Iota double pole, double throw switch question

Charles in SC · January 03, 2009, 07:44:08 PM

Does any one have experience with these? I just bought a unit with one in it and am not familiar with them, it also has an Iota 12 volt battery tender/charger. Some of the events I go to provide power thru a ground fault plug and I am wondering if the switcher will trip it.

Sean · January 03, 2009, 08:05:40 PM

What's the model/part# on the Iota? I can probably tell you something about it if you have that.

The Iota, per se, will not trip the GFCI. However, if you have an inverter in the coach, the required ground-to-neutral bond might well trip the GFCI before the incoming power can lift the bond. There are a couple of ways around this if you find it happening to you.

Can't say anything about the battery charger, as I have no experience with it.

-Sean
http://ourodyssey.blogspot.com

Charles in SC · January 03, 2009, 08:11:34 PM

Thanks Sean, on my old bus I had a plug that I either plugged into the generator or the shore power. I am reading 55 volts between the ground and neutral and am thinking it is coming thru the coil in the switcher, I am afraid this might trip a gfi plug. Any thoughts are welcome.

niles500 · January 03, 2009, 09:14:02 PM

I second that - Sean if you would expound on the various ways of overcoming GFI trips while hooking to shore power - this year is the first that I have encountered this problem and it is darn inconvenient - thanks

Sean · January 04, 2009, 06:40:59 AM

Quote from: Charles in SC on January 03, 2009, 08:11:34 PM
... I am reading 55 volts between the ground and neutral and am thinking it is coming thru the coil in the switcher, I am afraid this might trip a gfi plug.

You will need to track down the source of this stray voltage -- it won't be the transfer switch unless it is miswired somehow.

The first thing to check is proper ground-neutral bonding. I would also check for miswired appliances and fixtures.

The potential difference between ground and neutral will not, in and of itself, trip a GFCI. Only a difference between the hot current and the neutral return current will do this.

-Sean
http://ourodyssey.blogspot.com

Sean · January 04, 2009, 08:41:12 AM

Quote from: niles500 on January 03, 2009, 09:14:02 PM
I second that - Sean if you would expound on the various ways of overcoming GFI trips while hooking to shore power - this year is the first that I have encountered this problem and it is darn inconvenient - thanks

You will first need to determine the source of the tripping. It could be the inverter itself, or it could be the bonding relay either internal or external to the inverter.

My SW4024, which has no internal bonding relay, would trip a GFCI all by itself. It did this for over a year before we tracked down the source of the tripping to a filter capacitor in the unit. The cure is to remove a specific ground wire that, nowadays, Xantrex connects with a spade terminal to facilitate exactly this fix. (It is a ground for the filter, not a safety ground for the unit.)

If the source is the bonding relay (and pretty much any installation with a bonding relay will do this), there are a couple of methods.

The safest and most automatic method is to place a three-pole contactor in-line between the shore cord input and the transfer switch, and use a DPDT relay for your bonding. Run both hots and the neutral from the shore through the contactor. Connect one of the coil terminals to the incoming shore neutral, and the other terminal to one of the common terminals on the DPDT bonding relay. Connect the corresponding NO terminal on the DPDT relay to one of the incoming shore hots. This will ensure that the shore contactor only closes after the bonding relay fully energizes.

Connect the inverter neutral to the other common terminal of the bonding relay, and the ground to the corresponding NC terminal. Now connect the coil of the bonding relay between the neutral and one hot from the incoming shore. Now you have a system where the shore neutral will not be connected to the inverter until a few milliseconds after the ground bond is lifted.

Note that this method requires an external bonding relay -- it will not work with inverters that include the bonding relay internally (some of which already have mechanisms in place to prevent GFI tripping). Also note that this method connects the bond relay coil directly to the shore line, which means it will not lift when the generator runs. Either remove the bond in the generator, if possible, or you can add another DPDT relay ahead of the bonding relay that will switch the coil terminals over to a generator circuit when the genny runs.

This method also has the advantage of eliminating the possibility that a de-energized but still connected shore cord (such as when the shore breaker is off or tripped) will create a hazardous double-bond situation when the inverter takes over.

A simpler method is to add a momentary switch to lift the bond while the shore cord is being connected. This can either be an SPDT to momentarily energize the coil from an inverter circuit, or an SPST-NC in the neutral leading to the bonding relay. Here again, you need to have an external bonding relay. You also need to have some way to hold the momentary switch at the same instant you are connecting the shore cord. Lastly, the code-compliance of this method is shaky at best.

Or, you can do what I did. I built an adapter with a NEMA 5-15P right-angle plug on one end, with the cord exiting straight down, and a NEMA 5-15R on the other end. It's about 4" long. I then cut the ground tang of the plug in half with a hacksaw. (Definitely not code-compliant, since modifying a listed plug invalidates the listing -- but it's an adapter, not a modification to the coach system, and I won't pass it on when I sell the coach.) I connect my shore cord to this adapter, and then carefully insert the plug into the shore receptacle. Since the ground tang is now just a hair shorter than the hot and neutral tangs, power flows to the bonding relay before the ground connects. As I fully insert the plug, the ground makes contact, and all is correct once again. The right-angle nature of the plug ensures that the ground will remain fully seated during use.

This final method will work with both external and internal bonding relays, and will be the only solution (without making dangerous and unlawful changes to the coach wiring) if you have an inverter with an internal bonding relay that is tripping GFCIs. Just recognize that such a modified plug is a potential hazard, use it only when necessary, and be careful to ensure the ground is fully engaged.

-Sean
http://ourodyssey.blogspot.com

Len Silva · January 04, 2009, 11:16:10 AM

Sean,
I just want to comment here that in addition to your expertise, your writing and communication skills are just outstanding. Always easy to understand without a single wasted word. I am so glad you are here!

Sean · January 04, 2009, 12:12:47 PM

Quote from: Len Silva on January 04, 2009, 11:16:10 AM
... Always easy to understand without a single wasted word. ...

Thank you, Len. Although I think it ironic that you chose to post this after one of my most long-winded posts. A diagram, really, would have been so much more clear, but they take a lot more time to make up on the computer than describing it in text.

-Sean
http://ourodyssey.blogspot.com

niles500 · January 04, 2009, 08:53:24 PM

Sean, Thanks for such a expending such an effort - My Vanners do have the internal bonding relay - I have to say that I believe you covered it ALL as I have no questions, all perfectly clear - I just printed your tome and saved it - I'm going to give it to my electrician and let him do it - I don't want to let the smoke out of those babies - Thanks again