New shed wiring panel - sometimes plugged in - sometimes generator

[Goose_NC]

I have a portable shed that I am wiring a sub panel into. We will have lights, TV, AC, fridge, vent fan and a few receptacles for convivence. This shed will at times plugged in to an RV power pole (30 AMP). But because this property only has 100 amps total, I plug into a generator during events. Basically, I have wired this to be just like an RV. Where ground and neutral are the same at this box.

Talking with local electricians, most cannot understand the requirements of this situation. Some say I simply cannot do what I want to do and "be safe". There will not be an inspection.

I have not run the electrical from the main building yet. But that will be a 110VAC 30AMP breaker feeding an RV electrical with the 30 AMP RV receptacle, and a 15 amp receptacle. I just want to be sure I am not back feeding the main building something bad.

This is the panel I will be connecting to. https://www.homedepot.com/p/Connect...-with-Branch-Breakers-CESMPSC41GRHR/100669963

 

[mike93lx]

You need the feed from the main building to go into a transfer switch. That will allow you to shut off the feed and switch to another.

The neutral and ground cannot be bonded when connected to your main building.

 

[dave*99]

I'll post this idea with the thought it may or may not be correct.
I'm sure we will get some help from the GJ code experts shortly.

I'm assuming the shed has a cord and male plug to power it.

In the panel inside the shed, do not bond ground and neutral.
In the RV pedestal, do not bond ground and neutral.

When plugged into pedestal you rely on the neutral/ground bond in the main panel in the house.
When plugged into generator, you rely on the neutral/ground bond in the generator. It it does not have a bond, use a bonding plug - a plug with ground and neutral connected together for the purpose of bonding at the generator. Plug it into one of the generator receptacles. You may need a ground rod at the generator, I'm not sure.

There are some code references here:

Neutral Ground Bonding in an RV

I am sorry if you guys are sick to death of this topic, and I did try to read previous posts on this topic but I am still very much confused. I have recently been involved in some debate on this issue, and people seem to be quoting different NEC sections to support their viewpoint. It also...

forums.mikeholt.com

This may work too;

You need the feed from the main building to go into a transfer switch. That will allow you to **** off the feed and switch to another.

The neutral and ground cannot be bonded when connected to your main building.

But I don't know if you have a bathroom in the shed.

 

[dcg9381]

I plug into a generator during events. Basically, I have wired this to be just like an RV.

How do you feed the building currently? Through 30A cord?

It's not wired like an RV unless you have a transfer switch in there. That's how they do it with RVs with generators.

I have not run the electrical from the main building yet. But that will be a 110VAC 30AMP breaker feeding an RV electrical with the 30 AMP RV receptacle, and a 15 amp receptacle. I just want to be sure I am not back feeding the main building something bad.

I think you want "building on a cord" (feed). This violates NEC as it's not "permanent". So no electrician is going to do this for you.

What you do is put a sub-panel in the building with an interlock and generator feed (this is basically a manual transfer switch) inside the building. Feed the building from your main breaker.

 

[Goose_NC]

How do you feed the building currently? Through 30A cord?

It's not wired like an RV unless you have a transfer switch in there. That's how they do it with RVs with generators.



I think you want "building on a cord" (feed). This violates NEC as it's not "permanent". So no electrician is going to do this for you.

What you do is put a sub-panel in the building with an interlock and generator feed (this is basically a manual transfer switch) inside the building. Feed the building from your main breaker.

Correct about there no being a transfer switch.
Let me try to clarify - I have an 30A cord that feeds the shed panel. (I found a used RV 30A cord for sale locally.) This cord will either be plugged into a 30A RV panel box, or my generator, so it is a "manual transfer switch". When unplugged, the building does not have any power.
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I do not need an electrician to do this as I already have the internal building wiring completed, and tested, and it works off the generator. If I need to run a separate ground, I can do that and add a ground bus bar (correct term??) to the panel box.
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Just trying to be sure I am not back feeding when connected to the main building, via the RV panel.

 

[Goose_NC]

You need the feed from the main building to go into a transfer switch. That will allow you to shut off the feed and switch to another.

The neutral and ground cannot be bonded when connected to your main building.

It is a manual "transfer switch". I unplug from one source and plug into another.

 

[Goose_NC]

I just knew that I was going to confuse everyone. Apparently I cannot communicate well at all.

 

[dave*99]

Just trying to be sure I am not back feeding when connected to the main building, via the RV panel.

