Hello,I'm putting together a new trailer for my wife's business and I'm a bit stumped adding a transfer switch after the generator. I bought the WFCO 50 AMP TRANSFER SWITCH (WFCO T-57) Our generator is an Onan marquis 5500. The generator has 2 30amp breakers on it and 5 wires coming out. 2 Blacks, 2 Whites and 1 green. Nothing in the trailer runs over 120V, so I don't need to set it up for 240V. I just want 120V 60HZ. Attached is a picture of the install instructions for the transfer switch. I'm assuming for the terminals marked "generator" 1 black goes to L1, 1 black goes to L2, the whites both go together to Neutral and Green obviously to GND. Then my breaker box after the transfer switch, I'm only using L1 and Neutral on the load terminals. Does this all sound correct? Why is there a jumper installed between Neutral and AUX? Please someone correct me if I'm doing something incorrect.Thank you!!

If you have two hots, I would sure set up the breaker box with close to 50% of the loads on L1 and 50% on L2.You do not mention what shore power you have-- if 50 amp, the above setup (split load between L1 and L2) is pretty much a given.

88flaminchevy wrote:Why is there a jumper installed between Neutral and AUX? Please someone correct me if I'm doing something incorrect.Because as the directions say, you can use connect both L1 and L2 to the same 120V leg (giving up 240V) and if you do so, the neutral needs 2x the capability to handle both L1 and L2 in phase. They do this by doubling up aux and neutral. Seems a little hokey to me in that if aux or neutral were to fail in the transfer switch you'd end up overloading the other one without knowing it.I'm not sure if your generator is dual 120V or 240V. If it's 240V, I'd leave it like you have it with L1 and L2 to the 240V "hot" legs from the generator and don't worry about the aux jumper or connection. You shouldn't have anything in the trailer connected to the aux terminal if you leave L1/L2 as 240V. Just because the generator makes 240V, it doesn't mean you need to use 240V. You can still use both "sides" at 120V each. In your trailer, connect your 120V devices across L1/neutral or L2/neutral in a somewhat balanced fashion.If it's dual 120V (i.e. in phase), connect one white to neutral and the other to aux, but leave the shorting jumper in there.If you only have a 120V shore power cord, you can feed both L1 and L2 of the transfer switch with the one hot feed. Be sure you have proper breakers that won't exceed the capability of the single neutral wire or shore cord.

wolfe10 wrote:If you have two hots, I would sure set up the breaker box with close to 50% of the loads on L1 and 50% on L2.You do not mention what shore power you have-- if 50 amp, the above setup (split load between L1 and L2) is pretty much a given.Thank you for the response! Shore power will only be 15 amp. Its a mobile dog grooming trailer. If not using the generator, she will be plugging into a standard 3 prong outlet at her customers homes using a long heavy duty extension cord.The after the transfer switch setup is a little bit tricky because everything needs to go through our Xantrex Freedom 458 Inverter / Charger. She needs to be able to run all the equipment inside the trailer off the inverter batteries in the event the generator dies and she has no where to plug in to shore power. Any suggestions?? Can I not just use L1 and Neutral coming out of the transfer switch? If I do that, am I not using both power legs of the generator under load? This is where I'm a bit lost.....

"SUPPLIED JUMPERS" scream HIDDEN RE-CONNECT WIRE OPTION!Meaning that is NOT SPECIFICALLY IMPLIED that it is for a reconnectable generator. It is IMPLIED that it cannot be used with a 6-wire reconnectable stator and that by following the manufacturer's instructions, a potential of seventy amperes capacity at 120vac would be available. To say this is confusing is an understatement.It all depends on whether that model Onan has reconnectable stator leads.Note the flagrant use of the embarrassing word IMPLIED. You need to get ahold of the DIPSWITCHES at ONAN and let them sort this out.Side note:My 1st 250Kw Onan job had me in stitches. The control circuitry had more current transformers than the 3rd Ave Ell. I had no choice but to purchase a thousand dollars worth of Onan service manuals. Onan made the 2.5Kw and the 6.5NH models simple to understand. The rest of the Onans seem to be blood brothers with the Rubik's Cube.

like wolfe saidits not about 240vits all about having (2) 30amp 120v circuits from the generator to feed the RV that would normally have (2) 50amp circuits if using shore power, your gnerator is big for a 30amp transfer switch, you can't use all of the generator power, that switch is for (1) 30amp shore/generator feedtransfer switches have one output two inputs, the switch chooses which one is being usedyou have a choice use only (1) generator circuit one hot & neutralor get a 50 amp transfer switch, to switch both hots and the neutral does the TT have a 30amp shore cord or a 50amp shore cord ?or NO shore cord

