Getting juiced

[capta]

I'm at a loss.
I installed a dedicated outlet and breaker for the toaster oven. On the generator it works perfectly, as does the older undedicated outlet. However, on the inverter (3k modified sine wave) my wife gets shocked when touching the cabinet of the toaster oven when it's plugged into the dedicated outlet, but not the other one.
Any thoughts?

 

[Ralph Johnstone]

my wife gets shocked when touching the cabinet of the toaster oven when it's plugged into the dedicated outlet

The toaster may have a hot wire touching the cabinet so I would check the hot and neutral receptacles of the toaster to the casing first with an ohmeter. I'm assuming the toaster does work and the ground wire is not live. After that, try running a separate piece of temporary scrap wire from the disconnected ground wire of the troublesome outlet back to the boats 110V ground to see if there's continuity using an ohmeter again. Make sure the powers off in all of these checks just to keep it as painless as possible. Keep it simple to start and if that doesn't work ................. wait for others to chime in.

 

[capta]

The toaster may have a hot wire touching the cabinet so I would check the hot and neutral receptacles of the toaster to the casing first with an ohmeter. I'm assuming the toaster does work and the ground wire is not live. After that, try running a separate piece of temporary scrap wire from the disconnected ground wire of the troublesome outlet back to the boats 110V ground to see if there's continuity using an ohmeter again. Make sure the powers off in all of these checks just to keep it as painless as possible. Keep it simple to start and if that doesn't work ................. wait for others to chime in.

If any of these faults were with any two configurations of the 4 then I could see any of your suggestions as possible. But since it works fine on three of the 4 possible power sources I don't get it.

 

[Gunni]

I would suspect that your new dedicated outlet does not share a ground with your AC inverter.

 

[MitchM]

this can be really serious. test if t h toaster wiring is d effective by plugging into a known good new 120V outlet protected by a GFCI. (IF IT shocks your wife or TRIPS GFCI -- IT S A CRUMMY TOASTER. throw it away !) ABYC requires installed polarity indicators on new boats. get a polarity checker and plug it into this toaster out let AND other outlets on the boat. is the toaster outlet an old 2 slot or a newer 3 slot with a ground hole? is the outlet properly grounded per polarity indicator? is it a recent AC outlet extension 'add on' ? sometimes who ever wired it reverses the polarity of the outlet. (bad polarity wiring is 120 V hot line connects to neutral of load, hot off load going through circuit breaker wrongly connects to neutral .) sometimes the outlet itself is so old (70's boats...) it was never grounded. to quote USPS Marine Electric 101, "reversed polarity can energize all intentional and accidental grounds within the vessel and can create a lethal shock hazard...' on a proper 120V AC outlet the short vertical connects to HOT black , the tall vertical is neutral white and the 'round is ground.' old 120 V outlets often are NOT grounded, (have only 2 equal length slots) as on old boats they did not bother. if the outlet is not grounded a the 3 prong 'safety' adapter must be attached as a temporary fix, by connecting grounding wire of the adapter to a real ground...

 

[Ralph Johnstone]

But since it works fine on three of the 4 possible power sources I don't get it.

Aw crap, close but no cigar so far .

But am I correct in saying that there IS a connection between the hot wire and the toaster casing ? I can't see any other way of getting a shock from the casing. It's only a start but it has to be corrected or get a new toaster.

It's always difficult to deal with these problems at a distance ................ we can't wave our arms around to demonstrate a point.

 

[Gunni]

But am I correct in saying that there IS a connection between the hot wire and the toaster casing ? I can't see any other way of getting a shock from the casing.

What if the toaster had a short condition that was being grounded on a properly grounded circuit, but not grounded on the other problem circuit?

 

[Charles Erwin]

Is it correct that the problem is just the one receptacle (the new one) and then only when fed by one source - the inverter. By 'dedicated' do you mean the new receptacle is supplied by the inverter only?

Are all receptacles 110 vac (north america style - hot, neutral, and grounding)? Did you double check the polarity of the new receptacle? Is the oven three wire? If so, is safety green and neutral bonded to the oven case?

Keep in mind if there is internal oven bonding (white to safety green) very dangerous no matter which source is used and very big threat with reversed polarity at the new receptacle. Is safety green bonded to neutral at the inverter? Is the inverter auto switching or a mechanical rotary switch for all three wires?

Charles

 

[capta]

Is it correct that the problem is just the one receptacle (the new one) and then only when fed by one source - the inverter. By 'dedicated' do you mean the new receptacle is supplied by the inverter only?

Are all receptacles 110 vac (north america style - hot, neutral, and grounding)? Did you double check the polarity of the new receptacle? Is the oven three wire? If so, is safety green and neutral bonded to the oven case?

Keep in mind if there is internal oven bonding (white to safety green) very dangerous no matter which source is used and very big threat with reversed polarity at the new receptacle. Is safety green bonded to neutral at the inverter? Is the inverter auto switching or a mechanical rotary switch for all three wires?

Charles

Dedicated meaning the toaster oven is the only unit on that circuit.
Both the dedicated circuit and the galley outlets circuit are fed by the same 110 vac source on the panel. Wired identically. Hot, neutral and earth are all wired to the same bus bars. The wires just go to different breakers. Both power sources feed the same bus bars.
The dedicated outlet works fine on the generator. The galley circuit works fine on both the gen and inverter, so I don't see how it could be a fault in the unit.

