So I'm planning to put in a 100 amp sub panel that'll have a clothes dryer running off it. Code here says...

"A circuit of 30 amperes is required for an electric clothes dryer (section 220.18). Three insulated #10 wires (plus one #10 ground wire) are required to feed it, and a properly configured receptacle (3 pole with ground rated at 30 amps) is required. Make sure the bond strap between the dryer frame and neutral is removed and the equipment ground wire terminates on the chassis as described for range installations."

I think I understand all of that... normal 2 pole connection, remove the wire that connects to the frame, connect the rest as normal.

The next part says...

"Clothes dryers fed from a sub-panel are also required to have a separate equipment ground wire run to them, with a grounding type receptacle/pigtail employed. In this installation, the factory frame bond must be removed from the neutral terminal of the appliance, and the separate equipment ground shall terminate on the chassis."

So here is my question... I think I still run the 4 wires I normally would (red, black, white, ground) to the receptacle. I also run a separate ground wire to hook to the frame of the dryer. Is that right? Where do I need to run that grounding wire (to the sub panel, the main panel, or the grounding rod)? Does the wire just stick out of the wall in the laundry room?

Thanks,

John

I'm an electrician from Canada, and I'm not familiar with your national code, but I've never heard of or seen a separate ground wire run to the clothes dryer. As long as your plug is properly grounded and your cord ground is properly connected and not broken, then it would be sufficiently bonded to ground.

4 wire setups on new installations is the latest thing in the US. A properly connected 4 prong outlet and 4 wire cord should get you by the inspector.

OK, so it sounds like it's just worded in a weird way to me. Thanks for the quick replies on that. Here is my next question.

I have a 100 amp sub panel. The Service panel is roughly 40 feet away. I need to run conduit the entire way from the service panel to the sub panel for the feeder wire. I'm assuming this needs to be 1 1/4" schedule 40 (all interior for the run).

What size wire do I need for the panel? I've heard from some #3 and from others #4 copper THHN (?) wire.

Oh yeah, another question. My main service is mounted to the basement wall and has a pipe extending up to the joists that all of the circuits coming into the box feed into. The sub-panel is going to be flush with the wall (ie inset and the face is flush with the drywall).

Do I still need the pipe, or can I just put a grommet of some sort at the top of the box to protect the wire?


John

#4 is the minimum copper you can use. This results in a 2.6% drop at 1.25*100A and copper. 3% is the max.

THHN needs to be protected all the way.

There may be other service cables you can use that don't require conduit.

You might exceed the allowable conductors in your drop to the main box.

Reminder that the neutral and grounds remain separate in the sub-panel and you may have to buy a ground bar kit for the sub panel.

The size of the wire you need will depend on the breaker feeding it. If you are running cable inside the wall, you will need a strain relief where it goes into the box, coming out of conduit, only a bushing.

THHN needs to be in conduit. Hopefully, someone will back me up.

THHN is wire. As such, yes it does need to be inside something. Multiple wires bundled together is a cable. Some of them can be run inside walls as is until they enter a box. I do not see how my previous post could be interpreted as anything different.

#4 is the minimum copper you can use. This results in a 2.6% drop at 1.25*100A and copper. 3% is the max.

THHN needs to be protected all the way.

There may be other service cables you can use that don't require conduit.


I'll probably need to contact and electrical supply house. Home Depot here only carries the individual wires



You might exceed the allowable conductors in your drop to the main box.


Are you talking about the number of wires in the conduit? For TW style wires (which is all I can find a chart on so far) it lists 1-1/4" as the minimum conduit size for four #4 wires. Sounds like I might need to bump it up to larger conduit and wire.



Reminder that the neutral and grounds remain separate in the sub-panel and you may have to buy a ground bar kit for the sub panel.

Thanks

If you are running cable inside the wall, you will need a strain relief where it goes into the box, coming out of conduit, only a bushing.

