Electrical Question

A converter/charger has a small inrush current that causes pitting on shore power or extension cord plug blades and inside receptacles. If you listen closely you can hear a zap and in the dark you can see small flash when you plug in with the power still on. The pitting attracts dirt/carbon and over time will lead to resistance and overheating and possibly a meltdown. The photo below shows what can happen.

You should always turn off the power before plugging in either at the receptacle end or source end (panel). You should also ensure the plug blades are kept clean - use emery cloth as necessary. In the beginning, I had two 15 amp extension cords go up in smoke in our driveway due to not turning the power off. Then I installed a 30 amp RV recept. and disconnect switch next to it in our carport and no more problems. The plug blades on our 7 year old Marinco shore power cord look almost like new due to proper treatment.

On the "modern" style direct-bury pedestals, you can find labels that say to turn the power off before plugging in and unplugging.

If you ever see a receptacle in a pedestal like in the photo, I'd find another 30 amp site or a 50 amp site and use an adapter. The 30 amp recepts. in pedestals can sometimes be well used and abused and damage your shore power cord or even cause low voltage due to a bad connection.

SoundGuy wrote:
BTW, for those who say turn off the breaker at the campsite post before plugging in the answer is that's sometimes easier to say than to do ... I know of several parks here where the campsite post has no breakers at all, just receptacles, so when you plug in you're hot plugging.

Maybe in Canada but not in the US where the NEC requires a breaker/disconnect in all pedestals. You can always turn off the 30 amp (or 50) inside your RV.

Does it matter when/if you turn on the battery disconnect.

Well. I will give you two scenaros

One: Plugging in at an RV park
1: Turn OFF park breaker
2: Plug in
3: Turn breaker back on

In this scenario you may leave the battery connected or not your choice. IT should be turned on when connected so the battery can charge in most cases (There are exceptions but none of them have been made this century). If you already had the battery connected on the road (As I do) no need to disconnect.

NOTE: when you unplug. Start by turning OFF the park breaker.

Scenaro 2 Plugging in at homem LIVE outlet

It MIGHT make a difference. in which case you need to minimize load. but a better option would be to turn off the MAIN breakers in the RV before plugging in and again before unplugging Then turn them on once plugged in again.

SoundGuy wrote:
BTW, for those who say turn off the breaker at the campsite post before plugging in the answer is that's sometimes easier to say than to do ... I know of several parks here where the campsite post has no breakers at all, just receptacles, so when you plug in you're hot plugging. Here's one such example - duplex 15 amp receptacle at the top, a 30 amp below it, no breakers

Yes, you do, on occasion, find different circumstances and have to deal with them as you find them. That does not negate the advice to turn off the breakers, nor make it bad to so advise new people. It just means that sometimes, you just can't. That scenario also applies to almost everything you advise people to do. Do it when you can, but sometimes it just isn't feasible.

Battery switch on or off, the converter itself causes a heavy load just loading the capacitors. So unless the conv ac breaker is turned off, you are always going to have a load when plugging in, unless you have a breaker shutoff at the wall plug or pedestal.
The trick is, don't dilly daddle around,... "plug in fast".... the arc will be so minimal, it won't hurt a thing,.....or, that's worked for me for 40 yrs.

Arcing is much more of a problem when unplugging than when plugging in. The arc will not form when plugging in until the contacts have actually made contact (or very very nearly so) since it's starting from zero current and non-ionized air is a pretty good insulator. When unplugging, particularly with an inductive load, the current doesn't "like" to be broken and so it arcs, and the arcing ionizes the air, and ionized air is a better conductor than non-ionized so the arc continues for a bit as it's unplugged.

A stick welder starts the weld by striking or scratching the rod against the metal to be welded, but then separates them slightly once the arc has started. The arc doesn't start without the strike. While it's not exactly the same situation (the voltage when welding is lower and the current much higher), the same general principles apply.

Even without a load, a modern converter has a pretty substantial but brief inrush current when first plugged in as the capacitors in the switching power supply are charged. There often is a thermistor or other circuit to limit this somewhat, but it's still going to be a pretty decent pulse.

dougrainer wrote:
The battery disconnect has NOTHING to do with your 120 system or extension cord. It is just a 12 volt relay. Doug

That's not the point ... by leaving the battery connected the converter will when it sees 120 vac input power attempt to charge any battery sitting at anything less than 100% SOC. If the battery in question is significantly depleted the converter will instantly begin to draw several amps as it starts the bulk charging process and by definition will therefore cause a spark when the trailer's main service cable is plugged into a hot source. If the OP is not using an EMS that will prevent this then he would be wise to turn his battery disconnect switch to off before plugging into 120 vac shore power so the converter won't instantly go into bulk charge mode ... but you already know that. ;)

BTW, for those who say turn off the breaker at the campsite post before plugging in the answer is that's sometimes easier to say than to do ... I know of several parks here where the campsite post has no breakers at all, just receptacles, so when you plug in you're hot plugging. Here's one such example - duplex 15 amp receptacle at the top, a 30 amp below it, no breakers, and a water tap on the opposite side of the post.



In this case it's just that much more important to make sure there are no loads on the circuit before plugging in OR better still protect your rig with an EMS which will do this automatically for you. I do the latter.

The battery disconnect has NOTHING to do with your 120 system or extension cord. It is just a 12 volt relay. Doug

1. Turn off breaker on pedestal when either plugging in or unplugging RV, and it won't matter what order you do the power cord.

2. I never use my battery disconnect switch. I leave it powered all of the time with my Progressive Dynamics PD4655V converter/charger charging my AGM batteries 24/7/365. (I installed a 50/30/20GFCI pedestal at home.) But I always practice #1.

Thanks Soundguy and 2oldman, as mentioned, I had never even considered it before this morning, but have made a habit of turning the battery switch to the "on" position after I plug in the extension cord. Good to know I've been doing it the right way, and why. I've learned loads on this forum, thanks again.

All big loads should be off when plugging in. Arcs = not good.