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Old 09-05-2013, 12:16 PM   #1
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30 amp 240 receptacle

At my storage building I have a 30 amp 120 volt receptacle. I have blown the 30 amp fuse on the buss that it is connected to a few times, so I want to add more power. The easiest option is to pull in one more wire and connect another leg to get 240 and change the receptacle to a 50 amp. The wire will only be rated for 30 amps so it will only have 30 amp fuses installed. This basically doubles my current capacity and should eliminate any blown fuses.
Changing the wire and disconnect box to get a full 50 amps is much more involved.

Thoughts?
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Old 09-05-2013, 12:21 PM   #2
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Quote:
Originally Posted by rssnape View Post
At my storage building I have a 30 amp 120 volt receptacle. I have blown the 30 amp fuse on the buss that it is connected to a few times, so I want to add more power. The easiest option is to pull in one more wire and connect another leg to get 240 and change the receptacle to a 50 amp. The wire will only be rated for 30 amps so it will only have 30 amp fuses installed. This basically doubles my current capacity and should eliminate any blown fuses.
Changing the wire and disconnect box to get a full 50 amps is much more involved.

Thoughts?
That will work. I'm sure no code authority would be happy. If you are dealing with a fuse box that must be an old installation.
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Old 09-05-2013, 12:50 PM   #3
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It's coming off a box on a 400 amp buss bar. The fuses will match the rating of the lowest rated item, in this case the wire in the conduit. Yes it is about 40 year old industrial set up.

Thanks
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Old 09-05-2013, 01:32 PM   #4
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I guess you are aware that your MH is 120v so a 50 amp box should be wired as such. If you connect a 50 amp 240 dryer type box you will fry everything inside.
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Old 09-05-2013, 01:37 PM   #5
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Yep, 3 pole 4 wire receptacle. 14-50R
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Old 09-05-2013, 01:39 PM   #6
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It will work fine and there is no difference between 50 amp 4 wire socket as far as
wiring. Not so on the 30 amp sockets.
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Old 09-05-2013, 02:36 PM   #7
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Originally Posted by rssnape View Post
At my storage building I have a 30 amp 120 volt receptacle. I have blown the 30 amp fuse on the buss that it is connected to a few times, so I want to add more power. The easiest option is to pull in one more wire and connect another leg to get 240 and change the receptacle to a 50 amp. The wire will only be rated for 30 amps so it will only have 30 amp fuses installed. This basically doubles my current capacity and should eliminate any blown fuses.
Changing the wire and disconnect box to get a full 50 amps is much more involved.

Thoughts?
Your idea has some merit, and should increase the amount of available power. If you have an energy management system that detects the type of power, and automatically sheds loads to keep it under the available limit, it will be confused by this arrangement. There will be nothing that prevents it from allowing more than 30 amps per leg (other than the breaker feeding the outlet.) Not likely to be a serious issue, but something to be aware of, since you will have to do your own load management and rely on your management system.

So it should work, but is it legal? You say you want to pull an extra wire. Are the existing wires in conduit, and you are adding an extra single conductor? If so, is the conduit large enough to handle the extra power from the added conductor? Is there enough volume in the junction boxes to legally allow the addition of another conductor?

If the existing circuit is not in conduit, and is using jacketed non-metallic cable (Romex), then is it legal to run another cable in parallel to it? I would doubt that it would be legal to run a single non-jacket extra conductor outside of conduit. And does the junction box for the socket have enough volume to support the extra conductor?

Finally, while it's obviously bad to put a 30 amp socket on a 50 amp circuit, is it legal to put a larger socket on a smaller circuit? When you get right down to it, the breaker doesn't instantly trip when it goes over 30 amps, it may be possible to draw 35 or 40 amps on that wire for a while - will that be enough to heat things up and cause problems before the breaker trips?

And it doesn't hurt to say that the second hot line must be on the opposite supply phase from the existing hot line, because you will overload the existing neutral line if it isn't. But I think you know this since you're mentioning 240 volts.

I don't have the answers to all of these questions, but they should be answered before you do anything. It's so tough to give definitive suggestions without seeing the actual conditions, so it's always a good idea to get the a professional opinion from someone who can actually see the job conditions, even if you are planning on doing the work yourself. Often times, your local building inspector is willing to talk to a homeowner about planned work and give advice about what is an isn't safe and legal.

Theoretically, your idea will give more power to the RV, and your RV will be happier. But will it be legal, and more importantly safe? It would be better to find that out before doing the work rather than finding out the hard way.

Now, with all of this said, if you're going to be pulling new wire(s), why not just do it right and pull a new 50 amp 240 volt circuit and not have any issues? It's a little more up-front money and work, but in the end it's the right thing to do.

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Originally Posted by Melmoses View Post
I guess you are aware that your MH is 120v so a 50 amp box should be wired as such. If you connect a 50 amp 240 dryer type box you will fry everything inside.
As long as that 50 amp 240 volt dryer socket is a standard four prong socket, there will not be an issue. A 50 amp RV uses the exact same plug and socket as the modern 50 amp 120/240 volt 3 pole 4 pin dryer socket. The four pins consist of two hots, one neutral, and a ground.

