Originally Posted by arca (Post 618294)
Thanks man!

Hey, no problem!:thumbsup:

It's all worth it if it works out for you!

J

arca 03-27-2011 10:59 PM

[quote=BigJimmy;618268]Um, you need 14 or 12 gauge wire to match the gauge of the circuit conductors!

quote]

One quick thing, Jimmy:

What's "circuit conductor"? The wires in my wall appear to be of different sizes; the thinnest hot is probably 12 gauge, the other hot looks thicker and the neutral looks like 10 gauge to me. The guy, who sold me the wire said the minimum gauge for the ground wire is 14. If it needs to be bigger I can easily fish the new, thicker one with the one I just pulled.

Thanks.

BigJimmy 03-27-2011 11:15 PM

ARCA-

When I say "conductor," I mean "wire."


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