Grounding new converter

[billrector]

Hi,
I am replacing my converter and have removed the old one. There is a ground lug on this converter, but it was not connected to anything. The AC input to the converter was connected to the neutral bus, breaker, and ground.

With the new converter, there is a ground lug. I am assuming I can connect this to the AC ground....same ground I am connecting the AC input ground to?

[richard5933]

My converter has a dedicated copper wire which connects from the lug on its case to a lug on the trailer's frame. This was on the factory installed converter, and when I replaced it with the new Progressive Dynamics unit I ran a new green covered copper grounding conductor and replaced the grounding lug on the frame.

[billrector]

Originally Posted by richard5933

My converter has a dedicated copper wire which connects from the lug on its case to a lug on the trailer's frame. This was on the factory installed converter, and when I replaced it with the new Progressive Dynamics unit I ran a new green covered copper grounding conductor and replaced the grounding lug on the frame.

In my 2017, I don't see a "ground lug" on the frame. I'm assuming I can connect it to the AC ground bus.

[richard5933]

Originally Posted by billrector

In my 2017, I don't see a "ground lug" on the frame. I'm assuming I can connect it to the AC ground bus.

You can (and probably should) add one. Here's a photo of mine. It contains the grounding conductors from all the AC devices which require a ground connection (inverter, converter, etc) as well as a connection to the negative bus bar of the 12vdc system.

There is another grounding lug on the frame at the rear of the trailer where the 120vac circuit breaker panel is grounded.

[ITSNO60]

There is no need to connect the converter grounding lug to the AC ground, nor do you want to. As Richard said that lug is intended for the DC side and should be attached to the frame with a wire sized to match the DC output current of the converter.

[billrector]

Originally Posted by ITSNO60

There is no need to connect the converter grounding lug to the AC ground, nor do you want to. As Richard said that lug is intended for the DC side and should be attached to the frame with a wire sized to match the DC output current of the converter.

There is no easy way to get to the frame from the center of my trailer where the converter is. Here is a picture of what I have. So I have a negative dc bus bar and an ac ground bus bar right there. Don’t both of these go to the frame?

[ITSNO60]

Originally Posted by billrector

There is no easy way to get to the frame from the center of my trailer where the converter is. Here is a picture of what I have. So I have a negative dc bus bar and an ac ground bus bar right there. Don’t both of these go to the frame?

Yes, both should be electrically connected since the power cord coming into your trailer should be bonded to the frame. By bonding the 12 volt lug to the AC ground bus you would basically be sharing the path on the ground wire in your cord to the frame. The DC current is not looking to go to the AC ground and it won't. Not sure what would happen if you had an AC fault though, if it could damage anything before a breaker opened.

Since you said that your old converter didn't have this bond I might leave it off if everything works.

Richard what do you think?

[billrector]

Originally Posted by ITSNO60

Yes, both should be electrically connected since the power cord coming into your trailer should be bonded to the frame. By bonding the 12 volt lug to the AC ground bus you would basically be sharing the path on the ground wire in your cord to the frame. The DC current is not looking to go to the AC ground and it won't. Not sure what would happen if you had an AC fault though, if it could damage anything before a breaker opened.

Since you said that your old converter didn't have this bond I might leave it off if everything works.

Richard what do you think?

Thanks exactly what I have planned. The old one was not grounded through the lug....just through the AC input to the converter. I had no issues in 7 years.

[richard5933]

Originally Posted by ITSNO60

Yes, both should be electrically connected since the power cord coming into your trailer should be bonded to the frame. By bonding the 12 volt lug to the AC ground bus you would basically be sharing the path on the ground wire in your cord to the frame. The DC current is not looking to go to the AC ground and it won't. Not sure what would happen if you had an AC fault though, if it could damage anything before a breaker opened.

Since you said that your old converter didn't have this bond I might leave it off if everything works.

Richard what do you think?

My OEM Univolt most certainly had a grounding conductor which went from the case of the converter to the grounding lug on the frame.

My experience in the amateur radio world might have played into my thought process here, but I considered this to be a pretty standard safety procedure - the grounding of a metal case on a piece of equipment plugged into 120v power. Lots of equipment is installed this way, with a dedicated ground connection like this since it's not unheard of for the ground conductor in an outlet or power cord to fail.

There is absolutely no problem with the AC devices in your trailer sharing a chassis ground with the 12vdc system. All motorhomes that I've seen have their 120v systems grounded to the chassis, and they also have the 12vdc negative tied to the chassis.

