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Old 04-22-2010, 03:33 PM   #1
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Wiring A Portable Surge Protector to Protect Shore and Generator

I am going to buy the Portable 50A/240V Pro Electrical Management System


Dyer's RV (I hope) and I would like to wire it where it protected against Shore AND Generator Power. I know I could order a HARD wired one but I would like to be able to remove this one. This may not be my last Motor Home. I had one a couple years ago and like a DUMMIE I let it go with the MH when I sold it. This will not happen again.

I would like to be able to plug it in and leave it in my compartment. I know I will need to disconnect my Shore power cord from the transfer switch and install a plug on it. So I will have a HUGE 50amp drop cord. But I am not sure where I will have to wire the transfer (incoming power) in order to protect the coach. Can someone give me pointers on what I am going to need to protect them both?
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Old 04-22-2010, 04:29 PM   #2
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LeeB....Here is a photo of my power compartment with the SurgeGuard protector in the upper left corner.



Mine is only protecting the shore power. The black cable in the center of the screen, coming out of the transfer switch, originally connected to the black cable at the top of the box and ran to the rear of the power reel. I disconnected the cable from the transfer switch box and wired it to the top of the SurgeGuard. I bought an additional three feet of 4 lead cable at Home Depot and wired it from the Surgeguard to the transfer switch. If you do it without the generator, you would just add the cable ends where mine is attached at the top and bottom of the SurgeGuard and plug your in.

It is probably a better idea to protect yourself from the generator power too, but I only protected the shore power.

Without looking at it more closely, I'm guessing that one of the grey cables going into the transfer switch is the generator feed. The other grey cable would be the one you would want to tap into.
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Old 04-22-2010, 05:03 PM   #3
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Seems like the generator power would be a pretty constant, controlled source. I think I would be more concerned with the park power than the generator.
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Old 04-22-2010, 05:12 PM   #4
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If you want to protect both shore and generator power then you need to do it at the output of the transfer switch. You should have a gray conduit that goes from the transfer switch to the 120 volt circuit breaker panel. If you open the transfer switch and remove that then in its place add a new 4 conductor cable with #6 wire. On the other end put a 50 amp receptacle on the end of the wires in the gray conduit you would put a 50 amp plug. This should let you plug the surge protector into the output of the transfer switch and the plug the lead going the CB Panel into the output of the surge protector. All the parts should be available at Home Depot or Lowes.
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Old 04-22-2010, 07:28 PM   #5
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I can see this is going to be interesting... Thanks for Pic Diplomat Dan. I hope I can take some pictures of mine when I'm done.

Jeepsrule- Generators have been known to Freak Out. My thinking is should some happen I would rather replace the transfer switch then everything in my MH. We use the Generator quite a bit.

itdave..... Thanks for the run down....
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Old 04-23-2010, 09:03 AM   #6
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Quote:
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I can see this is going to be interesting...
Yes, electrical discussion often do get interesting...

Quote:
Originally Posted by LeeB View Post
Jeepsrule- Generators have been known to Freak Out. My thinking is should some happen I would rather replace the transfer switch then everything in my MH. We use the Generator quite a bit.
I totally agree. In fact, there was a post in another forum a few days ago where the voltage regulator on a guy's built-in Onan generator failed, and the generator started putting out over 160 volts. Fortunately, he had a Progressive EMS installed such that the generator was protected as well as the shore line, so the EMS clicked off because of the high voltage, and he suffered no damage in the coach. He was fortunate, it could've been expensive.

I have a hard-wired 50 A Progressive that I wired after the transfer switch, to specifically protect from such a failure. There are those who say it should be installed before the transfer switch, so that the transfer switch is protected, but I obviously disagree. The transfer switch is primarily a set of relay contacts, so they are not really susceptible to the types of failures that the EMS would prevent (their most common failure mode is arcing from switching while under heavy load, and an EMS will not protect against that.) Also, the transfer switch is a relatively inexpensive component, and I would rather risk the $100 or so it takes to replace that and instead protect the thousands of dollars of other equipment in the coach that could be damaged by a catastrophic generator failure (like a blown voltage regulator!)


Quote:
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You should have a gray conduit that goes from the transfer switch to the 120 volt circuit breaker panel. If you open the transfer switch and remove that then in its place add a new 4 conductor cable with #6 wire.
It may not be as simple as that. Odds are that if you look closely, you will find that the neutral wire on the output of the transfer switch is larger than the other wires, and a #6 conductor may not be sufficient. This is because most RV generators do not put out 240 volts -- they put out two legs of 120 volts that are in phase with each other. This means that the neutral wire carries the sum of the currents in the two hot legs, not the difference as would be the case with a true 240 volt output. To counter this, the neutral wire from the generator, through the transfer switch, and to the breaker box is over sized relative to the other wires.

