Generator inlet sizing help

[Mike1903]

I bought a portable generator that has two outputs:
L14-30R - max 30 amps at 240
14-50R - max 32 amps at 240v

gen will be about 100’ away from the panel. Should I go with 50a breaker or 30a breaker on panel (cables will be sized correctly)?

i am leaning towards 30a primarily as it will suffice my needs; i don’t need two extra amps and don’t see getting a bigger gen.

Am I missing anything by not going with 50a?

 

[nadogail]

IMHO, Bigger is Better, I try to allow for growth or "Mission Creep". I remember when a 100 Amp Electrical Service Panel was considered really big. It is now the minimum permissible size.

 

[Mike1903]

IMHO, Bigger is Better, I try to allow for growth or "Mission Creep". I remember when a 100 Amp Electrical Service Panel was considered really big. It is now the minimum permissible size.

Good reminder…. Still trying to find a use case for anyone needing more than 640kb of RAM

 

[pattenp]

Mainly because of distance I'd use the 50A outlet and size wiring accordingly.

 

[Mike1903]

Mainly because of distance I'd use the 50A outlet and size wiring accordingly.

Can you please explain why distance would be a factor here if each option is appropriately sized and voltage drops are minimized?

 

[slow]

#6 wire is significantly higher cost than #10. What loads do you plan to run on your generator? Resistive heat would push me to the 50 amp, but in all reality, unless you are at the threshold of the generator, 30 should be fine for most.

 

[Terry D]

I would do a 30 amp breaker, I would think if you went larger that you would have a chance of overloading the generator. You might want to go to a #8 wire for voltage drop. What size is the generator

 

[Mike1903]

#6 wire is significantly higher cost than #10. What loads do you plan to run on your generator? Resistive heat would push me to the 50 amp, but in all reality, unless you are at the threshold of the generator, 30 should be fine for most.

Heat pump, lights, fridge and freezer. Furnace, stove and water heater are on gas.
In winter times, I could turn off heat pump and switch to furnace which is on a 15a circuit. In summer times, I will need to manage heat pump/AC.... it is currently on a 30A breaker.

By resistive heat, you mean wiring is sized for a 30A breaker, it is running mostly at 30A or close to that and hence, will be generating heat versus a circuit sized for 50A but pushing 30A through it generating less heat?

 

[Mike1903]

I would do a 30 amp breaker, I would think if you went larger that you would have a chance of overloading the generator. You might want to go to a #8 wire for voltage drop. What size is the generator

• 9400 Starting Watts / 7500 Running Watts - Gasoline
• 8450 Starting Watts / 6750 Running Watts - LPG
• 6900 Starting Watts / 5500 Running Watts - Natural Gas

The numbers are bit misleading because they are summing up the output of all the outlets. In reality, the max I could use is 32A x 240V = 7,680W off the 50A outlet or 30A x 240v = 7,200W off the 30A outlet.

 

[slow]

resistive heat, meaning Electric heat strips in your HVAC, sometimes called Emergency heat. Typical generator loads are a high inrush and then a much lower continuous operating, other than if using resistive heaters, that are a continuous high load.

 

[Mike1903]

resistive heat, meaning Electric heat strips in your HVAC, sometimes called Emergency heat. Typical generator loads are a high inrush and then a much lower continuous operating, other than if using resistive heaters, that are a continuous high load.

got it, thank you.
i don't have resistive heat. it is a heat pump/ac on a 30A breaker up to 40F and then a high efficiency furnace on a 15A breaker when it gets colder.

 

[pattenp]

Can you please explain why distance would be a factor here if each option is appropriately sized and voltage drops are minimized?

At a 100ft you're getting into voltage drop territory, although minor. Using the 50A outlet with #6 wiring to the panel eliminates any voltage drop if you push the gen to the 30A limit. I was suggesting it since the gen has a 50A outlet. With that said if cost is an issue then go with using the 30A outlet. It's six of one or a half dozen of another.
Terry has a good suggestion with the 30A using #8 to negate any VD.

 

[theoldwizard1]

I don't have resistive heat. it is a heat pump/ac on a 30A breaker up to 40F and then a high efficiency furnace on a 15A breaker when it gets colder.

