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VACMAN · 03-14-2009, 11:32 AM

You keep hearing you should have a Surge protector on board.. Do some coaches have this built into to system? or is it something you should add?? My coach is a 2008 4354 DSDP...Vacman

David K · 03-14-2009, 12:50 PM

Quote:

Originally Posted by VACMAN

I think I get it now..L1-N-L2-Green earth G will work to plug in the RV...But L1-earth G-L2 will run the welder but screw up coach.. Simply by adding the N makes the difference..Is that the short of it?? VACMAN

Vacman

Norm had it correct when he replied above ---- L1 + netural makes up one 120 volt circuit and L2 + ground makes up the other 120 volt circuit. L1 comes from one side of the bus bar in a breaker box and L2 comes from the other bus bar in a breaker box. You do not want both L1 and L2 coming from the same bus bar. And as he said and you did finally, don't use the welder plug in or any other regular 220 plug. They are L1 + N + L2 and the ground is separate --- different type of configuration and will blow the items in the MH. The link that I posted in an earlier post actually has the wiring diagram coming from the meter base on your house which shows the separation of L1 and L2 (coming from different legs).

David K · 03-14-2009, 12:59 PM

Quote:

Originally Posted by VACMAN

You keep hearing you should have a Surge protector on board.. Do some coaches have this built into to system? or is it something you should add?? My coach is a 2008 4354 DSDP...Vacman

Vacman

What most people are referring to is a surge protector that is between the shore power source and your MH. I have a hard wired SurgeGuard surge protector wired in my MH. The shore cord plugs into the normal campground supply source then runs through the SurgeGuard and then into the normal plug in for the MH. When you initially plug in, the SurgeGuard checks the incoming current for under/over voltage, polarity, etc. It waits for a little over two minutes before it will allow current to pass on through to the MH -- this is done in case you have had a shut down with the air conditioning running -- it allows the head pressure on the air conditioning to go down before restarting it. In cases of over/under current conditions the SurgeGuard will shut down the inflow of current. There are other models out there that some other people use and some of them are hard wired as well as being "portable" -- ie, used at the plug in source (power pole). I went the hard wired way so the SurgeGuard is inside of the power area of my MH and not subject to thieft.

If you want to see a picture of the hard wired SurgeGuard, go to the top of the forum page and select photos, when there, select search and do a search of the user name of dknig288 ---- that is my photo post name. You will find a picture of my hard wired SurgeGuard in that area.

In my opinion, I would not go anywhere without surge protection of some sort -- especially with what the cost of the components in the MHs being what they are.

I am sure that others will "chime" in about what they use.

Jocat54 · 03-14-2009, 09:09 PM

Quote:

Originally Posted by Route 66

I believe a 240 volt 50 amp welder circuit is a 3 wire circuit with one 50 amp breaker and is 240 volts only.

RV 50 amp service is a 4 wire circuit with two 50 amp breakers and can be used a 240 volts 50 amps across L1 and L2, or 2 120 volt 50 amp circuits, L1 to N and L2 to N.

RV 50 amp service is the same as an electric range service.

The link previously mentioned above explains it all, with pictures.

All 240v service is two breakers, maybe tied together with a common trip bar, but you have to have 2 120v "legs" to get 240v.

Gary RVRoamer · 03-14-2009, 09:24 PM

I put a override switch on my EMS so I can force it into generator mode when I hook up the cheater box to two 120v sources that are in phase (aka "on the same leg"). That way I get to use the full power of whatever I have available. It's not too difficult to do with the Intellitec EMS - basically have to switch a 12v source to J2 pin 2 so that it thinks the genset is running.

porscheracer · 03-14-2009, 11:28 PM

Thanks, Gary. I'll have to figure out how to do that "cheat" on mine.

RV Wizard · 03-15-2009, 05:43 AM

Gary has discribed what I was stating about making your EMS think the generator is in use.

RVDude · 03-15-2009, 03:29 PM

In several parts of the country N and G are bonded - that is they are exactly the same coming off the exact same main panel bus bar.. Hence an L1-N-L2/G and L1-G-L2/N are *electrically* identical but not code compatible if the bare wire is used as the N.

This gives L1-L2 = 240VAC, L1-N or L2-N = 120VAC which is a typical 50A RV plug which is also a typical stove plug (3 vertical blades + 1 round). This is a national code standard plug.

I also think that national code allows this style plug to be wired in either the 120V (i.e. L1 and L2 "in phase" that is off the same line bus such that L1-L2=0VAC) OR the 240V (L1 and L2 "out of phase" that is different bus L1-L2=240VAC) configuration INTERCHANGEABLY at the rated 50A capacity. Again, in the 120V configuration L1-L2=0VAC and of course L1-N and L2-N are both 120VAC.

I further think that 50A @ 240VAC = 2 * 50A @ 120VAC. So a single 50A 240VAC breaker (actually a double breaker) will provide the full 50A 120V on both L1 and L2 legs.

Again code allows this plug to be wired either in the 120V or 240V configuration. Hence either may be used as your 50A supply in any 50A camper. Every CG I have stayed in thus far has L1-L2=240VAC further suggests that EVERY 50A camper will accept L1-L2=240VAC OR the other standard of L1-L2=0VAC (2 identical phase 120VAC legs) UNLESS you have a 240V appliance in your rig (then you need the 240V service but will do NO damage plugging into a 120V service - the appliance just won't work). The plug style dictates the standard wiring and amperage. If the receptacle is up to code and your plug fits you can use it.