I was more talking about the romex to each of the other circuits. Right now they all feed through a big pipe mounted to the top of the panel in the basement.

For the circuits coming into the sub-panel, do I still need a pipe like that since it'll be mounted in the wall?

I had hoped to clear up the confusion about wires and cables. THHN is a common grade of single wire. That is the only way it comes. NM-B is the most common type of cable. It most often has a black, white, and bare wire in it. A red too is common.

If you are feeding the sub panel from a breaker in the main panel, the wire needs to match that breaker. If you are tying to lugs on the buss, the wire must meet the rating of the main breaker.

All of the wiring can either be singles, such as THHN, in a conduit or raceway, or suitable cables just in the wall. You can feed the sub panel with singles in a conduit, and then run individual circuits using NM-B cables without conduit.


My main service is mounted to the basement wall and has a pipe extending up to the joists that all of the circuits coming into the box feed into.

I find this confusing. Usually the feed comes in one big pipe, and all the circuits go off in smaller conduits or cables. The existing pipe may not be big enough to add the feed wires to the sub panel. Remember, wires are sized to the breaker feeding them.

I looked around online but couldn't find any pictures that match my arrangement. I'll take a photo when I get home late tonight and post it.

Here is a picture of our main panel.

http://i212.photobucket.com/albums/cc291/bonzai95/Panel.jpg

The center conduit comes in from outside and contains the main service lines.

The two gray pipes on either side stop just above the joists and all of the wires for the rest of the circuits go through those.

My question is, since the sub panel will be enclosed in a wall, do I have to put a pipe up to the attic that all of the wires (not counting the line #4 cable from the main) go through?

I know I need to protect the wires going into the box from being cut on the edges of the knockouts, but can I do that with a grommet or hub of some sort instead of feeding the individual wires into individual romex connectors?

John

I have tried to stick to what I know. Better hope tkrussell checks in to answer that. He may also ask what other loads you plan besides the dryer.

Quite odd. I don't see the protective bushings on the ends of the open conduits. I suppose that the cables are stapled nearby.

I did a LOW voltage safety system which I did a similar thing. The only difference was at the top of the conduit I mounted a large J-Box. This allowed strain relieving all the ~1/4" diameter fire protection cables above the suspended ceiling. Nothing to staple too. I left a pull string in there too.

For your sub-panel there is no reason why the cable/conduit can't come in from the side of the main panel.

The single conduit method just makes it easier to add circuits later. In general, I don't think sheathed cables are allowed in conduit.

But, I suppose as Labman says we have to wait for tkrussel, the expert.

Well I certainly appreciate the help you've both provided.

I found a place nearby that sells 4/3 Romex with ground. A quick call to the local inspector confirmed that as long as the wire is run through the studs and is "protected from physical damage" that I don't have to have conduit to run to the sub-panel.

Here is all the circuits I'll have running off the sub panel (it's a lot).

Dryer - 30 amp
Laundry - 20 amp
Bedroom outlets - 15 amp arcfault
Bedroom outlets - 15 amp arcfault
Bedroom outlets - 15 amp arcfault
Bath & Hall outlets - 15 amp
Lights & Fan - 15 amp (1050 max wattage with everything running)
Lights & Fan - 15 amp (1165 max wattage)
Lights & Fan - 15 amp (1135 max wattage)

That covers all the lights, the bathroom fans, outlets, etc. The inspectors here like to see each bedroom have it's own circuit and to use the arc fault breakers. I tried to spread out the lighting circuits as evenly as possible. Each of those circuits are including a "future" ceiling fan with 200 watts figured for each, so for the time being each light and fan circuit will be under 1000 watts.

I'm a little worried that the #4 wire might be undersized if I put a 100 amp breaker on the main breaker box to feed the sub panel.

John

I did the calcs earlier. Ratings were based on 1.25 * 100 amps because the load is continuous or greater than 3 hours. 40' which is 80' of wire, Copper, 120 V, and <3% voltage drop.