[ITSNO60]

We may be talking about 2 different things here. The AC grounding should be taken care of by the equipment grounding conductor in the cord, and all metal parts of the converter should already be bonded to the EGC when it is sold as a complete product, either through a 3 conductor cord or a 3 conductor cable. No additional safety grounding should be required to be installed by the end user.

I was under the impression that the ground lug in question was on the 12 volt DC side of the converter, and was intended to carry negative 12 volt current to the frame for equipment that may only have a hot conductor for power and a negative conductor attached to the frame.

My new WFCO converter has 2 negative/ground lugs on the DC side as did my old PD converter. There is a conductor in each one with one going straight to the house battery negative and the other going to a lug on the RV frame. They are both electrically equivalent.

The metal parts of the converter are physically connected to each other and to the 120 volt EGC through the NM cable.

[ITSNO60]

So I found this and it looks like NEC does indeed have a bonding requirement for converters with metal enclosures to be bonded to the frame with a minimum #8 copper conductor.

I am going to have to look at mine again as I don't recall having a lug on the enclosure, but I also don't recall if the enclosure is metal or plastic.

[ITSNO60]

551.56 requires that the panelboard be bonded to the chassis but it also allows other exposed non-current carrying metal parts likely to become energized to be bonded to the panelboard, so the #8 bonding the panelboard to the chassis also serves to bond the converter when it is attached to the panelboard. In my case my old converter was screwed onto the panel with 4 #10 machine screws making it compliant with 550.20

Now my new WFCO converter and panel that I installed was manufactured as a unit just like my old PD system was, but my new panel is plastic. My new converter screws onto the plastic, but the converter itself has a metal heat sink and a metal flat cover on top, and a metal tray for the board to attach to, but the rest of it, including the mounting tray, is plastic. It has no bonding lug anywhere. The only AC grounding attachment is the green ground wire in the pigtail.

The DC side runs to a common double lug on the fuse board and on the second terminal of the double lug there is a #8 which goes to the chassis. So the heavy 12 volt negative wire that runs from my converter to my fuse board is effectively bonded to my chassis. So in order for this to be a bond to the AC side it would have to be electrically connected to the metal parts of my converter. Either that or the NEC intention is to bond the DC side which would explain why a minimum #8 is required when normally a #10 would suffice up to 60 amps per NEC 250.122, although I have not seen 250.122 mentioned in article 551 (yet). Could also be for physical protection.

Bill maybe you could post some pics of the converter and tell us if the old converter was screwed to your panel? If so, that was your bond and if you no longer have that bond with the new converter then your plan to bond to the ground bus is correct, using a #8 copper wire as your panel likely has the #8 bond to the chassis. (looking at the bottom hole in the small ground bus partly hidden behind that Wago it looks like could be a #8). Attaching a #8 to either of your 2 ground busses will effectively be bonding the converter to the chassis by way of the #8 from the panel.

If your new converter screws to your panel enclosure like the old one did there is no need to do anything more.

[ITSNO60]

Actually that bottom wire is probably your #10 ground from the 6/3 NM supply cable. Your #8 bond is likely attached to a lug on the back side of the panel enclosure. I don't remember if my old metal panel had the bond attached to a lug or to the bus, when I installed the new panel I attached it to the bus since the new enclosure is plastic.

[richard5933]

I think you're really over thinking this.

Lots of equipment out there has an external grounding lug and not all of it is converters or devices that have anything to do with 12vdc power.

In the amateur radio world nearly all equipment has an external grounding lug. My phonograph has one. I've installed water heaters in previous RVs that had external grounding lugs.

Power cords fail. People do stupid things like use a cheater device to plug them into non-grounded outlets. Ground loops exist. Outlets can be mis-wired, etc. Lots of reasons to have external grounding lugs.


When I see an external grounding lug (usually green screws) I ground them.

[ITSNO60]

Originally Posted by richard5933

I think you're really over thinking this.

Lots of equipment out there has an external grounding lug and not all of it is converters or devices that have anything to do with 12vdc power.

In the amateur radio world nearly all equipment has an external grounding lug. My phonograph has one. I've installed water heaters in previous RVs that had external grounding lugs.

Power cords fail. People do stupid things like use a cheater device to plug them into non-grounded outlets. Ground loops exist. Outlets can be mis-wired, etc. Lots of reasons to have external grounding lugs.


When I see an external grounding lug (usually green screws) I ground them.

Not over thinking, just figuring out why some converters, like mine and like the OPs, were not separately bonded and realizing that if attached to another bonded enclosure there is no need to go further. I like to know the why and not just blindly do something because it's there. What's wrong with that? In this case without researching some would have gone to the trouble of finding a way to the frame, which as it turns out, isn't necessary.

