Replace 30A Dryer Circuit with 50A Circuit for 2 PDUs

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Old 10-13-17, 09:38 PM
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Replace 30A Dryer Circuit with 50A Circuit for 2 PDUs

Hello everyone. I have a 30A circuit breaker in my home circuit breaker box (200A) for my dryer. I use natural gas for my dryer, so this circuit is never used. I would like to replace this circuit breaker with a 50A breaker (something like THIS). I would then like to instead of connecting this new circuit breaker to the existing electrical lines to the dryer circuit, run new electrical lines to my workshop garage. The distance from the breaker box to the workshop garage is about 25ft of grass, where I can easily dig a ditch for conduit. In the workshop garage, I wold like to have 2 outlets installed, both capable of sourcing 240V . I then plan to plug a 30A PDU (like THIS) to one of the installed outlets, and a 20A PDU (like THIS) to the other installed outlet.

My thought process is as follows:
1. I dig a trench (at least 6", probably will go 12") for rigid metal conduit (3/4") from the ground beneath the breaker box to the garage workshop. At the garage workshop, I install the LB to the conduit out of the ground and the necessary "through-the-wall" parts, like the conduit connector and box. I would run 6 gauge UF cable, like THIS.
2. I install 2 of these boxes in series. One box housing an outlet for the 30A PDU (NEMA L6-30P), something like THIS. The other box would house an outlet for the 20A PDU (L6-20P), something like THIS.
3. I call an electrician to come out to remove the existing (unused) 30A dryer breaker for the breaker box (image attached) and replace it with THIS, and have him connect the electrical wire from the conduit installed at the ground beneath the breaker box.

In theory, this gets a 50A 240V circuit supplying my 2 new workshop garage outlets (each rated for 50A), to be able to supply 1 30A PDU and 1 20A PDU, simultaneously. Am I correct? What am I missing? Any feedback/suggestions are much appreciated!
 
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Last edited by nbossert; 10-13-17 at 09:54 PM.
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Old 10-13-17, 10:40 PM
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I call an electrician to come out to remove the existing (unused) 30A dryer breaker for the breaker box (image attached) and replace it with THIS, and have him connect the electrical wire from the conduit installed at the ground beneath the breaker box.
Most electricians will not want to finish someone else's work. It's their name on the permit and their license at stake.

Neither the cable to or the breaker to the dryercan be used but the cable and receptacle can be left in place. You can use the slots in your panel where the breaker for the dryer receptacle was for the garage feed as you planned.

1. I dig a trench (at least 6", probably will go 12") for rigid metal conduit (3/4") from the ground beneath the breaker box to the garage workshop.
Why rigid? It is difficult to work with. Schedule 40 PVC at 18" would be a lot easier.

I would run 6 gauge UF cable, like THIS.
Best to use individual conductors in conduit. Cable is more difficult to pull. I'd suggest at least 1" PVC to make pulling easier even with individual wires. You will need two #6 black, one #6 white, and one #10 green.

What am I missing?
The subpanel with a bonded ground bar and an isolated neutral bar at the garage with branch circuit breakers sized to the PDU requirements. You will also need at least one ground rod at the garage.
 

Last edited by ray2047; 10-14-17 at 12:54 AM.
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Old 10-14-17, 09:13 AM
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HI, it doesn't appear that you planning on a panel in the garage, I would consider installing a larger breaker in the house panel and pulling # 4's to the garage and install a 6 circuit panel out there then supply your outlets from that panel 30,50 amp breakers,,as Ray stated most electricians,, including myself would not connect someone else's work.
Geo
 
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Old 10-14-17, 09:21 AM
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run new electrical lines to my workshop garage
Clarify, I don't see any existing circuits to the garage on the circuit index, so will this new circuit be the only circuit to the garage?
 
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Old 10-14-17, 01:18 PM
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Clarify, I don't see any existing circuits to the garage on the circuit index, so will this new circuit be the only circuit to the garage?
There is an existing circuit to the garage. I believe it's the 25 ("Out GFCI"). It's a single attachable garage to the right of my driveway portico archway (drive through to main 2 car detachable garage). So, I use it as a workshop. That circuit is only 20A, and I'm guessing the wiring isn't adequate enough for 50A total. Thoughts?
 
