converting two 120v lines to a 240v line?


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Old 11-26-07, 10:40 AM
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converting two 120v lines to a 240v line?

I've got a problem. I need heat in my garage. I don't have a gas line to the garage but I have two 120v lines. Is there any way to make those two lines into a 240 line? Most electric heaters that I seen suitable for a garage space of 250 sf need a 240 line. thanks
 
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Old 11-26-07, 10:46 AM
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No. You need to run a new line to the garage. You cannot combine two 120 circuits into a 240 volt circuit.

However, you can easily change one 120 volt line into a 240 volt line.
 
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Old 11-26-07, 10:57 AM
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If your gas prices are like mine electric is three times as much per BTU. Probably cheaper and simpler just to run gas. Especially when you figure the savings over time.
 
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Old 11-26-07, 11:16 AM
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Sorry, I forgot to mention that my 120v lines run underground because my garage is about twenty feet from the house and I'm not sure I have the space on my box for coverting a 120 line to a 240 line. thanks. I would like to be able to go the gas route but the only thing I've hook up before is a water heater. I know I have to run it underground but not sure how to run the line into the garage. thanks
 
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Old 11-26-07, 11:23 AM
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If you really have two separate 120 volt lines, then you have an unsafe situation and a code violation. However, if you have a multi-wire circuit then you are okay by code (assuming hooked up properly).

Either way, your only option to have both 120 and 240 volt circuits at the garage is to abandon what you have and run a new line for a sub panel at the garage.

If you have conduit feeding the garage then you maybe able to use it. If not, start digging.
 
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Old 11-26-07, 11:54 AM
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Depending on your garage construction, any portable electric heater, even a 240 volt unit, may have minimal effect in raising the temperature to what you want. Kind of like spitting in the ocean to raise the sea level.
 
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Old 11-26-07, 12:21 PM
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You should carefully examine the present feed to the garage. You say that you have two 120V circuits. However it is very possible that you have two separate circuit breakers supplying a 'multi-wire-branch circuit'. If you actually have two entirely separate 120V circuits, then you have a code violation.

In a MWBC, you get two 120V circuits, but on a single cable, with the two 'hot' conductors sharing a single 'neutral' conductor. Of particular benefit to you if you have an MWBC is that you _already_ have the desired 240V circuit. All that would be required to use an MWBC to feed a 240V load is to swap out the two 120V breakers for a single 240V breaker. The downside of this is that if you overload one 120V half, you will trip _both_ 120V circuits.

Examine the circuit(s) going to the garage, and describe them, and we'll be able to tell you what you have and what you can change to. In particular, describe the type and number of circuit breakers, the type and number of wires going to the garage, how those wires travel, and what sort of switches and devices you have where the conductors enter the garage.

As an aside: electric resistance heat is cheap to install but expensive to operate. It makes sense if you only need it for brief times, but not if you want the garage warm for extended use. In addition to looking at fuel based options, you might also consider 'mini-split' heat pump units. These are electrically operated air conditioning systems that can also provide heat. Also be sure to look at insulation to reduce the amount of heat needed to provide the desired temperature.

-Jon
 
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Old 11-26-07, 12:32 PM
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Originally Posted by racraft View Post
If you really have two separate 120 volt lines, then you have an unsafe situation and a code violation.
I understand that this is a code violation, but I've never gotten an explanation as to *why* this is is a code violation / unsafe. Can anyone explain the reason for this?
 

Last edited by chandltp; 11-26-07 at 01:05 PM.
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Old 11-26-07, 12:48 PM
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In the panel box at the house there are two 20 amp circuits for the garage and in the garage there is a fuse box with a 30 amp fuse for each circuit.
 
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Old 11-26-07, 12:53 PM
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You still have not answered the question.

How many wires and what type of wires go from the house to the garage?

Why are there 30 amp fuses in the garage?
 
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Old 11-26-07, 01:53 PM
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There are two black wires size 08, one from each circuit and only one green wire which I suppose it the ground running to the garage. I'm not sure about why there is such a big wire as compared to normal house wiring. Nor am I sure about the purpose of the 30 amp fuse for each line and the seperate fuse box, except for convenience. Could it be that by using a fuse box in the garage this does not violate the code?
 
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Old 11-26-07, 02:12 PM
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If there are two black wires, one from each breaker and a green wire then you do not a valid setup for any 120 voltage. Period.

Replace those wires immediately, or if possible add a white wire (if the setup is in conduit) also size 8. Then you can safely install a small sub panel at 30 or perhaps 40 amps.

