Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[drew gandy]

So I've been doing a little research on the multitude of 2000w range inverter generators on the market now. (Storm came across and wiped out power to a lot of homes a few days ago).

It seems that the link kits for these do NOT allow for 240v but instead for higher current at 120v. But, some of them appear to provide this power on 240V style connectors - apparently putting the same 'phase' on both hot terminals. These seem to be aimed at RV usage. But I'm having a hard time understanding how this won't lead to overloaded neutrals in systems where the neutrals are shared which is very common with 240v "split phase" power. 

What am I missing here? 

[Tim McCulloch]

So I've been doing a little research on the multitude of 2000w range inverter generators on the market now. (Storm came across and wiped out power to a lot of homes a few days ago).

It seems that the link kits for these do NOT allow for 240v but instead for higher current at 120v. But, some of them appear to provide this power on 240V style connectors - apparently putting the same 'phase' on both hot terminals. These seem to be aimed at RV usage. But I'm having a hard time understanding how this won't lead to overloaded neutrals in systems where the neutrals are shared which is very common with 240v "split phase" power. 

What am I missing here?

I went through this with RV generators - if there are no 240V loads, the gensets have independent 120V windings with their own "neutrals".  The neutrals are jumpered together for output purposes.

[drew gandy]

I went through this with RV generators - if there are no 240V loads, the gensets have independent 120V windings with their own "neutrals".  The neutrals are jumpered together for output purposes.

Am I to assume that the RV is also wired such that all circuits have their own neutrals?
If so, I guess that covers RVs.
But NOT other systems that might use the same 240v plug expecting 180 phase between the two 'hots'.
More and more it seems clear that we should not share neutrals no matter how tempting it might be...
And that makes me wonder about using 6/5 wire with california plugs instead of 6/4 - Double up the neutral.

[Tim McCulloch]

 Neutral carries the imbalance of current, so in split phase systems the neutral current cannot exceed the circuit rating.

[Steven Cohen]

The only 240 Volt inverter generator that I am aware of is the new Honda EU 7000. I think is also the first to use fuel injection.
The other inverters from Yamaha & Honda have a 30 amp, 120 volt connector. Which generator are you talking about?

So I've been doing a little research on the multitude of 2000w range inverter generators on the market now. (Storm came across and wiped out power to a lot of homes a few days ago).

It seems that the link kits for these do NOT allow for 240v but instead for higher current at 120v. But, some of them appear to provide this power on 240V style connectors - apparently putting the same 'phase' on both hot terminals. These seem to be aimed at RV usage. But I'm having a hard time understanding how this won't lead to overloaded neutrals in systems where the neutrals are shared which is very common with 240v "split phase" power. 

What am I missing here?

[drew gandy]

The only 240 Volt inverter generator that I am aware of is the new Honda EU 7000. I think is also the first to use fuel injection.
The other inverters from Yamaha & Honda have a 30 amp, 120 volt connector. Which generator are you talking about?

I'm talking about 120v linkable inverter generators that provide their "combined" output on a 240v style plug. Take for instance this Energizer brand linking kit.



It's my understanding that in this kit, both of the "hots" in the 14-50R connector are wired to the same 120V (same phase). If we connect this to a power distribution system that shares neutrals for circuits that are 180 degrees out of phase with each other, aren't we risking an overloaded neutral? 

[Tim McCulloch]

I'm talking about 120v linkable inverter generators that provide their "combined" output on a 240v style plug. Take for instance this Energizer brand linking kit.



It's my understanding that in this kit, both of the "hots" in the 14-50R connector are wired to the same 120V (same phase). If we connect this to a power distribution system that shares neutrals for circuits that are 180 degrees out of phase with each other, aren't we risking an overloaded neutral?

Great question.

Disclaimer:  Observations only, I've not opened up, used or laid hands on this device.

Each pig tail has 3 conductors, presumably line, neutral, ground.  The grounds and neutrals get bonded in the linking device.  But it's not a *circuit* between the 2 Lines, only the current from a line and its neutral are a circuit, so no, you can't overload an individual generator's neutral.  The neutrals are connected to a wiring device rated for the full load on each terminal.

The bigger question is there 240V from Line 1 to Line 2?  I'm thinking not, unless there's something else going on.  From the Home Despot description:

2 ports (120-Volt 50 Aamp 14-50R, 120-Volt 30 Amp L5-30R) are protected by rubber covers

It makes no mention of 240V so I think you're right.  From the pictures on the site it shows 2 dissimilar Energizer generators, this device, and couple of 5th wheel RVs in the background and that kind of reinforces my presumptions about this type of product.