I'm very familiar with bonding lugs on equipment but RVs are a little different. You typically don't see bonding lugs on household equipment and appliances, they are always grounded through the power cord or circuit EGC. Not even furnaces or water heaters. Only where things like nearby metal piping or pool equipment needs to be bonded to create an equipotential plane.

I don't believe bonding is there as a backup in case an EGC fails as you say, it's there to eliminate voltage gradients in situations where a person could come across one. Bonding and grounding are 2 different things. A bond is not a ground and not intended to clear a fault, it's there to eliminate a gradient between conductive surfaces. Fault clearing is the job of the EGC in every case. Can a bond carry fault current, yes by default it will if the EGC is included in the equation but it's intended purpose is to make everything electrically equal, not ground it.

Pretty sure the ground on the turntable is for hum.

[richard5933]

I understand what you're saying about the converter receiving its grounding through the enclosure it's mounted to, but I'm not sure I'd be comfortable relying on that alone.

By relying on the grounding through the enclosure there are more than a few potential failure points introduced. Especially on RVs which are often described as rolling earthquakes, connections have a way to work loose. Even with a direct path to the chassis for grounding there is a chance for failure due to surface corrosion, loose connections, etc. but on a piggyback grounding situation these are multiplied.

I'm not saying that your method is wrong, just that I prefer the belt & suspenders approach on this one.

[ITSNO60]

The converter, at least in my case, was an integral part of the entire load center and held in place with 4 machine screws to make one unit with one bonding conductor. Adding a second bonding conductor would be like running two bonding conductors to a single piece of equipment. Redundant and not needed IMHO, nor required.

Redundant grounding is only required in health care facilities and then only for equipment that comes into contact with patients. There is no requirement for redundant bonding

I understand it is desirable to have multiple grounding and bonding points in the communications field for various reasons, and not all for safety, but that's something I'm not too familiar with.

[gypsydad]

Originally Posted by billrector

Hi,
I am replacing my converter and have removed the old one. There is a ground lug on this converter, but it was not connected to anything. The AC input to the converter was connected to the neutral bus, breaker, and ground.

With the new converter, there is a ground lug. I am assuming I can connect this to the AC ground....same ground I am connecting the AC input ground to?

I just replaced mine also last week. The new converter (Li model) did not have a ground lug either, but I am using original metal chassis that the old converter was attached to for easy installation. The original chassis is grounded as it is connected to my fuse/power switch panel also. I still had exposed copper ground wire just hanging there with no where to go, so even though it was all grounded, I just sandwiched it between the last mounting screw and chassis connection. Not really needed but did not want a "dangling" wire.

[ITSNO60]

Originally Posted by gypsydad

I just replaced mine also last week. The new converter (Li model) did not have a ground lug either, but I am using original metal chassis that the old converter was attached to for easy installation. The original chassis is grounded as it is connected to my fuse/power switch panel also. I still had exposed copper ground wire just hanging there with no where to go, so even though it was all grounded, I just sandwiched it between the last mounting screw and chassis connection. Not really needed but did not want a "dangling" wire.

In that case I would want to make sure that the converter was not carrying the bond to the panel instead of vice versa, if the bond attached to the converter it would bond the panel when installed in the panel and should now be connected to the ground bus in the panel, or to a lug. If you don't see a #8 attached anywhere in or on your panel you need to move that old bonding jumper to the ground bus, or install a lug on the panel or on the converter for it if you want to comply with 551.

A lot of confusion here over bonding and grounding, they are 2 different things. Your panel is grounded yes but it also needs to be bonded to any and all metal parts surrounding it including the trailer frame, with the required size jumper.

[gypsydad]

Originally Posted by ITSNO60

In that case I would want to make sure that the converter was not carrying the bond to the panel instead of vice versa, if the bond attached to the converter it would bond the panel when installed in the panel and should now be connected to the ground bus in the panel, or to a lug. If you don't see a #8 attached anywhere in or on your panel you need to move that old bonding jumper to the ground bus, or install a lug on the panel or on the converter for it if you want to comply with 551.

A lot of confusion here over bonding and grounding, they are 2 different things. Your panel is grounded yes but it also needs to be bonded to any and all metal parts surrounding it including the trailer frame, with the required size jumper.

Understand; the original converter I replaced, had this wire tied from the panel to the chassis. I see the same wire buss it came from, tied to the overall frame with a screw in the frame, so confident it is same. The converter I installed is attached also metal to metal with connection screws. Nothing wrong with tucking the "dangling" bare copper wire between the frames as I screwed it together..no longer dangling.