 

[Charles Erwin]

I don't see how it could be a fault in the unit.

Your wife gets shocked when she touches the case? Where is she standing when this happens does she have a hold of something with her other hand. Do you get shocked? Did you measure AC voltage - oven case potential to AC neutral? When you do a measurement and it comes up that the case is AC energized there is no doubt the case is shorted to AC hot output. This can only happen if there is an internal oven short to case or if polarity is reversed and is neutral bonded to the case.

Too early in the game to guess or try to use reason just yet. Turn on the inverter - take a simple measurement between oven case and inverter neutral or inverter safety green - and tell us what happens.

 

[Ron20324]

While the outlet has a ground pin, my toaster oven is only a 2- prong cord.

 

[Bill Roosa]

Charles is on to it. If you stand not touching a car and pull off one of the spark plug wires you will not get shocked because there is not circuit. Touch the car or be standing in a puddle that your assistant also has a foot in and his hand on the ignition key and you both get a shock.
It could be that the properly grounded metal frame of the toaster is just making it easy to find that the thing your wife is standing on or holding in her other hand is actually energized.

 

[Dennis Kitchen]

It sounds like when you are switched on the generator your circuits all have good connections( low resistance) but when on the inverter perhaps your nuetral connection is weak ( high resistance ) . A fault in the toaster now finds an easier path to ground through the case and who ever touches it. If your nuetral and ground are joined inside the toaster, which is improper in a marineized application; the current will seek the lowest resistance path back to earth.
Does your inverter power your entire AC panel or only certain circuits? I would verify the connections of the nuetral lines from the inverter to any affected circuits.
Dennis

 

[capta]

Thanks.
Been really busy w/customs, etc. for arranging the new dink, but I'll get onto this soon.
Yes the inverter powers the whole electrical panel.
Funny thing is, my wife can be standing barefoot on the wood floor, not touching anything else and she still can feel it. It's more a tingle than a shock, barely noticeable, like someone lightly brushing her arm hairs in passing.
It's just strange. I installed the dedicated line for the 1500 watt toaster oven thinking the 30 odd year old wiring already in place wouldn't carry that load well. New tinned copper boat wire. New modern receptacles and connections. That old saying keeps running through my mind, "If it ain't broke, don't fix it." When will I ever learn?

 

[Benny17441]

I think you may have a grounding problem on that new circuit. Verify that the inverter is properly grounded. That toaster oven seems to be leaking current.

 

[Charles Erwin]

AC measurement would be useful to you and without same a complete solution is probably not possible.

Since you intend to use your wife instead of a meter -- does she sense this when oven is off/breaker is on?

A possible option is to use a double pole breaker so both legs to the dedicated outlet can disconnect - then keep the breaker off except when the oven is in use.

Meanwhile remember the outlet has to be: silver = white and gold = black.

 

[All U Get]

It helps me to draw it on paper. Those black wires get confusing.

All U Get

 

[jibes138]

Would a GFCI outlet help? If current is leaking to ground it should trip immediately. Won't fix what's wrong but might add a level of safety.

 

[walt]

I recently looked at putting a GFCI outlet on the output of an inverter for some level of safety running Christmas lights on the boat. The inverters I looked at were the smaller hardware store versions (400 watts and 150 watts) but they were not consistent in how the grounds were wired. One inverter had the DC ground connected to the AC green wire. The second inverter seemed to have no connection at all between the DC ground and the the AC green wire. The DC ground or the AC green may have gone to the inverter chassis somehow but I couldnt tell since most of the chassis was plastic.

Also, the AC output (hot and neutral) were floating with respect to the green wire on both of these inverters. Ie, the AC output had no low impedance reference to Green. Note that either at your house or on the boat, the AC source (like the marina breaker) will have the green and white wire connected and this is what references the AC current carrying wires to ground. GFCI has to have the reference in order to work.

So if I had connected a GFCI ACsocket to the output of the inverter by directly wiring up the black/white/green wires, it would likely have never tripped under any condition since the hot wires had no reference to the boats ground, green earth wire or water. Not really related to this case but to make the GFCI trip for my Christmas light case, I would have had to tie the GFCI white wire to the boats ground (which was connected to the water through the outboard).

For the OP, as suggested already.. Your toaster likely just has a two wire plug. Take an ohm meter and measure between each of those two wires to the toaster chassis. You should see an open circuit for both wires. Any resistance at all - even very high resistance - something is wrong.. time for a new toaster.

Second, connect up the AC source/circuit that does not cause the shock. Put the meter on AC volts and measure between black to white (hot to neutral), black to green (hot to earth ground) and then white to green (neutral to earth).

If this was at your land based house, you would see about 110 AC black to white, 110 AC black to green and close to zero white to green. Your AC circuit that does not shock may look like this. The inverter output may look more like 55 volts black to green and 55 volts white to green. There really isnt anything wrong with the way the inverter works.. but that may be related to why you get the non dangerous tingle shock???

 

[capta]

Your toaster likely just has a two wire plug.

Sorry, I did not address this sooner. The toaster oven has a 3 pin plug.