![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/SineWave.png\")
<\/figure>\n\n\n\nThe current waveform would look similar and alternates\ndirections, going in one direction during the positive portion of the cycle and\nthen reversing direction, or alternating direction, on the negative\nportion. That is what gives this type of\npower its name, alternating current.<\/p>\n\n\n\n
Voltages in an AC system are normally given by the effective\nheating caused by the voltage and are called \u201cRMS\u201d (for Root Mean Squared)\nvalues. As you can see from the graph,\nthe standard 120 VAC (volts alternating current) has a peak or maximum voltage\nof 170 volts.<\/p>\n\n\n\n
In your sticks and bricks home, the outlets, lights,\ntelevision and other appliances generally operate from 120 VAC. More power hungry devices like an electric\nrange or electric dryer operate from 240 VAC. \nThis happens because the power coming into your house has three\nwires: there are two wires that provide\na total of 240 VAC (the \u201chot\u201d wires) and a neutral voltage that sits half way\nbetween the two hot wires. If we use\nthis as our reference point, then we would see 120 VAC on one side, and 120 VAC\non the other side. The difference would\nbe when one side was going up (towards +170 volts) the other side would be\ngoing down (towards -170 volts) so the two 120 VAC lines would add together to\ngive you 240 VAC.<\/p>\n\n\n\n
This is going to become important when we look at how AC\npower is used in and RV. If your RV has\na 30 Amp service connection, then it gets a single hot line and a neutral, plus\na safety ground and only gets 120 VAC from the pedestal.<\/p>\n\n\n\n
If your RV has a 50 Amp service connection, then it gets two hot lines each of which can provide 50 Amps plus a neutral and a safety ground.\u00a0 If the pedestal is wired properly, then it will have the same 240 VAC power between the two hot leads.\u00a0 While you could have something in the RV that used the 240 VAC power, that is unusual except in some high end RVs and most RVs just hook things across one set of lead of the other.\u00a0 Because of the way RVs are wired, it is possible for the pedestal to have the same hot lead used for both connections to the outlet.\u00a0 While this is undesirable, and in violation of most electric codes, it is not unheard of.\u00a0 Also, some generators may provide separate leads to the two \u201csides\u201d of the AC power cord, in fact they are in phase so that you would not see the 240 VAC if you hooked a voltmeter across the two hot leads, but 0 volts instead. This isn’t going to be a problem in most RVs but you should be aware of the possibility. The biggest problem if the pedestal is wired this way is that the neutral wire size has to be doubled to make sure it can handle all of the current.<\/p>\n\n\n\n
Some RVs have internal electrical monitors that decide if\nyou have a 30 Amp or 50 Amp connection based on whether or not you have 240\nvolts coming in on the service connection and may limit your power consumption\nbased on this data. That is the topic\nfor another discussion, however.<\/p>\n\n\n\n
Why is all of this important?\u00a0 Because, if your power were all connected correctly, it wouldn\u2019t\u00a0 be an issue, but in the real world pedestals are miswired, wires and connections can fail, and voltages from the pedestal might not be within an acceptable range for proper operation.<\/p>\n\n\n\n
First let\u2019s cover transients, or surges, on the power\nlines. Surges can occur for a number of\nreasons. For example, when a motor\nstarts up it often needs a large surge of power to get the motor turning. This input surge can cause the 120 VAC line\nto drop, or sag, due to the large inrush current of the motor. This is negative surge and generally doesn\u2019t\nhave much effect on anything else because it is so short. There is also little that can be done about\nthese surges except to make sure that all of the wiring is done properly and\nall connections are secure.<\/p>\n\n\n\n
Surges where the voltage goes up significantly can happen\nfor several reasons. Sometime when a\nheavy load (high current device) goes off line, it results in a surge where the\nline voltage jumps up. Depending on how\nhigh and how long the surge might be, most of the time it isn\u2019t a problem, but\nif it is high enough and lasts long enough it can damage devices on the line,\nparticularly electronic devices such as computers or microwave ovens.<\/p>\n\n\n\n
Another type of surge is one caused by lightning strikes directly on a power line or nearby.\u00a0 These strikes can occur very close by with very high energy or a long way off but still coupled through the transmission lines to the pedestal you are plugged into and give you a short, but high, transient on the AC lines.<\/p>\n\n\n\n
These types of surges are where \u201csurge protectors\u201d are useful.\u00a0 They contain devices internally that can absorb large amounts of energy for short periods of time.\u00a0 They basically operate as electric clamps on the line to limit the peak voltage on the lines.\u00a0 They will typically clamp the voltage at somewhere above 200 volts peak.\u00a0 This type of energy is measured in its value of Joules which is a measure of how high the voltage goes and how long it stays there.\u00a0 Surge protectors are rated in the number of Joules they can absorb so the higher the Joule rating, the better job the surge protector can do.<\/p>\n\n\n\n