In my rig, for example, I have an 8k generator. It can put out 33.3 amps on each of the hots legs, which means that there can be up to 66.6 amps on the neutral. If you have a 10k generator, it can be up to 83.3 amps on the neutral. If you have larger than that, say a 12k generator, then it is likely to have a true 240 volt output, and the neutral wire should not be an issue. Furthermore, the total output of a 6k (or less) generator is low enough that it can't overload the neutral wire, so this is also a non-issue with the smaller units. But for units in the 8k to 10k range, it's something to think about.

So, by adding a #6 pigtail, a socket and plug, and a portable EMS after the transfer switch, it may be possible to overload the neutral in that pigtail, the neutral contacts in those connectors, or in the wires of the portable EMS. It's only a short length of wire we're talking about, so the heating from the higher current may not be an issue. Or is it? I'm not advising whether to do it or not, just pointing out some information that is not necessarily obvious. Anybody planning on doing this should be aware of the possible issues and make up their own mind.

When I went to do my installation, I bought a couple feet of #6 cable to use as a pigtail. When I realized what I was up against, I didn't end up using it. Instead, I found that there was more than enough slack in that gray conduit behind the breaker panel, that I could just cut off a short section from that, and use the factory wires to make a pigtail. As an alternative, one could buy a length of flexible conduit and some individual wires of the proper sizes to match the factory wiring -- it's all available individually by the foot.
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Old 04-23-2010, 05:26 PM   #7
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Yes, electrical discussion often do get interesting...

In my rig, for example, I have an 8k generator. It can put out 33.3 amps on each of the hots legs, which means that there can be up to 66.6 amps on the neutral. If you have a 10k generator, it can be up to 83.3 amps on the neutral. If you have larger than that, say a 12k generator, then it is likely to have a true 240 volt output, and the neutral wire should not be an issue. Furthermore, the total output of a 6k (or less) generator is low enough that it can't overload the neutral wire, so this is also a non-issue with the smaller units. But for units in the 8k to 10k range, it's something to think about.

So, by adding a #6 pigtail, a socket and plug, and a portable EMS after the transfer switch, it may be possible to overload the neutral in that pigtail, the neutral contacts in those connectors, or in the wires of the portable EMS. It's only a short length of wire we're talking about, so the heating from the higher current may not be an issue. Or is it? I'm not advising whether to do it or not, just pointing out some information that is not necessarily obvious. Anybody planning on doing this should be aware of the possible issues and make up their own mind.
OK as you said these discussions are interesting and hopefully informative. So now you made me look at the codes for AMP to Wire Size ratings. The size of wire to amps is related to voltage drop and heat buildup. Here is what I found. For a short run you can use a figure of 1amp/200 circular Mil. So since a #6 wire has a circular mil of 26244 you can carry 131 amp for a short distance. For very long distances a #6 wire can carry about 37 amps. The table did not define short and very long. I think both of those number are for open air and would be lower in a 4 conductor cable. So here is a copy from a table on cables
For reference, the ampacity of copper wire at 300C for common wire sizes
14 AWG may carry a maximum of 20 Amps in free air, or 15 Amps as part of a 3 conductor cable.
12 AWG may carry a maximum of 25 Amps in free air, or 20 Amps as part of a 3 conductor cable.
10 AWG may carry a maximum of 40 Amps in free air, or 30 Amps as part of a 3 conductor cable.
8 AWG may carry a maximum of 70 Amps in free air, or 50 Amps as part of a 3 conductor cable.

They do not list #6 but based on a #8 3 conductor being able to care 50 I can't see any issue with a #6 4 conductor cable carrying 66 amps on one of the 4 wires for a distance of less than two feet.

I also happen to have the original jumper that went from the cable reel to the transfer switch for shore power so I took a look at it, Here is what is stamped on the cable. For Model Home or Recreational Vehicle Use 50 amp - 3 #6 & 1#8. The #6 are the Red, Black and White while the Green is a #8. This is the same 40' cable that gets plugged into shore power where there are two 50 breakers so the Neutral could possible be carrying 100 amps on the shore power cable.

Bottom line I can't see where there is anyway you could overload a #6 wire as the neutral. Now I am not a EE and I have been wrong many times before so maybe I am missing something and I never object to airing on the side of caution.
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Old 04-23-2010, 06:32 PM   #8
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The table did not define short and very long.
Even without knowing their definitions, I agree with you -- I would think we're talking about very short distances here.