I hope you don't think you an run your heat pump ! Maybe with a MicroAir EasyStart

 

[Mike1903]

I hope you don't think you an run your heat pump ! Maybe with a MicroAir EasyStart

Not sure if I follow you. The heat pump is on a 30a breaker. If the startup/surge current exceeded 30a, wouldn’t that trip the breaker?

 

[pattenp]

Not sure if I follow you. The heat pump is on a 30a breaker. If the startup/surge current exceeded 30a, wouldn’t that trip the breaker?

Does that 30A circuit also power the inside air handler?

 

[Mike1903]

Does that 30A circuit also power the inside air handler?

Great point.
I wasn’t thinking of the air handler as it part of the furnace and on its own 15a circuit. I have ordered an energy monitor and will see what the combined amperage draw is from furnace and heat pump circuits.

 

[Terry D]

If you are running it on gasoline, 7500 watts/240 volts = 31.25 amps. I am sure there is some form of overload protection on the generator. Putting a 50 amp breaker inside will not get you more power. Maybe a 40 amp inside with # 8 wire since its a couple of amps above 30 amps, but these generators usually get installed using just a 30 amp. I would still do # 8 wire since the generator is 150' away. If you have a regular split system with a condenser/heat pump and a air handler inside. ( not a mini split ) Then I would think you probably have a 2-pole 30 amp for the outside unit and a separate 240 volt circuit for the air handler. As "Slow" pointed out, if the air handler has a heat package in it for emergency heat, that generator will not be able to power those heat strips. You will be able to tell by the breaker for the air handler, if its anything bigger than a 2-pole 15 or 20 amp, then there is most likely a heat package in there. Do you live in a climate with cold winters

 

[wyliesdiesels]

Not sure if I follow you. The heat pump is on a 30a breaker. If the startup/surge current exceeded 30a, wouldn’t that trip the breaker?

Nope because breakers dont instantly trip. They have a trip curve and inrush current only occurs for 100-200ms. Also, inrush current is 4x-8x FLA. that will be higher than the 30a breaker rating

Does your furnace have emergency/backup heat strips?

 

[Mike1903]

Nope because breakers dont instantly trip. They have a trip curve and inrush current only occurs for 100-200ms. Also, inrush current is 4x-8x FLA. that will be higher than the 30a breaker rating

Does your furnace have emergency/backup heat strips?

Air handler is on a 15a circuit as the backup is a high efficiency furnace and not heat strips/resistive heating. I should be fine for winters because I can turn off heat pump and use the furnace.
the use case I need to measure is current draw when heat pump is used as an ac combined with air handler. Power usually doesn’t go out in summers but when it does, it is on a hot day when grid is at its limits and air quality is bad outside (which means can’t open windows).

Whole house energy monitor is on its way and will measure the current draw. Will update soon.

Thank you very much!

 

[FMB4]

A typical recommendation is to go 25 - 30% 'bigger' than what think you'll need. Better to do it once than to later realized the you need more.

 

[Noltz]

Go 50A if you can afford it. Even if you use an adapter, you'll be set up to use a 50A should the need arise. I went with a 30A inlet, but fed with 8 gauge wiring to 'future proof' it. However I used Romex and found out after the NEC limits that to 45A... so I can't do a 50A inlet now. Learn from my mistake.

The 30A 100' cords are a few hundred dollars. 50A is significantly more. For the rare users I think 30A would be sufficient, but an adapter on a 50A inlet provides an option to move the generator closer and use a smaller, cheaper cord should the power outage be longer than expected.

 

[theoldwizard1]

Not sure if I follow you. The heat pump is on a 30a breaker. If the startup/surge current exceeded 30a, wouldn’t that trip the breaker?

That 30A breaker is normally connected to an INFINITE power source, you power company.

When connected to generator the instantaneous start current (many times higher) will pull down the voltage which will increase the current draw and trip the breaker in the generator.

MicroAir EasyStart reduces the "instantaneous" starting current.

 

[Mike1903]

Go 50A if you can afford it. Even if you use an adapter, you'll be set up to use a 50A should the need arise. I went with a 30A inlet, but fed with 8 gauge wiring to 'future proof' it. However I used Romex and found out after the NEC limits that to 45A... so I can't do a 50A inlet now. Learn from my mistake.

