Generator for emergency usage

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Q101ATFD

Member
Location
USA
This is my first post, and let me start by saying I'm a firefighter for a department where we maintain all of our equipment.

We just got a used "support" trailer that has 120VAC outlets and lighting, supplied by a 20A subpanel fed by a 30A RV style inlet cord. The generators we have only provide 120V/15A receptacles and an L6-20P 240V/20A 3 prong receptacle. Neither the generators nor the support trailer are equipped with ground rods. Not sure if the generators have a floating neutral or not, but the only way I can see to provide adequate power to the trailer, with a compatible plug, is to use one hot leg and the neutral from the 3-prong 240V receptacle the generator to the subpanel, without a ground. I know the current code guys would say to buy new generators or rewire the trailer, but we don't have the funding for that. Is there a float or bond scenario that would be better than others? What direction would some of you guys take?
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
What's the trailer's total connected load? If it's less than 15 amps, just replace the 30-amp RV-style plug with a 15-amp plug. (NEMA 5-15P)
If it's more than 15 amps, do that and plug the cord-connected appliances directly into the generator's receptacles instead of the trailer's.

(for reference: https://hubbellcdn.com/ohwassets/HCI/Bryant/literature/BRYANT_NEMAChart.pdf )
 

RumRunner

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
This is my first post, and let me start by saying I'm a firefighter for a department where we maintain all of our equipment.

We just got a used "support" trailer that has 120VAC outlets and lighting, supplied by a 20A subpanel fed by a 30A RV style inlet cord. The generators we have only provide 120V/15A receptacles and an L6-20P 240V/20A 3 prong receptacle. Neither the generators nor the support trailer are equipped with ground rods. Not sure if the generators have a floating neutral or not, but the only way I can see to provide adequate power to the trailer, with a compatible plug, is to use one hot leg and the neutral from the 3-prong 240V receptacle the generator to the subpanel, without a ground. I know the current code guys would say to buy new generators or rewire the trailer, but we don't have the funding for that. Is there a float or bond scenario that would be better than others? What direction would some of you guys take?

A few things I'd like to mention:

I take it, you have multiple generators since you alluded to them in four different instances. Do you connect them in parallel to handle high amperage load like air conditioning?

The 20 A sub panel does include an AC branch circuit but portable generators rated 2000 watts which is (likely what you have) would not be able to handle an RV AC. Two paralleled 2000 watts generators could handle the job. A 13,500 BTU AC is common in RVs.

Having said that, your L6-20P 240V 3-prong receptacle is a Hubble twist-lock plug—not a receptacle, hence the “P” suffix.

But, so much for pedantry. LOL

You would not be getting 240 volts out of that L6 20 P receptacle. . . rather 120 volts with hot, neutral and ground prongs. So, you would not need to rewire anything.

Make sure that if you decide to make your own adapter that would make it compatible with the industry standard 30 A RV plug, that L6 20 P 240 volt does not have a distinguishing feature from an exclusive 120 V twist-lock. The prongs are the same size whereas the 120 V has the prongs of different sizes. Although they appear identical.

The RV plugs, whether the “crowfoot” or the twist-lock style are RVIA standard (Recreational Vehicle Industry Association)

It would be a grave mistake to assume that a a building electrician without RV experience can handle wiring for RV's. Technicians undergo special training sponsored by RVIA and some are certified.

Since RV's are wired with two different voltages (12 VDC and 120 VAC), it is very easy to screw up the wiring that could destroy a quarter of million dollar vehicle.

A pre-assembled adapter is available from most RV supply house and Walmart.

I own an RV.
 

Craigv

Senior Member
Having said that, your L6-20P 240V 3-prong receptacle is a Hubble twist-lock plug—not a receptacle, hence the “P” suffix.

But, so much for pedantry. LOL

You would not be getting 240 volts out of that L6 20 P receptacle. . . rather 120 volts with hot, neutral and ground prongs. So, you would not need to rewire anything.

Make sure that if you decide to make your own adapter that would make it compatible with the industry standard 30 A RV plug, that L6 20 P 240 volt does not have a distinguishing feature from an exclusive 120 V twist-lock. The prongs are the same size whereas the 120 V has the prongs of different sizes. Although they appear identical.

If the generator has an L6-20R, then it has a 240 volt output. The 120 volt locking receptacle is an L5-20R. There is no safe way to use an L6-20R to get 120 volts, and the OP should not attempt any modifications or rewiring of plugs to derive 120 volts from it.

