I plan to install a small inverter (700W or less). There is no other AC on the boat and I will use only the receptacles built into the inverter. A very simple installation...maybe.
I am also trying to comply with ABYC. The inverter chassis ground cable must the same size or one size smaller than the DC positive feed.
So I bought a 700W inverter - marketed for use on boats - and the chassis grounding lug is tiny; way to small to properly fit a cable connector meeting the ABYC requirement. I looked at other small "marine" inverters online and they all seem to have similar tiny little grounding lugs.
I really was hoping to avoid spending $1k+ and in the process end up with a larger inverter than needed. I saw a suggestion somewhere to "sand off" the paint on chassis, drill a bigger hole, and just fasten the ground cable with nut-and-bolt (with a StSt washer between chassis and bolt).
What do you think? is this workable? Any other ideas or suggestions for a brand/model that capable of meeting ABYC without modification? Many thanks!!
Small inverter: chassis ground per ABYC
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atomvoyager
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Re: Small inverter: chassis ground per ABYC
The idea is that the chassis ground wire needs to be big enough that it can carry the current needed to blow the fuse without burning up In case of a short to the chassis. The chassis ground is a redundant path back to the negative bus so in the highly unlikely case of a failure inside the inverter, it will provide a path back to the negative bus. What may make the answer complicated is that this may be an issue that has different recommended remedy on a combo inverter/charger rather than a small stand alone inverter.
The size wire you use for the positive and negative feed wires to the inverter is large enough to prevent excess voltage drop. As I understand it, you don't necessarily need the chassis ground wire to be at least one size smaller than the 12v feed wires but rather just large enough to carry the load of the inverters power rating in order for the chassis ground wire not to melt and burn before the fuse blows. Another consideration is that It only creates an alternate current path if the chassis and DC negative are common inside the inverter. A continuity test with a meter will tell you if they are. Often they are not.
Your idea of using a large jumper wire from chassis ground terminal to negative terminal on inverter would not be an approved method because the chassis would then be in the normal DC circuit and all operating current would go thru the chassis DC positive to inverter chassis. Then the DC positive would supply high amps into the small chassis ground wire causing it to catch fire before blowing a fuse.
I found this comment on the Trawler Forum where it was discussed to death and the concensus is that you need a large seperate chassis ground to negative bus that is not just a jumper a few inches long between chassis and negative inverter post. Using a larger bolt for the connection is also recommended:
"The case ground (which should be no more than one size less than the DC cabling from the batteries) is there in case there is a DC short (or an AC short) but the ground has to also carry the possible large amperage discharge from the batteries to the case.
The most common mistake is that installers use the smaller AC gauge wire to ground the case. That is what my installer wanted to do, until I showed him the many, many admonitions not to, including in the manual, in books on boat electric, forums, and manufacturer sites."
https://www.trawlerforum.com/threads/el ... und.63893/
The size wire you use for the positive and negative feed wires to the inverter is large enough to prevent excess voltage drop. As I understand it, you don't necessarily need the chassis ground wire to be at least one size smaller than the 12v feed wires but rather just large enough to carry the load of the inverters power rating in order for the chassis ground wire not to melt and burn before the fuse blows. Another consideration is that It only creates an alternate current path if the chassis and DC negative are common inside the inverter. A continuity test with a meter will tell you if they are. Often they are not.
Your idea of using a large jumper wire from chassis ground terminal to negative terminal on inverter would not be an approved method because the chassis would then be in the normal DC circuit and all operating current would go thru the chassis DC positive to inverter chassis. Then the DC positive would supply high amps into the small chassis ground wire causing it to catch fire before blowing a fuse.
I found this comment on the Trawler Forum where it was discussed to death and the concensus is that you need a large seperate chassis ground to negative bus that is not just a jumper a few inches long between chassis and negative inverter post. Using a larger bolt for the connection is also recommended:
"The case ground (which should be no more than one size less than the DC cabling from the batteries) is there in case there is a DC short (or an AC short) but the ground has to also carry the possible large amperage discharge from the batteries to the case.
The most common mistake is that installers use the smaller AC gauge wire to ground the case. That is what my installer wanted to do, until I showed him the many, many admonitions not to, including in the manual, in books on boat electric, forums, and manufacturer sites."
https://www.trawlerforum.com/threads/el ... und.63893/
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mcmurton
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Re: Small inverter: chassis ground per ABYC
Thank you, James. I think I get it (no, not all the nuances in the trawler forum, egad, but my simple scenario). I did not mean to infer I'd put a jumper between the chassis ground lug and the inverter negative. I was just trying to figure a way to get a large enough connector on the chassis to run the proper size cable from the chassis to the negative bus...because the nuts on the chassis' itty bitty ground lug could fit right through the hole in the lugs of the battery cables supplied with the inverter; way to small for a proper/ABYC-sized ground.
Fair winds -
Mark
Fair winds -
Mark