With only two black wires and a green wire you do not have a valid setup for anything except for 240 volts, and only 240 volts.
 
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Old 11-26-07, 02:37 PM
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Is that what my fuse box in the garage is; a sub panel where I have two thirty amp fuses for two seperate lines?
 
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Old 11-26-07, 02:38 PM
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I do not know what you have in the garage, but you cannot use it as a sub panel. You will need to purchase and install a circuit breaker panel for the garage.
 
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Old 11-26-07, 02:56 PM
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In my panel every circuit breaker has a black connected to it except for the ac which has white wires connected to the breakers. The green wire which is the ground is attached to the ground on the panel and the ground at the fuse box. I guess I'm not understanding why is not code.
 

Last edited by godavid; 11-26-07 at 03:29 PM.
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Old 11-26-07, 03:27 PM
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Yes, that is what he is telling you.

For 120 volts you need a white (neutral) wire, a green (equipment ground) wire and a wire of some color other than green, white or grey for the "hot" conductor.

For 240 volts only you need two wires with a color other than white, grey or green along with the green equipment ground.

For 240 / 120 volts you need two wires with a color other than green, white or grey (hot leads) a white neutral wire and a green equipment ground.

Between the two "hot" leads is 240 volts. Between the neutral and each one of the "hot" leads is 120 volts.

Because your garage is a detached building you also need a ground rod and grounding electrode conductor to your subpanel. Within the subpanel there needs to be a ground bus that is bonded to the metal case and the neutral bus must be isolated from the case.
 
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Old 11-26-07, 03:29 PM
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No, it is not. There is no neutral. The green wire is being used as a neutral, which is wrong. It is also, most likely being used as a ground.

Replace the wiring, or add a proper neutral wire. Then install a proper sub panel, including a ground rod.
 
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Old 11-27-07, 08:18 AM
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Okay, need to set the record straight here as I understand it. The green wire is neutral and the wires running from the house to the garage run underground and the fuse box at the garage is grounded with steel pipe. The wire size is #10 instead of #8. The way I understand it, is that I can only run 30 amps through this size wire. Here is what I want to do. Run a 240 to the garage and put in a subpanel 4 space with 4 circuits. I want to run a heater off the 240 and a couple of 110 circuits for the lights and garage door opener. I also have an air compressor which is 110 but can be converter to 240. Will this work and what size do my circuit breakers need to be? thanks
 
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Old 11-27-07, 08:54 AM
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Anything is possible with more wire. And that's what you need -- more wire. Are you willing to run more wire? There is no way to get what you want safely with the wire you have now.

I suggest you plan this project exactly as you would if there was currently no electricity at all in the garage. We can help you with that.
 
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Old 11-27-07, 08:56 AM
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You need to add a 10 gage neutral wire. It needs to be white. Period. End of discussion.

You can then install a sub panel. It must be properly grounded. Your steel pipe is NOT a ground and cannot be one.

You will have 240 volts, 30 amps at the sub panel. Whether this is enough for the heater or the compressor or both at the same time depends on their requirements. You have ot told us their power requirements, so we cannot address them.

In my opinion, you need to install a 60 amp sub panel and go with larger wire than 10 gage, but that is up to you.
 
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Old 11-27-07, 09:22 AM
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If a steel rod is a proper ground than why can't a steel pipe be one? Also, if the panel is properly grounded then what need is there for a white neutral wire when the green serves as the neutral? To start over would mean digging the old wire up and replacing with the bigger wire. That would probably be okay except for the cost. The cost of the bigger wire vs pipe for natural gas. If I got to dig, I don't know, which is better the elecitricity or natural gas? The big question? thanks for the help.
 
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Old 11-27-07, 09:37 AM
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You may not use the green wire as a neutral. That is NOT allowed. The existing setup is a code violation and dangerous.

The ground rod needs to be a copper ground rod. You need a ground rod. You also need a ground wire all the way back to the main panel.

Why are you resisting doing this properly? You will fail inspection and have a dangerous setup if you do not follow code.

Do it right or don't do it.
 
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Old 11-27-07, 10:06 AM
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You are going to have to dig to correct the problem anyway so you can use the same trench for gas with suitable separation. The gas will provide more heat and will probably cost less to use.
 
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Old 11-27-07, 11:30 AM
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Grounding of subpanels is one of the issues that is sometimes quite difficult to grasp. In your main panel, you probably have a single terminal bar that does the job of both ground and neutral. It seems 'obvious' that a single wire should be able to connect this to the 'ground/neutral' bar in the subpanel. But this obvious point is _wrong_.

