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Old 04-23-2011, 12:24 PM   #1
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Re: GFCI vs Progressive Industries

Open ground and open neutral are both potentially dangerous, but detecting those does not protect you from a GFCI type incident.

In normal 110V operation, power flows between the Line and Neutral legs. In 220V, it would be between 2 Line legs. If any of the current in that flow "leaks" elsewhere, a GFCI is supposed to detect that and trip. If the amount of current present on Line doesn't equal the amount on Neutral (or Line 2 for 220V), then that current MUST have gone somewhere. That current will seek the shortest path to ground, which might be through a human, hence the desire to have a GFCI trip quickly.

Personally, I'd still use GFCI internally. There were some other threads recently about GFCI. GFCI saves lives. That's why it's in code now.

Hope this helps,
jim
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Old 04-23-2011, 02:12 PM   #2
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Re: GFCI vs Progressive Industries

Quote:
Originally Posted by Tesla
So, interior GFCI proponents .. where is your GFCI with respect to the main AC panel and how is it wired? Does anyone have a link to the appropriate product to install? Would it be the same thing for 30 and 50 amp service?

Thanks!
There are basically 2 ways of doing GFCI protection. One is a GFCI equipped circuit breaker (more expensive), and the other is via a GFCI outlet.

With the circuit breaker, your whole circuit is protected from the source. However, should you need to replace that breaker, it will cost more than a normal breaker.

The outlet would need to be the first one in the chain, and all the rest have to be tied to its LOAD side. It's a good idea to keep the GFCI in the same room with all the outlets it protects.

An alternative with the outlets is to make all your outlets be GFCI, and tie nothing to the LOAD side of any of them, and wire them in parallel like any normal outlet on a circuit. This can get expensive, but if a GFCI burns out, it only affects itself. Also, if it trips, it is immediately obvious where it occurred.

Most GFCI outlets are only rated for 15A of load. As with any kind of rating, running something near it's max rating will often cause it to have a reduced life. I believe some 20A GFCIs can be found, but will cost more.

Some GFCIs default to a tripped state if power is lost and restored. You likely don't want that in an RV, as our power gets disconnected often, or changed to alternate sources. Resetting the GFCI every time you do that would be a PITA.

TEST your GFCI at least once a month. This is very important, as GFCIs often fail in a way that they keep passing current. Safety first. Use an outlet polarity tester with GFCI test button (a good quality one, not an el-cheapo), and don't rely on the test button in the outlet itself.

With a 30A RV hookup, you *could* get away with a single 30A GFCI breaker as your main breaker. I don't know of any 220V 50A GFCI breakers, but if they exist, they would work the same way. For standard 120V breakers, I think you can get any size in GFCI versions.

Bear in mind I am not a licensed electrician. This advice is worth every penny you paid for it. Do your own research, look at the NEC, and make your own decision. Consult a licensed electrician if you still have doubts or questions.

hope this helps,
jim
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Old 04-23-2011, 02:15 PM   #3
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Re: GFCI vs Progressive Industries

The cheapest way to get GFCI protection for your BODY is to equip the first outlet on each string with a GFCI outlet. These WILL work behind other GFCI devices, I have them daisy-chained in my home. Even if you have 120/240-volt 50-amp service, the GFCI devices in the outlets or in a panel will generally be 120-volt devices.

The surge protection device you link to is a 120-volt device. You take your 120-volt power from Line 1 and Neutral. The device has an over-voltage sensor to protect your EQUIPMENT from a socket mis-wired with 208/240 volts AC. This is a good thing.

If the neutral is open, you have no 120-volt power to the bus except through the safety ground. The wiring on your bus should NOT connect the safety ground and neutral together like you would at the first disconnect fed by a utility meter. So an open neutral to a properly-wired bus would mean you have possibly dangerous voltage present on Line 1, but nothing works, so you go and identify the problem with the outlet. The proposed protector will shut down Line 1 if the neutral is open, so you do not have "hot" wires in the bus while you think the power is off.

If Line 1 is open, there is no power to anything, not even the surge protector.


Sidebar:
> In a 50-amp 120/240-volt system, an open Neutral is a real problem that can cause a lot of damage. As Baadpuppy explained, 240-volt power goes from Line 1 to Line 2. (This measures 208 volts if the service coming in is from a three-phase feed, but that is another discussion entirely) 120-volt power is balanced between Line 1 or Line 2 and the Neutral. Line 1 and Line 2 are connected to opposite sides of an alternator, so that one is going positive as the other goes negative, and then vice-versa. (They are 180 apart in alternator rotation or sine wave analysis.) If you have equal 120-volt draws on Line 1 and Line 2, current passes from the equipment on one line into the equipment on the other, and the Neutral passes no current. If the loads are not equal, the difference between loads is passed through the Neutral. For example, if Line 1 draws 35 amps and Line 2 draws 25 amps, the Neutral returns the excess 10 amps from Line 1 that is greater than the Line 2 load.

> If this 240-volt neutral goes open, the two 120-volt halves have nothing to balance them, and the 240 volts is divided by the net resistance of the equipment on each line. If both lines have balanced 120-volt current draws, there is no problem. When they aren't balanced, things burn up.

> Imagine only a 900-watt waffle iron on Line 1, and a 100-watt light bulb on Line 2. The light bulb has a higher resistance, as it allows less current to flow. If the normal combined load is 1000 watts, and the waffle iron is 900 of 1000, then its resistance is 10% of the total. The 100-watt light bulb has the remaining 90% of the resistance.

> If the neutral goes open, the waffle iron cannot return its excess current through the neutral, all its must all go through and be restricted by the resistance of the light bulb. The 240 volts is divided by the total of the two line resistances. The waffle iron sees 240 x 0.1 = 24 volts, and does not get hot. The light bulb sees 240 x 0.9 = 216 volts through the waffle iron, and is very bright until it pops. Imagine what would happen to a 100-watt TV set or computer on that line.

> As I said, an open neutral on a 240-volt feed is a very bad thing, almost as bad as a 240-volt Line 2 instead of neutral wired to the second pin on a 120-volt outlet.


An open ground will not adversely affect operation of your equipment, but it means you are not protected from shock. The only way I know of that a portable device could check for ground connectivity is to measure for power from Line 1 to ground. In the past, I have found that even the little bit of current to ground for my meter would trip GFCI protection for the outlet, if it is so protected. I can't say without using it if the protector is more sensitive than the meters I've used, and able to 'steal' test current without tripping GFCI.
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Old 04-23-2011, 02:17 PM   #4
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Re: GFCI vs Progressive Industries

Boy, it takes me a long time to type. Two responses since I started my diatribe.
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Old 04-23-2011, 04:53 PM   #5
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Re: GFCI vs Progressive Industries

Quote:
Originally Posted by Redbear
Boy, it takes me a long time to type. Two responses since I started my diatribe.
You conveyed a LOT of information in that 15 minutes. Much deeper than I got into it. Thanks for clarifying the distinction between equipment protection and life protection.

Quote:
Originally Posted by Tesla
Thanks Jim & Redbear!
Redbear, I think you tripped a 15-amp breaker in my brain!
LOL, I know what you mean.

The initial device listed is only for a 110V 30A RV feed. If you think you'll want to use 220V 50A RV feed, then you should get the EMS-PT50C instead. In any case, as Redbear clarified, you should definitely have GFCI on each circuit.

Another thing I noticed is that you listed the portable unit. I would recommend going with a hardwired unit, as these things aren't cheap and often grow legs and walk off on their own, often never being heard from again. Many people in the world enjoy the five finger discount.

jim
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