JackOfDiamonds
Well-known member
I'm wiring up a Reliance ProTran 2 generator transfer switch. These are common units available at Lowes etc. I see 2 things that seem to violate normal wiring principles.
1. Requires stepping down wire gauges in the main panel. The Reliance panel is pre-wired with 12-guage stranded wires. This is good for 20A breakers, even though most of the breakers in the transfer switch are are 15A. It is acceptable to use 12ga wire on 15A circuits. However it's NOT normally acceptable to step wire size down to a smaller gauge. When I wire up the transfer switch, I'm going to have to connect 12ga wire from the transfer switch directly to the existing 14ga house wiring. This is normally not allowed, but I guess it's an exception? Just a technicality? This doesn't bother me so much, because I don't see a safety issue as long as I use 15A breakers in the Reliance panel for 14ga house circuits. But I wonder how this is considered up to code.
2. Unconventional neutral wire gauge. The generator INPUT receptacle for the Reliance panel is a 30-amp, 4-wire unit. The Reliance panel is pre-wired with a 12ga neutral wire to the main panel. This wire doesn't connect anywhere in the Reliance panel itself, and seems designed only to connect from the main panel back to the the 30A input receptacle. I don't think the 12ga neutral is appropriate for a 30A feeder (explained below).
So my choice here is either wire the input receptacle with 10ga wire, like a normal branch circuit would require, but then I will be connecting that 10ga neutral wire to 12ga wire in the Reliance panel anyway, which is odd/silly and also breaks the principle of not changing wire gauges. Or I can wire the generator input receptacle with 12ga wire all the way to the main panel, since that's probably sufficient and it's what Reliance provided. Or I could rip out the 12ga wire Reliance provided, and wire 10ga all the way back to the panel neutral bar, like would be required for a branch circuit.
My thought process as to the 12ga neutral wire being undersize is as follows. 30A branch circuits require a neutral wire equal in size to the phase wires and the phase wire breaker. There is no separate breaker on neutral wires, and so a branch circuit's neutral wire is protected only by the main breaker on the phase wires. And while it's unlikely, we don't require loads to observe any max load on the neutral, so a 4-wire load might theoretically draw 30A of 120V load before the 30A breaker would trip, so the neutral wire has to be "oversized" to 30A to match the 30A phase breaker.
I understand the input receptacle is not a branch circuit, but its a feeder circuit. Feeder circuits to a panel are allowed to have neutral wires smaller than the phase wires under certain conditions, but this generator panel doesn't seem to be one of those. Feeder circuits can have smaller neutral wires IFF the neutral wire is sufficient to support all possible 120V loads in the panel. In other words, if you have a 100A sub-panel with mostly 240V breakers, and the only 120V load in that panel was a single 15A breaker, you could technically run only a 14ga neutral wire to that sub-panel. That would be stupid and nobody does it, because it doesn't allow future expansion, and because somebody could add more 120V breakers in the future and overload the neutral wire, but the code allows it because the code doesn't always require provision for future expansion, and only electricians are supposed to be adding/removing breakers, and electricians are supposed to do load calculations to confirm the panel supports any changes. The neutral wire can be smaller than the phase wires as long as it can carry the SUM of all the 120V breakers OR the main phase breaker, whichever is smaller.
Even though the generator input is a feeder circuit, so a smaller neutral MIGHT be allowed, there's no reason the neutral should be undersized in this case, because it's typical that almost the entire panel will consist of 120V loads, so the sum of the 120V breakers will almost certainly be greater than the 20A max for a 12ga wire, and so the neutral wire needs to be protected up to the main phase breaker size i.e. 30A so it can be protected by the 30A breaker on the generator. The only justification for an undersize neutral in this case would come from assuming the generator has a 20A breaker on the neutral specifically and I've never heard of that. Or just assuming a 20A+ load on a single leg is sufficiently rare that it should never happen, but it seems odd to "trust the generator" that much, especially with all the crazy generator adapters that exist.
1. Requires stepping down wire gauges in the main panel. The Reliance panel is pre-wired with 12-guage stranded wires. This is good for 20A breakers, even though most of the breakers in the transfer switch are are 15A. It is acceptable to use 12ga wire on 15A circuits. However it's NOT normally acceptable to step wire size down to a smaller gauge. When I wire up the transfer switch, I'm going to have to connect 12ga wire from the transfer switch directly to the existing 14ga house wiring. This is normally not allowed, but I guess it's an exception? Just a technicality? This doesn't bother me so much, because I don't see a safety issue as long as I use 15A breakers in the Reliance panel for 14ga house circuits. But I wonder how this is considered up to code.
2. Unconventional neutral wire gauge. The generator INPUT receptacle for the Reliance panel is a 30-amp, 4-wire unit. The Reliance panel is pre-wired with a 12ga neutral wire to the main panel. This wire doesn't connect anywhere in the Reliance panel itself, and seems designed only to connect from the main panel back to the the 30A input receptacle. I don't think the 12ga neutral is appropriate for a 30A feeder (explained below).
So my choice here is either wire the input receptacle with 10ga wire, like a normal branch circuit would require, but then I will be connecting that 10ga neutral wire to 12ga wire in the Reliance panel anyway, which is odd/silly and also breaks the principle of not changing wire gauges. Or I can wire the generator input receptacle with 12ga wire all the way to the main panel, since that's probably sufficient and it's what Reliance provided. Or I could rip out the 12ga wire Reliance provided, and wire 10ga all the way back to the panel neutral bar, like would be required for a branch circuit.
My thought process as to the 12ga neutral wire being undersize is as follows. 30A branch circuits require a neutral wire equal in size to the phase wires and the phase wire breaker. There is no separate breaker on neutral wires, and so a branch circuit's neutral wire is protected only by the main breaker on the phase wires. And while it's unlikely, we don't require loads to observe any max load on the neutral, so a 4-wire load might theoretically draw 30A of 120V load before the 30A breaker would trip, so the neutral wire has to be "oversized" to 30A to match the 30A phase breaker.
I understand the input receptacle is not a branch circuit, but its a feeder circuit. Feeder circuits to a panel are allowed to have neutral wires smaller than the phase wires under certain conditions, but this generator panel doesn't seem to be one of those. Feeder circuits can have smaller neutral wires IFF the neutral wire is sufficient to support all possible 120V loads in the panel. In other words, if you have a 100A sub-panel with mostly 240V breakers, and the only 120V load in that panel was a single 15A breaker, you could technically run only a 14ga neutral wire to that sub-panel. That would be stupid and nobody does it, because it doesn't allow future expansion, and because somebody could add more 120V breakers in the future and overload the neutral wire, but the code allows it because the code doesn't always require provision for future expansion, and only electricians are supposed to be adding/removing breakers, and electricians are supposed to do load calculations to confirm the panel supports any changes. The neutral wire can be smaller than the phase wires as long as it can carry the SUM of all the 120V breakers OR the main phase breaker, whichever is smaller.
Even though the generator input is a feeder circuit, so a smaller neutral MIGHT be allowed, there's no reason the neutral should be undersized in this case, because it's typical that almost the entire panel will consist of 120V loads, so the sum of the 120V breakers will almost certainly be greater than the 20A max for a 12ga wire, and so the neutral wire needs to be protected up to the main phase breaker size i.e. 30A so it can be protected by the 30A breaker on the generator. The only justification for an undersize neutral in this case would come from assuming the generator has a 20A breaker on the neutral specifically and I've never heard of that. Or just assuming a 20A+ load on a single leg is sufficiently rare that it should never happen, but it seems odd to "trust the generator" that much, especially with all the crazy generator adapters that exist.