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Old 10-14-17, 01:25 PM
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HI, it doesn't appear that you planning on a panel in the garage, I would consider installing a larger breaker in the house panel and pulling # 4's to the garage and install a 6 circuit panel out there then supply your outlets from that panel 30,50 amp breakers,,as Ray stated most electricians,, including myself would not connect someone else's work.
When you say #4, are you talking about 4 gauge electrical wire? If so, do you suggest two black, one white, and one green, as Ray suggests? Also, Ray suggested the ground (green) only needs to be 10-gauge. Is that correct? Also, do you mean something like THIS?
 
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Old 10-14-17, 01:37 PM
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Why rigid? It is difficult to work with. Schedule 40 PVC at 18" would be a lot easier.
I just read that's the way to go to reduce how deep I need to dig the trench. But I'll take your word for it.

Most electricians will not want to finish someone else's work. It's their name on the permit and their license at stake.
I totally understand. It just seems that I can do 90% of this, so I was hoping to do some on my own to reduce costs. Would an electrician at least entertain letting me dig the trench, or possibly buy the supplies? On the other hand, they may be able to get supplies cheaper.

Best to use individual conductors in conduit.
Do you have a link to what you mean exactly? I tried looking at Home Depot's website, but options seem limited. Or, THIS site.

The subpanel with a bonded ground bar and an isolated neutral bar at the garage with branch circuit breakers sized to the PDU requirements.
Something like THIS? If I do this, should I just go ahead and install at 100A circuit breaker to my main panel to feed this, in the event I ever want to pull more than 50A to the subpanel (I don't pull close to 100A to my house continuously anyway).

You will also need at least one ground rod at the garage.
Where does this connect?
 
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Old 10-14-17, 02:11 PM
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and install a 6 circuit panel out there then supply your outlets from that panel 30,50 amp breakers
Question on this. Let's say I have a 100A subpanel installed. Can I place 3 separate 240V 30A breakers in it, and then have each run to a 30A capable receptacle? If so, can I use a 20A PDU in a 30A receptable? I assume so.
 
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Old 10-14-17, 02:14 PM
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Now that you are talking about a detached garage and an attached garage I'm not sure which one the existing circuit goes to. If the detached garage has a power feed going to it and you are thinking about adding a second power feed then that's not allowed by the NEC. Only one circuit is allowed to provide power to a detached structure that is coming from another structure.
 
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Old 10-14-17, 02:41 PM
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Now that you are talking about a detached garage and an attached garage I'm not sure which one the existing circuit goes to. If the detached garage has a power feed going to it and you are thinking about adding a second power feed then that's not allowed by the NEC. Only one circuit is allowed to provide power to a detached structure that is coming from another structure.
OK. The Workshop Garage is actually attached, but I'm guessing that doesn't matter. If only one circuit is allowed, I assume the existing circuit must be disconnected - I don't see any problem with that since there is only 1 receptacle in there now anyway (maybe just that receptacle needs to be removed?)
I attached 3 pictures to help. The first is the main "detached 2 car garage" with the electrical box on the outside. 40ft away (grass) is the attached "Workshop Garage" I want to run this power to. I hope this helps to clarify!
 
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Old 10-14-17, 04:12 PM
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OK. The Workshop Garage is actually attached, but I'm guessing that doesn't matter. If only one circuit is allowed,
The way you wrote your post indicated a detached garage. If it is attached you can run as may feeds as you want. However the PDU's need to each be on a breaker sized to their power requirement.

2. I install 2 of these boxes in series. One box housing an outlet for the 30A PDU (NEMA L6-30P), something like THIS. The other box would house an outlet for the 20A PDU (L6-20P),
Nothing in general AC work is connected series. Do you mean daisy chained? What size breaker is recommended for each PDU.
 