The neutral conductor is intended to carry current. The equipment grounding conductor is not intended to carry current. If you use a single wire for both purposes (both neutral and ground) then you will get a small voltage imposed on every piece of metal connected to that ground conductor. The wiring to a subpanel is _required_ to have a separate ground and neutral wire. In the subpanel you are required to have _separate_ ground and neutral bars.

It is confusing because neutral is bonded to ground at your service entrance panel, and is _required_ to have this single bond. But at the same time the neutral is prohibited from being bonded to ground anywhere else.

There are some exceptions in the code, for example the 'grandfathered' use of the neutral to a range as the frame ground.

In your case there is a relevant exception: a feeder to a subpanel in a detached structure is permitted to use the _neutral_ as the grounding conductor, in which case neutral is bonded to ground in that panel. It sounds to me like this is the case in your situation. However in this case, the _neutral_ conductor must be white, and there are other requirements. The most important requirement if you are using this exception is that there are no metallic paths (pipes, fences, grounded cable TV wires) between the two structures. The fact that this conductor has green insulation is a code violation.

Now, the electrons don't care what color the insulation is, and it is entirely possible that your installation is reasonably safe, with the only code violation being one of insulation color. However having such a code violation raises a red flag: what else is wrong with the setup. As I said, the important thing to determine is if you have proper bonding and proper elimination of parallel paths. Someone who uses a green wire for neutral might not care about other safety codes, so having seen a green neutral you should proceed with caution.

In the _ideal_ case, you should take the time to study and understand how a subpanel is installed. Then run a proper set of conductors (two hots, a neutral, and a ground) from your main panel to your garage, and install a subpanel there. In this subpanel you could install a 240V breaker for the heater and 120V breakers for your various receptacle and lighting circuits. Since your goal is heat in your garage, this is how I recommend going about it. The only component that you should consider reusing from your existing installation is the underground conduit, and this only if it is not obstructed in any way.

-Jon
 
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Old 11-27-07, 02:37 PM
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Okay, I need to add a white neutral wire. The wires now are twelve inches deep, can I keep them 12 inches or do I have to go deeper. There is no conduit on the wires underground. The conduit is used coming out of the house and going into the ground and where it comes out of the ground it goes up about five feet and into the garage. What is suitable seperation, anyway?
 
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Old 11-27-07, 03:00 PM
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Okay, you need to add a cable assembly. If you have three individual wires, and they are just loose in the ground, this is also no good. You need either individual wires in conduit or you need a cable assembly. You need to go deeper than 12 inches.
 
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Old 11-28-07, 07:22 AM
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I've got two 20 amp circuit breakers at the main box and will be adding a 240 double pole breaker at the subpanel in the garage and two 120 circuit breakers after I run the new line from the house to the garage. I'm planning on installing a 70 amp box in the garage. Is the box too big and do I need a 240 circuit breaker at the main box too? thanks
 
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Old 11-28-07, 07:28 AM
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Yes, you need a 240 volt (double pole) breaker at the main panel. That breaker needs to be sized for the cable used. 30 amp for 10 gage, etc.

The breaker and the panel in the garage need to be at least as large as the breaker in the main panel, but can be larger.
 
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Old 11-29-07, 06:18 AM
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I trenched the ground for the new line yesterday and picked up 8/3 underground line. My question is: what kind of tool do you use to cut such big lines and can you use a regular stripper tool for the individual lines? My guess would be a bolts cutter, but I don't know. I purchased a 50 amp double pole breaker for the main box. Is that okay? thanks
 
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Old 11-29-07, 07:22 AM
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How did you come up with 50A for your 8/3 underground feeder? Did you use some online calculator? I'd like the link to that one if so.

Please tell me you did not just guess.
 
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Old 11-29-07, 07:25 AM
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8-3 UF taking 50 amps. Not okay. Try again.
 
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Old 11-29-07, 08:54 AM
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There are cable cutters designed for the purpose but yes bolt cutters will work. As others have said you will be limited to a 40a breaker at best.
 