Basically, I have wired this to be just like an RV. Where ground and neutral are the same at this box.

What do you mean ground and neutral are the same? Did you bond them in the panel in the shed? Don't. That puts neutral current on the ground wire going from the shed through the cord and RV pedestal and all the way back to the main panel in the house.

It is a manual "transfer switch". I unplug from one source and plug into another.

Back feeding:
How? You have one male plug from the building. It's either in the RV panel or in the generator. At no point is the generator even connected to anything when you are using the pedestal. Correct?

 

[mike93lx]

If the cord is unplugged from the generator and plugged into the main building, how is there risk of backfeeding?

Maybe pictures or a sketch would help

 

[Goose_NC]

What do you mean ground and neutral are the same? Did you bond them in the panel in the shed? Don't. That puts neutral current on the ground wire going from the shed through the cord and RV pedestal and all the way back to the main panel in the house.

Ah...okay. So I will buy a ground bar for the panel and run that to the grounding rod that I have to buy and install.

Back feeding:
How? You have one male plug from the building. It's either in the RV panel or in the generator. At no point is the generator even connected to anything when you are using the pedestal. Correct?

Correct. When plugged into the pedestal, the generator is not connected or used.

 

[dcg9381]

Correct about there no being a transfer switch.
Let me try to clarify - I have an 30A cord that feeds the shed panel. (I found a used RV 30A cord for sale locally.) This cord will either be plugged into a 30A RV panel box, or my generator, so it is a "manual transfer switch". When unplugged, the building does not have any power.
-
I do not need an electrician to do this as I already have the internal building wiring completed, and tested, and it works off the generator. If I need to run a separate ground, I can do that and add a ground bus bar (correct term??) to the panel box.
-
Just trying to be sure I am not back feeding when connected to the main building, via the RV panel.

Per code, you cannot have a "plug-in building".

Pragmatically, I don't see anything wrong with having a "manual" transfer means that is either plugged into the generator or the pedestal. None of that will back-feed. It can't because you only have one source.

Physically separate buildings need separate grounds rods, yes. 100%

You do want a ground bar, across the board. The neutral and ground are "bonded" at source (meaning the generator or at the main panel) depending on your current configuration..

There are real sparkies here that are much better than me... So YMMV.

 

[mm08822]

As long as there is only one possible source of power that can be connected to the trailer at any time, then the single cord is the "transfer switch ".

Yes, the neutrals and grounds must be seperated in the panel for safe usage.

I would call it a trailer and therefore NEC doesn't apply.

 

[Goose_NC]

As long as there is only one possible source of power that can be connected to the trailer at any time, then the single cord is the "transfer switch ".

Yes, the neutrals and grounds must be seperated in the panel for safe usage.

I am now going to look up how RVs handle this wiring. As they can be plugged in to a panel, or run off a generator (through the transfer switch).

 

[mike93lx]

I am now going to look up how RVs handle this wiring. As they can be plugged in to a panel, or run off a generator (through the transfer switch).

The key is the transfer switch. You are trying to avoid that part here

 

[mm08822]

It's pretty simple.....think of it this way, you either plug the cord into your recept or your neighbor's.
Once the neutrals and grounds are split, all is fine.

 

[dcg9381]

I am now going to look up how RVs handle this wiring. As they can be plugged in to a panel, or run off a generator (through the transfer switch).

Look up "transfer switch". They are handled (in an automatic way) the same way manual transfer switches are done. The magic is that they may bond / de-bond neutral.

You probably want a "residential transfer switch" if you want to go that way.

None of these will change the NEC violation on use of a cord to feed a building. But again, if you're going to continue to do that, you don't need anything else, you can't back-feed. Add a ground rod and a ground bar because you need it anyway.

 

[mm08822]

Yes, avoid the cost of unnecessary hardware. The single cord plugged into source A or source B provides the isolation. Cheap, to the point and safe.

The key is the transfer switch. You are trying to avoid that part here

 

[dave*99]

I don't think the OP needs a transfer switch. But just for discussion, an RV specific transfer switch SWITCHES the neutral between the shore power port and the generator port.

Neutral/ground bonds happen at the power sources. Not the transfer switch. Again, this is RV specific.

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[theoldwizard1]

If the cord is unplugged from the generator and plugged into the main building, how is there risk of backfeeding?

Maybe pictures or a sketch would help

CONCUR !

