| Author | Message | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: |
Folks, I need some help from the more experienced engineering types on this board. I am working through my wiring diagrams, and have come across a challenging problem with the installation of my Xantrex/Trace SW4024 inverter/charger. Here's the (lengthy) description: I originally (before settling on the Trace) had planned to have a standard 3-pole (two hots, one neutral) AC Automatic Transfer Switch (ATS) to switch between shore power (which might be as small as 15 amps/110 volts) and generator (which can deliver 60 amps/240 volts). The inverter/charger would have been one of several loads switched between these sources with the ATS. This design, however, does not take advantage of some of the automatic features of the high-end Trace unit, which is already equipped for dual inputs (Shore/Grid and Generator). So I am now reworking my diagrams to connect the grid input of the Trace to the shore cord and the generator input of the Trace to, naturally, the generator. The Trace does not have an internal ground-to-neutral bonding relay, and the installation instructions clearly spell this out and even provide diagrams for how to install such a relay externally to effect proper ground-to-neutral bonding when stand-alone, and disconnect same when grid-connected. However, these diagrams and instructions only show one AC input -- dual AC sources are not covered. The problem lies in the fact that the Trace's internal transfer switches only switch hots. The neutrals are internally tied together (both AC input neutrals and the AC output neutral are internally bonded). With only a shore cord to contend with, this is not a problem -- the ground bonding scheme suggested in the manual will work fine. However, the generator has the ground and neutral internally bonded as well. This is true whether the genny is running or not. (AFAIK, all generators are like this.) So as long as the generator neutral is wired to the neutral terminal of the Trace, plugging (the other AC neutral terminal) in to shore power will result in a ground loop through the generator. I've come up with several possible solutions to this, but none of them is pretty. That being said, I know the SW4024 is a popular inverter, and I assume most folks have both generators and shore cords, so someone has had to solve this before me. Thus my question: if this is your setup, what did you do to resolve this problem? Whew. Sorry for the long-windedness, and looking forward to your answers! -Sean | ||
| Jim Stacy (32.101.44.80)
Rating: N/A |
Sean, How about if you go with your original plan and use the transfer relay and only feed the landline input to the inverter? As you probably know, the relay will isolate the ground/neutral bond at the generator. Do not use a relay contact in the ground circuit, It is against code to switch the gound. You can use a relay to combine the ground with neutral, however. HTH Jim Stacy | ||
| Jayjay (152.163.188.227) Rating: N/A |
The coach chassis is always at ground potential and bonded with the neutral ,whether it is shore power, genset or battery bank. You cannot have a "ground-loop". it's a misleading misnomer. You could possibly have an ungrounded device, but not a loop, since a proper ground(ing) system is the end of the line for a current/voltage path. The Trace is internally bonded/grounded and is at the same potential as the genset ground/neutral, as long as the Traces is bolted/bonded to the coach chassis. A quality ohm-meter is indispensable at a time like this. Don't co-mingle equipment internal blueprints with installation prints. Hook it up, then set the meter for three decimal place read-out on the Ohm scale and you should show 00.000 Ohms between both device chassis and the coach chassis. E-mail me direct for more help if you need it. jarjaje@wmconnect.com HTH Cheers...JJ | ||
| Sean Welsh (Sean) (64.81.73.194)
Rating: N/A |
Perhaps I was not clear in my original posting, or maybe I stated the problem incorrectly. Code (NFPA 1192 as well as NEC) *and* safe practice mandate that the neutral and ground be bonded in only one place, and that place should be as far upstream as possible. In a correctly wired park, the neutral and ground will be bonded upstream of the receptacle -- usually either at the subpanel where the circuit breaker for the receptacle is located, or maybe all the way back at the transformer from which the subpanel derives. (If you need an explanation of why violating this can be dangerous, see the discussion in the "NEC Handbook.") So, if you have the neutral and the ground tied together anywhere in your coach, AND you plug your coach into shore power, you now have the neutral and ground bonded in two different locations. My error is in referring to this as a ground-neutral loop, which some have confused with a ground loop. What it really is is multiple ground-neutral bonds. This creates the potential for live current to be traveling through your ground system, including possibly the vehicle chassis. I'm not looking for advice on how to test grounding -- I have a great meter already, I'm an engineer, and I have designed hundreds of electrical distribution systems (mostly large fixed installations with tens of thousands of amp-hours of batteries, and 480-volt three phase AC). What I'm looking for is an engineering solution to the multiple bond problem -- I could do the engineering myself, selecting relays and/or transfer switches, etc. and stringing them together. But I figure someone on this board has had to do this already, and I don't want to reinvent the wheel. For what it's worth: The Trace does NOT have an internally bonded ground and neutral -- the installer must bond them somewhere else (see pp. 26-28 of the manual). And, as I mentioned in my original post, I don't want to revert to my original plan of only using the one input and having the transfer be completely external, because that precludes me from using the more sophisticated load-support features of the Trace. So my question remains: Who is using a Trace SW series box, both AC1 and AC2 inputs, and a hard-wired generator, and how did you solve this problem? Or am I really clearing new ground here? -Sean | ||
| David Anderson (66.90.195.97) Rating: N/A |
You might call Dick Wright at Wrico 541-744-4333. He is a guru when it comes to these things. I don't think you can accomplish this without a transfer switch. It looks like you want both power sources to go through the Trace and if both are on simultaneously, if my memory is correct, the Trace will default to AC1 in, even if AC2 in, is on at the same time. This stuff gets real tricky because only one phase of your genset or one phase of your shore cord feeds the trace at 110volts. The other phase bypasses the inverter and goes on to a panel. I used a 50amp transfer switch that switches all hots and neutrals. The load side of the transfer switch feeds a main panel. In that panel one of the breakers is a single pole 50amp breaker with a #6 wire that goes to the Trace "AC1 in". The Trace hot out goes to a subplanel (110volt only) that distributes power to all the circuits I want to run off the Trace. The genset powers the transfer relays. In idle state, the relays default to shore power. When genset is powered the relays bond the neutral to the ground lug for the genset. When the shorepower is on, all neutrals and ground are unbonded. Here is the part of my system that may raise your eyebrow. When no shore power is on and no genset running, I plug in a 50amp female plug into the end of my shore cord that has a #6 wire bonding jumper between neutral and ground. This makes my 50 amp main disconnect effectively bonded to itself. Its ground wire is bolted to the lug where my 12 volt neg wire is and where the ground wire for the Trace is, all in one place. I've explained this setup on the board before and everyone has all kinds of opinions about it. I don't know if it is code, but it makes my ground all in one place no matter what the power source. This, like you said only allows for one input to the Trace since the load side of the tranfer switch only has one output, so the Trace doesn't know if it is from genset, or shore power. I have thought about another relay on the load side of the tranfer switch that would, when power is supplied by genset, energize the relay and send power out another cable to "AC2 in" on the Trace, thus fooling it to think power is coming from a generator. This would allow the use of the sophisticated load support features of the Trace. At this point I haven't been able to justify doing that. Perhaps later on as I use the bus more I may need that and can add it later. This doesn't answer your question very well, but it is just an opinion on the way I did mine. David Anderson |