Quote:
I also happen to have the original jumper that went from the cable reel to the transfer switch for shore power so I took a look at it, Here is what is stamped on the cable. For Model Home or Recreational Vehicle Use 50 amp - 3 #6 & 1#8. The #6 are the Red, Black and White while the Green is a #8. This is the same 40' cable that gets plugged into shore power where there are two 50 breakers so the Neutral could possible be carrying 100 amps on the shore power cable.
Nope, it doesn't work that way. if the pedestal is properly wired, the most the neutral can carry is 50 amps, just like the two hots (which is why all the current carrying conductors are the same size.) The pedestal should be wired as a two pole 120/240 service, where measuring from either of the two hots to the neutral is 120 volts, but measuring between the two hots is 240 volts. With such a split phase 240 volt service, the current in the neutral will be the difference of the currents in the hot conductors, not the sum. The maximum current in the neutral will be 50 amps, which will happen if you are drawing 50 amps from one hot, and nothing from the other. If you then take that same situation and start drawing current from the other hot, the current in the neutral will go down. Taken to the extreme where you are drawing a full 50 amps from both hot lines, the neutral will have no current in it -- zero amps.

On the other hand, if the pedestal is wired incorrectly, so that both hots have the same polarity, and there is zero volts between them, then the neutral current will be the sum of the two hot currents, and you could get up to 100 amps on the neutral, and that is definitely not something that the shore cord was designed to do. Wiring the pedestal in this manner is a code violation, and can be dangerous. This is exactly the same situation as the generator, and why if you look at the wires between the generator and transfer switch, or transfer switch and breaker box, you will likely find a larger neutral to mitigate the dangers of such a circuit. You cannot take the shore cord pigtail and extrapolate that to the generator circuit, as they are using different rules.

Quote:
Now I am not a EE and I have been wrong many times before so maybe I am missing something and I never object to airing on the side of caution.
While I am an engineer, and I did take a bunch of EE courses, I am certainly not a power engineer nor an electrician. (I'm more into low power electronics.) I'm the first to admit that I don't know everything. But I know enough to know that a lot of the things that need to be taken into consideration are not immediately obvious. The codes are there for a reason, and the size wires that the manufacturer used are there for a reason, even if we don't understand them. Using larger wire for the neutral in the generator circuits is more expensive than using the smaller wires. Do you really think the RV manufacturers would spend money on that larger wire if it wasn't necessary? It's not necessary for the shore cord, since that is a proper balanced 120/240 circuit, so they didn't use a heavier neutral in that cable.

Again, I'm not trying to tell anybody what to do, nor am I saying that anything you said was wrong (other than 100 amps on the shore cord neutral.) And I'm not saying that using a #6 neutral is automatically dangerous. I'm just trying to point out some of the issues that may not be immediately obvious, so that folks can do their own research and make their own decisions. I would hate for someone to blindly hook things up without realizing the possible issues. Maybe it's safe, maybe it's not. I chose to err on the side of caution and used the same wire sizes as in the original circuit, rather than downsize it for a portion of the circuit. Maybe that wasn't necessary, but having used the larger wire, I have no concerns or worries, and I sleep like a baby in my rig, even though I'm only a few feet from those connections.

Overkill? Maybe, maybe not...
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Old 04-24-2010, 06:38 AM   #9
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Oh MY....... You guys have gone WAY over my head (which is nothing new) ..... I am not sure what to use now....

But thanks for the postings I Think......
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Old 04-24-2010, 06:49 AM   #10
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Oh MY....... You guys have gone WAY over my head (which is nothing new) ..... I am not sure what to use now....

But thanks for the postings I Think......
Think I would by the built-in unit and use the heaver wire. You can always pull it back out when you trade up.
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Old 04-24-2010, 06:51 AM   #11
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And wow you guys put out too much power on that one for the wiring in my brain. If I want one of these I think I'll find out where ShapeShifter is parked!
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Old 04-24-2010, 08:42 AM   #12
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Oh MY....... You guys have gone WAY over my head (which is nothing new) ..... I am not sure what to use now....

But thanks for the postings I Think......
It's really not that bad. If you follow the installation instructions they provide, and just match what's already in the coach as far as wire sizes and types, I think you'll do fine. You may also do fine if you get creative, but you'd be on your own if you do so.

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Think I would by the built-in unit and use the heaver wire. You can always pull it back out when you trade up.
I do plan on pulling mine out when I sell it (a long time from now.) I will probably just abandon the wires to the remote display (too much work to pull them out, and cheap enough to replace) but the rest of the pieces will stay with me. "Permanent Install" just means you don't want to be putting it in and taking it out all of the time. It doesn't mean that it can never be removed.

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If I want one of these I think I'll find out where ShapeShifter is parked!
Come on over, I'll be glad to help!

As soon as it arrives, my next project is to put an automatic Winegard Trav'ler dish up on the roof. Anyone want to help? I'll gladly help install your EMS for you in exchange.
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Old 04-25-2010, 06:42 AM   #13
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Drilling holes in someone else's roof sounds like fun
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Old 04-25-2010, 08:08 AM   #14
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Drilling holes in someone else's roof sounds like fun
A couple years ago I mounted an external GPS antenna on the roof. It took me a few minutes to bring myself to let that spinning drill bit actually touch the roof.

But after the first hole was in, the rest were easier. Since I've already drilled some holes once, I'm hoping this time won't be as much of an issue...
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