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Old 10-14-17, 04:19 PM
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So you are talking about running a new circuit from the panel that's in the same structure as is the garage work shop which is the garage that's below the upper living area with the window A/C, correct? You are not talking about running a circuit from the outside panel/meter on the detached garage back to the garage workshop? If from the panel within the same structure as the workshop then the existing circuit does not have to be abandoned. Sorry for the confusion but I'm trying to figure out where the panel you first pictured is located. I'm assuming it's in the two story structure with the window A/C.
 
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Old 10-15-17, 06:23 AM
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For appliances and equipment with cord-and-plug connections, the power plug implies the circuit amperage requirement.

For example a 30 amp plug needs a branch circuit with (at least 10 gauge wiring) and 30 amp breaker and 30 amp receptacle. Fifteen amp plugs (common U.S. 120 volt lamp fixture and appliance connections) can go on 15 or 20 amp branch circuits.
 
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Old 10-15-17, 06:42 PM
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Hello. Sorry for the confusion.

So you are talking about running a new circuit from the panel that's in the same structure as is the garage work shop which is the garage that's below the upper living area with the window A/C, correct? You are not talking about running a circuit from the outside panel/meter on the detached garage back to the garage workshop?
I included some images below. I have 2 garages - the first "Main Garage" is a 2-car garage, which I always considered "detached" since it's only connected to my home via a small roofline (see picture). The electrical box is mounted outside of this Main Garage. Then, I have a "Workshop Garage", which is 1-car sized, and is connected to the house via a portico above my driveway, and has a room above it with a window AC unit.

I'm now wondering if both garages are considered "attached". Regardless, from your responses, I'm guessing it is fine to run an additional circuit to the Workshop Garage.

For example a 30 amp plug needs a branch circuit with (at least 10 gauge wiring) and 30 amp breaker and 30 amp receptacle. Fifteen amp plugs (common U.S. 120 volt lamp fixture and appliance connections) can go on 15 or 20 amp branch circuits.
OK. But what if I want to plug in a 20A PDU to a 30A circuit? Meaning, can I just add 3 30A circuit breakers to the subpanel, all with at least 10 gauge wire, each to it's own individual 30A receptable. Then, just have a 20A PDU plugged into one of the receptacles? The reason I ask is, I may start with a 20A PDU on one of the circuit, but wire it as 30A to allow for upgrading to a larger PDU is necessary.
 
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Old 10-16-17, 01:00 PM
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Subpanel

Hi,4THHN could be used I would run 1or 1 1/4 PVC with 3 # 4s and a #6 ground fed from a 90 Amp breaker,as long as the building s are connected no matter how it would be treated as attached and any existing circuits could remain,those PDUs are Slick I have used them for rack mounting Servers,what is your application ?
Geo
 
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Old 10-16-17, 03:48 PM
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What do you mean by a small roofline?

The buildingss are attached if there is interior air space (including attic or crawl space) through connecting them through which interior grade wiring may be run.

The 20 amp equipment may not be plugged into a 30 amp circuit or a 30 amp receptacle except with an adapter in between equipped with a 20 amp breaker protecting a 20 amp receptacle for your 20 amp equipment. Such an adapter might resemble a power strip and fit the definition of a portable subpanel.

Or you could take one of your 10 gauge branch circuits, remove the 30 amp receptacle and substitute a temporary 20 amp receptacle and also substitute a 20 amp breaker in the panel supplying that branch circuit.

Or you could run an additional circuit to be a 20 amp circuit.
 

Last edited by AllanJ; 10-16-17 at 04:06 PM.
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Old 10-17-17, 08:51 PM
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4THHN could be used I would run 1or 1 1/4 PVC with 3 # 4s and a #6 ground fed from a 90 Amp breaker
Is THIS the type of conductors you are referring to? Will these suffice for the 3 #4s? Do you have a better recommendation for where to get it?

The buildingss are attached if there is interior air space (including attic or crawl space) through connecting them through which interior grade wiring may be run.
OK, thank you for clarifying. So, both garages are "attached" then.

The 20 amp equipment may not be plugged into a 30 amp circuit or a 30 amp receptacle except with an adapter in between equipped with a 20 amp breaker protecting a 20 amp receptacle for your 20 amp equipment. Such an adapter might resemble a power strip and fit the definition of a portable subpanel.
OK thank you. I will likely run the subpanel off a 90A breaker, then have 3 30A breakers in the subpanel. I will use 30A PDUs.