BTW -
1) A 50A 240V breaker is actually a double breaker spanning both panel buses.
2) Run length has a significant affect on wire size.
3) The amperage running down N in a 240VAC setup is the difference in the current being pulled by the L1/L2 legs. Hence if you are pulling a full 50A off BOTH L1 AND L2 the current on the N is 0A. Also if say L1 is at 50A and L2 is at 0A then N will show 50A. Of course we always hope the G always has 0A or we have a dangerous ground fault - current is bleeding someplace.

4) And MOST importantly a L1-L2=240VAC setup will require MUCH smaller wire size than the L1-L2=0VAC (120VAC only) setup.

A final thought is that I believe the default position for your xfer switch is shore feed, hence, your xfer switch will connect by default to whatever shore power (be it "cheated" that is 120VAC config or not which is the 240VAC config) unless there is power from the genset feed to trigger the xfer switch over to that feed side.

Comments????????

Gary RVRoamer · 03-19-2009, 07:22 AM

Quote:

Comments????????

RVDude: Can't see anything wrong with what you said.

RustyJC · 03-19-2009, 07:46 AM

Yes, there's a problem with L1 and L2 being in phase in a 50 amp outlet when applied to 120/240VAC RV service. Neutral leg currents are additive, so if L1 is carrying 50 amps and L2 is carrying 40 amps, then the neutral leg current will be 50 + 40 = 90 amps if the hot legs are in phase. Theoretically, the neutral leg could be exposed to 100 amps if both hot legs were carrying 50 amps. Thus, if L1 and L2 are in phase, the neutral leg in a 120/240VAC RV service application can be easily overloaded since the shore power cord conductor is sized for 50 amps, just like the hot legs - this can result in melted neutral conductors and even electrical fires. That's why this is a definite no-no and campground recepticles should be checked to ensure that L1 to L2 = 240VAC before hooking up!

If the hot legs are out of phase by 180* as they would be on a correct 120/240VAC RV service (i.e., the service is being fed by the output of a center-tapped transformer), then the neutral leg current would be 50 + (-40) = 10 amps in our example and could never be over 50 amps (50 + (-0) = 50 amps).

Although mentioned in the post above, this potentially dangerous problem is worthy of a standalone caution.

Rusty

RVDude · 03-19-2009, 08:08 AM

Rusty further emphasizes the 120v vs 240v wiring difference for the std RV (or stove) recepticals. All RVs will accept either config. If the voltage across L1-L2=0v then you have a 120v setup (in phase=same main bus tap off) where the wiring (reqd by code) better be able to handle 100A down the N. In a L1-L2=240v setup you have a 240v setup (180 out oof phase different main bus tapoff) the wiring will be much smaller. Mostly 240v pedestals out there for this very reason.

David K · 03-19-2009, 08:33 AM

Rusty -- that is what I was trying to say but, you said it much better than I. The legs for the 120v need to be "out of phase" or from different sides of the breaker box -- not from the same bus bar as the most of the 240v in our houses are done. In the house, phase does not become a consideration as the appliance will use the "in phase" 120v and the neutral wire does not have to worry with the "additive" effect of the 220v -- it don't happen. I will have to remember the "in phase" and "180 degree out of phase" phrases for future reference -- this topic seems to "pop" up quite frequently.

porscheracer · 03-20-2009, 08:31 AM

As I stated before, many motorhomes will reject the L1 and L2 being on the same leg. If I hook up to that configuration, it senses and indicates 30A service. Probably a good thing, since I don't really want to be sending 100A back down the MH neutral.

Roadking · 03-20-2009, 02:20 PM

As stated when your RV EMS detects L1 and L2 are in-phase it configures your EMS as either a 30amp source or a 20 amp source (depending on switch settings). A 50amp to 30amp adapter ties L1 and L2 together and hence applies the same phase to each of the legs on the RV, and hence the EMS senses the source as 30 amps, or 20 amps.

Many RVs with 50 amp connections carry a 7.5KW generator. Assuming voltage and current are in phase (which is not true for inductive loads such as AC motors, but lets assume they are) then POWER = Voltage times Current. So a 7.5KW generator operating at 125Volts will provide approximately 60 amps of current. 7500 Watts = 125Volts times 60 amps (again, assuming voltage and current are in phase).

Rarely will the generator actually produce a full 60 amps, and hence, the neutral wire will not be overloaded in generator mode. However, "cheating" the EMS into thinking it is in generator mode, and pulling a full load on a power source that has both L1 and L2 in phase could overload the neutral. As previously stated.. you could potentially pull 100amps on the neutral if both legs L1 and L2 had 50 amps available and you were indeed pulling full capacity. Therefore you should not be creative by "faking " your EMS in generator mode unless you know for certain you are never pulling more than 50 amps Overloading the neutral could cause a fire anywhere along the neutral path all the way back to the main breaker panel where adequate sized neutral wires exist.

On the other hand, if you know the maximum loads your coach pulls on each leg then perchance you may be able to manage the risk. For instance, when I was on my own meter at one particular resort I used a cheater/adapter to get the "out of phase" L1/L2 power. My L1 source had a 30 amp breaker and my L2 source had a 20 amp breaker. The only time I would trip a breaker (the 20 amp) is when the Dryer, Hotwater Heater, and 2nd AC compressor were all running at the same time. So normally, I rarely pulled more than a total 50 amps as I recall only tripping a breaker once.

I also know under normal common sense conditions with my 7.5KW generator running I have never pulled more than 45 amps total. I'm sure I could add an electric heater while running the AC and pull more, but besides me, who would do that?? This means it would be highly unlikely that I would overload a neutral wire as my max draw would typically be only 45 amps. Your coach may be different and if you don't know you should not risk any fires or potential damage.