The 30A 100' cords are a few hundred dollars. 50A is significantly more. For the rare users I think 30A would be sufficient, but an adapter on a 50A inlet provides an option to move the generator closer and use a smaller, cheaper cord should the power outage be longer than expected.

Thank you for sharing your experience; I really appreciate it.
Cost is important but it is not the primary factor. I rather do it right. Still owe it to the owner prior to the prior owner of the home to spend good coin on a high efficiency furnace and a heat pump/w AC. Still saving me money…

I like the idea of setting everything up for 50a and doing a 50a to 30a adapter. I am on F-150 lightning reservation and depending on the cost will likely either do 30a off the truck outlet or full 80a solution (in which case i will have two home backup options).

 

[Mike1903]

That 30A breaker is normally connected to an INFINITE power source, you power company.

When connected to generator the instantaneous start current (many times higher) will pull down the voltage which will increase the current draw and trip the breaker in the generator.

MicroAir EasyStart reduces the "instantaneous" starting current.

Scary thing is that there is no breaker on the gen.
I’m pretty sure that I am all setup for power outages during winter. I need to take measurements to see if heat pump in ac mode + air handler can be served by the gen.

the crazy thing is that hotels were all sold out when power went out this summer and it was 400$+/night. May have to get a bigger gen to make sure that staying home is an option and lend an extension to the neighbors to run lights/fridge.

 

[Terry D]

Is your generator plug on the outside of the house 150' away from the panel of is the generator 150' away from the plug on the outside of the house.

 

[Terry D]

Go 50A if you can afford it. Even if you use an adapter, you'll be set up to use a 50A should the need arise. I went with a 30A inlet, but fed with 8 gauge wiring to 'future proof' it. However I used Romex and found out after the NEC limits that to 45A... so I can't do a 50A inlet now. Learn from my mistake.

The 30A 100' cords are a few hundred dollars. 50A is significantly more. For the rare users I think 30A would be sufficient, but an adapter on a 50A inlet provides an option to move the generator closer and use a smaller, cheaper cord should the power outage be longer than expected.

#8 NM-b is limited to 40 amps, not 45 amps. All NM-b must use the 60 degree column of the ampacity chart of the NEC. I know this is only 5 amps from what you are talking about, but since there is not a 45 amp breaker, the NEC allows you to go up to the next size, which would be 50 amps. And in this case, a violation

 

[Mike1903]

Is your generator plug on the outside of the house 150' away from the panel of is the generator 150' away from the plug on the outside of the house.

The distance between panel and the gen is about 125’. Depending on where we put the inlet, the length of the hardwired section and the extension cord will vary.

 

[Terry D]

The distance between panel and the gen is about 125’. Depending on where we put the inlet, the length of the hardwired section and the extension cord will vary.

I would try to make the hardwired part as long as possible

 

[theoldwizard1]

Scary thing is that there is no breaker on the gen.
I’m pretty sure that I am all setup for power outages during winter. I need to take measurements to see if heat pump in ac mode + air handler can be served by the gen.

See if you can find the LRA (locked rotor amperage). That is about close as you can find for the starting current.

 

[dcg9381]

I bought a portable generator that has two outputs:
L14-30R - max 30 amps at 240
14-50R - max 32 amps at 240v

Recommend finding the parts diagram for that generator and see if it indicates the actual breakers that are in use by those circuits if they are separate. I've had a "surprise" with at least one 5500 watt generator.

I use the 14-50R outlets everywhere. Obviously, you can use either... But I like to "future proof". The other advantage, I've seen (over time) a lot of pretty chewed up and melted 30A RV outlets (120V) - so I tend to "over outlet". We have several 14-50R that are fed by 30A breakers.

I'd change my mind if you tend to use 14-30Rs for other things. We use 14-50 as we do a lot of RV setups.

 

[Mike1903]

I would try to make the hardwired part as long as possible

Thx. I’m trying to decide if inlet should be placed on the side of the house or extend the circuit outdoors close to the gen. The first option would be all run in the crawlspace and the second option would also require conduit or UF. Will see what electrician prices it out at.

 

[Mike1903]

Recommend finding the parts diagram for that generator and see if it indicates the actual breakers that are in use by those circuits if they are separate. I've had a "surprise" with at least one 5500 watt generator.