Last edited by ray2047; 11-29-07 at 09:20 AM.
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Old 11-29-07, 09:43 AM
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Correct me if I'm wrong and I'm sure that will happen since I cue'ing in on this web site to learn a few things but it is to my understanding that #6 wire is rated at 60amp and #8 at 40. There is no fifty amp wire available and you can run fifty amp with the #8 wire. To the guy that said #8 can be cut with regular wire cutters, he must be one hell of a man. This is underground wire and coated in plastic. And far as my skill and knowing what my limits are, I'm not afraid of electricity as long as the power off when I'm work on any project. I'm really gratful for the information I get on this web. I mean, if I had not ask about installing a 240 circuit and learned that my wiring was not in code. I would not have had to run a ditch witch for four hours yesterday, and spend all this money for new wiring, and so forth. thanks again
 
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Old 11-29-07, 10:20 AM
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You cannot run 50 amps through 8 gage UF-B.

Cut the wire with a hacksaw if you want. Strip it (carefully) using a utility knife.
 
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Old 11-29-07, 10:55 AM
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To the guy that said #8 can be cut with regular wire cutters, he must be one hell of a man.
I deleted that comment after a few minutes of thought however just for the record if you strip the outer jacket first, cut each conductor individually, and have large end nippers or linesman pliers it is possible... just not easy. Hacksaw is a good choice kicking myself a bit for not thinking of it.
 
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Old 11-29-07, 03:34 PM
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Sorry about the unnecessary comment, tired. Anyway, does anyone have any tips on getting the line through the PVC. Do I glue it first or can I put it together, run the wire through and then glue it? Do I have to use a special glue? By that, I mean there is different pvc glues. At least that is what the orange box sells. Is the electrical pvc different than any other pvc? thanks again
 
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Old 11-29-07, 03:56 PM
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Woah!

I strongly recommend that you slow down here, buy a copy of wiring simplified, and read it! There are a bunch of different details that you need to understand and consider prior to doing an electrical installation. A website such as this one can only answer questions that you ask; we don't know the things that you don't even know to ask, and we don't know what incorrect assumptions that you are making when you ask your questions.

The _best_ way to use this website is to first read the background books, and then ask questions about the things that you don't understand, and to get your plans verified.

In one post you mention a cable assembly, in another post you mention conduit. In general, you use one or the other.

When you install a conduit system, you must install it complete from pull point to pull point. You have to do all of the necessary gluing and assembly, and then you pull the wires in. With PVC conduit, you use ordinary solvent welding glue, and you make sure that the conduit is installed and the glue dried before pulling the conductors. Do _not_ piece the conduit together with the wires inside; the glue can actually damage the insulation on the wires.

There are a number of different techniques for getting a 'pull rope' into the conduit; then you use the pull rope to grab your conductors and pull them in. You can assemble the conduit with your pull rope inside, you can push a steel 'fish tape' in to the conduit and then pull the rope through; for short runs you can even just push the conductors into the conduit.

There is no explicit prohibition against putting cables into conduit, however this is more difficult to do, the conduit must be larger, and there is no particular benefit. So when people use conduit, they generally pull separate wires in the conduit, and when people use cable assemblies, they don't bother with conduit. (Note that short sections of conduit are commonly used with cable assemblies to provide physical protection, for example at the buildings with the cable simply buried.

8/3 NM or UF cable can only be used at 40A. One of the benefits of using loose wires in conduit is that 8ga loose conductors may be used at 50A.

How deep have you made your trench? There are different requirements for different locations.

-Jon
 
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Old 12-03-07, 10:56 AM
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Thanks for the suggestions, they have been very helpful. I did purchased the book wiring simplified and have read it. I don't know about anybody else, but it is really hard to read reference books. I've got a couple of questions that I need clarification on. From inside the main building to the service panel do I need to run pvc when using uf cable? The other question is: do I need a main disconnect at the feeder panel inside the garage? thanks again for the help.
 
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Old 12-03-07, 11:24 AM
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UF cable inside a structure is treated the same as NM ('Romex') cable. It does not need to be in conduit, but does need to be properly mounted for physical protection. This could be done with conduit, but more commonly is done by pulling the cable through holes bored in floor joists, or stapling the cable to 'running boards'. If the cable is thick enough, it may be stapled to the underside of the joists.

Any separate structure _requires_ a main disconnect. This does not need to be a breaker, but commonly is. For your use, the simplest way to do this is to have a main breaker in the garage subpanel.

-Jon
 
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Old 12-03-07, 12:17 PM
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Sorry, I was not specifc enough on running the uf cable to the main panel. I will run the uf cable through pvc pipe from the outside of the basement wall to the inside. The distance from where is comes in from the outside to the main panel is about two feet. Do I need to run pvc pipe to the main panel from where is comes in from the outside? thanks again
 
 

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