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Old 08-04-2019, 09:37 AM   #1
Join Date: Mar 2018
Posts: 70
Shore power surge protector?

I searched and didn’t find anything on the subject. I’m looking to protect the van just incase I plug into a bad power supply.

It seems there are two price points of surge protectors at $100 and $250. The jargon describing them has me lost. More expensive units have Over/Under Voltage Protection and Reverse Polarity Detection/Protection.

Opinions? Do people use these?



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Old 08-04-2019, 10:38 AM   #2
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I strongly suggest you get a surge protector with reverse polarity detection and over/undervoltage.

Since you say you don't get the jargon, let me explain:
First, there is reverse polarity detection. The wiring for an RV connection is pretty simple: hot, neutral, ground. As in all 120VAC, the post should tie ground and neutral together, and your rig should tie the chassis to ground. However, the level of skill the maintenance guys at the various parks have varies from "licensed, bonded, professional electrician" to "I ain't shocked muhself too much today". If the outlet is wired backwards, many bad things can happen: you pop the breaker when you plug in, you burn up your wiring, you electrify the chassis of your vehicle. Having a protector that you plug in first to verify the wiring was done by a higher mammal before you risk your rig is a good idea.
Next is ground fault current interruption, or GFCI. This disconnects the power if electricity is flowing anywhere it shouldn't be, like through you. Ideally, the pedestal should have this, but again, it depends upon the skill level of the park's sparky. Having a unit you can trust can literally save your life.
Then there is surge protection. This means that if the voltage gets way too high, devices called Metal Oxide Varistors (MOVs) will shunt the voltage away from your rig. Depending upon if the overvoltage is a short pulse or a continuing fault, the MOVs may be able to just shrug it off, or will give their lives to save your rig (and blow the breaker in the surge protector). The amount of pulse a MOV can take is rated in Joules, which is a measure of energy (100J is the amount of energy a 100W load consumes in one second). Anything less that 1500J is basically useless, especially for a 30A RV connection - considering that 30A @120V is 3600 Watts, a 200% surge can deliver 1500J in less than a quarter second. Look for at least 2000J.
Then there is overvoltage and undervoltage protection. This is different from surge protection - surges are many hundreds of volts, overvoltage would be 140VAC instead of 120VAC. Over and undervoltage happen because the park's wiring is not up to the job. Of the two, you are more likely to see undervoltage: the typical cause is you are in a park, and at the end of the day all the 40 foot A classes and fifth wheel trailers come in, hook up, and turn on the air conditioning full blast and fire up the microwave to make dinner. The park's power system is overloaded, and the voltage sags from the nominal 120VAC to 100VAC, or even down to 90VAC. Suppose you had your air conditioning on - what happens is that the compressor either a) can't make enough power to work, and stalls, or b) starts drawing more current to make up for the reduced voltage. Either one will cause the compressor to start running hot, and can burn it up.

The other scenario is over-voltage: once all those big rigs get cooled down and their air conditioning units cycle off, the park voltage can swing up as the loads go away. Now, instead of 120VAC, you might see 140VAC. The surge protector part of the adapter won't trip on that, but it could damage parts of your rig's electrical system.

Now, there are two possible ways your adapter can deal with this: it can either disconnect the load completely - you have no air conditioning at all, but you don't burn it up - or it can try to convert the voltage back up to normal. The first option is easy to do in a small adapter, but the second option requires what is known as an autoformer (the technical term is automatic auto-transformer). Autoformers are big, heavy, and expensive. If what you are looking at can be held in one hand, it isn't an autoformer.

Now, the two units you linked to: both of them have pretty skimpy surge protection - I've seen more surge protection is a plain-old office power strip for 15A. They have miswire protection, but I don't see GFCI. I'd suggest you look at this:
That gets you more of what you need with reasonable specs.
The other pieces of advice I can give you:
1) ALWAYS plug the surge protector in FIRST. Verify it didn't detect a fault, THEN plug your rig in.
2) Get some silicone dielectric grease, and put it on the contacts of both the adapter and your shore cable - it will help prevent corrosion and make easier to plug and unplug.

For under/over voltage protection, that can be handled by the right kind of inverter - my Magnum MSH-4024 will do over/under voltage protection by disconnecting from shore power if the voltage goes too far out of spec, and switching to inverter power. You can also get an autoformer.

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Old 08-04-2019, 11:27 AM   #3
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Is this really needed? Your SMB should have the same surge protector every house and RV has always had, a breaker box. Bad plug and it flips your breaker. Perhaps I'm oversimplifying but I've never seen the need for such.
Currently vanless. Weird.
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Old 08-04-2019, 02:25 PM   #4
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Breakers are NOT surge protection. They protect against an over-current, true, but by the time a breaker trips, the surge will have already fried your systems. Breakers take many hundreds of milliseconds to trip, and that if and only if the current is severely over limit.
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Old 08-04-2019, 02:30 PM   #5
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Old 08-11-2019, 08:59 PM   #6
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Originally Posted by 86Scotty View Post
Is this really needed? Your SMB should have the same surge protector every house and RV has always had, a breaker box. Bad plug and it flips your breaker. Perhaps I'm oversimplifying but I've never seen the need for such.
I think it depends a bit on what you're powering inside the van. If you're just running a battery charger, you probably don't need much surge protection. If you've got an A/C unit, microwave, TV, computers...that might be different.

Personally I'm usually running just the battery charger and maybe the occasional netbook, so I don't worry too much about it -- literally everything else is running off the 12V battery and is isolated from any surges. I have a polarity detector and a voltmeter that I check when I first connect, to look for anything egregiously wrong, but that's it.

1990 E-250 Sportsmobile w/ penthouse top, converted when new by SMB Texas.
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