Transfer SW on Main and Sub Panel with two Gennys?

[bugman-74]

Hey Fellas,
Just trying to get confirmation I wont run into any unexpected electrical gotchas: I have a 400A main panel on the house with a Reliance 50A manual transfer switch (#R510A) that I use a generator with. A ways away I have a detached building with a 125A subpanel. The subpanel is fed from the 400A main. No funny business - main panel is bonded, and there are no MWBC's in either building.

For simplicity of operation for others in the household (not interested in an interlock) I would like to also install a small manual transfer switch on that detached building for use with a second (small) generator. Both generators would potentially be used simultanously (one connected to the 400A panel's transfer SW, and the other connected to the 125A panel's transfer SW).

Am I in for any surprises?

 

[mm08822]

I think you want a 3pole manual transfer switch at the garage to switch the neutral also.
Otherwise, with each gen most likely having bonded neutrals, there could be unexpected current flow.
I'd have to draw this out later to check if only a 2 pole switch is a problem.

 

[mike93lx]

If you have two properly installed transfer switches, it will be fine. Not sure if it will matter, but I'd be inclined to use a transfer switch in the shop that also switches the neutral.

Edit... Typed this up and didn't post before @mm08822

 

[theoldwizard1]

I do not like the style of trasfer switches you have at the house. Difficult to install and you have a limited number of circuits that can be switched to generator power. Not a sparky, but my understanding of that type of transfer switches is that the circuits NOT covered are still connected to power company feed.

What is your issue with an interlock in the panel in the detached building ? It completely disconnects power coming from building #1. TRUE ISOLATION !

 

[bugman-74]

I think you want a 3pole manual transfer switch at the garage to switch the neutral also.
Otherwise, with each gen most likely having bonded neutrals, there could be unexpected current flow.
I'd have to draw this out later to check if only a 2 pole switch is a problem.

I believe the Genny (portable inverter style) is floating neutral, as the transfer switch only switches the hots. I also use a battery power station occasionally in lieu of one genny, which is certainly using floating neutral.

 

[bugman-74]

What is your issue with an interlock in the panel in the detached building ? It completely disconnects power coming from building #1. TRUE ISOLATION !

Primary transfer switch is owned and has been installed for years. In my case it is more straight forward for my family to use vs. turning off a slew of breakers and remembering which/how many they can turn on without overload. Agree they are harder to install, and the additional wiring makes a mess inside the panel.

 

[theoldwizard1]

I think you want a 3pole manual transfer switch at the garage to switch the neutral also.
Otherwise, with each gen most likely having bonded neutrals, there could be unexpected current flow.
I'd have to draw this out later to check if only a 2 pole switch is a problem.

A generator interlock IS a 2 pole transfer switch.

 

[mm08822]

A generator interlock IS a 2 pole transfer switch.

It can be and many times is. But not exclusively. Read up on separately derived systems.

You don't understand "True Isolation" either.

 

[theoldwizard1]

Primary transfer switch is owned and has been installed for years. In my case it is more straight forward for my family to use vs. turning off a slew of breakers and remembering which/how many they can turn on without overload.

I am NOT recommending changing anything in Building #1 !

Agree they are harder to install, and the additional wiring makes a mess inside the panel.

Put the interlock in Building #2. Don't worry about turning circuits off except for water heater, heat pump-A/C, compressor, welder. Even with a small (<5000W) portable generator, it is highly unlike you would overload. Even if you do, that is why the interlock and the generator have breakers !

If you are using a 120VAC only generator, you can actually connect L1 to L2 in the cord connecting the generator to the inlet receptacle. Everything will work SAFELY (you said no MWBC) except for 240VAC loads.

 

[theoldwizard1]

It can be and many times is. But not exclusively. Read up on separately derived systems.

You don't understand "True Isolation" either.

You are correct !

 

[mike93lx]

Don't worry about turning circuits off except this list of circuits to turn off.

 

[mike93lx]

@bugman-74 just curious, do you actually have a 400a main panel or a pair of 200's?

