Electrical puzzle

[Corvidae]

I've been trying to sort out the wiring on my 82 Gallart. As far as I can tell, the boat is and always has been a 110v shore power system, with probably a 30amp shore plug.

The current mystery is a small subset of the outlets around the settee. They were reading 20 volts while all the rest were reading 117 (shore power). I checked the wiring, and they seemed to be wired hot to ground rather than to neutral. Swapped that around and all seemed good, 117 on every outlet in the boat. With a stray 20 volts from neutral to ground that I needed to track down. Several candidates for that, but still working on it.

Then this morning the shore power exploded (Totally unrelated to my boat, who puts a marina junction box below the water level anyway?!?) So we unplug the shore power line, and fire up the generator. Every outlet came up fine except the settee plugs were again reading 20volts.

So now i'm confused to say the least. I don't have a split rail turning 220 into two 110 circuits. The shore power is 110 and a ground on three wires, the generator runs through an autotransformer kicking it down to 110, that goes into our autotransfer switch, then shore/generator power runs to a 3k inverter charger which outputs to the rest of the boat.

I'm seriously iffy on the inverter/charger. It seems to be reading 1 volt lower than what the battery is actually at, making it want to charge or shut off wrong. Outside of that though, it does run, it's putting out the right voltage to every other outlet on the boat. It's just being cantankerous about charging voltages. Which in no way explains to me why I have a few outlets only showing 20 volts when running on the generator.

[skipmac]

Off the top of my head I think more information needed to do a remote diagnosis BUT like all things electrical, it's very logical. One idea, is the shore power or generator or both separated into two 110 circuits? Not necessarily 220 split into two 110 legs but running through two different switches or circuit breakers? That would be one place that things were swapped around.

Otherwise, start at one end and trace all the wires back to the other end. also, get a meter to check that all the AC outlets are wired the same way (don't depend on wire color or location) at the panel, any switches, circuit breakers or anywhere else there is a connection.

[Corvidae]

Shore and generator power are each on a single pair of wires at 110. (Standard 30amp shore power plug) The generator does run 220, that gets broken down to two 110 circuits by the autotransformer. One of which is disconnected (verified wire is disconnected), the other runs into the transfer switch with the shore power. Regardless of shore/generator power, the transfer switch puts out 110, that then gets sent to the inverter/charger then off to the main panel.

My current suspect is that there's something wrong with a ground/neutral somewhere. I'm just at a loss as to how that turns into 20 volts.

[mario f]

Maybe a floating ground or neutral? in addition to miss wire. Between ground and neutral should be 0v.
As above trace wires carefully-

[NPCampbell]

You had neutral and ground reversed on the plug and it only measured 20 volts? I'm assuming boats are like homes and neutral is wired to ground in the main panel? If that's the case then where's the 20 volts coming from? Could the settee circuit have something in the circuit that is wired serially instead of in parallel? Or, you may have a bad connection. A voltage meter typically has an impedance in the low megohm range. Since you only measured 20 volts I would assume the resistance of the remainder of the circuit is 5-6 times the meter or around 10 megohms which may indicate a bad or corroded connection?

[boatpoker]

Originally Posted by NPCampbell

You had neutral and ground reversed on the plug and it only measured 20 volts? I'm assuming boats are like homes and neutral is wired to ground in the main panel? If that's the case then where's the 20 volts coming from? Could the settee circuit have something in the circuit that is wired serially instead of in parallel? Or, you may have a bad connection. A voltage meter typically has an impedance in the low megohm range. Since you only measured 20 volts I would assume the resistance of the remainder of the circuit is 5-6 times the meter or around 10 megohms which may indicate a bad or corroded connection?

No neutral and ground not joined on the boat. They are joined at generators and inverters via auto switching.

Joining neutral and ground on a boat will introduce AC into your DC wiring since your AC ground and DC negative are bonded and likely hurt someone badly.

[NPCampbell]

Originally Posted by boatpoker

No neutral and ground not joined on the boat. They are joined at generators and inverters via auto switching.

Joining neutral and ground on a boat will introduce AC into your DC wiring since your AC ground and DC negative are bonded and likely hurt someone badly.

If neutral doesn't tie to ground then testing it should be pretty easy. Trip the main breaker and disconnect/switch off all power sources and devices on the settee circuit. Test for open circuits between every lead and use a 3 prong extension cord to test for <2 ohm conductivity back to the respective leads at the main panel/genset/inv.