[Jonathan Johnson]

Assumption: both "hots" on the NEMA 14-50R receptacle of the parallel kit are wired to the same "phase" which is where the "hots" of both generators are connected in parallel.

So here's what I see: each generator provides a maximum of 20A to the kit, for a total of 40A 120V, distributed across both hot legs of the NEMA 14-50R. One leg could see up to 40A, the other could see zero. That means that 40A will flow on the neutral. The neutral conductor of the RV cord is rated for 50A. In this scenario, even though it's fully imbalanced, the current on the neutral doesn't exceed capacity of the cordset, because the current on either hot is limited by the capacity of the generators -- a total of 40 amps.

Now, if you parallel two larger generators, capable of providing 30A (or more) at 120V each, then you could conceivably overload the neutral.

[Dave Garoutte]

The only 240 Volt inverter generator that I am aware of is the new Honda EU 7000. I think is also the first to use fuel injection.
The other inverters from Yamaha & Honda have a 30 amp, 120 volt connector. Which generator are you talking about?

My Yammie EF6300 does 23A of 240v.

[Stephen Swaffer]

Assumption: both "hots" on the NEMA 14-50R receptacle of the parallel kit are wired to the same "phase" which is where the "hots" of both generators are connected in parallel.

So here's what I see: each generator provides a maximum of 20A to the kit, for a total of 40A 120V, distributed across both hot legs of the NEMA 14-50R. One leg could see up to 40A, the other could see zero. That means that 40A will flow on the neutral. The neutral conductor of the RV cord is rated for 50A. In this scenario, even though it's fully imbalanced, the current on the neutral doesn't exceed capacity of the cordset, because the current on either hot is limited by the capacity of the generators -- a total of 40 amps.

Now, if you parallel two larger generators, capable of providing 30A (or more) at 120V each, then you could conceivably overload the neutral.

On that particular link kit, it says "circuit breaker protected".  It is not clear of both receptacles are protected-but I would hope so, in which case even larger gennys would be safe.

[Jonathan Johnson]

On that particular link kit, it says "circuit breaker protected".  It is not clear of both receptacles are protected-but I would hope so, in which case even larger gennys would be safe.

The concern would be if you loaded 30 amps on one leg, and 30 amps on the other (and both legs were connected in parallel, not opposite legs of 120/240V service), that would add up to 60 amps on the neutral. If the legs are protected by 50A breakers (but the neutral has no breaker) there's no protection for the neutral and it could be overloaded.

[Jonathan Johnson]

For sake of not making assumptions, here's the schematic of the Firman* model 1201 paralleling kit. With respect to the NEMA 14-50R receptacle, the "hots" from the generators are tied together, then pass through a single-pole 50A breaker, then to both "hot" poles of the receptacle which are tied together.

This shows that you cannot overload the neutral, because the sum of the hot legs should not exceed the ampacity of the neutral. I do note, however, that it uses 10 AWG wire, which is usually rated at 30A -- though I understand in certain applications that can be acceptable for 50A. I am not qualified to judge if this is a valid application of that overrating.

https://www.firmanpowerequipment.com/shop/parallel-kit-50amp-1201/

*Note that is Firman, not the Furman we're familiar with.

[Stephen Swaffer]

10 AWG does seem undersized-but AWG is only part of what determines "ampacity"-the other is the temperature rating of its insulation-Type TFE lists an ampacity of 107 for #10.  Though I doubt they used that here-there are insulations that would allow 50A ampacity without damaging the wire-but they will run warmer than we are used to.  In my day job, I use a TGGT wire that has insane ampacity ratings-however when you derate for the ambient where it is used it is closer to what we expect.

Not trying to be arguementative-just pointing out that merely knowing the wire gauge doesn't tell me the safe OCPD.  The NEC (which mainly applies to installations) limits OCP for #10 to 30 amps with a fine print note-regardless of the actual ampacity otherwise indicated-but OCP is not the only thing determined by ampacity calcs.

[drew gandy]

This shows that you cannot overload the neutral, because the sum of the hot legs should not exceed the ampacity of the neutral.

I wish I had time to draw this out. My concern is not overloading the neutral in the generator or even the 'feeder' but various neutrals in the downstream distro. If it has 12ga neutrals for 20A circuits and you feed it from one of these generator setups, I think, you could conceivably put 30+ amps on that 12 ga neutral - inside your distro or subfeed from that panel. 