Here\u2019s the thing with surge protectors: they can dissipate enough energy to protect\nfrom a lot of common surges, but they will not offer much protection from a\ndirect lightning strike since the energy in a lightning strike is 10,000 or\nmore times the rating of a practical surge protector.<\/p>\n\n\n\n
The other thing is that surge protectors themselves are subject\nto what amounts to electrical wear. Each\ntime they are energized they give up a small portion of their ability to absorb\nmore energy. Given enough use they do\nwear out and lose their ability to work effectively.<\/p>\n\n\n\n
But surge protectors only protect for a small part of what\ncan go wrong with an electrical supply. \nLet\u2019s look at some of the other problems that can occur,.<\/p>\n\n\n\n
The voltage source is not within the allowed limits. Generally speaking, your appliances and\nelectronic devices allow for some variation around the nominal 120 VAC. Each device may have its own specification\nbut the standard requires that the service provide between 114and 126 VAC. It also provides that equipment operate\nbetween 104 and 127 VAC so there is some margin. Not every utility or manufacturer is going to\nadopt or adhere to these standards but they are good places to start to\nunderstand what is needed.<\/p>\n\n\n\n
A device which provides only surge protection can do nothing\nto protect you from voltages that are outside the range of 104 to 127 VAC\nexcept for high voltage transients of short duration. This is where a more sophisticated device is\nneeded. This device should certainly\ninclude a surge protector as part of its design, but needs to do more.<\/p>\n\n\n\n
The first thing it needs to do is constantly monitor the incoming voltage to make sure it doesn\u2019t go outside the expected range.\u00a0 It should have some built in timing function so that it will allow short term variations (such as caused when a motor goes on or off line and can cause a momentary condition which self corrects).\u00a0 <\/p>\n\n\n\n
One of the most common situations that occurs is in a park where the wiring is less than adequate to provide 30 or 50 Amps to all of the pedestals connected on that line.\u00a0 In summer when lots of A\/C is being used the demand for current on the line increases.\u00a0 The further away from the main electric service you are, the longer the line is going to be, and when more and more A\/C units are coming on line the voltage drop along the line increases.\u00a0 If the wiring is not robust enough to handle this, your voltage will continue to drop.\u00a0 At some point, it may go below a value that is safe for the A\/C motor to keep operating.\u00a0 You would rather the system shut off than continue to operate and burn out your A\/C unit.\u00a0 It is annoying if this happens, but a good Energy Management System (EMS) will drop you off line and give you a fault code as to why it took that action.<\/p>\n\n\n\n
While a higher sustained line voltage (above our desired\nvoltage of 127 VAC) is less likely due to wiring or load issues, it can occur\nif there is a fault somewhere in the electrical system. In a 50 Amp connection, when the total\nvoltage coming in is 240 VAC, a bad neutral connection can cause an imbalance\nin the system and one side can go up in voltage, while the other side sags in\nvoltage. This can result in a\nsimultaneous condition where one side is high and the other is low, but because\nof the complexity of the AC system, the imbalance does not have to be equal. So a bad neutral can cause a fault from too\nhigh voltage, too low voltage, or both conditions simultaneously.<\/p>\n\n\n\n
A good EMS can provide protection from all of these various\nissues. Here\u2019s how to hook one up:<\/p>\n\n\n\n
First, let\u2019s start with the pedestal itself.<\/p>\n\n\n\n We are going to assume that you also have an on board\ngenerator in your rig.<\/p>\n\n\n\n If you have both, then it is likely that you also have a\ntransfer switch to control which source is in use.<\/p>\n\n\n\n The function of the transfer switch is to select one, and\nonly one, of the sources of energy. In\nmost systems, the switch is wired to give priority to the generator so if you\nhave both connected, the generator is given priority and the switch will\ndisconnect the pedestal if the generator is running.<\/p>\n\n\n\n Either of these sources can provide energy to the coach<\/p>\n\n\n\n Once the energy gets to the RV breaker panel, it is\ndistributed throughout the RV by a series of breakers and associated circuit\nwiring.<\/p>\n\n\n\n At this point, you have to consider just how you want to\ninstall and use your EMS. If you want to\nuse a portable unit, you would just plug the EMS into the pedestal and then\nyour RV cord into the EMS system. \nHowever, unless your generator is selected by plugging your RV cord into\na generator outlet socket, you would not have an option to use the EMS with\nyour generator. <\/p>\n\n\n\n That is a common choice and sometimes the only practical way\nto use an EMS because it just isn\u2019t feasible to wire the EMS into the RV. You do give up the ability of the EMS to make\nsure your generator isn\u2019t acting up, unless you can also plug the RV into a\ngenerator outlet.