As a follow up to a previous post, I have a generator – portable – and want to run parts of my house on it. There’s 3 ways- Direct into panel, automatic transfer switch, or manual transfer switch.
Direct into panel, or as the industry calls it “the dead man’s connection”, is a cable that connects your generator directly into your breaker panel. The “dead man’s” moniker comes from is you have your generator connected and the land power at the SAME TIME – your portable generator will fail. And when it fails, it can be “trips a protection circuit” to “the generator explodes”. Here’s an article from a generator supplier:
Beware of Backfeeding – How NOT to Connect a Portable Generator (electricgeneratorsdirect.com)
That’s not to say this option is unusable – there’s some safety devices for direct connections. First, the port or cable connects to a breaker set near the top of the panel, then there’s physical latch (interlock) where the main breaker and the generator breaker cannot be on at the same time:
When the main breaker is off, the interlock can slide up and allow the generator breaker to turn on.
Now, this option has a caveat – your portable generator most likely will not run everything in the house, so you will need to turn off breakers in the panel to what you don’t want to run. And, you’ll need a manual way of knowing when the land power is back on (neighbor, sms alert, etc). During the last Houston hurricane (Nicholas), my neighbor had a dead’s man’s cable and I made sure he turned off his main power breaker before he hooked it up.
Now for automatic transfer switches – these are usually reserved for whole-home generators – as they hook between your panel and the power meter. Like the panel interlock, you’ll need to size your generator for your house load – the whole point of ATSes are they flip the house to generator – you won’t have time to turn off ACs or laundry, etc. Plus, they’re the most expensive option.
Finally, the manual transfer switch. I believe this is the best option for connecting a portable generator to a house. You will isolate individual circuits in the breaker box and run then through the transfer switch. For example:
Here, the refrigerator is on line F – the line into the house will plug into the breaker. With an MTS, you wire the “line” side of the ATS to the breaker in the panel (feed from land power line) and the return from MTS with a wire nut to the line going to the house. The MTS has a source switch on each line, so in “line” mode, it’s allowing the land line to run through the MTS, through the MTS breaker, and then into the house. when the MTS line is set to “gen,” for generator, it ISOLATES the circuit in the house from the land line and uses the generator input in the MTS.
The advantage of this – we isolate the loads in the house from the land line – no feedback is possible. Second, since we’re not running every circuit in the house, we can leave a light on that’s still wired in the panel, and when it comes on, we know that power’s back.
My process for moving to and from generator:
- Setup generator and start up – main breaker off
- Set all breakers off in MTS
- Turn off panel breaker (as a precaution when power comes back on or to remove load on MTS)
- Flip MTS sources to GEN
- Generator breaker on – this energizes the generator in
- MTS breaker on one at a time – monitor load on meters
Returning to power from generator:
- Turn off MTS breakers
- Generator master breaker off (no load from generator)
- Flip MTS circuits to “LINE”
- Flip main panel breakers to on
I believe it’s best to not have a load on the MTS when switching – to do with arcing from the contacts while switching and lowering their lifespan.
How much? Well, the MTS can be purchased online for around $400. Add about an hour of electrician time to hook it up. Plus the extension cables – they were about $450. I use a 10′ 50a RV cable (NEMA 14-50p to C6375r) for the connection from generator to MTS, then a 35′ NEMA 14-50 extension cable.
The economics? $3000 vs $15,000. Manual and safe vs automatic, whole home and yearly maintenance fees.