I will add that connecting ground and neutral at any point EXCEPT IN THE FIRST DISCONNECT is not legal or safe !

Also, unless you install a breaker panel in the shed, or some kind of "inline" fuse/breaker, all circuits in the shed will be capable of drawing 30A which will likely overload the wires/outlets inside the shed. The right thing to do is install a 2-space/4-circuit sub inside the shed with a separate ground. Then run all 15A circuits in the shed from that.

If your feed is 120V/30A you CAN connect L1 to L2 in the panel. This means you will have no 240V capability. If all 4 circuits are pulling 15A, you will trip a breaker, probably up-line, because most (all?) of these small subs are main lug (not main breaker).

If you don't want to "feed" the shed (is this even legal?) with a NEMA TT-30 plug, (i.e. hardwire to either the house/RV pole or a generator inlet) you need a SPDT switch (rated for 30A), like a Leviton 1287 (not motor rated).

 

[dave*99]

I have a portable shed that I am wiring a sub panel into.

Also, unless you install a breaker panel in the shed, or some kind of "inline" fuse/breaker, all circuits in the shed will be capable of drawing 30A which will likely overload the wires/outlets inside the shed.

Hmmm.

 

[theoldwizard1]

I don't think the OP needs a transfer switch. But just for discussion, an RV specific transfer switch SWITCHES the neutral between the shore power port and the generator port.

Neutral/ground bonds happen at the power sources. Not the transfer switch.

Why can't he just use a standard 30A SPDT ahead of the distribution panel in the shed ? Connect all grounds together. Connect all neutrals together.

Yes, this would mean that the neutral at the generator inlet is connect to the house and the ground at the generator inlet is connected to the house.

(Your picture confuses me !)

 

[dave*99]

Why can't he just use a standard 30A SPDT ahead of the distribution panel in the shed ? Connect all grounds together. Connect all neutrals together.

Yes, this would mean that the neutral at the generator inlet is connect to the house and the ground at the generator inlet is connected to the house.

(Your picture confuses me !)

If his generator has neutral and ground bonded, and so does his main panel in the house, just think of the mess you created when the generator is plugged in.
And if the neutral and ground are not bonded at the generator, then you rely on the bonding back at the house. Another big mess.

 

[wyliesdiesels]

I have a portable shed that I am wiring a sub panel into. We will have lights, TV, AC, fridge, vent fan and a few receptacles for convivence. This shed will at times plugged in to an RV power pole (30 AMP). But because this property only has 100 amps total, I plug into a generator during events. Basically, I have wired this to be just like an RV. Where ground and neutral are the same at this box.

what is an RV power pole? you mean a service strictly for an RV? 120v only?

knowing the capacity of the electrical service is meaningless without also knowing the load and/or doing a load calc. what else do you have running on this property?

as far as the generator goes, what are you plugging the generator into? we really need more info here
also, neutral and ground should NOT be bonded anywhere past the main service panel.... youre just asking for trouble doing otherwise.

Talking with local electricians, most cannot understand the requirements of this situation. Some say I simply cannot do what I want to do and "be safe". There will not be an inspection.

if youre connecting a generator to an electrical service without the proper lockout (interlock) or transfer switch, then yeah the electricians wont understand why you want to do it that way because ITS UNSAFE. they are correct that you cannot do this and be safe. who cares about inspections. do you want to potentially electrocute someone?

I have not run the electrical from the main building yet. But that will be a 110VAC 30AMP breaker feeding an RV electrical with the 30 AMP RV receptacle, and a 15 amp receptacle. I just want to be sure I am not back feeding the main building something bad.

This is the panel I will be connecting to. https://www.homedepot.com/p/Connect...-with-Branch-Breakers-CESMPSC41GRHR/100669963

and you want to use this to feed other receptacles and lights as well? i wouldnt use this to do that. get a regular subpanel so you have more capacity.

 

[wyliesdiesels]

Correct about there no being a transfer switch.
Let me try to clarify - I have an 30A cord that feeds the shed panel. (I found a used RV 30A cord for sale locally.) This cord will either be plugged into a 30A RV panel box, or my generator, so it is a "manual transfer switch". When unplugged, the building does not have any power.

make sure that the panel does not have a bonded neutral.

If the generator does, and you dont plan to connect this to another building, leave the bond on the generator. if you plan to connect it to another building, then remove the bond and make a bonding plug.

