Connecting Jackery 1500/2000 into Distribution Panel

[macheung]

OK now I need a drink. Have never envisioned this before. With the circuit shown, assuming both hot out-of-phases are loaded equally, there would be zero amps measured on the neutral wire?

View attachment 61506

Well I see how one tries to save on wires by essentially sharing the neutral line of a 4 conductor wire on two circuits, instead of using 2 x 2 conductor wires. Normally, this doesn’t matter as the red and black hits are opposite in phase so the neutral cancels out, and will never be higher than 1x load of the red or black. So the neutral will never be over loaded. However, if one uses a backfeed breaker that shorts the red and black hots, then it is possible for the neutral to carry 2x the max current which will overload it as the red and black are now in phase and adds.

This is not going to happen with a backfeed of only 15A as the backfeed input breaker will trip before this line overloads. But I can see how this can be an issue if the backfeed is say 30A and each of the shared breaker is pulling in their max, causing the neutral to overload as it will take 30A when it is rated for sal 15A. Not super likely to happen, but possible.

 

[Hedges]

This is not going to happen with a backfeed of only 15A as the backfeed input breaker will trip before this line overloads.

Single pole 15A breaker, e.g. in the inverter, that is correct.

A 2-pole 15A backfeed breaker in the panel, with both poles wired to a single 120V 30A source, could put 15A into Red and 15A into black, for 30A into White.

 

[macheung]

Single pole 15A breaker, e.g. in the inverter, that is correct.

A 2-pole 15A backfeed breaker in the panel, with both poles wired to a single 120V 30A source, could put 15A into Red and 15A into black, for 30A into White.

Very true, but if your inverter is only rated for 15A, the inverter will shut down when it puts more than 7.5A into the red, 7.5A into the black and 15A into the white. This isn't ideal as the inverter is protecting the circuit, not the breaker. Effectively, you want the wire to be sized to the inverter, not the breaker. The breaker is just functioning as on-off switch.

 

[macheung]

It was correctly noted earlier that if you connect the jackery or a single phase AC source of a two pole breaker by using a jumper wire to short the poles together, it maybe possible to overload the neutral before any single pole of the breaker trips as both hots are in phase and neutral current adds up. Normally the hots are out of phase and neutral current is almost zero.

Now, in case of a jackery, the inverter would trip before major damage happens as the max output is only 1800w or around 16A (2200w or 20A for the larger jackery 2000). However, to be safer, one can wire up an inline fuse to the neutral, this way if an overload does happen and the inverter doesn’t cut out, the fuse will blow.

 

[Hedges]

Fused neutral? I don't usually see that.

If trying to protect branch circuits when feeding both legs of panel from a source > 2500W, you would have to add fuses to branch circuit neutrals within the breaker panel. If those blow, the neutral wire through the house would become electrically hot because the line would still be connected. Not likely a problem with most devices, but some older appliances (like early TVs) had neutral tied to chassis.

Instead, I would put a 20A fuse/breaker in line (not neutral) from the inverter/generator.)

Portable GFCI interrupt both line and neutral, to take care of the problem where an outlet could be wired backwards and "line" is hot. Opening both ensures nothing hot in the connected device (so long as ground isn't miswired!)

House wiring is usually 12 awg with 20A breaker. The ampacity of 12 awg is actually 30A. Sometimes 14 awg is used, with 14A breaker. Ampacity of 14 awg is actually 20A.

That's why I say I wouldn't worry about an inverter or generator feeding both legs of a breaker panel if no more than 2500W, 20A continuous at 120V.

If you have a higher wattage inverter or generator, and it is only 120V, consider using a transformer for 120/240V. It could be left wired to an interlocked backfed breaker, and it could have a plug for connecting the inverter (you'd have to go out of your way to get a plug for > 20A)

 

[macheung]

Got this info from Jackery for surge capacity for the Jackery 1500.

It looks like this can handle up to 3000w for 30 seconds, which is very good to handle surge or even temporary large loads such as a sump pump.