Portable Generator to Panel

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Therealcrt

Senior Member
Location
Kansas City
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Electrician
Superintendent has a job trailer that needs power.
He is buying a 9500w portable generator. The panel in the job trailer has a 100a main breaker. Can he purchase the twist lock 240v cord inlet that plugs into the generator and then hook up the other end of the cord directly to the main breaker? So when the generator is running it provides power to the panel.
 
Proper way would be to put in an inlet and plug into that. If there is any chance this will be connected to the grid, then an interlock would be needed. Also, a backfed 30A or 40A breaker should be installed.
 
Little Bill said:
Proper way would be to put in an inlet and plug into that. If there is any chance this will be connected to the grid, then an interlock would be needed. Also, a backfed 30A or 40A breaker should be installed.
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It will never be connected to the grid.. it's a job trailer that the panel needs power via the generator. Why couldn’t I just use the 50a Inlet cord and wire it directly to the main breaker
 
If there is never a situation where you are simultaneously connecting to two power sources, then you don't need an interlock.

Running a circuit from an externally mounted 'inlet' box to the main breaker in the panel is a compliant and clean solution for connecting a portable generator to the panel.

You might be able to run a cable directly from the panel to a plug, but there are a number of issues that can be a pain to address if you want a compliant installation.

1) You can't run flexible cords in walls (not allowed to be a substitute for building wiring), so if the panel is inside the trailer you already have a problem.

2) A 'pendant' cord from a panel requires careful strain relief, so that when the cord is moved around you don't damage the conductors or their termination.

3) Most terminations (and I'll bet all main breaker lugs) are not rated for the fine stranded wire used in flexible cords. So once you have the flexible cable in the panel, you need a transition to ordinary building wire anyway.

4) When you are driving the trailer to a new location, you are going to have this cable with a heavy plug on the end dangling out, so you'd have to spend time carefully tying it down, and you would need to provide some way to tie it down for transport.

There is a reason that RVs have power inlets rather than permanently attached cords. Follow that lead.

-Jon
 
Therealcrt said:
It will never be connected to the grid.. it's a job trailer that the panel needs power via the generator. Why couldn’t I just use the 50a Inlet cord and wire it directly to the main breaker
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Are you going to just throw the cord out the window to plug into the generator?
Are you going to pile the cord up in the trailer everytime you move the trailer?

Much simpler to install the inlet with normal wiring from the panel, as Jon mentioned, the fine stranded wire isn't made to go in lugs.
Plug-unplug the cord as needed.
 
Don't most travel trailers have cord to plug in. They do have limited ocpd though following the cord. Where is the cord terminated in the trailer if not hooked to panel lugs?
 
winnie said:
If there is never a situation where you are simultaneously connecting to two power sources, then you don't need an interlock.

Running a circuit from an externally mounted 'inlet' box to the main breaker in the panel is a compliant and clean solution for connecting a portable generator to the panel.

You might be able to run a cable directly from the panel to a plug, but there are a number of issues that can be a pain to address if you want a compliant installation.

1) You can't run flexible cords in walls (not allowed to be a substitute for building wiring), so if the panel is inside the trailer you already have a problem.

2) A 'pendant' cord from a panel requires careful strain relief, so that when the cord is moved around you don't damage the conductors or their termination.

3) Most terminations (and I'll bet all main breaker lugs) are not rated for the fine stranded wire used in flexible cords. So once you have the flexible cable in the panel, you need a transition to ordinary building wire anyway.

4) When you are driving the trailer to a new location, you are going to have this cable with a heavy plug on the end dangling out, so you'd have to spend time carefully tying it down, and you would need to provide some way to tie it down for transport.

There is a reason that RVs have power inlets rather than permanently attached cords. Follow that lead.

-Jon
Click to expand...
Not all RV’s have flanged inlets, I have two that have permanent cords from the factory with factory male cord cap, and a third I changed to a flanged inlet so I could use a longer cord than what the factory had. It appears this is a temporary construction trailer, and temporary power does not have to meet as stringent requirements as permanent power.
 
winnie said:
If there is never a situation where you are simultaneously connecting to two power sources, then you don't need an interlock.

Running a circuit from an externally mounted 'inlet' box to the main breaker in the panel is a compliant and clean solution for connecting a portable generator to the panel.
Click to expand...
winnie said:
There is a reason that RVs have power inlets rather than permanently attached cords. Follow that lead.

-Jon
Click to expand...
Agreed!!!!
 
hillbilly1 said:
Not all RV’s have flanged inlets, I have two that have permanent cords from the factory with factory male cord cap, and a third I changed to a flanged inlet so I could use a longer cord than what the factory had. It appears this is a temporary construction trailer, and temporary power does not have to meet as stringent requirements as permanent power.
Click to expand...

I agreed that one could have a cord attached to the panel rather than using an inlet, and did my best to describe the requirements for doing so.

I stand by using the inlet as the _better_ solution.

I'm sure we've all seen field built power distribution boxes where SO cord comes out of a panel, NM clamps used to hold the SO, finely stranded wire terminated directly to the breakers. IMHO this is not code compliant even in a temporary installation. Do the exact same thing but have a proper SO cord grip and a suitable transition from fine stranded wire (say a pin adapter rated for fine stranded wire) and the installation is kosher.

-Jon
 
Little Bill said:
Much simpler to install the inlet with normal wiring from the panel, as Jon mentioned, the fine stranded wire isn't made to go in lugs.
Click to expand...

Just to clarify: it is the lugs (in most panels) that are not made to accept fine stranded wire. Fine stranded wire has to get connected somehow, and there are terminals/lugs specifically designed for it.

If you have reason to connect fine stranded wire to a standard lug, there are 'pin adapters' available which crimp on to the fine stranded wire. NSI Polaris also sells insulated splices made for fine stranded conductors. Many crimp lugs and crimp splices are rated for fine stranded wire.

-Jon
 
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