-
I do not need an electrician to do this as I already have the internal building wiring completed, and tested, and it works off the generator. If I need to run a separate ground, I can do that and add a ground bus bar (correct term??) to the panel box.
-
Just trying to be sure I am not back feeding when connected to the main building, via the RV panel.

the panel should have an isolated neutral bus and a ground bus. generator will have the bonding

this way when you plug into "shore power" the neutral bonding is still only at the main service panel elsewhere. you dont want bonded neutral in 2 or more places

 

[wyliesdiesels]

Ah...okay. So I will buy a ground bar for the panel and run that to the grounding rod that I have to buy and install.

yes you need a ground bar. you need to connect the ground from the generator to this ground bar. you should also have 2 grounding electrodes already that connect to the ground bar you are adding. grounding electrodes are required for detached structures.

and again make sure neutral isnt bonded in this panel

 

[wyliesdiesels]

I am now going to look up how RVs handle this wiring. As they can be plugged in to a panel, or run off a generator (through the transfer switch).

an RV wont be wired any differently. the bonding is established at the source as it should be- either the main service panel at the RV park (not in the pedestal where the RV plugs in at or the panel inside the RV) or at the generator...

 

[wyliesdiesels]

The key is the transfer switch. You are trying to avoid that part here

but he doesnt need a transfer switch unless he doesnt want to use the illegal cordage as the "manual transfer switch"

 

[wyliesdiesels]

CONCUR !

I will add that connecting ground and neutral at any point EXCEPT IN THE FIRST DISCONNECT is not legal or safe !

Also, unless you install a breaker panel in the shed, or some kind of "inline" fuse/breaker, all circuits in the shed will be capable of drawing 30A which will likely overload the wires/outlets inside the shed. The right thing to do is install a 2-space/4-circuit sub inside the shed with a separate ground. Then run all 15A circuits in the shed from that.

If your feed is 120V/30A you CAN connect L1 to L2 in the panel. This means you will have no 240V capability. If all 4 circuits are pulling 15A, you will trip a breaker, probably up-line, because most (all?) of these small subs are main lug (not main breaker).

If you don't want to "feed" the shed (is this even legal?) with a NEMA TT-30 plug, (i.e. hardwire to either the house/RV pole or a generator inlet) you need a SPDT switch (rated for 30A), like a Leviton 1287 (not motor rated).

congrats. great advice. didnt find anything wrong here...

 

[ddurrett896]

I have a portable shed that I am wiring a sub panel into. We will have lights, TV, AC, fridge, vent fan and a few receptacles for convivence. This shed will at times plugged in to an RV power pole (30 AMP). But because this property only has 100 amps total, I plug into a generator during events. Basically, I have wired this to be just like an RV. Where ground and neutral are the same at this box.

Talking with local electricians, most cannot understand the requirements of this situation. Some say I simply cannot do what I want to do and "be safe". There will not be an inspection.

I have not run the electrical from the main building yet. But that will be a 110VAC 30AMP breaker feeding an RV electrical with the 30 AMP RV receptacle, and a 15 amp receptacle. I just want to be sure I am not back feeding the main building something bad.

This is the panel I will be connecting to. https://www.homedepot.com/p/Connect...-with-Branch-Breakers-CESMPSC41GRHR/100669963

It's simple and everyone is going to tell me it's illegal/dangerous but if you have a half brain, it's fine.

Wire generator inlet box to house panel with 30 amp breaker.
Wire generator inlet box to shed panel with 30 amp breaker.
Always leave both 30 amp breaker off when not in use.

Using house power: Plug shed to house, flip on house 30 amp breaker, flip on shed 30 amp breaker
Using generator power: Plug shed to generator, flip on shed 30 amp breaker, house 30 amp amp beaker stays off

Use a generator cord between shed and house/generator in both scenarios.

 

[theoldwizard1]

Duplicate

 

[theoldwizard1]

unbond the generator !

And if the neutral and ground are not bonded at the generator, then you rely on the bonding back at the house. Another big mess.

From GJ Electrical FAQ

4-wire feeder to DETACHED building:

Of course, the generator and TT-30 do not have a ground.

 

[dave*99]

Why can't he just use a standard 30A SPDT ahead of the distribution panel in the shed ? Connect all grounds together. Connect all neutrals together.

Yes, this would mean that the neutral at the generator inlet is connect to the house and the ground at the generator inlet is connected to the house.

(Your picture confuses me !)