Or you could run an additional circuit to be a 20 amp circuit.
This is also a possibility. I will think about it. Is there any concern with have a 90A breaker feeding the subpanel, but only having 3 breakers adding up to 80A (30A + 30A + 20A)?

One other question. When I run the conductors underground through PVC conduit (at least 18" underground), I have it come back up to surface at the Workshop Garage and pass the conductors through a penetration into the Workshop Garage. For this portion, what are the conductors required to pass through through the penetration? I imaging the PVC conduit running up the side of the outer wall of the Workshop Garage to a PVC Type LB Conduit Body. Then, I imagine the conductors simply passing through a hole I drill to enter the Workshop Garage --- but I assume the conductors must be contained in something (a piece of PVC conduit?) when passing through this penetration. Once on the other side, I imagine the conductors entering a junction box like THIS (must it be metal, or does PVC work as well). By the way, the Workshop Garage is finished (drywall without insulation)... are there any additional special requirements considering this?
From there, I would have the conductors run through another piece of PVC up to the subpanel.

Finally, when I run the 30A receptacles from the subpanel - what's the difference between THIS and THIS?
 
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Old 10-18-17, 12:08 AM
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The first is 240 v receptacle and the second is a 120/240 receptacle. You need the first one.
 
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Old 10-18-17, 06:23 AM
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... adding up to 80 amps ./..
The sum of the breaker ratings in the subpanel may greatly exceed the rating of the feed cable and the breaker in the supra-panel. 'But you need to expect that the total power to be drawn at any given time can be handled by the feed. (Do the PDUs run 24/7 and draw their normal working load continuously?)

Continuous loads should not exceed 80% of a circuit's rating. But a continuous load device equipped with a, say, 30 amp plug, is supposed to survive on a 30 amp circuit and therefore draw no more than about 24 amps continuously, If it were intended to draw all 30 amps continuously it should have been equipped with a 40 amp cord and plug. Meanwhile an intermittent load, such as a vacuum cleaner, that drew 30 amps from time to time and/or used for short periods of time (NEC defines continuous as drawing that current for 3 hours), may be equipped with a 30 amp plug.

Using the rules for continuous loads and panel breakers, it is okay to have two 30's and one 20 amp breaker in a panel fed by a circuit with 75 amp breaker but you should plan and install a larger feed if you intend to use two 30 amp and one 20 amp device all at the same time. Or you can have three 30 amp circuits for the PDUs plus a 20 amp circuit temporarily used for one of the 3 PDUs (20 amp model) and eventually used for lights.

Style THHN wire may not be buried, even in a conduit. Use THWN or THHN/THWN wire, the latter of which might be labeled "THHN" together with a footnote "rated for wet locations."
 

Last edited by AllanJ; 10-18-17 at 06:52 AM.
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Old 10-18-17, 10:33 AM
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The PVC must be installed in as a complete system before any conductors can be pulled in .
Here is a link to the conductors. http://www.southwire.com/Southwire.htm
Geo
 
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Old 11-08-17, 03:43 PM
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Hello I have another question. Once I install the subpanel, I want to run wires from 3 separate 30 amp circuit breakers to three separate 30 amp 240 volt receptacles. Must I run each receptacles wires through individual conduits to each receptacle's single gang box? Further should I run for individual conductors to each receptacle (2 hot, 1 neutral, and 1 ground)? Or, is the neutral even required?
 
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Old 11-10-17, 07:44 AM
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Multiple circuits can share one conduit as long as the pipe doesn't exceed 40% fill. Since we're talking 30A circuits that means up to 5 #10 wires in 1/2" EMT. If you're running 20A circuits, a 1/2" EMT can take 9 #12 wires. All circuits in the same conduit can share the same ground wire, or if you're using a fully assembled metal conduit and junction box system the boxes and pipes can be the ground. A pure 240V circuit like those used for woodworking machinery do not require a neutral wire -- only use 2 hots and a ground. Some specialty equipment, cooking appliances or cloths dryers do also require the neutral.
 
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