For instance if you have a dual 20A breaker in your distro and out of that you feed 12/4 wire to a quad box (each duplex on it's own circuit) and you put 2 dimpacks on that quad box (one on each circuit) you can load that neutral with more than 20A of current. If you have a true 240V generator feeding this distro, the neutral will not see more than 20A current. As Tim said earlier, the neutral takes up the imbalance. Again, a drawering would really help. I'll see if I can find some time to scribble something up.

Secondly, while discussing the 'ampacity' of different ga wires, one of the big determiners is the heat dissipation capability. If you bundle the wires together in a service cord then the 'ampacity' is supposed to be derated because the heat dissipation is significantly less than for loose conductors of the same size.
You know, just to confuse things even more.

Thanks btw for finding that 'Fireman' schematic. 
Now I know for sure that some of these are simply paralleled together.

[Tim McCulloch]

Where's Sokol?

[Stephen Swaffer]

Drew,

You are correct in thinking that could overload a neutral.  More than once I have come across "multiwire branch circuits"-the NEC term for shared neutrals that are fed off the same phase becasue someone did not understand what was hapening when they re-arrranged breakers.

I would also question if the neutral could be overloaded if your example quad box was used on a 3 phase system where harmonics could be present and the 2 phases are not 180 opposed.

The safe way would be a five wire cable with dedicated neutrals.  Of course, then you have 4 current carrying conductors instead of 2 (a neutral is ignored if it is only carrying unbalanced current)-which ususally gts you into the derating you mentioned.  Of course, the derating is done from the actual ampacity rating of the conductor-not the maximum breaker size specified by the Fine Print Note for small wires.

[Mike Sokol]

That's why those parallel kits are only available for smaller 2,000 to 3,000 watt inverter generators. Yes, they do parallel the outputs and can only make 120 volts. And yes, the neutral current will be additive rather than subtractive as they would be in a split-phase 120/240-volt service. But as others have mentioned there's not enough combined amperage with these small generator to overload the neutral conductor. That's why a pair of 2,000 watt generators in parallel can use a 30-amp twist=lock or TT-30 connector, and a pair of 3,000 watt generators in parallel can use a 14-50 receptacle. Be aware that these parallel capable inverter generators are not neutral-ground bonded which can make some amps and stage gear operate erratically or not at all. In that case you'll want to use a neutral bonding plug to create a bonded neutral for your stage power.   

So I've been doing a little research on the multitude of 2000w range inverter generators on the market now. (Storm came across and wiped out power to a lot of homes a few days ago).

It seems that the link kits for these do NOT allow for 240v but instead for higher current at 120v. But, some of them appear to provide this power on 240V style connectors - apparently putting the same 'phase' on both hot terminals. These seem to be aimed at RV usage. But I'm having a hard time understanding how this won't lead to overloaded neutrals in systems where the neutrals are shared which is very common with 240v "split phase" power. 

What am I missing here?

[Tim McCulloch]

Drew... it took a little longer for your 'bigger question' to sink in with me.   

Yes, in a multi-wire branch circuit one could overload the neutral of the branch circuit using this kind of "service".  The generator combiner is safe for the reasons Mike & I pointed out but that's a narrower view of your question.

Powering a distro would be dicey depending on how subsequent wiring and loading was done.

You pointed out another reason why combining small, portable generators can be considered a kludge; for some applications (like powering campers and RVs that don't have multi-wire branch circuits or genuine 240V loads) they'll work as intended, for others... there are complications.

[Rob Spence]

That's why those parallel kits are only available for smaller 2,000 to 3,000 watt inverter generators. Yes, they do parallel the outputs and can only make 120 volts. And yes, the neutral current will be additive rather than subtractive as they would be in a split-phase 120/240-volt service. But as others have mentioned there's not enough combined amperage with these small generator to overload the neutral conductor. That's why a pair of 2,000 watt generators in parallel can use a 30-amp twist=lock or TT-30 connector, and a pair of 3,000 watt generators in parallel can use a 14-50 receptacle. Be aware that these parallel capable inverter generators are not neutral-ground bonded which can make some amps and stage gear operate erratically or not at all. In that case you'll want to use a neutral bonding plug to create a bonded neutral for your stage power.

Hey Mike. Nice to hear from you!

[ProSoundWeb Community]