The L6-20 and L5-20 may look similar, but the blades are NOT the same size and it is virtually impossible to plug in the wrong combination. All nema configurations are designed so that it's not possible to plug into the wrong voltage.
 

RumRunner

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
If the generator has an L6-20R, then it has a 240 volt output. The 120 volt locking receptacle is an L5-20R. There is no safe way to use an L6-20R to get 120 volts, and the OP should not attempt any modifications or rewiring of plugs to derive 120 volts from it.

The L6-20 and L5-20 may look similar, but the blades are NOT the same size and it is virtually impossible to plug in the wrong combination. All nema configurations are designed so that it's not possible to plug into the wrong voltage.
This is where building electricians differ from an RV electricians. When you plug-in a 240 volt RV plug whether it's a twist-lock or straight blades, it comes with four prongs that feeds a 50 Amp sub panel.

OP has 30 Amp sub panel with 30 Amp plug 3 prongs.
 

Craigv

Senior Member
This is where building electricians differ from an RV electricians. When you plug-in a 240 volt RV plug whether it's a twist-lock or straight blades, it comes with four prongs that feeds a 50 Amp sub panel.

OP has 30 Amp sub panel with 30 Amp plug 3 prongs.

In his second paragraph, the OP stated the trailer has, "a 20a subpanel fed by a 30a RV style inlet cord."

But I'm unclear why you responded to my post with this, especially the part about an RV 50 amp plug, which is completely unrelated to the OP's questions. Are you for some reason assuming I'm unfamiliar with the various wiring configurations used in RV's?
 

Q101ATFD

Member
Location
USA
Thanks for approving the thread and the thoughtful replies. I'll clarify a few things - but I certainly didn't expect all the responses so soon - thanks! When I said "generators," I only meant the type of generators the department uses for portable power, and there will only ever be one generator supplying the trailer. I want to stick with the L6-20 connector because we have plenty long cord reels of that type that power portable 240VAC ventilation fans (for house fires) with the same connector.

The power load in the trailer isn't too great - 4 small fluorescent lights and 4 15A duplex receptacles which power a 1200W saw, a 250W fan, and a few battery chargers at the most.

I ended up buying a Hubbell HBL2325SW inlet online and will install that next week, replacing the RV style cord that goes to the 120VAC panel. The plan is to just run two wires, 1 hot and neutral from the inlet to the panel, and not connect anything to the other hot prong. The next question is since the 120VAC outlets are grounded style, should I bond the ground to the neutral at the panel? I think all of the power tools we have are double insulated without a ground prong anyways, so it may be a moot point.
 

Craigv

Senior Member
Thanks for approving the thread and the thoughtful replies. I'll clarify a few things - but I certainly didn't expect all the responses so soon - thanks! When I said "generators," I only meant the type of generators the department uses for portable power, and there will only ever be one generator supplying the trailer. I want to stick with the L6-20 connector because we have plenty long cord reels of that type that power portable 240VAC ventilation fans (for house fires) with the same connector.

The power load in the trailer isn't too great - 4 small fluorescent lights and 4 15A duplex receptacles which power a 1200W saw, a 250W fan, and a few battery chargers at the most.

I ended up buying a Hubbell HBL2325SW inlet online and will install that next week, replacing the RV style cord that goes to the 120VAC panel. The plan is to just run two wires, 1 hot and neutral from the inlet to the panel, and not connect anything to the other hot prong. The next question is since the 120VAC outlets are grounded style, should I bond the ground to the neutral at the panel? I think all of the power tools we have are double insulated without a ground prong anyways, so it may be a moot point.

Hmm....

Why are you replacing a 120v inlet plug with a 240v inlet plug, on a 120 volt system? If you plug this trailer into the L6-20R on the generator, all of your 120 volt gear will be fed 240 volts.

Why would you rewire the trailer's subpanel feed without an equipment grounding conductor?

It seems, from this and your first post, that you are thinking about trying to derive 120 volts from the generator's 240 volt L6-20R receptacle by bootlegging one of the (240v) extension cord's phase legs over to the equipment ground connection on its plug or socket end. This is a bad idea. It's also unnecessary.

Whether you must comply with NEC, or OSHA regs, or not, a "custom" cord will eventually cause a problem when it's used for its intended purpose rather than for this one-off use. But both OSHA and NEC do not permit the use of either cordsets or plugs/receptacles in ways for which the product is not listed. So changing voltages is not permitted.

Locking plugs and receptacles are readily available for 120v 15 and 20 amp circuits....L5-15, and L5-20.

The generator has a 120v receptacle. Why not use it?
 
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