 

[mm08822]

You are correct !

So dont make statements like that. It could kill someone!

 

[mm08822]

Don't worry about turning circuits off except this list of circuits to turn off.

Some even use color coding.

 

[mike93lx]

I love this.

OP: I don't want an interlock.

Response: Just get an interlock for no justifiable reason beyond my preferences.

 

[bugman-74]

@bugman-74 just curious, do you actually have a 400a main panel or a pair of 200's?

400A main - Eaton HP402442

 

[mike93lx]

400A main - Eaton HP402442

That's legit!

 

[wyliesdiesels]

I would like to also install a small manual transfer switch on that detached building for use with a second (small) generator.

the "small" transfer switch will need to be rated for the same amperage as your feeder (125a) so it wont exactly be small and like others said, it should switch the neutral as well so will need to be 3 pole.

 

[wyliesdiesels]

I believe the Genny (portable inverter style) is floating neutral, as the transfer switch only switches the hots. I also use a battery power station occasionally in lieu of one genny, which is certainly using floating neutral.

you dont want 2 gens on the same service with connected neutrals by way of feeder

the genset or battery station @ the garage will need to be switched to a bonded neutral along with the 3 pole TS that switches the neutral. you dont want a floating neutral because then breakers will not trip upon ground fault. also, having an unswitched neutral on the feeder will cause some weird issues with breakers tripping when there is a ground fault. best to just isolate both panels and power sources completely

 

[wyliesdiesels]

turning off a slew of breakers and remembering which/how many they can turn on without overload.

but how much equipment will they really be running the garage during a power outage with small genset? i highly doubt this will be an issue. regardless, with an interlock you will still have the switched neutral issue

 

[bugman-74]

the "small" transfer switch will need to be rated for the same amperage as your feeder (125a)

Not sure I'm following. Lets say I want to be able to transfer 6 circuits between line and genny using this transfer switch on the subpanel. Why would said transfer switch need to be rated any higher than the circuits it is transfering?

 

[bugman-74]

you dont want a floating neutral because then breakers will not trip upon ground fault. also, having the neutral not switch on the feeder will cause some weird issues with breakers tripping when there is a ground fault.

But this isnt unique to my subpanel/2 generator/2 transfer switch configuration, correct? Isnt it the result of any floating neutral generator setup (regardless if connected to subpanel or not)?

This article was helpful

 

[bugman-74]

but how much equipment will they really be running the garage during a power outage with small genset? i highly doubt this will be an issue. regardless, with an interlock you will still have the switched neutral issue

Its not about how much stuff will be running, its about the error-proofing and simplifying for others in my household with limited knowledge. Subpanel has over 20 circuits (potential for 40 with tandems, if it was full). Having only 4 or 6 options pre-selected, removing all avenues for mistakes, no long-winded printed instructions (do this first, then turn these off, then...), and no overload concern is a necessity for me

 

[mm08822]

Not sure I'm following. Lets say I want to be able to transfer 6 circuits between line and genny using this transfer switch on the subpanel. Why would said transfer switch need to be rated any higher than the circuits it is transfering?

That transfer PANEL you linked to is only 2 pole. It is not a transfer SWITCH switching 2 hots AND the neutral.

 

[wyliesdiesels]

Not sure I'm following. Lets say I want to be able to transfer 6 circuits between line and genny using this transfer switch on the subpanel. Why would said transfer switch need to be rated any higher than the circuits it is transfering?

well you didnt specify you wanted a branch circuit transfer switch so i thought you were gonna use a TS that switched the entire feed to the detached building (due to the neutral issue). Regardless, that TS does not switch the neutral so that wont work.

 

[micromind]

It's difficult to understand all the stuff here but if you have 2 gens operating in parallel, they will need to be synched together.

 

[bugman-74]

It's difficult to understand all the stuff here

You got that right - I'm not convinced this is a well-understood topic. Reliance controls says "no problem," lol. Note that I am not 'paralelling' (phase alignment) the generators

well you didnt specify you wanted a branch circuit transfer switch so i thought you were gonna use a TS that switched the entire feed to the detached building (due to the neutral issue). Regardless, that TS does not switch the neutral so that wont work.