I use the 14-50R outlets everywhere. Obviously, you can use either... But I like to "future proof". The other advantage, I've seen (over time) a lot of pretty chewed up and melted 30A RV outlets (120V) - so I tend to "over outlet". We have several 14-50R that are fed by 30A breakers.

I'd change my mind if you tend to use 14-30Rs for other things. We use 14-50 as we do a lot of RV setups.

Do you run 30a inlets or go with 50a inlets + 50 to 30 adapter?

 

[AP514]

Hey OP
Sounds like you have a *Firman* Tri Generator from Costco...I just set one of those up for my buddy.
the 50Amp setup is Way More Money..only do this if your planning on a larger generator in the near future.
I would stay with the 30 Amp 4 prong plug on that unit

 

[u3b3rg33k]

I bought a portable generator that has two outputs:
L14-30R - max 30 amps at 240
14-50R - max 32 amps at 240v

gen will be about 100’ away from the panel. Should I go with 50a breaker or 30a breaker on panel (cables will be sized correctly)?

i am leaning towards 30a primarily as it will suffice my needs; i don’t need two extra amps and don’t see getting a bigger gen.

Am I missing anything by not going with 50a?

portable generator says to me you're keeping it. If i'm buying a place, a 30A hookup is almost worthless, a 50A hookup means something. 50A means I can hook up much bigger generator without having to rip it all out and do it again.

And your numbers are wrong. 30A means 24A, 50A means 40A. that's over 66% more power allowed continuously. who's to say you won't decide your generator is too small and you want to upgrade in a year?

 

[Noltz]

#8 NM-b is limited to 40 amps, not 45 amps. All NM-b must use the 60 degree column of the ampacity chart of the NEC. I know this is only 5 amps from what you are talking about, but since there is not a 45 amp breaker, the NEC allows you to go up to the next size, which would be 50 amps. And in this case, a violation

I'm sure you're right. I was looking at SimPul's site, not the NEC (well I'm Canadian but still) and their chart says 8-3 can handle 45. Doesn't matter though, the options are 30 and 50. So I have a very low-loss 30A inlet lol. I also have a 6-3 THHN feeding a 14-50 in the garage for an EV I don't own yet. I could convert that to an input. But I mention my story only to OP so they consider putting in the biggest option that's feasible. I have a 30A breaker and an interlock on mine.

 

[Mike1903]

Hey OP
Sounds like you have a *Firman* Tri Generator from Costco...I just set one of those up for my buddy.
the 50Amp setup is Way More Money..only do this if your planning on a larger generator in the near future.
I would stay with the 30 Amp 4 prong plug on that unit

ha… psychic! That’s the one I have.

 

[dcg9381]

Do you run 30a inlets or go with 50a inlets + 50 to 30 adapter?

I build my own cords. So it'd be a 30A @ 240V "male" on the generator side to the appropriate 50A plug on the house inlet side. I'm assuming you have the right overload on the generator. He's right about 50A costing more. Dunno about "a lot" more. You'll probably never use more than 30A @ 240v on a place that size, so either way you're good.

 

[u3b3rg33k]

I have a CS63 6ga cord that I picked up (new) for a song. if I didn't shop around I could've easily paid 3-4x what I did for it. heck I couldn't afford to build it with the ends at list prices for what I paid, nevermind 100' of 2-2-2-6(?) copper.

 

[theoldwizard1]

I build my own cords. So it'd be a 30A @ 240V "male" on the generator side to the appropriate 50A plug on the house inlet side. I'm assuming you have the right overload on the generator. He's right about 50A costing more. Dunno about "a lot" more. You'll probably never use more than 30A @ 240v on a place that size, so either way you're good.

OP wants to run a heat pump ! Running current plus other loads could be more than 30A.

 

[dcg9381]

OP wants to run a heat pump ! Running current plus other loads could be more than 30A.

yikes.. Yea. You'll likely need 240V for that (there are 120V options). I'm in the south - there are various conditions below freezing where a heat pump will not get it done. Make sure you (OP) get one designed for the type of cold conditions where you are.... I spent most of snow-apocalypse in Texas alternating heat pumps because they were darn near useless... We had to suppliment with propane in the shop to keep it above 50 degrees.