Need help adding a transfer switch | Good Sam Community

16 Replies

88flaminchevy
Explorer
Dec 17, 2015
Funny, I had it setup with no transfer switch but decided to change it. This whole setup is in my wife's pet grooming trailer and I just didn't want her to have to mess with a bunch of cords and connections. It looks so much cleaner with the transfer switch and everything is handled automatically. Since I've already purchased and installed the transfer switch, I think I'll probably just keep it. But, you guys have been a huge help! I think I'm headed in the right direction now. I was playing with it yesterday and I'm pretty sure it's setup wrong because If I try and pull more than 15A on one power leg, it trips only 1 breaker on the generator and I loose all power. I'll need to get behind the control panel on the generator and change it to the 2 wire setup so that doesn't happen anymore.
Bobbo
Explorer III
Dec 17, 2015
Another vote for no transfer switch. Just something else to go wrong. Put in a square box and wire a 30 amp female socket to the generator's output. When not plugged into a shore pedestal, keep the shore cord plugged into the generator's outlet.

Simple and foolproof.
MrWizard
Moderator
Dec 17, 2015
2 wire 60hz.. the middle drawing

is the one you want to use

and i agree you can eliminate the transfer switch, by using a plug connection from the Onan power so, it plug into Onan or plug into shore power
totally fool proof
beemerphile1
Explorer
Dec 17, 2015
I would eliminate the transfer switch. When using shore power, plug into that. When using generator, plug the shore cord into the generator. Simple and foolproof.

How can you operate from 15a shore power but need 30a from the generator?
88flaminchevy
Explorer
Dec 16, 2015
I appreciate all the help here. I think my question got off track or misunderstood at some point. Lets try this..... The picture below is my 3 wiring options for the Onan. Again, once I get to the transfer switch, I want only 1 120V line coming out. I need to be sure I'm actually utilizing the generators full load capability because at times I may be pulling up to 30 amps out of that 1 line. I know if I do this wrong, I'm really only using one circuit on the generator and only that one circuits breaker will trip on the generator if I overload it.
MEXICOWANDERER
Explorer
Dec 01, 2015
" Sounds to me like you need to hire a professional electrician, you cannot possibly follow the different advice of all these "experts" "

Think he's capable of phoning Onan and asking for a wire diagram for a gen recommect?
wnjj
Explorer II
Dec 01, 2015
Other online reading seems to indicate that your generator is likely only 120V, but with 2 separate circuits. This means L1 and L2 are in phase and the 2 neutrals combined carry the total current. This situation is why the aux terminal exists. With 5500W, 45A are available. With only 35A capable per contact, the neutral current gets shared between the neutral and aux terminals.

In your case if you only plan to pull power from L1, you will have 22.5A available (2750W). In other words, L1 to neutral will work fine for a 120V system.

Since you said you plan to run this through an inverter/charger L2 will be wasted unless you want to connect something like an air conditioner to it for use only while on generator power.
MrWizard
Moderator
Dec 01, 2015
Quote from your info L1 and L2 are rated for 35 amps each

I don't care what the seller , Mfg, or distribute says
But 35 amp contacts will not carry 50 amps
So that is not a 50 amp switch

But yes you should be able to wire that to the Onan genset
But if you ever plug into 50 amp shore power which is connected to a double pole 50 amp circuit breaker, be careful to keep you loads down to 30 amps per leg
rhochnadel
Explorer
Dec 01, 2015
Sounds to me like you need to hire a professional electrician, you cannot possibly follow the different advice of all these "experts".
time2roll
Nomad
Dec 01, 2015
The hots are known a L1 and L2 as in Line 1 and Line 2. So connect the generator to those terminals. The neutrals will go to Neutral and Aux that is jumpered to the Neutral. Ground to ground terminals.

Shore line (cord) and Load (RV) will be similar with just one neutral.

Is there an issue with this? I do assume you have a 50 amp RV with two main breakers.

The 15 amp 120v utility cord needs the hot to connect to both the hot connections in the transfer switch shown.

As far as powering everything with the inverter... that is a romantic gesture but most RVs can kill four batteries in less than an hour if everything is running. Not sure that is very effective. Best to describe the actual loads in your custom build for best results.