Try sketching that whole plan out and compare it to the diagrams in post 31.

 

[mm08822]

From GJ Electrical FAQ

4-wire feeder to DETACHED building:

Of course, the generator and TT-30 do not have a ground.

Try sketching that whole plan out and compare it to the diagrams in post 31.

In this situation, the above diagram only adds unnecessary information. (Ignore it.)

 

[theoldwizard1]

Try sketching that whole plan out and compare it to the diagrams in post 31.

 

[Goose_NC]

LOL...way to complicated for what it is!
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I have a breaker panel that is for power distribution. Light and fan on one circuit, left side of building has 3 outlets (lamps and device charging. Right side of building has a circuit for small fridge and TV and vent fan. Also have one circuit for running a griddle or coffee pot. We usually a butane stove for cooking.
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Now to explain how the power gets to the building. I have a 30 AMP RV cord that is wired to the L1 and L2 in the panel, and the neutral to the one bar, and I will put in a ground bar into the panel (it was not included in this panel).
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I will run a 30AMP 110VAC to a pole with a RV panel (TT-30R NEMA). Same as what I plug my RV into at home. When power is available, I will plug my shed into this pole.
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When I need to run off my generator, I will unplug from the RV panel power pole, and plug into the generator. Hence the "manual transfer switch" comment I made.
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I have obtained the understanding I needed from the posts here. The only adjustment I need is to put in a grounding bar and separate the ground and neutral. 20 minutes at the panel. once I buy the parts. I was over thinking this project. I previously had a 1978 RV that served me well for 3-4 years. Ran that RV on a 100 foot 10 gauge extension cord from a 20 amp plug.
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This is a temporary building on leased property. My group has been there for 25+ years. If my group decides to relocate, I can relocate this portable building or sell it. This old property only has 100 amp service, and the landlord will not allow us to upgrade to 200 amp service, for many reasons. 25+ years ago no one thought about getting older the demand for more power and comfort features. The biggest current draw is the stove (soon to become a gas stove. When we have bands (3 or 4 members) they just need two separate 20 amp circuits.
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Thanks for the posts!

 

[wyliesdiesels]

It's simple and everyone is going to tell me it's illegal/dangerous but if you have a half brain, it's fine.

Wire generator inlet box to house panel with 30 amp breaker.
Wire generator inlet box to shed panel with 30 amp breaker.
Always leave both 30 amp breaker off when not in use.

Using house power: Plug shed to house, flip on house 30 amp breaker, flip on shed 30 amp breaker
Using generator power: Plug shed to generator, flip on shed 30 amp breaker, house 30 amp amp beaker stays off

Use a generator cord between shed and house/generator in both scenarios.

umm what? you havent done anything to prevent backfeed onto the grid.... try again

 

[ddurrett896]

umm what? you havent done anything to prevent backfeed onto the grid.... try again

Did you not read this sentence?

Using generator power: Plug shed to generator, flip on shed 30 amp breaker, house 30 amp amp beaker stays off

 

[dcg9381]

Using generator power: Plug shed to generator, flip on shed 30 amp breaker, house 30 amp amp beaker stays off

There's a reason that's not allowed and is a Really Bad Idea. OP is way better off to leave it like it is.

ATS, interlock, or how the OP has it now: It's physically impossible to screw it up.

Add a human and a process you have to remember, that's where things go wrong. And if the OP doesn't screw it up, the next human that buys that place likely will.

 

[ddurrett896]

There's a reason that's not allowed and is a Really Bad Idea. OP is way better off to leave it like it is.

ATS, interlock, or how the OP has it now: It's physically impossible to screw it up.

Add a human and a process you have to remember, that's where things go wrong. And if the OP doesn't screw it up, the next human that buys that place likely will.

I'm still lost as to how he would backfeed the grid. The grid is feeding the house power the entire time in both scenarios - he just need to get power to the shed.

The only dangerous thing about the setup I posted is the house 30 amp break on WITH THE SHED NOT PLUGGED IN and a kid reaches up and touches the inlet connection that has power.

 

[wyliesdiesels]

Did you not read this sentence?

Using generator power: Plug shed to generator, flip on shed 30 amp breaker, house 30 amp amp beaker stays off

that doesnt positively PREVENT backfeed. there is still a possibility as someone could flip that breaker back on

the only way to PREVENT backfeed is with an interlock or transfer switch, merely turning the breaker off is not sufficient