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Old 05-20-2019, 11:42 AM   #1
Mini-Skoolie
 
Join Date: Jul 2018
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Inverter creating hot skin!

Hi all,

I recently wired my Thomas vista for shore and inverter power. Both systems are grounded (or bonded) to the wirebrushed seat rail w/ a 3/8” stainless steel bolt and ring terminal connectors. The shore power is working great! However, when I turned on my xantrex prowatt 1000 inverter yesterday I encountered a big problem- my non contact voltage detector went off whenever I moved it close to *any* metal part of the frame/chassis. Scary! The inverter appeared to working normally otherwise, although I didn’t attempt to plug anything in before turning it off. This particular model has a “chassis ground” connection in addition to the positive and negative 12v connections, and that’s what I used per the instructions to connect to the chassis frame. The negative goes to the shunt of my battery monitor, which is connected on the other side to the battery negative. The inverter manual states “the neutral conductor of the inverter AC output is connected to the chassis ground. Therefore, when the chassis is connected to ground, the neutral conductor is also grounded.” I’ve read a few forum posts that suggest this is the possible culprit.

I had previously planned on hardwiring the inverter to an ATS, but given the hot skin I’m not sure how to proceed. Perhaps hardwiring would circumvent the ground/neutral bonding issue.

Anyway, any advice is much appreciated! This stuff scares the hell out of me and I like to play it as safe as possible.

Thanks!

Sam
www.instagram.com/bedbusandbeyond
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Old 05-20-2019, 01:04 PM   #2
Bus Crazy
 
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So I guess the first thing to mention is that a non-contact voltage tester isn't the definitive test for a hot skin; a volt meter is. The NCVT are convenient and useful but sometimes results have to be verified with a real meter. The thing about measuring with a meter is that all measurements are one point relative to another point. One might measure the vehicle skin with reference to.. what? Well, it depends on what other thing a person might touch to complete the circuit and receive a shock. For example, the earth outside, the plumbing inside, the chassis of large or small appliances, etc.


Is the negative side of the inverter battery supply also connected to chassis? It (probably) should be. I learned this the "easy" way while bench testing a Xantrex MSW inverter several years ago. I touched the inverter case with one hand and touched battery negative with the other and took a 60 volt ac shock. Later I found it mentioned in the manual that the battery negative should be tied to the inverter chassis to prevent this.



Sounds like you've taken care to get your shore and inverter grounds connected to the bus chassis. That's good. There's one thing to note, however: we don't want the inverter to provide a neutral-ground bond when the bus is connected to shore power. How might this happen? If the inverter case is connected to the bus chassis and its neutral is fixed to the load center's neutral bar, and if shore neutral and ground conductors are connected likewise. The inverter is then a hidden ground-neutral bond. Make sure you have a multi-wire transfer switch so that both the inverter's neutral and hot are disconnected when using shore power.


An easy way to make sure the transfer connections all work out is to wire only the shore power cord to the load center, and wire only an outlet to the inverter. Plug the shore power cord to the inverter outlet when the inverter is to be used.
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Old 05-20-2019, 01:40 PM   #3
Bus Geek
 
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Does your inverter provide neutral ground bonding?
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Old 05-23-2019, 12:36 PM   #4
Skoolie
 
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Quote:
Originally Posted by neuronmisfires View Post
Hi all,

I recently wired my Thomas vista for shore and inverter power. Both systems are grounded (or bonded) to the wirebrushed seat rail w/ a 3/8” stainless steel bolt and ring terminal connectors.

Exactly how are they wired? When you say 'both systems', what do you mean by that (as opposed to one system with separate AC inputs)? They're not operating in parallel, are they?
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Old 05-23-2019, 07:22 PM   #5
Mini-Skoolie
 
Join Date: Jul 2018
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Hey familywagon! Apologies for the late reply- I’ve been working on installing my butcher block and sink. I didn’t think to test the skin with a multimeter, but that’s not a bad idea. I figured I’d play it safe since I want to hardware the inverter anyway. To answer your question, the negative supply side of the inverter (aka my battery monitor shunt) was not grounded as I was worried about having multiple ground connections to the inverter. Sounds like I messed up! Should I run a ground connection from the shunt regardless? My 12v fuse block and charge controller negatives are also on there.

My automatic transfer switch arrived today so I’m going to wire both the inverter and the shore power through it. I think it’s multiple wire but I’ll take a look to make sure- def playing it safe.

I also now have two separate AC load centers: one for shore power stuff like A/C, and another that will be solely be used for outlets by both the shore power and inverter.

Woof! This stuff is complicated, but I’d like to be able to charge my toothbrush ��
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Old 05-23-2019, 07:25 PM   #6
Mini-Skoolie
 
Join Date: Jul 2018
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pNwsteve- I’m about to find out! Gotta read up on the inverter manual re:hardwiring.

Thehubbardbus- the shore power and inverter circuits were completely separate at the time of my first post and potential hot skin condition. I’m going to draw up a diagram because this stuff is getting far too complicated!
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