My fault - yes Reliance R510A on main panel and was planning on a Reliance A306A on subpanel.

 

[bugman-74]

Regardless, that TS does not switch the neutral so that wont work.

Doesnt this assume a bonded neutral generator? Why wouldnt it work with a floating neutral generators?

Having trouble understanding what exactly the error/fault condition is. Does anything change if I only used 1 generator at a time?

 

[wyliesdiesels]

It's difficult to understand all the stuff here but if you have 2 gens operating in parallel, they will need to be synched together.

OP hasnt stated anything that would indicate he would be paralleling the gensets

 

[wyliesdiesels]

You got that right - I'm not convinced this is a well-understood topic. Reliance controls says "no problem," lol. Note that I am not 'paralelling' (phase alignment) the generators


My fault - yes Reliance R510A on main panel and was planning on a Reliance A306A on subpanel.

neither of those switch the neutrals.

 

[wyliesdiesels]

Doesnt this assume a bonded neutral generator? Why wouldnt it work with a floating neutral generators?

Having trouble understanding what exactly the error/fault condition is. Does anything change if I only used 1 generator at a time?

you cant have neutral bonded in 2 places at the same time.

when you use a generator for standalone circuits, you need to have the generator bonded because that is how breakers trip during ground faults. if your generator has a floating neutral and you use a branch circuit TS, there will be no bond in the subpanel, only a bond upstream of those TS breakers which wont come into play since the neutral return current is going to the generator NOT the main service panel. the neutral current returns to the source (the generator). so you will want a bonded neutral on the genset since its the source of power.

Basically you need to understand what the purpose of the neutral bond is.

 

[dave*99]

I’m still wading through this thread to understand better. I’m writing this out to see if I got it right.

But I believe the problem with the 2 generator and 2 TS configuration the OP describes is:

With his layout the neutral and ground are bonded at the SEP. That’s correct. Normally you use an unbonded single generator with that setup.

But 2 generators is the question. And those should be unbonded to respect the bond at the SEP.

But neutral currents and fault currents on that setup become an issue.

Hence the discussion and need to switch neutrals. It’s because there are 2 power sources.

If the TS at the smaller outbuilding gets a TS that switches the neutral is the problem solved? And once the neutral is switched and it’s running on genny 2 where are we bonding? At the second TS? On the gen position. And Gen 2 is also unbonded. That seems to track.
But that falls apart if the second TS is on Gen and
Well it’s complicated. Maybe that second TS has to transfer the entire feed to that building. Not a small subset of breakers.
Comments welcome

 

[mm08822]

I’m still wading through this thread to understand better. I’m writing this out to see if I got it right.

But I believe the problem with the 2 generator and 2 TS configuration the OP describes is:

With his layout the neutral and ground are bonded at the SEP. That’s correct. Normally you use an unbonded single generator with that setup.

But 2 generators is the question. And those should be unbonded to respect the bond at the SEP.

But neutral currents and fault currents on that setup become an issue.

Hence the discussion and need to switch neutrals. It’s because there are 2 power sources.

If the TS at the smaller outbuilding gets a TS that switches the neutral is the problem solved? And once the neutral is switched and it’s running on genny 2 where are we bonding? At the second TS? On the gen position. And Gen 2 is also unbonded. That seems to track.
But that falls apart if the second TS is on Gen and
Well it’s complicated. Maybe that second TS has to transfer the entire feed to that building. Not a small subset of breakers.
Comments welcome

You got it.
He needs a 3pdt xfer switch for the entire sub panel. The 2nd gen could be bonded at the gen (preferred) or do it in the xfer switch in gen mode.

The transfer panel OP wants won't cut it as it is only 2pole switching. It is for the simplest of setups, which he does not have.

Color code the cb's and manage it that way. Cb's are just sideways light switches.