If it's an older socket with only three pins (no neutral) then it would be a very bad thing to connect to, whether it be 30 amps or 50 amps.
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Old 09-05-2013, 04:00 PM   #8
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It is in conduit and the box is a 2 gang handy box. The problem is the conduit likely would not handle wire rated for 50 amp and it is a clamp on disconnect onto the 400 amp buss not sure we have a 50 amp.
My only concern is the phase. It is 3 phase, but my maintenance guy says he can give me another leg to make 240. My question/ concern is the second phase 180 degrees out? I don't understand 3 phase completely, but my guy has never done me wrong in the 30 years he's worked for me.
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Old 09-05-2013, 04:20 PM   #9
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I have a question. In the picture you have provided, the cord that is plugged into that receptacle, is it a 50 to 30 adapter cord or is it the actual feed cord from the coach?
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Old 09-05-2013, 06:02 PM   #10
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I have a question. In the picture you have provided, the cord that is plugged into that receptacle, is it a 50 to 30 adapter cord or is it the actual feed cord from the coach?
50 to 30 dog bone
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Old 09-05-2013, 07:05 PM   #11
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Actually, in a true 3 phase, it is 120 degrees out but that actually will not be a problem. I assume your maintenance guy knows this but voltages will also need to be correct.

Since the bus already has a 120v leg fed from it, it will likely be what the industry calls a 208 Y connection or a 240V Delta connection. The concern would be that if it is a grounded delta, you will have 240V 3 phase with a neutral. What this means to you is that there are only 2 of those phases you can connect to a single phase load ( your 50A 240v receptacle). You or your maintenance man will need to be careful in identifying which leg of the 3 phase is "wild" and not use it. You can use the other 2 phases with no problem.

If the 3 phase is a Y it will actually be a grounded 208/120 volt system. The beauty here is that all phases to ground here are 120V so there is no "wild" leg and you can use any 2 of the 3 phases off the buss duct. Drawback is that it is actually 208 volts single phase. I am not sure the 50 amp wired coaches have moved to 240v appliances and ac or not but I doubt it since many parks still only offer 30a 120v. If in fact the loads in a 50a coach are still only 120v then you would never know the difference. I also could not answer the problems with the inverters but I assume they are also still fed with 120V.

I agree with others that as long as your overcurrent protection is lower than the wire and device capacity, you will be OK as far as safety from overcurrent and heating. I also cannot answer what load shedding devices in your coach might do but I suspect they are also using 120v circuits and they will only act if the current is too high. You are fused under that so you should blow the fuses if you are loaded too heavy. I think the trip curve issue mentioned earlier with fuses and especially breakers would be the same or worse with an actual 50 amp rated circuit rather than your 30A rated circuit. You may have to monitor loads to avoid tripping your overcurrent device.

If you or your maintenance man do not understand this I would recommend finding an electrician who does. You could cause a lot of costly damage if you get it wrong. Hope this helps.
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Old 09-06-2013, 02:39 AM   #12
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I did the same thing only with single phase. can run both a/c s and ref no problem.
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Old 09-06-2013, 05:25 AM   #13
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Actually, in a true 3 phase, it is 120 degrees out but that actually will not be a problem. I assume your maintenance guy knows this but voltages will also need to be correct.

Since the bus already has a 120v leg fed from it, it will likely be what the industry calls a 208 Y connection or a 240V Delta connection. The concern would be that if it is a grounded delta, you will have 240V 3 phase with a neutral. What this means to you is that there are only 2 of those phases you can connect to a single phase load ( your 50A 240v receptacle). You or your maintenance man will need to be careful in identifying which leg of the 3 phase is "wild" and not use it. You can use the other 2 phases with no problem.

If the 3 phase is a Y it will actually be a grounded 208/120 volt system. The beauty here is that all phases to ground here are 120V so there is no "wild" leg and you can use any 2 of the 3 phases off the buss duct. Drawback is that it is actually 208 volts single phase. I am not sure the 50 amp wired coaches have moved to 240v appliances and ac or not but I doubt it since many parks still only offer 30a 120v. If in fact the loads in a 50a coach are still only 120v then you would never know the difference. I also could not answer the problems with the inverters but I assume they are also still fed with 120V.

I agree with others that as long as your overcurrent protection is lower than the wire and device capacity, you will be OK as far as safety from overcurrent and heating. I also cannot answer what load shedding devices in your coach might do but I suspect they are also using 120v circuits and they will only act if the current is too high. You are fused under that so you should blow the fuses if you are loaded too heavy. I think the trip curve issue mentioned earlier with fuses and especially breakers would be the same or worse with an actual 50 amp rated circuit rather than your 30A rated circuit. You may have to monitor loads to avoid tripping your overcurrent device.

If you or your maintenance man do not understand this I would recommend finding an electrician who does. You could cause a lot of costly damage if you get it wrong. Hope this helps.
It is 208 3 phase. And yes my maintenance man understands this much better than I. He maintains all our equipment. 5 air compressors, numerous process heaters, dc rectifiers, builds process controls from scratch, plumbing, mechanical, you name it he can do it.

My coach is a 1997 and I'm pretty sure there is no load shedding device.

Thanks for your detailed reply!
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Old 09-06-2013, 05:48 AM   #14
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At my storage building I have a 30 amp 120 volt receptacle. I have blown the 30 amp fuse on the buss that it is connected to a few times, so I want to add more power. The easiest option is to pull in one more wire and connect another leg to get 240 and change the receptacle to a 50 amp. The wire will only be rated for 30 amps so it will only have 30 amp fuses installed. This basically doubles my current capacity and should eliminate any blown fuses.
Changing the wire and disconnect box to get a full 50 amps is much more involved.

Thoughts?
How long is that run from the main box?
As you mentioned a storage shed, I am curious is your wire is under sized for the length of the run. While #10 is normal, longer runs (I add runs that will have constant loads) need to be up sized.
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