<\/p>\n\n\n\n I chose to install the EMS inside the RV and it is wired\nthis way.<\/p>\n\n\n\n By wiring it in this fashion, the EMS makes sure that the\npower is clean no matter the source. \nHere\u2019s a photo of the actual installation.<\/p>\n\n\n\n Our unit is from Progressive Industries. They are a recognized manufacturer of Energy\nManagement Systems, but not the only one. \nIn no particular order, here are the manufacturers I was able to find\nwith a Google search. There may be\nothers out there as well.<\/p>\n\n\n\n Progressive\nIndustries https:\/\/www.progressiveindustries.net\/our-products<\/a><\/p>\n\n\n\n Southwire\nSurge Guard https:\/\/rvpower.southwire.com\/products\/surge-protection\/<\/a><\/p>\n\n\n\n The last point I will make is that, yes we have had a\nsituation where the EMS became active and shut down our power. I will never know how many times the surge\nprotection may have stopped some incoming transients from entering the RV\nbecause that is silent and no record is kept of such events. But we did have an issue in one park during\nthe summer. The system would shut down\nour RV during hot afternoons.<\/p>\n\n\n\n By the time it was shut down, the display showed normal\npower, but the error code display showed that it had shut down due to low\nvoltage on one side of the 50 Amp service. \nThis was caused by bad wiring within the campground.<\/p>\n\n\n\n I was able to show this to the campground staff, and they\nallowed me to plug into the adjacent site which was unoccupied at the time so\nwe were able to keep using the A\/C. They\nhad an electrician look at the system and he was able to identify a loose\nconnection at the main service panel. He\ncorrected that and the power was back to being OK.<\/p>\n\n\n\n Do I know for sure that the A\/C would have been\ndamaged? No, but that isn\u2019t a test I\nwant to run.<\/p>\n\n\n\n When you consider that the one A\/C unit would have cost over\n$1000 to replace, the less than $300 I spend on the EMS had paid for itself\nmore than 3 times over. You may never\nrun into an issue where the EMS cuts your power to protect your RV, but\nconsider how much it could cost if you had to replace multiple appliances in\nyour RV and trade that against the cost of the unit.<\/p>\n\n\n\n plugin units don\u2019t require any modifications to your unit and may be right for your circumstances. Installation of the permanently wired units is simple if you understand basic electric power wiring or you may need to have an electrician on RV mechanic do the installation for you, so that can add to the cost. Either way, you will have to decide what to do with the advice given here.<\/p>\n","protected":false},"excerpt":{"rendered":" RVs of all types have two electrical systems: a 12 volt, automotive style DC power system and a residential style 120 volt AC power system. Understanding both of these systems is necessary to get the best use of your RV. We will do a series to explain some of the intricacies of both systems and […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","footnotes":""},"categories":[4,5],"tags":[],"class_list":["post-220","post","type-post","status-publish","format-standard","hentry","category-technical","category-upgrades-mods"],"_links":{"self":[{"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/posts\/220","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/comments?post=220"}],"version-history":[{"count":1,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/posts\/220\/revisions"}],"predecessor-version":[{"id":229,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/posts\/220\/revisions\/229"}],"wp:attachment":[{"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/media?parent=220"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/categories?post=220"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rv4x40.com\/index.php\/wp-json\/wp\/v2\/tags?post=220"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/Pedestal-1.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/Generator.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/Switch.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/Plain-System.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/EMS-Drawings.jpg\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/rv4x40.com\/wp-content\/uploads\/2019\/05\/A7300930-Custom-1024x683.jpg\")
<\/figure>\n\n\n\n\n RV Electrical Protections Features\n List<\/strong>\n <\/td><\/tr> <\/td><\/tr> \n Electrical\n Ratings\n <\/td><\/tr> \n Surge\n Suppression Level (in Joules)\n <\/td><\/tr> \n UL\n Listed\n <\/td><\/tr> \n Input\n Under\/Over Frequency Detection\n <\/td><\/tr> \n Input\n Under\/Over Voltage Protection\n <\/td><\/tr> \n Input\n Under\/Over Frequency Protection\n <\/td><\/tr> \n Input\n Open Neutral Protection\n <\/td><\/tr> \n Input\n Open Ground Protection\n <\/td><\/tr> \n Miswired\n Pedestal Protection\n <\/td><\/tr> \n Weather\n Resistant (Portable Unit)\n <\/td><\/tr> \n Source\n Diagnostic Display\n <\/td><\/tr> \n Maximum\n Spike Current\n <\/td><\/tr> \n Surge\n Failure Indicator\n <\/td><\/tr> \n Time\n Delay on Power Up\n <\/td><\/tr> \n Optional\n Remote Display\n <\/td><\/tr> \n Field\n Serviceable\n <\/td><\/tr> \n Warranty\n <\/td><\/tr> \n Ease of Installation (Fixed Unit)\n <\/td><\/tr><\/tbody><\/table>\n\n\n\n