voltage on the neutral of a trace sw inverter

[Lloyd]

Hi All,

I just exercised my self. Or did I?

The boat I am just finishing a re-wire stem-stern-AC/DC. The boat had a Trace SW 3000 already installed. But When I took the panel apart there was no safety ground to the shore power panel, nor was the unit chassis grounded in any way, it was floating. The bigger problem or so I thought was the previous installer, used a 4 wire dryer plug, and pigtail, he then proceeded to clamp the cables minus the jacket so hard that the clamp bit into the shore side neutral wire. My ohm meter showed conductivity to the case, and the shore side neutral. I installed a new 3 wire feed to and from the panel, and also case grounded the case to the ships ground bus with a #1 cable.

When I ran my normal start-up, which is to energize the inverter from battery power before shore side power energize, and check for stray voltages. The first thing I noticed was that the reverse polarity light on the main AC panel was lit. That's an indicator of stray voltage.

I took my multi-meter and checked all the buses. No voltage on the shore bus L-1 to neutral or L-1 to ground, but I did find 60 volts on the shore neutral to ground bus. Then as expected found voltage on the inverter out L-1 to neutral (118 volts) and found 119 volts on the inverter L-1 to safety ground...but what concerned me was, I again found 60 volts on the inverter neutral to ground bus.

Now I am concerned, so I began to diagnose and trace wires, all is connected as it should be, So I demo the inverter, everything is as it should be, but I noticed the the inverter has a common bus to all three neutrals inside, including the shore/gen/inverter-out, all three neutrals tied together.

ABYC requires that  inverters have a separate neutral on the output that auto ties it to the safety ground when ever it is in inverter mode( ie disconnected from shore/gen power).

I got home to late to call John, so I did a google, this is what I found, I am completely dumbfounded, of all the inverters I have installed, I have never found 60 volts floating on the N to G.

FAQs
Power Inverters


Voltage measurement issues (AC output)

      I've installed the modified sine wave inverter and it's working okay. However, the output voltage doesn't seem right. There is 124 vac between the hot and neutral pins but the safety ground is not at 0 volts with respect to the neutral pin. Instead, the safety ground appears to float about halfway between the neutral and hot pin voltage. Please explain what's going on!

      This FAQ applies to Xpower, PROwatt, Portawattz, Jazz and Xantrex inverters, including the inverters integral to Powerpacks.

      Your inverter is designed to have loads plugged directly into it and not be permanently connected to an AC distribution system. The fact that the inverter is not a permanent installation means the US NEC (United States National Electrical Code) doesn't apply, and the NEC is the main place where the requirement resides for single-phase 120Vac or 240Vac systems to have neutral bonded to earth. The US standard for inverters of this sort, UL458, does not have a requirement for a bonded neutral on the output of inverters.

      Regarding the voltage that the you are measuring, the ground does not float halfway, rather the neutral is not at 0 volts. The grounding is correct, in that loads plugged in will have their chassis held at the same ground potential as the chassis of the inverter, but the neutral has approximately 60V on it instead of the usual 0V. The impact of that is minimal, since wiring and equipment connected to the neutral side of the circuit are required by safety standards to be treated as if they were at 120Vac. This is because there are many receptacles that are wired backwards or 2-prong plugs that are not polarized. As a result the 60V neutral is not accessible to the user, and any shock hazard presented is mitigated by lack of access.

      The main safety agencies, CSA, UL, and ETL, have all approved inverters with this half-voltage on the neutral scheme, and the manuals contain warnings not to AC hardwire any of these inverters.

Now granted the abpve quote is from xantrex who bought trace, and the sw is not listed, but I have the same issues...I don't want to BBQ any of my clients.

What say you??  any ideas.

Enlav, I look forward to hearing from you.

Lloyd

[rcavictim]

A good friend and retired electronics instructor let the magic smoke out of his Xantrex XP-1000, 12 VDC to 120 VAC mod sine inverter when he tied the device's neutral output connection to the device's earth ground connection via a plug inserted in the inverter output socket. Needless to say he was not impressed.  I have three of the same inverter and do not plan to make the same mistake.  I do recall that a standard neon outlet wiring tester does not light up in the proper code when plugged into the AC outlet on one of these inverters.

[Tom Reed]

So I guess that inverter won't work with GFI recepticals.

[sailawayrb]

It's been a while since I dug into ABYC schematics...but from my recollection each one typically only deals with the specific subject being covered by the nearest paragraph.  All of a boats grounds should go to a common ground bus...and then to the boats bonding system and the water.  Typically the inverter contains a relay which connects the neutral and ground together when the inverter providing boat power, but opens this connection when the inverter is charging the batteries.  Perhaps this relay has failed?  I also seem to recall something about some older Trace models perhaps NOT even having this relay.

Bob B.

[sailawayrb]

Here's a link that alludes to the relay and what I mentioned previously:

http://www.kyocerasolar.com/pdf/specsheets/2500.pdf

"...neutral switching follows ABYC standards..."

Bob B.

[Chris]

I have smoked a few inverters at my house. I had a Trace SW 2512 that failed. Hooked up a "Cheap" modified sign wave via a plug without the ground wire (Two pronged plug) to the house, worked ok. I then hard wired it up to the main panel( hot, neutral, ground) with ground and neural tied via the main panel and poof, smoked it. Many "Cheap" inverters have to have a floating neutral or poof.
In the above case, I am not too sure what is going on, but Outback inverters have inverters for RV vechicals where the neutral floats, at least I think it does. They are different from the home wired version. A boat is sort of like a RV. Code requirments on a boat re neutral grounding, I don't know?
May be the neutral is issolated and is floating?

[Lloyd]

Well as it turns out Trace made 2 different SW's one for mobile/marine and one of the land/grid tie. The only diff is that the mobile includes a N-G tie in the transfer relay. This particular project was the land version installed on a mobile.

The bizarre part is the installation manual that came with this inverter eludes to adding a N-G switching relay at the panel or just let the inverter do it. It wasn't until the version 4.01 came out, that the manual clarifies, by stating that the the SW in fact has no N-G relay built into the transfer relay and must be installed by the installation contractor...separate!!

Problem solved. I installed a spdt Dayton 120v coil relay. The coil is energized when ever the shore/gen bus sees 120 ac.

The DP is wired, inverter neutral to ground bus through the poles normally closed, then when energized by the shore/gen bus, the poles open..... = no neutral to ground tie = No Smoke.



Lloyd

[Chris]

Lloyd,

Glad you got it sorted out. Make a diagram of what you did and stick it in the manual.

My computer control panel for my 20 KW genset went Kaput. I jerry rigged a system using a bunch (three) 12 volt relays and some push button switches so I could get the gen back on line and have low oil and high temp safety. I can't find the scrap of paper with my sketch of the schematic. Everytime I try to figure out what I did hurts my head. I can remember what I did repairing stuff twenty years ago, but what I did 6 months ago is a blurr. Must be too many aluminium beer cans.

Chris

[Lloyd]

Thanks Chris,

I always include a full schematic of my work for the ships log.

Here is the relay,http://www.grainger.com/Grainger/DAYTON-Power-Relay-5X847 and cover http://www.grainger.com/Grainger/DAYTON-Relay-1EGH7 used.

This is good for all mobile inverter, and or gen sets lacking a n-g.

Lloyd